The OPA627 really sings

Status
Not open for further replies.
Jump to Latest
C

carlosfm

Member
Joined 2003
#1
At request of several families😀 , my PM is full of questions:bawling: , 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.😉
😎
 
#6
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
 
#11
Biasing at around 10ma with "normal" 1% film resistors works like a charm for me.😎

matjans said:
and, of course, *proper* supply bypassing.
Click to expand...

That should always be done, or it won't sound as it should.😉
But that, I think, should be clear by now, after so much talk.😀

Note: this server has more crashes than Windows.:clown:
To post this note not I took some 10 minutes, plenty of patience and retries.
See you maby tonight, it's no good now.:bawling:
 
#12
Nuuk said:
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! 😉
Click to expand...

Nuuk, that's not strange at all.
The OPAs, and most of the modern/fast op-amps, need a good layout and PSU bypassing. They are very picky.
The fact that an NE5534 works better on a circuit doens't mean nothing to me, I find it normal, I've experienced that too many times.
Put the right caps where they are needed and youl'll have the OPA627 (and many more) largely outperforming the NE5534.

But then again, if you like the NE5534's sound, I don't discuss that.:angel:
 
#14
Re: Re: The OPA627 really sings

PMA said:


Carlos,

I am going to check it this evening.

Cheers, Pavel
Click to expand...

OK - I have done it. It does not work for every opamp. But it does work for the OPA627.

My application is the voltage stage in my new amplifier project (error correction amp). The opamp is supplied from +/-18.5V (LM117+LM337). I have chosen the 2.7k resistor from the opamp output to -Vs.

For OPA627, the improvement is substantial. The effect is in clearer mids and highs and the overall resolution for the complex music. The music is more liquid. And the "tail" dissappears. Absolutely positive, nothing to complain. Only very very well designed discrete circuit is capable to give same sound quality as OPA627 with increased Iq.

The biasing against -Vs does not work for AD797 and brings no effect for OPA134.
 
#15
mlloyd1 said:
thanks for the tip!

have you noticed any negative impacts on thermal performance, dc offset/drift and noise?

mlloyd1
Click to expand...

No.
It just gets a little hot, but nothing to worry about.
DC-offset remains the same.

PMA said:
The biasing against -Vs does not work for AD797 and brings no effect for OPA134.
Click to expand...

My experience with the OPA132/2132 too, I feel it doesn't make a difference with this one.:angel:

PMA said:
OK - I have done it.
Click to expand...

You're fast.😀

PMA said:
It does not work for every opamp. But it does work for the OPA627.
Click to expand...

:angel:

PMA said:
For OPA627, the improvement is substantial. The effect is in clearer mids and highs and the overall resolution for the complex music. The music is more liquid. And the "tail" dissappears. Absolutely positive, nothing to complain. Only very very well designed discrete circuit is capable to give same sound quality as OPA627 with increased Iq.
Click to expand...

Oh yes!
Amen. :angel:

:happy1: :cheerful: :nod:
:usd:

Note: I have here several new op-amps for some time to test but don't really feel the need... I'm lazy...
I'm not so convinced if it's possible to better a well implemented OPA627/37...
I use them for years and I just love them.:hbeat:
 
#17
Now try this

After all the benefit shown from a simple R between V- and output, read how bad this is for sound...

http://tangentsoft.net/audio/opamp-bias.html

Then try the cascoded JFET baising. I biased to 2.5mA using the JFET method and found the OPA627 sound to open up, especially in highs and mids. Bass was about the same. I think my experience is described in the High-end pre-amp for my GC thread.

Maybe I'll try the higher levels Carlosfm suggests, but I have seen a post on headwize suggesting that higher than 3mA added grain to the sound.

Having said all that, I think that the THS4061 UNBIASED still sounds better than a 3mA biased OPA627...😉 , especially in the highs. Clear, but delicate, this being in the IV stage of a DAC.

Maybe I'll try the bias on THS4061 tonight....
 
#18
Re: Re: Re: The OPA627 really sings

PMA said:

The biasing against -Vs does not work for AD797 and brings no effect for OPA134.
Click to expand...

Perhaps you should try biasing with a little lower current and use a JFET CCS instead.I tried that years ago on a AD797 with good results.I used a 2mA CCS biased to -rail.I guess that the 0,5mA output stage bias in AD797 isn´t enough...
Once I tried 2mA CCS´s with LM6172 and that really improved alot.

Nicke
 
Status
Not open for further replies.
Top Bottom