[[email protected]]

What are your thoughts on this?

They want $22 for the circuit board. Not sure what the components
cost.

[Scott Dorsey]

wrote:
What are your thoughts on this?

On what?

They want $22 for the circuit board. Not sure what the components
cost.

Who does? What is the front end? Is there a transformer? If so,
expect that to be the majority of the cost.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Tobiah[_5_]]

Oh, you want the link I suppose!

http://sound.whsites.net/project66.htm

On Saturday, November 5, 2016 at 3:37:23 PM UTC-7, Scott Dorsey wrote:
wrote:
What are your thoughts on this?

On what?

They want $22 for the circuit board. Not sure what the components
cost.

Who does? What is the front end? Is there a transformer? If so,
expect that to be the majority of the cost.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Don Pearce[_3_]]

On Sat, 5 Nov 2016 15:43:48 -0700 (PDT), Tobiah
wrote:

Oh, you want the link I suppose!

http://sound.whsites.net/project66.htm

On Saturday, November 5, 2016 at 3:37:23 PM UTC-7, Scott Dorsey wrote:
wrote:
What are your thoughts on this?

On what?

They want $22 for the circuit board. Not sure what the components
cost.

Who does? What is the front end? Is there a transformer? If so,
expect that to be the majority of the cost.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

There's no +48V phantom.

d

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[Mike Rivers[_2_]]

On 11/5/2016 6:52 PM, Don Pearce wrote:
There's no +48V phantom.

That's part of what makes it a DIY project. There's no power supply or
box either.

--

For a good time, call http://mikeriversaudio.wordpress.com

[Phil Allison[_4_]]

Tobiah wrote:


Oh, you want the link I suppose!

http://sound.whsites.net/project66.htm


They want $22 for the circuit board. Not sure what the components
cost.


** The PCB allows two low noise per-amps to be built.

By the time you have purchased all the small components, a pair of 10kohm reverse log pots and XLR sockets the total cost will be over $40.

The NE5532 can be swapped for a TL072 with some saving and less current draw, but stick with the recommended 2N4403 input transistors or you will not get anywhere near the specified low noise.

The idea is that it would be incorporated inside equipment that lacked such pre-amps.

..... Phil

[Mike Rivers[_2_]]

On 11/5/2016 6:26 PM, wrote:
What are your thoughts on this?
http://sound.whsites.net/project66.h.../project66.htm
They want $22 for the circuit board. Not sure what the components
cost.

Since Phil is around here, you might ask him about whether it's even
available currently. I notice that the date on the linked web page is 2008

The circuit is pretty common, very much like a Mackie, maybe even
exactly like a Mackie. I didn't compare the schematic for component values.


--

For a good time, call http://mikeriversaudio.wordpress.com

[gareth magennis]

"Mike Rivers" wrote in message ...

On 11/5/2016 6:26 PM, wrote:
What are your thoughts on this?
http://sound.whsites.net/project66.h.../project66.htm
They want $22 for the circuit board. Not sure what the components
cost.

Since Phil is around here, you might ask him about whether it's even
available currently. I notice that the date on the linked web page is 2008

The circuit is pretty common, very much like a Mackie, maybe even
exactly like a Mackie. I didn't compare the schematic for component values.


--

For a good time, call http://mikeriversaudio.wordpress.com





Allen&Heath use this circuit also.

Gareth.

[Phil Allison[_4_]]

Gareth magennis:


Allen&Heath use this circuit also.



** The A&H GS3000 desk has a mic-pre that is fairly similar, other models use a simplified topology and one has dual gang control that varies the gain of the op-amp as well as the diff pair.

A variety of pnp input transistors are used too, one of them being the 2N4403.

The basis topology dates from the late 1970s and is used in countless desks - for low noise and flat response at all gain settings it is very hard to beat.

Ane alternative is to use an input transformer stepping the mic impedance up to about 10kohms and then an op-amp like the NE5534 as in early Soundcraft and Peavey desks. If the transformer has a CT, this make supplying 48V phantom a cinch.



..... Phil

[Scott Dorsey]

In article , Mike Rivers wrote:
On 11/5/2016 6:26 PM, wrote:
What are your thoughts on this?
http://sound.whsites.net/project66.h.../project66.htm
They want $22 for the circuit board. Not sure what the components
cost.

Since Phil is around here, you might ask him about whether it's even
available currently. I notice that the date on the linked web page is 2008

The circuit is pretty common, very much like a Mackie, maybe even
exactly like a Mackie. I didn't compare the schematic for component values.

This circuit is pretty much what you will find in any transformerless mike
preamp with a couple exceptions.. everything from Millennia to Mackie. It is
as good as the front end is allowed to be.

The 2N4403 is not exactly a low noise transistor but if you're careful about
where you get them and cull out the occasional outlier, they can work pretty
well in this circuit. The thing about the 2N4403 is that it's sold as a
swithing transistor with very relaxed specifications on the datasheet, and it
only has to meet the specifications. Most of the time it does much better,
but not always. This is the difference between spending three cents for a
transistor and three dollars.

Now... this said... if you build this, you're still in for building a
power supply and the power supply is going to be more expensive than the
circuit itself. Add a nice machined case and the cost goes up even more.
But, if you build it well with good parts it will outlast any of the consumer
stuff you'll find at that price range.

I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right. If there aren't, mylars might be a good plan. I might
also dramatically increase the values of C2 and C3 well beyond the values
needed to get good response.

You're going to need to add some input capacitors on this as well if you add
a phantom supply, so put that into your price equation.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right.

C1 is the more interesting case.

m

[Don Pearce[_3_]]

On Mon, 7 Nov 2016 05:36:04 -0800 (PST), wrote:



I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right.

C1 is the more interesting case.

m

It is. It has to be big to keep a low impedance relative to 22 ohms in
the high gain situation.

But looking at the topology it is clear that both C2 and C3 could have
been eliminated by returning the overall feedback (R12) to Q1. That
would have set the DC bias in the front end, and C1 could have been
dispensed with too. A matched pair for Q1/3 - preferably in a single
can - would make that more than feasible.

d

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[Don Pearce[_3_]]

On Mon, 07 Nov 2016 13:52:57 GMT, (Don Pearce) wrote:

On Mon, 7 Nov 2016 05:36:04 -0800 (PST), wrote:



I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right.

C1 is the more interesting case.

m

It is. It has to be big to keep a low impedance relative to 22 ohms in
the high gain situation.

But looking at the topology it is clear that both C2 and C3 could have
been eliminated by returning the overall feedback (R12) to Q1. That
would have set the DC bias in the front end, and C1 could have been
dispensed with too. A matched pair for Q1/3 - preferably in a single
can - would make that more than feasible.

d

Should have added: Maximum gain is set by the collector current of
Q1/3, which is of the order of 1mA. That gives an intrinsic Gm-based
emitter resistance of about 26 ohm (total 52) which appears in series
with the actual 22 ohm resistor.

d

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[Scott Dorsey]

Don Pearce wrote:
On Mon, 7 Nov 2016 05:36:04 -0800 (PST), wrote:

I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right.

C1 is the more interesting case.

m

It is. It has to be big to keep a low impedance relative to 22 ohms in
the high gain situation.

But looking at the topology it is clear that both C2 and C3 could have
been eliminated by returning the overall feedback (R12) to Q1. That
would have set the DC bias in the front end, and C1 could have been
dispensed with too. A matched pair for Q1/3 - preferably in a single
can - would make that more than feasible.

The bad news is that a matched pair like the THAT array dramatically
increases the parts cost but then again you're saving the cost of some caps
too.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Phil Allison[_4_]]

Scott Dorsey wrote:

What are your thoughts on this?
http://sound.whsites.net/project66.htm



This circuit is pretty much what you will find in any transformerless mike
preamp with a couple exceptions.. everything from Millennia to Mackie. It is
as good as the front end is allowed to be.

The 2N4403 is not exactly a low noise transistor but if you're careful about
where you get them and cull out the occasional outlier, they can work pretty
well in this circuit.


** The 2n4403 is still one of the best available devices for low noise at microphone impedances. The measured noise figure of 1dB speaks for itself.


I disagree strongly about there being no problem with DC bias on modern
electrolytics,


** Disagree all you like, but there is no issue.


I might
also dramatically increase the values of C2 and C3 well beyond the values
needed to get good response.



** Using 10uF caps as shown gives a -3dB point under 1Hz.


..... Phil

[Scott Dorsey]

Phil Allison wrote:

I disagree strongly about there being no problem with DC bias on modern
electrolytics,

** Disagree all you like, but there is no issue.

Run some numbers, it's very interesting to watch. You still get a dramatic
increase in distortion near the zero crossing. It's enough distortion you
can use that old HP 334 and see it with a test jig. It's not anywhere near
as bad as it was with the capacitors of the seventies though.

I might
also dramatically increase the values of C2 and C3 well beyond the values
needed to get good response.

** Using 10uF caps as shown gives a -3dB point under 1Hz.

Check out Doug Self's book on power amplifier design. Again, the issue
isn't the frequency response, it's distortion from the ripple across the
capacitor. You want the lowest possible ESR and one way to get that is
to use a capacitor with already low ESR and then oversize it considerably.

Some people bypass electrolytics with film caps to achieve the same results
and this can work if you actually measure it and make sure you're doing what
you think you are.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Phil Allison[_4_]]

Scott Dorsey wrote:


I disagree strongly about there being no problem with DC bias on modern
electrolytics,


** Disagree all you like, but there is no issue.


Run some numbers, it's very interesting to watch. You still get a dramatic
increase in distortion near the zero crossing. It's enough distortion you
can use that old HP 334 and see it with a test jig.


** There is NO distortion in the arrangement AS SHOWN !!

Polarised electros operate perfectly in bi-polar mode long as the AC voltage across them does not exceed a few hundred millivolts.


** Using 10uF caps as shown gives a -3dB point under 1Hz.

Check out Doug Self's book on power amplifier design. Again, the issue
isn't the frequency response, it's distortion from the ripple across the
capacitor.


** Which does not exist in the circuit shown as the 10uF caps are DC biased.


You want the lowest possible ESR ...


** Massive irrelevance.



...... Phil

[geoff]

On 8/11/2016 2:40 p.m., Scott Dorsey wrote:

Some people bypass electrolytics with film caps to achieve the same results
and this can work if you actually measure it and make sure you're doing what
you think you are.
--scott


....and the even then the 'purists' will only use polyprop caps.
(primary cap or as a bypass)

geoff

[gareth magennis]

"Phil Allison" wrote in message
...

Scott Dorsey wrote:

What are your thoughts on this?
http://sound.whsites.net/project66.htm



This circuit is pretty much what you will find in any transformerless mike
preamp with a couple exceptions.. everything from Millennia to Mackie. It
is
as good as the front end is allowed to be.

The 2N4403 is not exactly a low noise transistor but if you're careful
about
where you get them and cull out the occasional outlier, they can work
pretty
well in this circuit.


** The 2n4403 is still one of the best available devices for low noise at
microphone impedances. The measured noise figure of 1dB speaks for itself.


I disagree strongly about there being no problem with DC bias on modern
electrolytics,


** Disagree all you like, but there is no issue.


I might
also dramatically increase the values of C2 and C3 well beyond the values
needed to get good response.



** Using 10uF caps as shown gives a -3dB point under 1Hz.


..... Phil








The Allen & Heath MixWiz3 has a very similar circuit but omits (shorts) C2
and C3, the op-amp having a somewhat different front end.

Gareth.

[Phil Allison[_4_]]

gareth magennis wrote:



The Allen & Heath MixWiz3 has a very similar circuit but omits (shorts) C2
and C3, the op-amp having a somewhat different front end.



** Got a link to the schem ?

Earlier Mix Wizes used a bare bones version of the topology with a dodgy looking phantom arrangement.


.... Phil

[Peter Larsen[_3_]]

On 07-11-2016 13:35, Scott Dorsey wrote:

[Allison mic pre]

You're going to need to add some input capacitors on this as well if you add
a phantom supply, so put that into your price equation.

I would expect that to always be a must, minimum 52 volts ...

--scott

Kind regards

Peter Larsen

[gareth magennis]

wrote in message
...

What are your thoughts on this?

They want $22 for the circuit board. Not sure what the components
cost.




FWIW, Reverse Log pots are now commonly available, they didn't used to be.

http://www.ebay.co.uk/itm/Reverse-Au... 6uMPFGoCyCZ-A



Gareth.

[Phil Allison[_4_]]

gareth magennis wrote:



FWIW, Reverse Log pots are now commonly available, they didn't used to be.

http://www.ebay.co.uk/itm/Reverse-Au... 6uMPFGoCyCZ-A



** Nothing stops you using a regular log pot operating in the reverse sense, with gain increasing in the CCW direction.

A very satisfactory solution is to use a 12 position rotary switch and a chain of 11 resistors wired across adjacent contacts.

For 4 dB steps, the values a

15, 27, 39, 68, 100, 180, 270, 470, 1k, 1.5k & 3.9k



...... Phil

[geoff]

On 7/11/2016 5:00 p.m., Phil Allison wrote:

** Nothing stops you using a regular log pot operating in the reverse sense, with gain increasing in the CCW direction.

A very satisfactory solution is to use a 12 position rotary switch and a chain of 11 resistors wired across adjacent contacts.

For 4 dB steps, the values a

15, 27, 39, 68, 100, 180, 270, 470, 1k, 1.5k & 3.9k



..... Phil


Makes for more accurately repeatable settings too, if that's a benefit
to one's particular way of working.


geoff

[JackA]

On Saturday, November 5, 2016 at 6:26:52 PM UTC-4, wrote:
What are your thoughts on this?

They want $22 for the circuit board. Not sure what the components
cost.

Did I ever tell you the story, I worked in R&D and boss gave me a book on Operational Amplifiers. Inside was a instructions and parts list for a Phono Cartridge preamplifier. I designed and etched the PC Boards, boss helped me select only but the best components for low noise, even had the Grade A DIP Op Amps I needed (4). I built it and it worked like a champ!! Was even featured in a High Fidelity magazine. Decades passed, and I found the author, Walter Jung, online, so I thanked him for his great design!! Oh, and HE said he liked my MP3 snippets (on site) I enhanced!!

Jack

p.s. Electronic Parts continue to be tough to find!!