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Universal buffer/headamp based on OPA1622
Universal buffer/headamp based on OPA1622
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Old 6th May 2016, 01:31 PM   #21
OlegSh is offline OlegSh
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Universal buffer/headamp based on OPA1622
Quote:
Originally Posted by Sergey888 View Post
...Dont make it large, since cutoff will depend on pot position.
BTW, that is why my EMI filter is at the moment before the attenuator which is going to be in the same box. I hope I will not have too much EMI inside of chassis. May be I can skip the EMI filter on the OPA1622 board but I'll keep the pads for it in case I ever need it.
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Old 6th May 2016, 02:35 PM   #22
Shaq888 is offline Shaq888  Ukraine
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I would still put some minimal filtering. You'll be surprised how much EMI can be carried in the box with wires coming in and out.

Last edited by Shaq888; 6th May 2016 at 02:37 PM.
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Old 8th May 2016, 01:10 AM   #23
johnc124 is offline johnc124  United States
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Really great project and impressive measurements!

As for common-mode distortion, I was well aware during the design phase that it wasn't going to be perfect. Improving the common-mode distortion (with a high source impedance mismatch) would have limited the input voltage range of the amplifier significantly, making it much more difficult to use on lower supply voltages. In my own testing I've found the performance to be comparable to the LM4562 with a 10k source impedance mismatch, which is respectable. For applications requiring extremely low CM distortion, the OPA1642 performs beautifully.
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Old 8th May 2016, 04:17 AM   #24
Shaq888 is offline Shaq888  Ukraine
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Well, you haven't seen what I consider impressive yet

Yeah, floating cascode can add some hassle.
I would say it was somewhat better than 4562 I measured. Could be due to sample to sample variation. Also, I've seen some noise (popcorn noise, I guess) issues with 4562. It was obviously dependent on batch. Some pretty much didn't have it at all. Doesn't sound like a huge issue for audio, but can be off putting.

Last edited by Shaq888; 8th May 2016 at 04:22 AM.
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Old 8th May 2016, 10:02 AM   #25
OlegSh is offline OlegSh
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Universal buffer/headamp based on OPA1622
Thanks for looking at my project, John! I really appreciate it!
I must admit that reaching the performance figures of LM4562 and have an ability to drive headphones is more than enough for my needs. So I'll happily continue with my project

Regards,
Oleg
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Old 8th May 2016, 04:19 PM   #26
johnc124 is offline johnc124  United States
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I just meant the CM distortion figures were similar. The LM4562 and the OPA1622 are two very different animals in terms of their intended applications. I looking forward to following along with your progress!
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Old 8th May 2016, 04:20 PM   #27
johnc124 is offline johnc124  United States
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Quote:
Originally Posted by Sergey888 View Post
Well, you haven't seen what I consider impressive yet

Yeah, floating cascode can add some hassle.
I would say it was somewhat better than 4562 I measured. Could be due to sample to sample variation. Also, I've seen some noise (popcorn noise, I guess) issues with 4562. It was obviously dependent on batch. Some pretty much didn't have it at all. Doesn't sound like a huge issue for audio, but can be off putting.
I can say that all of the OPA16xx op amps are screened for this in production because I consider it unacceptable.
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Old 9th May 2016, 10:13 AM   #28
Shaq888 is offline Shaq888  Ukraine
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I guess it adds a fair bit of a testing time
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Old 9th May 2016, 10:36 PM   #29
OlegSh is offline OlegSh
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Universal buffer/headamp based on OPA1622
Hi John,

I understood about the difference between the opamps and the CM distortion figures, thanks! I am currently reworking the design a bit. The current layout is a bit tight so I'll add some PCB real estate to fit slightly bigger filter capacitors before the regs and EMI filter cap to the input, and rearrange output pins and EN pin connection.

Regards,
Oleg

Last edited by OlegSh; 9th May 2016 at 10:47 PM.
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Old 16th May 2016, 02:22 PM   #30
OlegSh is offline OlegSh
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Universal buffer/headamp based on OPA1622
Default Updated PCB

Attached is the updated version of the PCB. It can now be used in balanced, inverting or non-inverting configuration depending on which parts are populated. The PCB size is 9x3 cm now. I dropped 0603 size so now the smallest SMD parts are 0805. The space around the OPA1622 is tightly packed but the board can still be soldered by hand, even the OPA1622 if heated from below through the via in thermal pad.

I hope I did not compromise the design by allowing too many options.
Any comments and suggestions are welcome!

Regards,
Oleg
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