The OPA627 really sings

carlosfm · 5th August 2004, 09:56 AM

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.

Sunsun22 · 5th August 2004, 11:16 AM

Hi Carlos,

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

Sunny

Algar_emi · 5th August 2004, 11:33 AM

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

Algar_emi · 5th August 2004, 11:36 AM

Hi Carlos. Do you think this trick can also improve the OPA2604 sound?

Thanks...

analog_sa · 5th August 2004, 12:09 PM

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.

Sunsun22 · 5th August 2004, 12:40 PM

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

Nuuk · 5th August 2004, 01:02 PM

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!

PMA · 5th August 2004, 01:05 PM

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

Upupa Epops · 5th August 2004, 01:46 PM

To PMA : By biasing you must use Caddock or bulk metal Vishay

, with cheaper ones will not results convincing

, remember on this !

matjans · 5th August 2004, 02:53 PM

and, of course, *proper* supply bypassing.

5th August 2004, 09:56 AM	#1
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	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.

5th August 2004, 01:02 PM	#7
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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5th August 2004, 11:16 AM	#2
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	Hi Carlos, Do you need any special type of resistor to do this biasing? Sunny

5th August 2004, 11:33 AM	#3
Algar_emi diyAudio Member Join Date: Oct 2002 Location: Canada, Qc	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

5th August 2004, 11:36 AM	#4
Algar_emi diyAudio Member Join Date: Oct 2002 Location: Canada, Qc	Hi Carlos. Do you think this trick can also improve the OPA2604 sound? Thanks...

5th August 2004, 12:09 PM	#5
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	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.

5th August 2004, 12:40 PM	#6
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	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

5th August 2004, 01:46 PM	#9
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	To PMA : By biasing you must use Caddock or bulk metal Vishay , with cheaper ones will not results convincing , remember on this !

5th August 2004, 02:53 PM	#10
matjans diyAudio Member Join Date: Aug 2003 Location: Utrecht, NL	and, of course, proper supply bypassing.