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Old 18th June 2019, 10:04 PM   #1
amoroz is offline amoroz  United States
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Default Looking for help with a design (paid)

Hi folks,

First time poster and occasional (but appreciative!) lurker here. I'm a professional musician and have been working on a battery powered headphone amp/mixer/limiter for several months. I have the project in fairly presentable shape in Eagle CAD and am planning to have it assembled (it involves a lot of SMT components so I am unable to build and test it at home), but before I do, I'm hoping to have someone experienced in analog audio design look over the schematic and board layout to check for major issues, potential improvements, etc.

The circuit is not terribly complex -- it's a virtual earth summing mixer with two stereo inputs and one mono input, a bunch of selectable analog filters in the mono input path, and an optional post-mix limiter IC. I built an earlier version of this project two years ago and have since been using it regularly, so I'm pretty confident that those original design elements are at least functional, if perhaps not ideal. The new version employs some op amp topologies and ICs I'm less familiar with, plus several component footprints I made from scratch.

Not sure what the most appropriate forum for a question like this is, so mods, please feel free to move the thread if necessary. Also – apologies in advance if this kind of thing has been asked here before! I searched for similar inquiries and didn't find anything relevant, but it's very possible I missed something.

Any leads would be much appreciated!


Thanks,

Andrew
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Old 18th June 2019, 10:53 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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The biggest pitfall with the pcb layout is grounding, especially if you have power supply on the pcb too. The power supply should be kept separate from the audio and star grounded.

I got caught out with a USB mixer where I Just mixed in all the ground and it had 1vac hum with inputs shorted !
The smoothing capacitors have short bursts of high current impulses going into the capacitors so can modulate the zero volt line if not laid out correctly.

Just publish your circuits on here and I am sure many will come along and tear it to pieces !
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Old 18th June 2019, 11:11 PM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by amoroz View Post
I'm hoping to have someone experienced in analog audio design look over
the schematic and board layout to check for major issues, potential improvements, etc.
Just post it here and I suspect that you will hear plenty, for free.
You should certainly check your custom footprints very carefully,
since errors in these are likely, and will be hard to catch here.

Last edited by rayma; 18th June 2019 at 11:24 PM.
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Old 19th June 2019, 07:18 AM   #4
amoroz is offline amoroz  United States
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I appreciate the quick replies! I have certainly considered posting it here or on one of the other electronics forums. However, I would prefer to hire someone, strange as that may sound. Beyond the headphone amp and limiter functionality, the project is also sort of an experimental attempt to solve a common problem encountered by some musicians wearing in-ear monitors and other hearing protection. As far as I can tell, its approach is somewhat novel; at least, I can’t find much evidence that it’s been tried before – possibly with good reason, ha! If it did achieve the intended effect, I wouldn’t want to write off the possibility of packaging it into something marketable. I realize that prospect may be far fetched, to say the least! But given the longevity and wide accessibility of information on the internet, for now it seems prudent not to post the project in its entirety.

That being said, any recommendations as far as where to find paid help along these lines would be welcome. I know it might get expensive, but within the limits of my budget, that would be preferable to going ahead without any assistance and risking complete failure.

Andrew
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Old 26th June 2019, 03:00 PM   #5
airborne11b is offline airborne11b  United States
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This is just a thought, you may contact some local universities' electrical/electronics engineering department. Market your project as a senior capstone project to analyze and optimize your circuit. They may do it for free and they will certainly try to do a good job as their grade will depend on it. That being said, it may take 1-2 semesters before you get your answers.
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