Microphone Builders

Re: accordion mic

parenthetical@... (thet) — Sat, 12 Apr 2025 22:02:01 -0700

What are you actually trying to achieve?

There's lots of pitfalls in my suggested circuit. It isn't a tried and tested project, and will almost certainly require revision and troubleshooting. I wouldn't recommend it for a beginner.

Looking at it now it seems overcomplex. If you add a third mic each side it gets even more complex, how would you balance them? I'm already not that happy with my arrangement of balance pots (R2 R25) and level pots (R3 R15).

If you only want to amplify one side of the accordion then you could use essentially half the circuit, and use a single opamp instead of a dual - so simpler.

A version which didn't stack the power supplies would also be simpler to get right, at the expense of more current draw.

On 12/04/2025 20:19, jc.selles via groups.io wrote:

Re: accordion mic

jc.selles@... — Sat, 12 Apr 2025 12:19:16 -0700

Hello

Yes I meant this circuit. I a near future I will try to built it more or less as you sudgested it : a single opamp but with three capsules for each sides.聽

聽

What do you mean by a simpler circuit?

聽

I would like to have a way to control the volume on this preamp but I am starting to feel that's too complex for me.

聽

/g/MicBuilders/topic/phantom_powered_fet_preamp/112208360

聽

Anyway thanks a lot. This is a beautiful collaborative thread.聽

Re: accordion mic

parenthetical@... (thet) — Sat, 12 Apr 2025 08:39:06 -0700

I take it you mean this?

https://halfshavedyaks.xyz/forumimages/4mic2chanV3.png

I'd completely forgotten I did that!

It was never built, whoever was asking for it never got back to me I think.

If you disconnect one XLR you halve the power available so not good. The unused side of the opamp will still draw power, but both sides will be powered from a single XLR.

However if you only wanted a single XLR version for one side of the accordion, then you could use a much simpler circuit overall.

Or you could make it with two 1641 opamps instead of a single 1642, and separate the power for each, that would essentially be two totally separate but identical circuits, and would be robust for using just one. It's more parts overall though.

On 11/04/2025 20:57, jc.selles via groups.io wrote:

Re: accordion mic

jc.selles@... — Fri, 11 Apr 2025 12:57:15 -0700

Hello, sorry for the topic revival

As an accordion player I am really interested in this project.

I was wondering what would happen if only one of the two XLR is connected?

thank you.

This is a really interesting discussion.

Re: phantom powered fet preamp question

c.sawyers@... (Craig Sawyers) — Fri, 11 Apr 2025 08:53:09 -0700

If you have a look at Siegfried Linkwitz's site, there is an alternative method of using that microphone here聽https://www.linkwitzlab.com/sys_test.htm#Mic

Craig

Re: phantom powered fet preamp question

jc.selles@... — Fri, 11 Apr 2025 06:17:12 -0700

Thank you

I forgot to mention that I want to put it inside an instrument. That's why I would like to have control of the volume.

聽

Re: phantom powered fet preamp question

ryckebusch@... (Jules Ryckebusch) — Fri, 11 Apr 2025 06:03:56 -0700

This is basically unity gain and going into a mic preamp. That鈥檚 the best place to adjust the gain

Best Regards,

Jules Ryckebusch聽

Phantom Power Condenser Microphone 鈥� Mute & Power Control Circuit

kandoit7@... (kandoit7) — Fri, 11 Apr 2025 05:27:55 -0700

Hi everyone,

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I'm working on a circuit to control the power supply and mute function of a phantom-powered condenser microphone.

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The general concept is mostly in place, and I鈥檇 love to get your feedback, especially if you have ideas for improvements or alternative approaches.

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I've attached the schematic for reference.

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Here's a quick rundown of how it works:

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-An NE555 timer is used to generate a trigger pulse when a pushbutton is pressed once.

-This trigger drives an 817 optocoupler to toggle the power (ON/OFF).

-The optocoupler, in turn, controls the 24V supply鈥攔egulated through a Zener diode鈥攚hich powers both the condenser mic and an LED via three FETs.

-While the supply is nominally 24V, due to component losses, the actual output voltage is around 16V.

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I鈥檓 also considering replacing the current switching mechanism with a latching circuit for more reliable control.

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Any input, suggestions, or shared experiences would be greatly appreciated. I'm especially curious if anyone has tackled a similar design.

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Thanks in advance!

phantom powered fet preamp question

jc.selles@... — Fri, 11 Apr 2025 04:39:00 -0700

Hello,

聽

I build this preamp and I was wondering if there is a way to control the audio volume?

My best guess so far would be to add two capacitors beside C3 and C6 and wire a dual pot. But it seems very ugly.

Thanks a lot and have a nice day.

Re: FET OPAs for mikes

homero.leal@... (Homero Leal) — Thu, 10 Apr 2025 21:10:40 -0700

:)

As Jerry Lee said, the OPA1655 could be the closest to the specs: 4nV鈭欻z聽聽@1kHz, and 2.9nV鈭欻z聽聽@10Khz. 3.9mA quiescent current, and it also has low distortion.

Here is the Vn graph, from the PDF spec sheet.

Stay salty and sandy! :)

Regards!

Re: FET OPAs for mikes

ricardo_lee@... (Richard Lee) — Thu, 10 Apr 2025 18:36:09 -0700

What do you think about having a 2SK170 or a聽LSK189聽FET and an OPA1611, using the OCCAM-3B configuration,聽from Zapnspark?

In Jurassic times, I did a lot of work trying to splice a LN transistor into a DIP OPA.聽 My most successful was with LM301 cos you can disable the i/p stage and feed the LN transistor output into the offset pins.

聽

When 5532/4 came out, all this work went into the Don't Recycle bin.聽 We were Beta testers for the original 5534, called Mullard 1034 at the time.

Not strictly a single OPA solution, but if you need really low noise, this may be a good option.

Homero, don't forget I'm a REAL beach bum.聽 This is just a mental exercise on Jurassic topics for me cos the weather is too bad to go diving聽

Re: FET OPAs for mikes

homero.leal@... (Homero Leal) — Thu, 10 Apr 2025 10:06:46 -0700

Hi Richard, nice to be in touch!

What do you think about having a 2SK170 or a聽LSK189聽FET and an OPA1611, using the OCCAM-3B configuration,聽from Zapnspark?

Not聽strictly聽a single OPA solution, but if you need really low noise, this may be a good option.

Kind regards!

El mi茅, 9 abr 2025 a la(s) 2:08鈥痑.m., Craig Sawyers via groups.io (c.sawyers=tech-enterprise.com@groups.io) escribi贸:

Re: FET OPAs for mikes

c.sawyers@... (Craig Sawyers) — Wed, 09 Apr 2025 01:08:23 -0700

Indeed bias cancellation is a hidden evil in recent (and not so recent) audio opamps. It is simply omitted from the specs, and in the neat and ideal noise calculations with resistive generator impedances.

Thanks for spotting that for the OPA210. And like I said, even ignoring bias compensation it only gains you a mere 0.6dB SNR as compared with the 5534 in MM SNR.

And that is something in favour for the 5534 and 5532 still - no bias compensation. And still available in 8-pin DIL packages. I just wish that they had the comprehensive set of performance graphs of more recent devices.

Sorry to hear of what ever has caused the beach bum from quitting the beach. Following a five month chest infection that needed kick ass antibiotics to kill, I'm luckily back to firing on all cylinders.

Craig

Re: FET OPAs for mikes

ricardo_lee@... (Richard Lee) — Tue, 08 Apr 2025 21:00:30 -0700

On Tue, Apr 8, 2025 at 01:21 AM, Craig Sawyers wrote:

And the only bipolar opamp to beat the NE5534 is the OPA210. 2.2nV/rootHz at 1kHz, an amazing 2.5nV/rootHz at 10Hz, and crucially for MM cartridges current noise of 400fA/rootHz (same as for the NE5534). It is just better in all respects than the Neanderthal NE5534

Thanks for these suggestions Craig.

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OPA210 has EVIL input bias current cancelling.聽 The damning evidence is its +/- input bias current spec.聽 These invariably have much higher noise for stuff with different impedances on each input pin like single OPA RIAA preamps.聽 You may remember us looking at the ???? preamps with Steve Sells and finding significant improvement replacing OP27 or OP37 with 5534 on their RIAA

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It's more than a decade since I last looked at this seriously https://www.proaudiodesignforum.com/forum/php/viewtopic.php?t=423&start=30

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Wayne (and NWavGuy IIRC) measured NJM 2068, sadly Unobtainium today, quieter than LM 4562 so env < 2.5nV/rtHz @ 1kHz and inv good enough in to beat 5534.聽 Of course da Jurassic NJM topology (dating back to Raytheon 4136 ie much older than 5534) can't give 1 ppzillion THD like more modern stuff but good enough for an old beach bum like me.

聽

BTW, I hope you are not suffering various health issues like me which may mean I need to give up the beach

Re: FET OPAs for mikes

jerryleemarcel@... (Jerry Lee Marcel) — Tue, 08 Apr 2025 02:20:49 -0700

On Tue, Apr 8, 2025 at 04:55 AM, Jules Ryckebusch wrote:

Look at this one:聽https://www.ti.com/lit/ds/symlink/opa1633.pdf?ts=1744049024408聽 One of my reasons for choosing the OPA1642 was idle current. The OPA1633 聽has >10ma which for a phono preamp with external supply is not an issue聽

Best Regards,
聽

Jules Ryckebusch

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OPA1633 is a bipolar differential amp with an Optimum Source Impedance of about 800 ohms. hardly suitable for a MM preamp.
You must have confused it with another.

OPA1655/56 are JFET with 2.9nV/sqrtHz IN density.

聽

Re: FET OPAs for mikes

c.sawyers@... (Craig Sawyers) — Tue, 08 Apr 2025 01:21:06 -0700

ADA4625-2 bifet from Analog Devices is 3.3nV/rootHz at 1kHz, and 5.5nV/rootHz at 10Hz. Current noise 4.5fA/rootHz at 1kHz

The OPA828 JFET has 4nV/rootHz at 1kHz, 7.5nV/rootHz at 10Hz, and 1.2fA/rootHz current noise. Available as a dual OPA2828. Surface mount of course.

And the only bipolar opamp to beat the NE5534 is the OPA210. 2.2nV/rootHz at 1kHz, an amazing 2.5nV/rootHz at 10Hz, and crucially for MM cartridges current noise of 400fA/rootHz (same as for the NE5534). It is just better in all respects than the Neanderthal NE5534.聽 And available as a dual OPA2210.

If you put it into my RIAA amp spreadsheet, for typical cartridge R and L the OPA210 only finds you 0.6dB improvement in SNR as compared to the NE5534. For a factor of 5 times greater cost. But distortion is vanishingly low, it only draws 2.5mA quiescent, and inevitably is only surface mount. And cheerfully drives 600 ohms with no degradation in distortion.

Craig

Re: FET OPAs for mikes

ryckebusch@... (Jules Ryckebusch) — Mon, 07 Apr 2025 19:55:35 -0700

Look at this one:聽https://www.ti.com/lit/ds/symlink/opa1633.pdf?ts=1744049024408聽 One of my reasons for choosing the OPA1642 was idle current. The OPA1633 聽has >10ma which for a phono preamp with external supply is not an issue聽

Best Regards,

Jules Ryckebusch聽

Re: FET OPAs for mikes

ricardo_lee@... (Richard Lee) — Mon, 07 Apr 2025 19:32:06 -0700

It's actually for a Jurassic application with of no modern importance;聽 RIAA MM preamps in DIYaudio.聽 I'm surprised that NE5534 is still one of the best for this; slightly beaten only by $$$ OP627 or Unobtainium NJM2068.

聽

In theory, a FET OPA with <3.5nV/rtHz & low 1/f, popcorn noise bla bla should trounce 5534

Re: FET OPAs for mikes

ryckebusch@... (Jules Ryckebusch) — Mon, 07 Apr 2025 15:26:27 -0700

I am using the OPA1642. It is 5.1nV鈭欻z. The OPA1652 is 4.5聽nV鈭欻z聽 Both are very good. What is your noise floor based on out of curiosity?

Jules

FET OPAs for mikes

ricardo_lee@... (Richard Lee) — Mon, 07 Apr 2025 14:39:33 -0700

I'm a bit out of touch with modern OPAs but note there are a number of new DIY mikes using FET OPAs like Homero's Charis and the OPA Alice.

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I'm after a FET OPA with less than 3.5nV/rtHz noise @ 1kHz and good 1/f, popcorn noise bla bla.

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What do you guys use and recommend ?聽