I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo? Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm

Thanks,
-Ryan

On 10 Mar 2004 19:37:21 -0800, (Ryan) wrote:

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo? Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm


From the picture, and frfom Philips's data sheet at

http://www.semiconductors.philips.co...db/pip/tda7050

it looks like this is what they're doing:

(View with a fixed-pitch font like Courier New)

+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +-----------------+-----------------+ |
| | | | | | |
+-----+---|-\U1A +---|-\U2A +---|-\U3A
| | ------+ | ------+ | ------+
[R] +---|+/ | +---|+/ | +---|+/ |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | | | | |
[R] +---|+\U1B | +---|+\U2B | +---|+\U3B | |
| | --+ | | | --+ | | | --+ | |
+-----+---|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | | [C] [C] | | | [C] [C] | | | [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | | |
| | | | | | | | | | | | |
LIN---+ +3v | | | +3v | | | +3V | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

It's hard to read the values of the resistors on the front end, but the
markings seem to be four digits long ending in a "1" which means they're
probably 1%ers and, therefore, can't have a resistance higher than 9760
ohms.

From

http://www.boostaroo.com/specs.html


the Boosteroo spec's a gain of 12dB with 40mW out into 16 ohm
headphones, so that's 800mV RMS.

They say that the 12dB gain is an increase in volume, but they don't say
what the reference volume is, so they're probably talking voltage gain,
which would be a gain of 4 for 12dB.

So, for 800mVRMS out they're looking for 200mVRMS in, or around a half a
volt, Peak to Peak.

Unfortunately, they don't specify the input impedance anywhere, so
depending on what you get out of your line outputs, and how heavily they
can be loaded, using a pot to attenuate the line outputs may just load
them down too much for the thing to be useful. Just for grins I'd tie
10k pots across the line inputs and run the pot wiper and ground to the
boostaroo just to see what happens. If that fails you could, of course,
unsolder the surface mount resistors and replace then with outboard
pots. Pretty easy mod if you want to do it. Post back if you're
interested.

--
John Fields

On 10 Mar 2004 19:37:21 -0800, (Ryan) wrote:

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo? Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm


From the picture, and frfom Philips's data sheet at

http://www.semiconductors.philips.co...db/pip/tda7050

it looks like this is what they're doing:

(View with a fixed-pitch font like Courier New)

+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +-----------------+-----------------+ |
| | | | | | |
+-----+---|-\U1A +---|-\U2A +---|-\U3A
| | ------+ | ------+ | ------+
[R] +---|+/ | +---|+/ | +---|+/ |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | | | | |
[R] +---|+\U1B | +---|+\U2B | +---|+\U3B | |
| | --+ | | | --+ | | | --+ | |
+-----+---|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | | [C] [C] | | | [C] [C] | | | [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | | |
| | | | | | | | | | | | |
LIN---+ +3v | | | +3v | | | +3V | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

It's hard to read the values of the resistors on the front end, but the
markings seem to be four digits long ending in a "1" which means they're
probably 1%ers and, therefore, can't have a resistance higher than 9760
ohms.

From

http://www.boostaroo.com/specs.html


the Boosteroo spec's a gain of 12dB with 40mW out into 16 ohm
headphones, so that's 800mV RMS.

They say that the 12dB gain is an increase in volume, but they don't say
what the reference volume is, so they're probably talking voltage gain,
which would be a gain of 4 for 12dB.

So, for 800mVRMS out they're looking for 200mVRMS in, or around a half a
volt, Peak to Peak.

Unfortunately, they don't specify the input impedance anywhere, so
depending on what you get out of your line outputs, and how heavily they
can be loaded, using a pot to attenuate the line outputs may just load
them down too much for the thing to be useful. Just for grins I'd tie
10k pots across the line inputs and run the pot wiper and ground to the
boostaroo just to see what happens. If that fails you could, of course,
unsolder the surface mount resistors and replace then with outboard
pots. Pretty easy mod if you want to do it. Post back if you're
interested.

--
John Fields

On 10 Mar 2004 19:37:21 -0800, (Ryan) wrote:

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo? Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm


From the picture, and frfom Philips's data sheet at

http://www.semiconductors.philips.co...db/pip/tda7050

it looks like this is what they're doing:

(View with a fixed-pitch font like Courier New)

+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +-----------------+-----------------+ |
| | | | | | |
+-----+---|-\U1A +---|-\U2A +---|-\U3A
| | ------+ | ------+ | ------+
[R] +---|+/ | +---|+/ | +---|+/ |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | | | | |
[R] +---|+\U1B | +---|+\U2B | +---|+\U3B | |
| | --+ | | | --+ | | | --+ | |
+-----+---|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | | [C] [C] | | | [C] [C] | | | [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | | |
| | | | | | | | | | | | |
LIN---+ +3v | | | +3v | | | +3V | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

It's hard to read the values of the resistors on the front end, but the
markings seem to be four digits long ending in a "1" which means they're
probably 1%ers and, therefore, can't have a resistance higher than 9760
ohms.

From

http://www.boostaroo.com/specs.html


the Boosteroo spec's a gain of 12dB with 40mW out into 16 ohm
headphones, so that's 800mV RMS.

They say that the 12dB gain is an increase in volume, but they don't say
what the reference volume is, so they're probably talking voltage gain,
which would be a gain of 4 for 12dB.

So, for 800mVRMS out they're looking for 200mVRMS in, or around a half a
volt, Peak to Peak.

Unfortunately, they don't specify the input impedance anywhere, so
depending on what you get out of your line outputs, and how heavily they
can be loaded, using a pot to attenuate the line outputs may just load
them down too much for the thing to be useful. Just for grins I'd tie
10k pots across the line inputs and run the pot wiper and ground to the
boostaroo just to see what happens. If that fails you could, of course,
unsolder the surface mount resistors and replace then with outboard
pots. Pretty easy mod if you want to do it. Post back if you're
interested.

--
John Fields

On 10 Mar 2004 19:37:21 -0800, (Ryan) wrote:

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo? Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm


From the picture, and frfom Philips's data sheet at

http://www.semiconductors.philips.co...db/pip/tda7050

it looks like this is what they're doing:

(View with a fixed-pitch font like Courier New)

+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +-----------------+-----------------+ |
| | | | | | |
+-----+---|-\U1A +---|-\U2A +---|-\U3A
| | ------+ | ------+ | ------+
[R] +---|+/ | +---|+/ | +---|+/ |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | | | | |
[R] +---|+\U1B | +---|+\U2B | +---|+\U3B | |
| | --+ | | | --+ | | | --+ | |
+-----+---|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | | [C] [C] | | | [C] [C] | | | [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | | |
| | | | | | | | | | | | |
LIN---+ +3v | | | +3v | | | +3V | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

It's hard to read the values of the resistors on the front end, but the
markings seem to be four digits long ending in a "1" which means they're
probably 1%ers and, therefore, can't have a resistance higher than 9760
ohms.

From

http://www.boostaroo.com/specs.html


the Boosteroo spec's a gain of 12dB with 40mW out into 16 ohm
headphones, so that's 800mV RMS.

They say that the 12dB gain is an increase in volume, but they don't say
what the reference volume is, so they're probably talking voltage gain,
which would be a gain of 4 for 12dB.

So, for 800mVRMS out they're looking for 200mVRMS in, or around a half a
volt, Peak to Peak.

Unfortunately, they don't specify the input impedance anywhere, so
depending on what you get out of your line outputs, and how heavily they
can be loaded, using a pot to attenuate the line outputs may just load
them down too much for the thing to be useful. Just for grins I'd tie
10k pots across the line inputs and run the pot wiper and ground to the
boostaroo just to see what happens. If that fails you could, of course,
unsolder the surface mount resistors and replace then with outboard
pots. Pretty easy mod if you want to do it. Post back if you're
interested.

--
John Fields

"Ryan" wrote in message
om

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo?

Why not use Radio Shack's (or competitive) in-line headphone volume control
on the input?

Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm

Thanks for this link. I've always wondered what was inside mine, but didn't
want to damage the case.

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

BTW, if you power a Boostaroo with 5 VDC, it puts out about 1.4 volt RMS at
clipping. I do that with a power supply that was left over after Comcast
upgraded my cable modem.

"Ryan" wrote in message
om

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo?

Why not use Radio Shack's (or competitive) in-line headphone volume control
on the input?

Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm

Thanks for this link. I've always wondered what was inside mine, but didn't
want to damage the case.

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

BTW, if you power a Boostaroo with 5 VDC, it puts out about 1.4 volt RMS at
clipping. I do that with a power supply that was left over after Comcast
upgraded my cable modem.

"Ryan" wrote in message
om

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo?

Why not use Radio Shack's (or competitive) in-line headphone volume control
on the input?

Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm

Thanks for this link. I've always wondered what was inside mine, but didn't
want to damage the case.

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

BTW, if you power a Boostaroo with 5 VDC, it puts out about 1.4 volt RMS at
clipping. I do that with a power supply that was left over after Comcast
upgraded my cable modem.

"Ryan" wrote in message
om

I'm sure some of you are familiar the with the "Boostaroo", a small
headphone amplifier (http://www.boostaroo.com). Also sold at Radio
Shack, best buy, etc, possibly under other names.

The problem is this doesn't have a gain control, you are supposed to
use the vol control on the input device. Well the input device is an
XM radio, which doesn't have a volume control, just line out. This is
going on a motorcycle. I was wondering if someone knew if it would be
possible to add a gain control to the boostaroo?

Why not use Radio Shack's (or competitive) in-line headphone volume control
on the input?

Maybe it would be as
simple as varying the input voltage to the device? Here is an article
about the boostaroo that has a pic of the inside and talks a little
bit about how it works.
http://www.dansdata.com/boostaroo.htm

Thanks for this link. I've always wondered what was inside mine, but didn't
want to damage the case.

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

BTW, if you power a Boostaroo with 5 VDC, it puts out about 1.4 volt RMS at
clipping. I do that with a power supply that was left over after Comcast
upgraded my cable modem.

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the IC's it
contains.
0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

TonyP.

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the IC's it
contains.
0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

TonyP.

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the IC's it
contains.
0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

TonyP.

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it seems to
me to convey quite a number of misapprehensions about the Boostaroo's
technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the IC's it
contains.
0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

TonyP.

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it
seems to me to convey quite a number of misapprehensions about the
Boostaroo's technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.

Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

The Boostaroo is a handy-dandy little gizmo. It's a high quality voltage
amplifier as well as being a headphone amp with gain.

Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

More negative feedback with stability, less nonlinear distortion.

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it
seems to me to convey quite a number of misapprehensions about the
Boostaroo's technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.

Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

The Boostaroo is a handy-dandy little gizmo. It's a high quality voltage
amplifier as well as being a headphone amp with gain.

Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

More negative feedback with stability, less nonlinear distortion.

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it
seems to me to convey quite a number of misapprehensions about the
Boostaroo's technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.

Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

The Boostaroo is a handy-dandy little gizmo. It's a high quality voltage
amplifier as well as being a headphone amp with gain.

Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

More negative feedback with stability, less nonlinear distortion.

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

However, even though the site is positive about the Boostaroo, it
seems to me to convey quite a number of misapprehensions about the
Boostaroo's technical performance. Please check this page out:

http://www.pcavtech.com/pwramp/boostaroo/

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.

Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

The Boostaroo is a handy-dandy little gizmo. It's a high quality voltage
amplifier as well as being a headphone amp with gain.

Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

More negative feedback with stability, less nonlinear distortion.

"Arny Krueger" wrote in message
...
"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest
peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a 16 ohm
load. Into a 600 ohm load, I could probably believe it.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

Agreed, if it really performs as well as that I might buy a couple myself
:-)

TonyP.

"Arny Krueger" wrote in message
...
"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest
peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a 16 ohm
load. Into a 600 ohm load, I could probably believe it.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

Agreed, if it really performs as well as that I might buy a couple myself
:-)

TonyP.

"Arny Krueger" wrote in message
...
"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest
peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a 16 ohm
load. Into a 600 ohm load, I could probably believe it.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

Agreed, if it really performs as well as that I might buy a couple myself
:-)

TonyP.

"Arny Krueger" wrote in message
...
"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions that are
widely used with portable audio gear. Their graphs start with a lowest
peak
output voltage of about 1.8 volts. The device is clipping at that point in
my tests. I just backed off the levels until it was well out of clipping.
0.775 volts is enough to power the more sensitive earphones. It's also 0
dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a 16 ohm
load. Into a 600 ohm load, I could probably believe it.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something
like 1.4 volts at clipping. With my 7506s, this is more than enough.

Agreed, if it really performs as well as that I might buy a couple myself
:-)

TonyP.

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions
that are widely used with portable audio gear. Their graphs start
with a lowest peak output voltage of about 1.8 volts. The device is
clipping at that point in my tests. I just backed off the levels
until it was well out of clipping.

0.775 volts is enough to power the more sensitive earphones. It's
also 0 dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a
16 ohm load. Into a 600 ohm load, I could probably believe it.

Actually, the test load was composed of 15 ohm 1/4 watt resistors.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something like 1.4 volts at clipping. With my 7506s, this is more
than enough.

Agreed, if it really performs as well as that I might buy a couple
myself :-)

Or just start with one... They are as close as the nearest RS store.

;-)

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions
that are widely used with portable audio gear. Their graphs start
with a lowest peak output voltage of about 1.8 volts. The device is
clipping at that point in my tests. I just backed off the levels
until it was well out of clipping.

0.775 volts is enough to power the more sensitive earphones. It's
also 0 dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a
16 ohm load. Into a 600 ohm load, I could probably believe it.

Actually, the test load was composed of 15 ohm 1/4 watt resistors.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something like 1.4 volts at clipping. With my 7506s, this is more
than enough.

Agreed, if it really performs as well as that I might buy a couple
myself :-)

Or just start with one... They are as close as the nearest RS store.

;-)

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions
that are widely used with portable audio gear. Their graphs start
with a lowest peak output voltage of about 1.8 volts. The device is
clipping at that point in my tests. I just backed off the levels
until it was well out of clipping.

0.775 volts is enough to power the more sensitive earphones. It's
also 0 dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a
16 ohm load. Into a 600 ohm load, I could probably believe it.

Actually, the test load was composed of 15 ohm 1/4 watt resistors.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something like 1.4 volts at clipping. With my 7506s, this is more
than enough.

Agreed, if it really performs as well as that I might buy a couple
myself :-)

Or just start with one... They are as close as the nearest RS store.

;-)

"TonyP" wrote in message
u

"Arny Krueger" wrote in message
...

"TonyP" wrote in message
u

Your results are simply *amazing* considering the performance of the
IC's it contains.

Not necessarily. The chip specs show output under test conditions
that are widely used with portable audio gear. Their graphs start
with a lowest peak output voltage of about 1.8 volts. The device is
clipping at that point in my tests. I just backed off the levels
until it was well out of clipping.

0.775 volts is enough to power the more sensitive earphones. It's
also 0 dBu, standard audio production operating levels.

Sure, but it looks to me like those figures were obtained without a
16 ohm load. Into a 600 ohm load, I could probably believe it.

Actually, the test load was composed of 15 ohm 1/4 watt resistors.

0.0009 % THD at 38 mW output (0.775V into 16 ohms) with 3V supply.
Are you REALLY sure about that?

Yes. It works even better with a 5 volt power supply. It puts out
something like 1.4 volts at clipping. With my 7506s, this is more
than enough.

Agreed, if it really performs as well as that I might buy a couple
myself :-)

Or just start with one... They are as close as the nearest RS store.

;-)

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

--
John Fields

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

--
John Fields

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

--
John Fields

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

--
John Fields

On Sun, 14 Mar 2004 15:07:18 -0600, John Fields
wrote:

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

---
Actually, looking at the picture more critically reveals that the input
resistors and amp inputs are (probably) lined up like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R1] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R3] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R4] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R2] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

Also, looking at U3-5 reveals a wide trace, which is common practice
with power supply wiring. U2-4 also sports this wide trace, which is
consistent with Figure 5 of Philips's data sheet, pin 4 being shown as
ground. Notice also that the trace fron U2-4 forks as it proceeds
downward from pin 5 and appears to pick up one end of R3, one end of R4,
and what could be some wide pads used to terminate the shield or the
shield's drain wire and what appears to be the negative side of the
supply wiring. (Note the big "NEG" by the pad).

Now, if one end of R3 is grounded and R1R3 is a voltage divider, the
other end of R3 should be connected to one end of R1 and to pin 2 of all
of the amps. We can see that U1-2 is connected to a trace which appears
to connect one end of R1, one end of R3, U2-2 and a via. U3 also
terminates in a via, and my guess is that those vias are connected
together on the rear of the board, hooking everything up as shown in
the schematic, above. All that's left is the input to R1, and it
probably comes in on the red wire with a trace on the rear of the board
connecting the pad the red wire's soldered into to the via on the so-far
unconnected end of R1.

Continuing, if R2R4 is also a voltage divider, and we wanted to get the
phase right between the left and the right channels, We'd need to apply
the attenuated signal to the - input (pin 3) of the amps.

Looking at the picture reveals that U3-3 does, in fact connect to what
looks like the junction of R2 and R4. U1-3 and U2-3 connect to vias
which, for my money, are connected to each other and to U3-3 on the rear
of the board. As we saw before, it looks like the other end of R4 is
connected to ground through the wide trace, which only leaves the input
to R2 to figure out. That end of R2 is connected to a via which is
close enough to the pad the white wire's soldered into to make it almost
nonsensical for them not to be connected together. If they are, then
everything's been sorted out and the four resistors are just a couple of
flat, passive, voltage dividers being used as input attenuators.

Then there's the question you brought up regarding the difference in
gain between that given in the Philips data sheet (26dB) and that given
by the Boosteroo folks as 12dB. That's a 14dB difference, which means
that the voltage divider has to attenuate the input signal by 14dB.

So, for

dB = 20 log n

where the n is the ratio of the voltage into the divider to the voltage
out of it,

log n = dB/20 = 14/20 = 0.7,


so the ratio is the antilog of 0.7, or about 5:1.


Our divider then looks like this:

5Vout
|
[R1]
|
+----Vout
|
[R2]
|
0V


Normalizing Vout and R2 to 1 gives us

5
|
[R1]
|
+----1
|
[1]
|
0V

and allows us to calculate the value of R1:


R1 = R2 (E1-E2)/E2


So, R1 = 1 (5-1)/1 = 4R2

Which means that our resistors have to have a resistance ratio of 4:1
for our output voltage to be one fifth of the input voltage.


Relating that back to the Boostaroo means that for 12dB of voltage gain
R1 = 4R3 and R2 = 4R4.

Looking at the picture again, it's really difficult to tell what's what
with the resistor values, but If I took a stab at it, I'd say it looks
like R3 is labelled "1001" which would make it a 1000 ohm 1% resistor.
Four times that would be 4000 ohms, and the closest 1% value is 4020
ohms, which R1 _might_ be... Anyway, that would make the ratio right.

Interestingly, R2 looks like it's labelled "1001" and R4 could be "4021"
which would mean that if they are, and the circuit's wired like I think
it is, They've been soldered into each others's slots!

I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

Or maybe somebody else has a clue?

--
John Fields

On Sun, 14 Mar 2004 15:07:18 -0600, John Fields
wrote:

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

---
Actually, looking at the picture more critically reveals that the input
resistors and amp inputs are (probably) lined up like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R1] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R3] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R4] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R2] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

Also, looking at U3-5 reveals a wide trace, which is common practice
with power supply wiring. U2-4 also sports this wide trace, which is
consistent with Figure 5 of Philips's data sheet, pin 4 being shown as
ground. Notice also that the trace fron U2-4 forks as it proceeds
downward from pin 5 and appears to pick up one end of R3, one end of R4,
and what could be some wide pads used to terminate the shield or the
shield's drain wire and what appears to be the negative side of the
supply wiring. (Note the big "NEG" by the pad).

Now, if one end of R3 is grounded and R1R3 is a voltage divider, the
other end of R3 should be connected to one end of R1 and to pin 2 of all
of the amps. We can see that U1-2 is connected to a trace which appears
to connect one end of R1, one end of R3, U2-2 and a via. U3 also
terminates in a via, and my guess is that those vias are connected
together on the rear of the board, hooking everything up as shown in
the schematic, above. All that's left is the input to R1, and it
probably comes in on the red wire with a trace on the rear of the board
connecting the pad the red wire's soldered into to the via on the so-far
unconnected end of R1.

Continuing, if R2R4 is also a voltage divider, and we wanted to get the
phase right between the left and the right channels, We'd need to apply
the attenuated signal to the - input (pin 3) of the amps.

Looking at the picture reveals that U3-3 does, in fact connect to what
looks like the junction of R2 and R4. U1-3 and U2-3 connect to vias
which, for my money, are connected to each other and to U3-3 on the rear
of the board. As we saw before, it looks like the other end of R4 is
connected to ground through the wide trace, which only leaves the input
to R2 to figure out. That end of R2 is connected to a via which is
close enough to the pad the white wire's soldered into to make it almost
nonsensical for them not to be connected together. If they are, then
everything's been sorted out and the four resistors are just a couple of
flat, passive, voltage dividers being used as input attenuators.

Then there's the question you brought up regarding the difference in
gain between that given in the Philips data sheet (26dB) and that given
by the Boosteroo folks as 12dB. That's a 14dB difference, which means
that the voltage divider has to attenuate the input signal by 14dB.

So, for

dB = 20 log n

where the n is the ratio of the voltage into the divider to the voltage
out of it,

log n = dB/20 = 14/20 = 0.7,


so the ratio is the antilog of 0.7, or about 5:1.


Our divider then looks like this:

5Vout
|
[R1]
|
+----Vout
|
[R2]
|
0V


Normalizing Vout and R2 to 1 gives us

5
|
[R1]
|
+----1
|
[1]
|
0V

and allows us to calculate the value of R1:


R1 = R2 (E1-E2)/E2


So, R1 = 1 (5-1)/1 = 4R2

Which means that our resistors have to have a resistance ratio of 4:1
for our output voltage to be one fifth of the input voltage.


Relating that back to the Boostaroo means that for 12dB of voltage gain
R1 = 4R3 and R2 = 4R4.

Looking at the picture again, it's really difficult to tell what's what
with the resistor values, but If I took a stab at it, I'd say it looks
like R3 is labelled "1001" which would make it a 1000 ohm 1% resistor.
Four times that would be 4000 ohms, and the closest 1% value is 4020
ohms, which R1 _might_ be... Anyway, that would make the ratio right.

Interestingly, R2 looks like it's labelled "1001" and R4 could be "4021"
which would mean that if they are, and the circuit's wired like I think
it is, They've been soldered into each others's slots!

I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

Or maybe somebody else has a clue?

--
John Fields

On Sun, 14 Mar 2004 15:07:18 -0600, John Fields
wrote:

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

---
Actually, looking at the picture more critically reveals that the input
resistors and amp inputs are (probably) lined up like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R1] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R3] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R4] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R2] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

Also, looking at U3-5 reveals a wide trace, which is common practice
with power supply wiring. U2-4 also sports this wide trace, which is
consistent with Figure 5 of Philips's data sheet, pin 4 being shown as
ground. Notice also that the trace fron U2-4 forks as it proceeds
downward from pin 5 and appears to pick up one end of R3, one end of R4,
and what could be some wide pads used to terminate the shield or the
shield's drain wire and what appears to be the negative side of the
supply wiring. (Note the big "NEG" by the pad).

Now, if one end of R3 is grounded and R1R3 is a voltage divider, the
other end of R3 should be connected to one end of R1 and to pin 2 of all
of the amps. We can see that U1-2 is connected to a trace which appears
to connect one end of R1, one end of R3, U2-2 and a via. U3 also
terminates in a via, and my guess is that those vias are connected
together on the rear of the board, hooking everything up as shown in
the schematic, above. All that's left is the input to R1, and it
probably comes in on the red wire with a trace on the rear of the board
connecting the pad the red wire's soldered into to the via on the so-far
unconnected end of R1.

Continuing, if R2R4 is also a voltage divider, and we wanted to get the
phase right between the left and the right channels, We'd need to apply
the attenuated signal to the - input (pin 3) of the amps.

Looking at the picture reveals that U3-3 does, in fact connect to what
looks like the junction of R2 and R4. U1-3 and U2-3 connect to vias
which, for my money, are connected to each other and to U3-3 on the rear
of the board. As we saw before, it looks like the other end of R4 is
connected to ground through the wide trace, which only leaves the input
to R2 to figure out. That end of R2 is connected to a via which is
close enough to the pad the white wire's soldered into to make it almost
nonsensical for them not to be connected together. If they are, then
everything's been sorted out and the four resistors are just a couple of
flat, passive, voltage dividers being used as input attenuators.

Then there's the question you brought up regarding the difference in
gain between that given in the Philips data sheet (26dB) and that given
by the Boosteroo folks as 12dB. That's a 14dB difference, which means
that the voltage divider has to attenuate the input signal by 14dB.

So, for

dB = 20 log n

where the n is the ratio of the voltage into the divider to the voltage
out of it,

log n = dB/20 = 14/20 = 0.7,


so the ratio is the antilog of 0.7, or about 5:1.


Our divider then looks like this:

5Vout
|
[R1]
|
+----Vout
|
[R2]
|
0V


Normalizing Vout and R2 to 1 gives us

5
|
[R1]
|
+----1
|
[1]
|
0V

and allows us to calculate the value of R1:


R1 = R2 (E1-E2)/E2


So, R1 = 1 (5-1)/1 = 4R2

Which means that our resistors have to have a resistance ratio of 4:1
for our output voltage to be one fifth of the input voltage.


Relating that back to the Boostaroo means that for 12dB of voltage gain
R1 = 4R3 and R2 = 4R4.

Looking at the picture again, it's really difficult to tell what's what
with the resistor values, but If I took a stab at it, I'd say it looks
like R3 is labelled "1001" which would make it a 1000 ohm 1% resistor.
Four times that would be 4000 ohms, and the closest 1% value is 4020
ohms, which R1 _might_ be... Anyway, that would make the ratio right.

Interestingly, R2 looks like it's labelled "1001" and R4 could be "4021"
which would mean that if they are, and the circuit's wired like I think
it is, They've been soldered into each others's slots!

I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

Or maybe somebody else has a clue?

--
John Fields

On Sun, 14 Mar 2004 15:07:18 -0600, John Fields
wrote:

On Sun, 14 Mar 2004 04:45:44 -0500, "Arny Krueger"
wrote:


Also notice that they Philips the chip with ca. 26 dB gain. The Boostaroo
seems to use negative feedback to cut that gain dramatically. See the
resistors in the picture at http://www.dansdata.com/boostaroo.htm ? My
guess is that they operate one chip as an input buffer and power amp, and
run the other two as unity gain buffers.

---
I disagree.

The number of resistors and the pins they're connected to on the
amplifiers leads me to believe that they're merely two voltage dividers
used as input attenuators to all six amplifiers; three for the left
channel and three for the right. Something like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

If you have trouble reading this using a fixed-pitch font, I'll post a
real schematic if you want one.

---
Actually, looking at the picture more critically reveals that the input
resistors and amp inputs are (probably) lined up like this:


+3V +3V +3V
| | |
+--[+C]--+ +--[+C]--+ +--[+C]--+
| | | | | |
RIN---+ | GND | GND | GND
| | | |
[R1] +----|------------+----|------------+ |
| | 8 | 8 | 8
+-----+-2-|-\U1A +-2-|-\U2A +-2-|-\U3A
| | 7-----+ | 7-----+ | 7-----+
[R3] +-1-|+/ | +-1-|+/ | +-1-|+/ |
| | 5 | | 5 | | 5 |
| | | | | | | | | |
GND---+-----+----+------------+----+------------+----+------------+
| | | | | | | |
[R4] +-4-|+\U1B | +-4-|+\U2B | +-4-|+\U3B | |
| | 6-+ | | | 6-+ | | | 6-+ | |
+-----+-3-|-/ |+ |+ | +-|-/ |+ |+ | +-|-/ |+ |+ |
| | [C] [C] | |3 [C] [C] | |3 [C] [C] |
[R2] +---------|---|---|-+-------|---|-----+ | | |
| | | | | | | | | |
LIN---+ | | | | | | | | |
| | | | | | | | |
L R GND L R GND L R GND
\ / \ / \ /
OUT 1 OUT 2 OUT 3

Also, looking at U3-5 reveals a wide trace, which is common practice
with power supply wiring. U2-4 also sports this wide trace, which is
consistent with Figure 5 of Philips's data sheet, pin 4 being shown as
ground. Notice also that the trace fron U2-4 forks as it proceeds
downward from pin 5 and appears to pick up one end of R3, one end of R4,
and what could be some wide pads used to terminate the shield or the
shield's drain wire and what appears to be the negative side of the
supply wiring. (Note the big "NEG" by the pad).

Now, if one end of R3 is grounded and R1R3 is a voltage divider, the
other end of R3 should be connected to one end of R1 and to pin 2 of all
of the amps. We can see that U1-2 is connected to a trace which appears
to connect one end of R1, one end of R3, U2-2 and a via. U3 also
terminates in a via, and my guess is that those vias are connected
together on the rear of the board, hooking everything up as shown in
the schematic, above. All that's left is the input to R1, and it
probably comes in on the red wire with a trace on the rear of the board
connecting the pad the red wire's soldered into to the via on the so-far
unconnected end of R1.

Continuing, if R2R4 is also a voltage divider, and we wanted to get the
phase right between the left and the right channels, We'd need to apply
the attenuated signal to the - input (pin 3) of the amps.

Looking at the picture reveals that U3-3 does, in fact connect to what
looks like the junction of R2 and R4. U1-3 and U2-3 connect to vias
which, for my money, are connected to each other and to U3-3 on the rear
of the board. As we saw before, it looks like the other end of R4 is
connected to ground through the wide trace, which only leaves the input
to R2 to figure out. That end of R2 is connected to a via which is
close enough to the pad the white wire's soldered into to make it almost
nonsensical for them not to be connected together. If they are, then
everything's been sorted out and the four resistors are just a couple of
flat, passive, voltage dividers being used as input attenuators.

Then there's the question you brought up regarding the difference in
gain between that given in the Philips data sheet (26dB) and that given
by the Boosteroo folks as 12dB. That's a 14dB difference, which means
that the voltage divider has to attenuate the input signal by 14dB.

So, for

dB = 20 log n

where the n is the ratio of the voltage into the divider to the voltage
out of it,

log n = dB/20 = 14/20 = 0.7,


so the ratio is the antilog of 0.7, or about 5:1.


Our divider then looks like this:

5Vout
|
[R1]
|
+----Vout
|
[R2]
|
0V


Normalizing Vout and R2 to 1 gives us

5
|
[R1]
|
+----1
|
[1]
|
0V

and allows us to calculate the value of R1:


R1 = R2 (E1-E2)/E2


So, R1 = 1 (5-1)/1 = 4R2

Which means that our resistors have to have a resistance ratio of 4:1
for our output voltage to be one fifth of the input voltage.


Relating that back to the Boostaroo means that for 12dB of voltage gain
R1 = 4R3 and R2 = 4R4.

Looking at the picture again, it's really difficult to tell what's what
with the resistor values, but If I took a stab at it, I'd say it looks
like R3 is labelled "1001" which would make it a 1000 ohm 1% resistor.
Four times that would be 4000 ohms, and the closest 1% value is 4020
ohms, which R1 _might_ be... Anyway, that would make the ratio right.

Interestingly, R2 looks like it's labelled "1001" and R4 could be "4021"
which would mean that if they are, and the circuit's wired like I think
it is, They've been soldered into each others's slots!

I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

Or maybe somebody else has a clue?

--
John Fields

"John Fields" wrote in message


I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

I only have one Boostaroo. As mentioned in the
http://www.dansdata.com/boostaroo.htm article, they are REALLY hard to snap
apart. I don't have the neat vise the author has. I'm very happy just
listening to the one Boostaroo that I have.

I sincerely hoped that the time I put into
http://www.pcavtech.com/pwramp/boostaroo/ was enough to satisfy the cosmic
needs of knowledge about the Boostaroo...

I think this is the first time I've been criticized for posting test results
that were unbelievably good!

;-)

Thanks John for your well-studied speculations.

"John Fields" wrote in message


I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

I only have one Boostaroo. As mentioned in the
http://www.dansdata.com/boostaroo.htm article, they are REALLY hard to snap
apart. I don't have the neat vise the author has. I'm very happy just
listening to the one Boostaroo that I have.

I sincerely hoped that the time I put into
http://www.pcavtech.com/pwramp/boostaroo/ was enough to satisfy the cosmic
needs of knowledge about the Boostaroo...

I think this is the first time I've been criticized for posting test results
that were unbelievably good!

;-)

Thanks John for your well-studied speculations.

"John Fields" wrote in message


I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

I only have one Boostaroo. As mentioned in the
http://www.dansdata.com/boostaroo.htm article, they are REALLY hard to snap
apart. I don't have the neat vise the author has. I'm very happy just
listening to the one Boostaroo that I have.

I sincerely hoped that the time I put into
http://www.pcavtech.com/pwramp/boostaroo/ was enough to satisfy the cosmic
needs of knowledge about the Boostaroo...

I think this is the first time I've been criticized for posting test results
that were unbelievably good!

;-)

Thanks John for your well-studied speculations.

"John Fields" wrote in message


I couldn't find any schematics anywhere on the web, so I guess to end
the guesswork a trip to Radio Shack, $20, and a little more "reverse
engineering" would do it. Problem is, I don't need one, and I hate to
spend the $20 for something I don't need. Maybe you could take one of
yours apart (in the interest of science?^) and post what you find?

I only have one Boostaroo. As mentioned in the
http://www.dansdata.com/boostaroo.htm article, they are REALLY hard to snap
apart. I don't have the neat vise the author has. I'm very happy just
listening to the one Boostaroo that I have.

I sincerely hoped that the time I put into
http://www.pcavtech.com/pwramp/boostaroo/ was enough to satisfy the cosmic
needs of knowledge about the Boostaroo...

I think this is the first time I've been criticized for posting test results
that were unbelievably good!

;-)

Thanks John for your well-studied speculations.

"Arny Krueger" wrote in message
...

I think this is the first time I've been criticized for posting test
results
that were unbelievably good!
;-)

No criticism at all, if true. I just wonder if your 16 ohm load was
disconnected without you knowing. (I originally thought it was just a simple
typo)
Given what we now know about the boosteroo circuit, I still can't see how
you can obtain those figures from that IC into a 16 (or 15) ohm load.

TonyP.

"Arny Krueger" wrote in message
...

I think this is the first time I've been criticized for posting test
results
that were unbelievably good!
;-)

No criticism at all, if true. I just wonder if your 16 ohm load was
disconnected without you knowing. (I originally thought it was just a simple
typo)
Given what we now know about the boosteroo circuit, I still can't see how
you can obtain those figures from that IC into a 16 (or 15) ohm load.

TonyP.

"Arny Krueger" wrote in message
...

I think this is the first time I've been criticized for posting test
results
that were unbelievably good!
;-)

No criticism at all, if true. I just wonder if your 16 ohm load was
disconnected without you knowing. (I originally thought it was just a simple
typo)
Given what we now know about the boosteroo circuit, I still can't see how
you can obtain those figures from that IC into a 16 (or 15) ohm load.

TonyP.