[John Larkin]

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

[Fred Bloggs[_2_]]

On Mar 2, 11:40*am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

[John Larkin]

On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs
wrote:

On Mar 2, 11:40*am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

Which textbook?

John

[Arny Krueger]

"John Larkin"
wrote in message

On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs
wrote:

On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape
head/mic preamp circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice
headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys
have fun playing with circuits, whether they make a lot
of sense or not.

John

Bizarre??? Just a standard buffered input CE with
negative feedback DC bias to stabilize the operating
point against Vbe and reverse leakage collector current
change with temperature- a textbook circuit...

Which textbook?

I don't know about textbooks, but it was a pretty standard circuit back in
1965 when I built a high performance RIAA preamp as an undergraduate project
as part work for my degree in engineering. if memory serves, it was in the
RCA transistor manual. I later built a number of these as standard parts of
Heathkits.

And voila, here's a schematic of a Dyna PAT-4 with essentually the same
circuit:

http://home.comcast.net/~g.e.dunn/PAT4/schem.jpg

The challenge that I had in 1965 was to build it using PNP germanium
switching transistors which weren't all that linear, were speced for beta =
20 and had no noise spec. The prof made a tactical error that he corrected
the next year - he didn't specify how many transistors or any other parts
that I was limited to use.

So, I built two amps with the circuit illustrated above, cascaded them, and
used 4 darlington pairs for the transistors, rather neatly solving the beta
problem. If memory serves the first stage was RIAA and the second was flat
with a gain of 10.

The thing ran rings around any commercial circuit that we compared it to,
whether SS or tubed both on the bench and in listening tests. In my travels
through the lab's parts bin, I also found a stash of appropriate-valued mil
spec metal film resistors, etc. As a commerical product, it might have had
to sell for $100s.

[m II]

"Arny Krueger" wrote in message
news
"John Larkin"
wrote in message

On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs
wrote:

On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape
head/mic preamp circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice
headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys
have fun playing with circuits, whether they make a lot
of sense or not.

John

Bizarre??? Just a standard buffered input CE with
negative feedback DC bias to stabilize the operating
point against Vbe and reverse leakage collector current
change with temperature- a textbook circuit...

Which textbook?

I don't know about textbooks, but it was a pretty standard circuit back in
1965 when I built a high performance RIAA preamp as an undergraduate project
as part work for my degree in engineering. if memory serves, it was in the
RCA transistor manual. I later built a number of these as standard parts of
Heathkits.

And voila, here's a schematic of a Dyna PAT-4 with essentually the same
circuit:

http://home.comcast.net/~g.e.dunn/PAT4/schem.jpg

The challenge that I had in 1965 was to build it using PNP germanium
switching transistors which weren't all that linear, were speced for beta =
20 and had no noise spec. The prof made a tactical error that he corrected
the next year - he didn't specify how many transistors or any other parts
that I was limited to use.

So, I built two amps with the circuit illustrated above, cascaded them, and
used 4 darlington pairs for the transistors, rather neatly solving the beta
problem. If memory serves the first stage was RIAA and the second was flat
with a gain of 10.

The thing ran rings around any commercial circuit that we compared it to,
whether SS or tubed both on the bench and in listening tests. In my travels
through the lab's parts bin, I also found a stash of appropriate-valued mil
spec metal film resistors, etc. As a commerical product, it might have had
to sell for $100s.

----

Jeeezzzz You must be old.

I remember cutting my teeth on my first big project in 1968 on a Heathkit
stereo amplifier. The RIAA network was a secret bunch of components
encapsulated so the user could not tell what hidden secrets were installed.

I finally through that kit out a few years ago on a move cleanup. Many
repairs taught me a few things about power transistor output circuits and
why to not increase the length of the speaker connection screws until they
hit the chassis out the back of the terminal strips. Even took a few
warranty repairs at the shop. After about 6 sets of output transistor
replacements it came back with clearance holes behind them....duh!


mike

[John Larkin]

On Wed, 2 Mar 2011 17:24:13 -0500, "Arny Krueger"
wrote:

"John Larkin"
wrote in message

On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs
wrote:

On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape
head/mic preamp circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice
headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys
have fun playing with circuits, whether they make a lot
of sense or not.

John

Bizarre??? Just a standard buffered input CE with
negative feedback DC bias to stabilize the operating
point against Vbe and reverse leakage collector current
change with temperature- a textbook circuit...

Which textbook?

I don't know about textbooks, but it was a pretty standard circuit back in
1965 when I built a high performance RIAA preamp as an undergraduate project
as part work for my degree in engineering. if memory serves, it was in the
RCA transistor manual. I later built a number of these as standard parts of
Heathkits.

I used to design language labs and recording studios/mixers, and we
used that circuit a lot for tape heads and mic amps. It was called
"the GE circuit", don't know why.


And voila, here's a schematic of a Dyna PAT-4 with essentually the same
circuit:

http://home.comcast.net/~g.e.dunn/PAT4/schem.jpg

The challenge that I had in 1965 was to build it using PNP germanium
switching transistors which weren't all that linear, were speced for beta =
20 and had no noise spec. The prof made a tactical error that he corrected
the next year - he didn't specify how many transistors or any other parts
that I was limited to use.

I think I used 2N3391s, silicon NPNs, which were the black [1] GE
cylindrical epoxy transistors with the flange on the bottom and the
concave top, where they poured the epoxy in. 1968, approximately.

People here were discussing a low-parts-count headphone amp, and it
occurred to me that this configuration is a lot of bang for a few
parts, as a power amp. I thought the bipolar-mosfet thing was cute,
but then I'm easily amused.

John

[1] their early ones used brown epoxy and were photosensitive.

[Fred Bloggs[_2_]]

On Mar 2, 4:33*pm, John Larkin
wrote:
On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs





wrote:
On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

Which textbook?

John- Hide quoted text -

- Show quoted text -

Just about any textbook that goes into bias point sensitivity analysis
of transistor circuits- you remember the S- functions, mainly ICQ
stability. The big three were HFE, VBE, and ICBO. Then the rest of
your circuit is just ac-bypass and the shunt-series feedback for
signals. I've seen it dozens of times.

[John Larkin]

On Wed, 2 Mar 2011 14:55:18 -0800 (PST), Fred Bloggs
wrote:

On Mar 2, 4:33*pm, John Larkin
wrote:
On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs





wrote:
On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

Which textbook?

John- Hide quoted text -

- Show quoted text -

Just about any textbook that goes into bias point sensitivity analysis
of transistor circuits- you remember the S- functions, mainly ICQ
stability. The big three were HFE, VBE, and ICBO. Then the rest of
your circuit is just ac-bypass and the shunt-series feedback for
signals. I've seen it dozens of times.

I bet you haven't seen the bipolar+mosfet version, with inductive
pullup, used as a power amp.

John

[Fred Bloggs[_2_]]

On Mar 2, 5:58*pm, John Larkin
wrote:
On Wed, 2 Mar 2011 14:55:18 -0800 (PST), Fred Bloggs





wrote:
On Mar 2, 4:33 pm, John Larkin
wrote:
On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs

wrote:
On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp....

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

Which textbook?

John- Hide quoted text -

- Show quoted text -

Just about any textbook that goes into bias point sensitivity analysis
of transistor circuits- you remember the S- functions, mainly ICQ
stability. The big three were HFE, VBE, and ICBO. Then the rest of
your circuit is just ac-bypass and the shunt-series feedback for
signals. I've seen it dozens of times.

I bet you haven't seen the bipolar+mosfet version, with inductive
pullup, used as a power amp.

John- Hide quoted text -

- Show quoted text -

I believe the collector inductor and/or transformer are used to
significantly increase the efficiency of the output stage, where that
consideration outweighs the additional cost.

[Fred Bloggs[_2_]]

On Mar 2, 5:58*pm, John Larkin
wrote:
On Wed, 2 Mar 2011 14:55:18 -0800 (PST), Fred Bloggs





wrote:
On Mar 2, 4:33 pm, John Larkin
wrote:
On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs

wrote:
On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp....

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...

Which textbook?

John- Hide quoted text -

- Show quoted text -

Just about any textbook that goes into bias point sensitivity analysis
of transistor circuits- you remember the S- functions, mainly ICQ
stability. The big three were HFE, VBE, and ICBO. Then the rest of
your circuit is just ac-bypass and the shunt-series feedback for
signals. I've seen it dozens of times.

I bet you haven't seen the bipolar+mosfet version, with inductive
pullup, used as a power amp.

John- Hide quoted text -

- Show quoted text -

I don't see the MOSFET being all that much of a change. And as for the
inductor pull-up, this just doesn't make sense for low wattage high
impedance headphone loads. Your inductive reactance needs to be a good
few integer multiples of the load impedance, making these things
prohibitively large if not unobtainable for a headphone app- you would
use far less iron/ ferrite by boost switching your supply to
accommodate the output swing...guess that's why I've never seen the
inductive pullup here.

[Bitrex]

On 3/2/2011 11:40 AM, John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Neat, like a parafeed amplifier. The choke will have to be pretty big
for audio frequencies...

I can think of a modification that would give more gain for the negative
feedback to "work" with: change the input transistor to a JFET, get rid
of the capacitor and extra resistor in the bias stabilization circuit,
and just stick a resistor in the emitter lead of the output transistor.
Then, move the load resistor of the first stage down and connect an
NPN transistor with a current limiting resistor to the output between
that load resistor and the power supply. If I've figured things out
correctly you then have a gyrator load for the first stage. The bias
should still be self-stabilizing too, because of the DC drop across the
output load inductor.



Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

Yup!


John

[Bitrex]

On 3/2/2011 3:11 PM, Bitrex wrote:
On 3/2/2011 11:40 AM, John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Neat, like a parafeed amplifier. The choke will have to be pretty big
for audio frequencies...

I can think of a modification that would give more gain for the negative
feedback to "work" with: change the input transistor to a JFET, get rid
of the capacitor and extra resistor in the bias stabilization circuit,
and just stick a resistor in the emitter lead of the output transistor.
Then, move the load resistor of the first stage down and connect an NPN
transistor with a current limiting resistor to the output between that
load resistor and the power supply. If I've figured things out correctly
you then have a gyrator load for the first stage. The bias should still
be self-stabilizing too, because of the DC drop across the output load
inductor.


Nope, sorry, cancel that, it won't work. The output stage has gain and
the gyrator won't work properly.

[John Larkin]

On Wed, 02 Mar 2011 15:11:37 -0500, Bitrex
wrote:

On 3/2/2011 11:40 AM, John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Neat, like a parafeed amplifier. The choke will have to be pretty big
for audio frequencies...

You could just use a power resistor and tweak the drain voltage
operating point. It's just not as elegant.

John

[Bitrex]

On 3/2/2011 4:32 PM, John Larkin wrote:
On Wed, 02 Mar 2011 15:11:37 -0500, Bitrex
wrote:

On 3/2/2011 11:40 AM, John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Neat, like a parafeed amplifier. The choke will have to be pretty big
for audio frequencies...

You could just use a power resistor and tweak the drain voltage
operating point. It's just not as elegant.

John



The circuit I'm working on now as my "exercise in simplicity" from the
thread a while back uses another transistor for the load on the output
stage, simulating an inductor. This also has the advantage in Class A
of being able to set the idle current to half of the desired maximum
output current, instead of the usual need to set the idle at the full
output current.

If I remember correctly I think if one uses a resistive load the
quiescent idle current will have to be _more_ than the maximum output
current to get the desired output current into the load when the
transistor shuts down, because of the drop across the resistor.

I think I have an unhealthy obsession with simulated inductors.

[John Larkin]

On Wed, 02 Mar 2011 16:50:46 -0500, Bitrex
wrote:

On 3/2/2011 4:32 PM, John Larkin wrote:
On Wed, 02 Mar 2011 15:11:37 -0500, Bitrex
wrote:

On 3/2/2011 11:40 AM, John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Neat, like a parafeed amplifier. The choke will have to be pretty big
for audio frequencies...

You could just use a power resistor and tweak the drain voltage
operating point. It's just not as elegant.

John



The circuit I'm working on now as my "exercise in simplicity" from the
thread a while back uses another transistor for the load on the output
stage, simulating an inductor. This also has the advantage in Class A
of being able to set the idle current to half of the desired maximum
output current, instead of the usual need to set the idle at the full
output current.

If I remember correctly I think if one uses a resistive load the
quiescent idle current will have to be _more_ than the maximum output
current to get the desired output current into the load when the
transistor shuts down, because of the drop across the resistor.

Yes, you can swing almost all the way to the rails with a
constant-current load, as opposed to a resistor, so it's more
efficient... like an inductor. The inductor allows close to 2x Vcc p-p
voltage swing, if that matters.

But the constant-current load bumps the active parts count by 50% !!!

I think you could do a nice headphone amp with one mosfet. Or go nuts
and use a GaN fet.

John

[Vladimir Vassilevsky[_2_]]

John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

[John Larkin]

On Wed, 02 Mar 2011 17:21:23 -0600, Vladimir Vassilevsky
wrote:



John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


The one on the left, with the base and gate connected, is sure cute.


John

[Bitrex]

On 3/2/2011 6:30 PM, John Larkin wrote:
On Wed, 02 Mar 2011 17:21:23 -0600, Vladimir Vassilevsky
wrote:



John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


The one on the left, with the base and gate connected, is sure cute.


John


I'm having a little trouble with the operation of that one. The way
it's set up, assuming the output sits at 0 volts won't the input BJT be
cut off?

[John Larkin]

On Wed, 02 Mar 2011 19:26:29 -0500, Bitrex
wrote:

On 3/2/2011 6:30 PM, John Larkin wrote:
On Wed, 02 Mar 2011 17:21:23 -0600, Vladimir Vassilevsky
wrote:



John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


The one on the left, with the base and gate connected, is sure cute.


John


I'm having a little trouble with the operation of that one. The way
it's set up, assuming the output sits at 0 volts won't the input BJT be
cut off?

Jfets usually run at negative gate voltage. Assume the transistor base
is at +0.7. The jfet source will be at some more positive voltage,
+2.5 maybe. That's enough to run the transistor.

Actually, you can cascode a transistor into the source of a fet that
has a grounded gate. In that case, the source/collector voltage might
be a volt or two. You would have to look at the fet transfer curve,
and know the design operating current, to see exactly what that
voltage might be.

The problem with jfets is the huge part-to-part variation in Idss and
transfer curves. A 10:1 datasheet spread in Idss isn't unusual.





+10v
|
|
|
d
gnd---------g
s
|
|
+------ Vs
|
|
10K
|
|
|
gnd

For a typical vanilla jfet in this circuit, Vs might be +1 to +4 volts
maybe.

John

[Bitrex]

On 3/2/2011 8:06 PM, John Larkin wrote:
On Wed, 02 Mar 2011 19:26:29 -0500, Bitrex
wrote:

On 3/2/2011 6:30 PM, John Larkin wrote:
On Wed, 02 Mar 2011 17:21:23 -0600, Vladimir Vassilevsky
wrote:



John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


The one on the left, with the base and gate connected, is sure cute.


John


I'm having a little trouble with the operation of that one. The way
it's set up, assuming the output sits at 0 volts won't the input BJT be
cut off?

Jfets usually run at negative gate voltage. Assume the transistor base
is at +0.7. The jfet source will be at some more positive voltage,
+2.5 maybe. That's enough to run the transistor.

Yep - I'm not a complete "n00b"... What I mean though is with
that circuit with the input BJT's emitter at ground if its base is at
0.7 volts the minute its base goes negative it's going to cut off.
Maybe the emitter should be connected to the negative supply?


Actually, you can cascode a transistor into the source of a fet that
has a grounded gate. In that case, the source/collector voltage might
be a volt or two. You would have to look at the fet transfer curve,
and know the design operating current, to see exactly what that
voltage might be.

I'm foggy on how such a cascode reduces noise - improved distortion,
bandwidth, and PSRR I can understand but how does two transistors end up
less noisy than one? I know with tubes a cascode was considered a low
noise alternative since two triodes in cascode would have lower noise
than a single pentode, with similar gain.


The problem with jfets is the huge part-to-part variation in Idss and
transfer curves. A 10:1 datasheet spread in Idss isn't unusual.





+10v
|
|
|
d
gnd---------g
s
|
|
+------ Vs
|
|
10K
|
|
|
gnd

For a typical vanilla jfet in this circuit, Vs might be +1 to +4 volts
maybe.

John

[Phil Hobbs[_2_]]

John Larkin wrote:
On Wed, 02 Mar 2011 19:26:29 -0500, Bitrex
wrote:

On 3/2/2011 6:30 PM, John Larkin wrote:
On Wed, 02 Mar 2011 17:21:23 -0600, Vladimir Vassilevsky
wrote:



John Larkin wrote:


I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

Here is a couple of very low noise audio circuits for the same purpose:

http://www.abvolt.com/misc/inputs_audio.jpg

I like BJT and JFET in cascode.


The one on the left, with the base and gate connected, is sure cute.


John


I'm having a little trouble with the operation of that one. The way
it's set up, assuming the output sits at 0 volts won't the input BJT be
cut off?

Jfets usually run at negative gate voltage. Assume the transistor base
is at +0.7. The jfet source will be at some more positive voltage,
+2.5 maybe. That's enough to run the transistor.

Actually, you can cascode a transistor into the source of a fet that
has a grounded gate. In that case, the source/collector voltage might
be a volt or two. You would have to look at the fet transfer curve,
and know the design operating current, to see exactly what that
voltage might be.

The problem with jfets is the huge part-to-part variation in Idss and
transfer curves. A 10:1 datasheet spread in Idss isn't unusual.





+10v
|
|
|
d
gnd---------g
s
|
|
+------ Vs
|
|
10K
|
|
|
gnd

For a typical vanilla jfet in this circuit, Vs might be +1 to +4 volts
maybe.

John



BF862s are much better--cutoff to full on in half a volt or so. Their
transconductance is so high that even with a 2.5:1 range of I_DSS, the
spread of V_GS is pretty reasonable.

They're also very quiet, go about 700 MHz, and cost 20 cents. Other
than that, they stink.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

[John Fields]

On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:



I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

---
JF

[John Larkin]

On Wed, 02 Mar 2011 18:36:25 -0600, John Fields
wrote:

On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:



I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?


You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?


Chickenleg work!

John

[Bill Sloman]

On Mar 3, 2:11*am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields



wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

He's not playing your game, which involves telling John Larkin how
cute his circuits are.

Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

Chickenleg work!

It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.

--
Bill Sloman, Nijmegen

[John Larkin]

On Wed, 2 Mar 2011 17:59:58 -0800 (PST), Bill Sloman
wrote:

On Mar 3, 2:11*am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields



wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

He's not playing your game, which involves telling John Larkin how
cute his circuits are.

He's not designing circuits, which is what this newsgroup is about.

You aren't either. Both of you start to cluck and peck when people do
design circuits. No surprise.



Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

Chickenleg work!

It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.

You can't look at a circuit this simple and see what it's doing? OK,
no surprise.

John

[John - KD5YI]

On 3/2/2011 8:32 PM, John Larkin wrote:
On Wed, 2 Mar 2011 17:59:58 -0800 (PST), Bill Sloman
wrote:

On Mar 3, 2:11 am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields



wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

He's not playing your game, which involves telling John Larkin how
cute his circuits are.

He's not designing circuits, which is what this newsgroup is about.

You aren't either. Both of you start to cluck and peck when people do
design circuits. No surprise.



Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

Chickenleg work!

It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.

You can't look at a circuit this simple and see what it's doing? OK,
no surprise.

John

Well, I thought designing a circuit included supplying component values.
No?

[MakeNoAttemptToAdjustYourSet]

On Wed, 02 Mar 2011 18:32:42 -0800, John Larkin
wrote:

He's not designing circuits, which is what this newsgroup is about.

Bull****. You do not know the facts in the first case you cite, and
you are off the mark in the second case you cite.

Electronics is far more than a mere circuit. There are several
physical disciplines involved. This group is about ALL aspects of the
science of electronics design, and that extends BEYOND only circuits.

Grow the **** up, you mouthy little school marm wanna be bitch!

You have no clue what John does or does not do.

So you need to grow the **** up in that respect as well, you ****y
little bitch.

[Bill Sloman]

On Mar 3, 3:32*am, John Larkin
wrote:
On Wed, 2 Mar 2011 17:59:58 -0800 (PST), Bill Sloman



wrote:
On Mar 3, 2:11 am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields

wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp....

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue..
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

He's not playing your game, which involves telling John Larkin how
cute his circuits are.

He's not designing circuits, which is what this newsgroup is about.

You aren't either. Both of you start to cluck and peck when people do
design circuits. No surprise.



Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

Chickenleg work!

It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.

You can't look at a circuit this simple and see what it's doing? OK,
no surprise.

Without the component values, it does take a moment's thought, which
is wasted on a bizarre (if simple) circuit with few potential
applications.

--
Bill Sloman, Nijmegen

[John Fields]

On Wed, 02 Mar 2011 18:32:42 -0800, John Larkin
wrote:

On Wed, 2 Mar 2011 17:59:58 -0800 (PST), Bill Sloman
wrote:

On Mar 3, 2:11*am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields



wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:

I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

He's not playing your game, which involves telling John Larkin how
cute his circuits are.

He's not designing circuits, which is what this newsgroup is about.

---
Well, I'd say that the ratio of my technical to non-technical articles
is about 10:1, while yours is about 1:10, and over the years I'd be
willing to bet that I've posted about 10 times more designs, fully
worked out, with component values included and, lately, simulated,
than you have.
---

You aren't either. Both of you start to cluck and peck when people do
design circuits. No surprise.

---
Actually, what you like to call "clucking and pecking" is nothing more
than criticism, but you try to cast it in a light which mitigates its
validity by besmirching the veracity of the criticizer.
---


Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?

Chickenleg work!

It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.

You can't look at a circuit this simple and see what it's doing? OK,
no surprise.

John

---
If he can't, so what?

Why not make it better by helping him out with a few component values
and a circuit description instead of making it worse by insulting him
for no reason?

---
JF

[TheQuickBrownFox]

On Wed, 02 Mar 2011 17:11:41 -0800, John Larkin
wrote:

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.


You sound like one of these punks they put on TV that spews nonsense as
if it was once a colloquialism.

You know nothing about folks here, yet you constantly spout off little
particulars from the depths of YOUR brain, and attribute them to those
you attack as if they are factual.

You are worse than the poorly raised punk ****s that are all over the
streets. They have an excuse. You were supposed to remember your
upbringing, yet you thumb your nose at that and everyone around you ,
which *you* have decided belong on your personal **** list.

You are almost as immature as Terrell, and that is at a very close
second.

Hey John... Grow the **** up.

[John Larkin]

On Wed, 02 Mar 2011 19:49:28 -0800, TheQuickBrownFox
wrote:

On Wed, 02 Mar 2011 17:11:41 -0800, John Larkin
wrote:

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.


You sound like one of these punks they put on TV that spews nonsense as
if it was once a colloquialism.

You know nothing about folks here, yet you constantly spout off little
particulars from the depths of YOUR brain, and attribute them to those
you attack as if they are factual.

You are worse than the poorly raised punk ****s that are all over the
streets. They have an excuse. You were supposed to remember your
upbringing, yet you thumb your nose at that and everyone around you ,
which *you* have decided belong on your personal **** list.

You are almost as immature as Terrell, and that is at a very close
second.

Hey John... Grow the **** up.

Hey, DimmerMan, post us a circuit.

John

[John Fields]

On Wed, 02 Mar 2011 17:11:41 -0800, John Larkin
wrote:

On Wed, 02 Mar 2011 18:36:25 -0600, John Fields
wrote:

On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:



I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?


You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

---
I'm playing, all right, just not the way you find acceptable, which is
to heap adulation on you.

But there's nothing new there, since you almost always blame the
mirror when its reflection doesn't please you.
---

Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?


Chickenleg work!

John
---
Methinks the chicken resides on _your_ roost, since by not doing the
legwork he avoids any criticism which could arise from errors he might
make.

---
JF

[John Larkin]

On Thu, 03 Mar 2011 06:12:05 -0600, John Fields
wrote:

On Wed, 02 Mar 2011 17:11:41 -0800, John Larkin
wrote:

On Wed, 02 Mar 2011 18:36:25 -0600, John Fields
wrote:

On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:



I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG


Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?


You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

---
I'm playing, all right, just not the way you find acceptable, which is
to heap adulation on you.

You're whining about everything but the circuit. Diversionary tactic.

Old hen.

John

[John Fields]

On Thu, 03 Mar 2011 07:16:33 -0800, John Larkin
wrote:

On Thu, 03 Mar 2011 06:12:05 -0600, John Fields
wrote:

On Wed, 02 Mar 2011 17:11:41 -0800, John Larkin
wrote:

You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.

---
I'm playing, all right, just not the way you find acceptable, which is
to heap adulation on you.

You're whining about everything but the circuit. Diversionary tactic.

Old hen.

John

---
I see.

Now I'm supposed to be coerced into getting into an argument with you
about your crap circuit?

Better luck next time, dude.

---
JF

[[email protected]]

On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre : http://tubetime.us/?p=85
I'm sure someone here will love it


-Lasse

[John Larkin]

On Thu, 3 Mar 2011 14:42:40 -0800 (PST), "
wrote:

On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre : http://tubetime.us/?p=85
I'm sure someone here will love it


-Lasse

Wild. Sort of a single-slope ADC and a PWM driver. I wonder what the
sensitivity is like.

I bet you do a similar thing with a single tiny-logic schmitt gate.
Vaguely a superregenerative idea, namely triggering along a slowly
decaying exponential.

John

[John Larkin]

On Thu, 03 Mar 2011 16:04:06 -0800, John Larkin
wrote:

On Thu, 3 Mar 2011 14:42:40 -0800 (PST), "
wrote:

On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre : http://tubetime.us/?p=85
I'm sure someone here will love it


-Lasse

Wild. Sort of a single-slope ADC and a PWM driver. I wonder what the
sensitivity is like.

I bet you do a similar thing with a single tiny-logic schmitt gate.
Vaguely a superregenerative idea, namely triggering along a slowly
decaying exponential.

John


Yeah, this might work:

ftp://jjlarkin.lmi.net/Schmitt_Radio.JPG


John

[John Fields]

On Thu, 3 Mar 2011 14:42:40 -0800 (PST), "
wrote:

On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre : http://tubetime.us/?p=85
I'm sure someone here will love it


-Lasse

---
11 !!!

---
JF

[Chieftain of the Carpet Crawlers]

On Thu, 3 Mar 2011 14:42:40 -0800 (PST), "
wrote:

On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre : http://tubetime.us/?p=85
I'm sure someone here will love it


-Lasse

Pretty good stuff.

It will go way over Sloman's head.

[Bill Sloman]

On Mar 4, 3:31*am, Chieftain of the Carpet Crawlers
wrote:
On Thu, 3 Mar 2011 14:42:40 -0800 (PST), "



wrote:
On 2 Mar., 17:40, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:

ftp://jjlarkin.lmi.net/GEcircuit.jpg

but it occurred to me that it might also make a nice headphone amp...

ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG

Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.

John

speaking of bizarre :http://tubetime.us/?p=85
I'm sure someone here will love it

-Lasse

* Pretty good stuff.

* It will go way over Sloman's head.

Along with the hundred other things a boy can do with a 555.

So someone has used a 555 to make a less than impressive radio-
receiver. Why would anybody be interested, if they hadn't fixated on
the device early in their career and never moved on?

--
Bill Sloman, Nijmegen