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Old 5th August 2004, 09:56 AM   #1
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Cool The OPA627 really sings

At request of several families , my PM is full of questions , here's the trick.
It's easier than you think.

On some op-amps you notice better sound by doing this, on other ones you don't.
But the OPA627 really needs this to sing properly.

As simple as a resistor from V- to output, biasing the op-amp in to class-A at between 5 to 10ma.
For +/-18v PSU I use 2k, and for +/-15v PSU I use 1.8k.
You can use anything that bias it from 5 to 10 ma, it's not critical, although I usually go for around 10ma.

No need to use jfets to do this, just try it with a resistor at around these values and be amazed.
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Old 5th August 2004, 11:16 AM   #2
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Hi Carlos,

Do you need any special type of resistor to do this biasing?

Sunny
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Old 5th August 2004, 11:33 AM   #3
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Hi Sunsun22. Let us know if you implement this trick on the ML38 if it improve the ML38 sound.

Didi you found the round can IC to DIP adapter for the ML38 upgrade?

Thanks...

SB
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Old 5th August 2004, 11:36 AM   #4
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Hi Carlos. Do you think this trick can also improve the OPA2604 sound?

Thanks...
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Old 5th August 2004, 12:09 PM   #5
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At the time when i tested the OPA627 and decided it's not my cup of tea i used a FET CCS at output set to 2 mA. Indeed, it does improve the sound, but not enough to make it listenable.
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Old 5th August 2004, 12:40 PM   #6
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I will try this trick on my ML38 and let you know later. However, I am still waiting for some parts from Farnell to upgrade the PCB. According to Farnell, my parts will arrive by next Monday, I'll give it a judgement after a few days of sit in.

Up to this moment, I still cannot find the adapter for the MAT02/03 but I think I am not going to change it at this moment because MAT02/03 are pretty expensive and I need a few more of them to match. Too costly.

Sunny
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Old 5th August 2004, 01:02 PM   #7
Nuuk is offline Nuuk  United Kingdom
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When I biased my OPA627's into class A, I thought they actually sounded slightly worse!

AFAIK, the circuit was fine and there was an improvment with the NE5534's when used in the same circuit.

Strange thing this hobby!
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Old 5th August 2004, 01:05 PM   #8
PMA is offline PMA  Europe
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Default Re: The OPA627 really sings

Quote:
Originally posted by carlosfm
But the OPA627 really needs this to sing properly.

As simple as a resistor from V- to output, biasing the op-amp in to class-A at between 5 to 10ma.

Carlos,

I am going to check it this evening.

Cheers, Pavel
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Old 5th August 2004, 01:46 PM   #9
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To PMA : By biasing you must use Caddock or bulk metal Vishay , with cheaper ones will not results convincing , remember on this !
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Old 5th August 2004, 02:53 PM   #10
matjans is offline matjans  Netherlands
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and, of course, *proper* supply bypassing.
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