help with op amp headphone amp hum and distortion - Page 8

gregas · 4th March 2021, 03:41 AM

Hey Rick.
So I'm adding those 1/4w resistors to my order
Plus 4k7. Thanks.
https://www.mouser.ca/ProductDetail/652-3006P-1-103-LF/
How's this look for the trimpot?

Rick PA Stadel · 4th March 2021, 03:58 AM

Those are pretty standard, and pretty decent. Wouldn't mind if they would pick a tempco sign, and not just specify +/-200ppm. Or a little better cycles/life (only "200" means you can't, as a practical matter, just keep a handful of these in your prototyping parts box and expect them to be reliable when you pull one out -- check/measure every use!)

If you get 10k trimpots, you shouldn't need the 4k7's. (Unless I booted the arithmetic ..

!)

gregas · 4th March 2021, 04:20 AM

How about this for the perfboard?
https://www.mouser.ca/ProductDetail/...9HVnuJCg%3D%3D

Ok so no need for the 4k7 resistor

Rick PA Stadel · 6th March 2021, 05:17 AM

Yep, that looks just fine.

As long as you get 0,042" holes on 0,1" centers, and it's FR-4, you're getting pretty standard stuff.

gregas · 7th March 2021, 02:35 AM

Rick,
I've been thinking. I have that leftover veroboard that i removed all those components off with the mosfets. I could probably cut that to size and just use it instead of the perfboard. I don't think saving a bit of space is a big issue here, is it? I could also mount it to some stand off spacers mounted to the mounting screws for the headphone amp veroboard.

Rick PA Stadel · 7th March 2021, 07:01 PM

Should be OK. But the ground lead from C1 on the bias circuit will need a short, direct (no service loop) connection, close to the pad between the bypass capacitors on the AD817 supply leads -- pins 4 and 7.

And if the bias circuit occupies somewhat less space, that's good thing.

Maybe don't worry about the mounting. Try to think of the little added circuit as a test assembly, instead of something permanent that needs to be properly secured.

Uhh .. one other thing I should probably mention: Sockets are not recommended for op-amps with bandwidth this high. Not sure what to suggest to change at this point in the project, though. Hopefully the rail bypass caps are close by.

Cheers

gregas · 8th March 2021, 12:15 AM

Hey Rick,
Thanks for the response.

I believe the sockets were used here's the ability to swap out chips.
Sounds like a major part of my problem is the chip that was chosen.

If the temp compens circuit works and I'm happy with the headphone amp, I would then find a way to mount it?

Rick PA Stadel · 11th March 2021, 07:06 AM

Yup!

About the 'swap out chips' .. a lot of people have a lot of fun doing that. Trouble is, an op-amp is NOT an op-amp, is NOT an op-amp, etc ..

Not all flavors are directly interchangeable. Some of the times that someone complains about the exceedingly poor sound quality of an amp they subbed in, it's oscillating ultrasonically, or otherwise behaving poorly. And lacking an oscilloscope they have no idea(!), then they blame it on *fake* parts, or chalk it up to some other specious excuse.

Cheers

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4th March 2021, 03:41 AM	#71
gregas diyAudio Member Join Date: Nov 2018 Location: Toronto	Hey Rick. So I'm adding those 1/4w resistors to my order Plus 4k7. Thanks. https://www.mouser.ca/ProductDetail/652-3006P-1-103-LF/ How's this look for the trimpot?

4th March 2021, 03:58 AM	#72
Rick PA Stadel diyAudio Member Join Date: Apr 2017 Location: greater Kansas City	Those are pretty standard, and pretty decent. Wouldn't mind if they would pick a tempco sign, and not just specify +/-200ppm. Or a little better cycles/life (only "200" means you can't, as a practical matter, just keep a handful of these in your prototyping parts box and expect them to be reliable when you pull one out -- check/measure every use!) If you get 10k trimpots, you shouldn't need the 4k7's. (Unless I booted the arithmetic .. !)

4th March 2021, 04:20 AM	#73
gregas diyAudio Member Join Date: Nov 2018 Location: Toronto	How about this for the perfboard? https://www.mouser.ca/ProductDetail/...9HVnuJCg%3D%3D Ok so no need for the 4k7 resistor

6th March 2021, 05:17 AM	#74
Rick PA Stadel diyAudio Member Join Date: Apr 2017 Location: greater Kansas City	Yep, that looks just fine. As long as you get 0,042" holes on 0,1" centers, and it's FR-4, you're getting pretty standard stuff.

7th March 2021, 07:01 PM	#76
Rick PA Stadel diyAudio Member Join Date: Apr 2017 Location: greater Kansas City	Should be OK. But the ground lead from C1 on the bias circuit will need a short, direct (no service loop) connection, close to the pad between the bypass capacitors on the AD817 supply leads -- pins 4 and 7. And if the bias circuit occupies somewhat less space, that's good thing. Maybe don't worry about the mounting. Try to think of the little added circuit as a test assembly, instead of something permanent that needs to be properly secured. Uhh .. one other thing I should probably mention: Sockets are not recommended for op-amps with bandwidth this high. Not sure what to suggest to change at this point in the project, though. Hopefully the rail bypass caps are close by. Cheers

8th March 2021, 12:15 AM	#77
gregas diyAudio Member Join Date: Nov 2018 Location: Toronto	Hey Rick, Thanks for the response. I believe the sockets were used here's the ability to swap out chips. Sounds like a major part of my problem is the chip that was chosen. If the temp compens circuit works and I'm happy with the headphone amp, I would then find a way to mount it?

11th March 2021, 07:06 AM	#78
Rick PA Stadel diyAudio Member Join Date: Apr 2017 Location: greater Kansas City	Yup! About the 'swap out chips' .. a lot of people have a lot of fun doing that. Trouble is, an op-amp is NOT an op-amp, is NOT an op-amp, etc .. Not all flavors are directly interchangeable. Some of the times that someone complains about the exceedingly poor sound quality of an amp they subbed in, it's oscillating ultrasonically, or otherwise behaving poorly. And lacking an oscilloscope they have no idea(!), then they blame it on fake parts, or chalk it up to some other specious excuse. Cheers