# Hiring somebody to draw a stereo headphone amplifier circuit

#### allisonr

Joined Aug 16, 2016
27
Hello,

I'm looking for somebody knowledgeable who can draw a working circuit meeting certain requirements, a low-noise, high adjustable gain, portable battery-powered microphone amplifier with stereo input (two mics) and headphones output with a maximum sound level limiter.

Any electronic part can be used, as long as it is relatively common, has good performance and is one of the best for its price range in terms of quality, noise etc.
Each single part (mic, transistor, IC, etc.) should ideally cost within $20 (except headphones, since I already have them or would change them from time to time), unless something really superior is found at a slightly higher price, for example$25.

Requirements:
- low noise (as low as reasonably possible, so no place for LM386 and the like)
- high sensibility
- high, adjustable gain (as high as possible within this price range and without decreasing sound quality too much)
- sound level limiter (to prevent hearing damage when gain is set high but microphones bump into something)
- portable (weighing less than 2.2 lbs/1kg)
- battery powered (possibly something rechargeable such as 1.2v AA or 3.7v 18650 Lithium)
- two microphones input, each having as output one headphone channel
- pickup frequency range 50-18000 Hz (mostly would be wild animal calls and insect songs)
- reliable in high humidity (possibly rainproof microphones since they'd be exposed while the other parts would be within a plastic box)
- working at a wide temperature range (-20/+45°C or -4/+113°F)
- reasonable working time, like 24h for each freshly recharged battery/set of batteries
- edit: as a forum member rightfully pointed out, an on/off low frequency cutoff swith would be nice to be included

Let me know how much are you asking for this, I need just a working circuit drawing and will buy parts and assemble it by myself, thank you.

Allison

Last edited:

#### dannyf

Joined Sep 13, 2015
2,197
An el cheapo ne5532 will do. Unless you have some weird headphone.

#### allisonr

Joined Aug 16, 2016
27
An el cheapo ne5532 will do. Unless you have some weird headphone.
Headphones aren't a problem since I'd always pick up another kind that suits the circuit better. Also, since I'd like to squeeze the most for $20/electronic part, wouldn't there be other opamps outperforming a$0.20 NE5532? Just wondering, I'm open to suggestions.

#### ronv

Joined Nov 12, 2008
3,770
Hello,

I'm looking for somebody knowledgeable who can draw a working circuit meeting certain requirements, a low-noise, high adjustable gain, portable battery-powered microphone amplifier with stereo input (two mics) and headphones output with a maximum sound level limiter.

Any electronic part can be used, as long as it is relatively common, has good performance and is one of the best for its price range in terms of quality, noise etc.
Each single part (mic, transistor, IC, etc.) should ideally cost within $20 (except headphones, since I already have them or would change them from time to time), unless something really superior is found at a slightly higher price, for example$25.

Requirements:
- low noise (as low as reasonably possible, so no place for LM386 and the like)
- high sensibility
- high, adjustable gain (as high as possible within this price range and without decreasing sound quality too much)
- sound level limiter (to prevent hearing damage when gain is set high but microphones bump into something)
- portable (weighing less than 2.2 lbs/1kg)
- battery powered (possibly something rechargeable such as 1.2v AA or 3.7v 18650 Lithium)
- two microphones input, each having as output one headphone channel
- pickup frequency range 50-18000 Hz (mostly would be wild animal calls and insect songs)
- reliable in high humidity (possibly rainproof microphones since they'd be exposed while the other parts would be within a plastic box)
- working at a wide temperature range (-20/+45°C or -4/+113°F)
- reasonable working time, like 24h for each freshly recharged battery/set of batteries

Let me know how much are you asking for this, I need just a working circuit drawing and will buy parts and assemble it by myself, thank you.

Allison
It sounds like an amplifier for a parabolic microphone?
It is a fairly simple project. Maybe you could find an electret microphone you like first. And if you can give an idea of how much amplification is needed. For example would you want a whisper for 3 feet away to be at full volume.

#### allisonr

Joined Aug 16, 2016
27
It sounds like an amplifier for a parabolic microphone?
It is a fairly simple project. Maybe you could find an electret microphone you like first. And if you can give an idea of how much amplification is needed. For example would you want a whisper for 3 feet away to be at full volume.
Not exactly, since I'd like microphones to not be that directional but either omni or cardioid.
I don't have any preference over parts, microphones included, hence I'm entrusting the person picking up this offer.
About gain, as anything else in this task, as performant as the cost constraints allows. I wouldn't mind to hear nightingales singing behind the hill.
I know there have to be compromises between noise and gain, I'd be inclined to indulge on the gain side since being adjustable, I'd always switch to slightly less gain and higher audio quality, however as previously said, the only constraints are parts price.

#### dannyf

Joined Sep 13, 2015
2,197
You can do better than a ne5532 spec wise but not sure soundwise.

If you are brave, try those CFA opamps, particularly xdsl modem drivers. My favorite is ad815 but most of them will provide performance far beyond what a human eye can discern.

Another options is a composite amp, an opamp buffered by an emitter follower or a diamond buffer, either discrete or like a bf634 - they are quite hard to find and expensive when you do find them. CFA opamp is a better approach.

Be warned: those amps are incredibly fast and requires careful layout that may be beyond the skills of most layout engineers.

#### allisonr

Joined Aug 16, 2016
27
You can do better than a ne5532 spec wise but not sure soundwise.

If you are brave, try those CFA opamps, particularly xdsl modem drivers. My favorite is ad815 but most of them will provide performance far beyond what a human eye can discern.

Another options is a composite amp, an opamp buffered by an emitter follower or a diamond buffer, either discrete or like a bf634 - they are quite hard to find and expensive when you do find them. CFA opamp is a better approach.

Be warned: those amps are incredibly fast and requires careful layout that may be beyond the skills of most layout engineers.
I see, thank you. For some reason I thought that there was at least some linear distribution of performance in this price range and given that gain could be adjusted at very high levels, any distortion and noise would stand out more, hence my question.
Unfortunately I'm not skilled enough to make a choice and building what you're suggesting, so once again I'm entrusting somebody else for this.

Allison

#### dannyf

Joined Sep 13, 2015
2,197
Ne5532 is one amazing opamp. Many people look down on it because of its low price, and from that, perceived low performance. It was considered high performance decades ago but spec-chasers have abandoned it.

Cmoy is a headphone amp and can be built around a 5532.

#### allisonr

Joined Aug 16, 2016
27
Ne5532 is one amazing opamp. Many people look down on it because of its low price, and from that, perceived low performance. It was considered high performance decades ago but spec-chasers have abandoned it.

Cmoy is a headphone amp and can be built around a 5532.
I see, I may have been influenced by this page (https://tangentsoft.net/audio/opamps.html) that put NE5532 under any other opamp except TL072 and called it "jellybean" (so, low quality), while praised others like OPA627 (which looks available at good prices too, unless those OPA672 AP/BP are unwanted variants).

#### dannyf

Joined Sep 13, 2015
2,197
Those newer bb parts have better specs but I'm not sure if our ears can the improvement over 5532.

I was at a conference in the 1990s when someone demoed 20 741s, daisybchained together, vs a copper wire and no one person could reliably tell them apart.

Those were recording engineers. So don't believe those hype without your trying them out first.

#### allisonr

Joined Aug 16, 2016
27
Those newer bb parts have better specs but I'm not sure if our ears can the improvement over 5532.

I was at a conference in the 1990s when someone demoed 20 741s, daisybchained together, vs a copper wire and no one person could reliably tell them apart.

Those were recording engineers. So don't believe those hype without your trying them out first.
I understand, my main concern was that while electronic parts have outmatched human senses decades ago, a high-gain application would magnify any imperfection/noise belonging to a certain IC, hence my thought on parts better than NE5532.

#### Wendy

Joined Mar 24, 2008
22,569
Checkout this chip It is meant to be a low noise preamp. It hasn'tbeen expensive whem I buy them. It is a standard dual op amp so aRegular circui woud work

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#### GopherT

Joined Nov 23, 2012
8,012
I see, I may have been influenced by this page (https://tangentsoft.net/audio/opamps.html) that put NE5532 under any other opamp except TL072 and called it "jellybean" (so, low quality), while praised others like OPA627 (which looks available at good prices too, unless those OPA672 AP/BP are unwanted variants).

There is a difference between pleasant audio sound to the human ear and technical performance. Many of the op amps on that TangentSoft page are marketed to data acquisition, not audio. Also, the writer of that article is driving these op Amps beyond their specifications. Most are not designed to directly drive a pair of headphones. Actually, I don't think any are specified for a 32 ohm load.

NE5532 and 5534 are very good amps for audio and sound very natural with little background noise - especially background noise you would notice in an outdoor arena where wind across the microphone will be your biggest concern.

#### dannyf

Joined Sep 13, 2015
2,197
high-gain application would magnify any imperfection/noise b
While the concerns are generally true, it is hard to envision them to be a concern for a headphone amp.

You are building a headphone amp, right?

#### dannyf

Joined Sep 13, 2015
2,197
My experience with audio has been that whenever possible, you want the lowest possible spec before sacrificing sound quality. That means low speed amp, high current capability, low dampen factor, and low gain / thus low feedback.

Of the all the amps I have built, my favorite is jlh1969m, amazing sound quality, ability to drive reactive low, low feedback and seem less transition between class a and class b operations.

#### allisonr

Joined Aug 16, 2016
27
Checkout this chip It is meant to be a low noise preamp. It hasn'tbeen expensive whem I buy them. It is a standard dual op amp so aRegular circui woud work
Thank you

There is a difference between pleasant audio sound to the human ear and technical performance. Many of the op amps on that TangentSoft page are marketed to data acquisition, not audio. Also, the writer of that article is driving these op Amps beyond their specifications. Most are not designed to directly drive a pair of headphones. Actually, I don't think any are specified for a 32 ohm load.

NE5532 and 5534 are very good amps for audio and sound very natural with little background noise - especially background noise you would notice in an outdoor arena where wind across the microphone will be your biggest concern.
I see, didn't make this distinction before, thanks for pointing it out.

While the concerns are generally true, it is hard to envision them to be a concern for a headphone amp.

You are building a headphone amp, right?
Right

My experience with audio has been that whenever possible, you want the lowest possible spec before sacrificing sound quality. That means low speed amp, high current capability, low dampen factor, and low gain / thus low feedback.

Of the all the amps I have built, my favorite is jlh1969m, amazing sound quality, ability to drive reactive low, low feedback and seem less transition between class a and class b operations.

I'd sacrifice some sound quality for a higher gain (which would be adjustable anyway, so allows for temporarily select lower quality/higher gain or higher quality/lower gain).

#### GopherT

Joined Nov 23, 2012
8,012
And your desire to attenuate loud inputs will create distortion of its own since a non-linearity is introduced to achieve this.

#### allisonr

Joined Aug 16, 2016
27
And your desire to attenuate loud inputs will create distortion of its own since a non-linearity is introduced to achieve this.
Well I assume that loud inputs aren't a constant but rather an exception, and that the limiter is there to protect my hearing from these unexpected events.

#### dannyf

Joined Sep 13, 2015
2,197
Quality sound for solid state amplifiers means primarily headroom and low negative feedback.

Headroom is to minimize clipping. Low negative feedback is to avoid transient distortions.

If your input signal is so strong that it requires attenuation, going high gain is the opposite of what you want to do.

For most headphones, a headphone amps primary job is impedance transformation. (Voltage) gain is typically the least of your concerns.