Good replacment for BB OPA 2604/604

[carlosfm]

Originally posted by AnthonyAsh
Hi Carlos.Iread some article about biasing opa627 with 10k resistor.The main drawback is (according the publication) is dependenci between out signal and current trough opa627,so it is like class a,but again not really,because current depends of out level.Because I never before biased opa627 in A,what you think about it? Is it really "hearable" improvement?

I know that, but that's a very low biasing, and not at all optimized for the OPA627.
For a +/-15v psu, try 1.8k, for +/-18v, 2k.

I suppose you have missed this:
The OPA627 really sings

[AnthonyAsh]

I will try it,it actually very easy to implement and listen,then spend time in discussions
BTW ,I've got good results with 10uf Black Gape P-K in decoupling+0,1 polypropylene+wima 2200pf.They must be connected directly to pins,i put BG on back side,and polypropilene on chip botton. And I've got some improvement of sound.
I heard very good is BG N 0,1 uF,will try it soon.

[Gasho]

I used AD825 in my RCD990 mod. I put them in I/V , filter , output (coupled with Mundorf Supreme ) . Sound is top rate by every point of view. I did not try 627 , but i don´t think it will do better than much faster AD825(much shorter settling time , faster rise time...).

OPA2604 can be very good performer in line stage preamp section.
The very important thing is the level of negativ feedback used with this and other OP-s (if we dont count the quality of PS). I discovered that NFB resistors ratio must be close to 1:10 , 1K to ground /10K from output to invert input. Sound was very transparent fast and neutral.

I dont think that OP-s distorzion can afect sound that much. I mean we are talking abuot 0.0003% for 1KHz step.
It is nothing compared to some tube or discrete designs which are musical, and neutral .
I think the quality of perifer components and PS around OP ,are of bigger imprtance than the type of OP(I am talking of good ,and fast OP-s) .

[carlosfm]

Originally posted by Gasho
OPA2604 can be very good performer in line stage preamp section.

I agree with you, it sounds better on a line preamp than inside a CDP (either for I/V or for buffering).
This thread started because of mods to a CDP.
I always find the OPA2604 a little "rude", coarse sounding here, specially in the midband and treble.
The OPA2132 is superior in either role, and the LM6172 is (most of the times) even better.
What I haven't tried was feeding the OPA2604 with +/-24V.

[IanAS]

Originally posted by carlosfm Aug '04

I haven't tested the THS4061, so I can't comment.
I have them here to make a test.
With those beautiful specs I have a feeling...
It may even be that working with the BUF634 they outperform the OPA627.
And alone?
Possibilities are plenty, but I have no time now.

Originally posted by carlosfm Oct '04

I spent some good moments this night playing with my small battery-powered preamp, one that I made some years ago for tests.
It uses a double op-amp.
I use it with my favourite double op-amp: the LM6172.
Tonight started testing op-amps, again.
Here's what I tested:

- LM6172
- OPA2132
- NE5532 (from Signetics)
- THS4062
- AD826
- AD8620

And the winner is: LM6172.
It beats the OPA2132 by a very small margin, it's almost on par, you have to be an experient listener to pick the differences.
The THS4062 made my speakers move with the movement of the pot. As I predicted, it has input DC-offset. Not bad sounding, but there's better and I think this is not indicated for audio use, it has some peculiarities for a voltage-feedback op-amp.
The Signetics NE5532 is not bad at all, but... nah. A little synthetic sounding.
The AD826 has a common characteristic usually found on AD op-amps: a recessed midband. Not neutral, veiled midband, not for me.
The AD8620 confirmed my first test some time ago: a "thin" treble, it lacks "body" and harmonics, it's a girl treble.

Carlos has the OPA 637 now beaten the LM6172 for you?

[IanAS]

And what about the 4061?

[carlosfm]

Originally posted by IanAS
Carlos has the OPA 637 now beaten the LM6172 for you?

I was just talking about double op-amps.
And notice: nothing's universal.
The OPA627/37 is better than the LM6172, but it's not a night and day improvement.
Also, an op-amp can't be the best everywhere.
The 627/37 are amongst the best, but I have had better results with the AD847 in a particular application.

[carlosfm]

Originally posted by IanAS
And what about the 4061?

I have recently used the THS4062 (the same, but double) on the headphone output of a cdp and the results were very good.
But I don't have much experience with it on other circuits, so I can't comment much more.

[Gaucho]

Originally posted by carlosfm
I always find the OPA2604 a little "rude", coarse sounding here, specially in the midband and treble.

I find the OPA2604 sounds rather screechy. It sometimes sounds as if the musicians aren't quite playing in proper time. It's among the worst of the many op-amps I've tried, JRCs included.

I've have an AD8620BR (I'll be useing it with an SOIC-to-DIP adaptor) and a OPA2277P on order, they should arrive on Monday. I'll post my impressions of these chips in a few days. FWIW the OPA2277s are the stock op-amps in the RCD-1072.

[Gaucho]

The OPA2277 is now my favorite BB chip, far better then the OPA2132! I'm very pleased with it, it has a very lovely top-end. It doesn't seem quite as fussy about PS bypassing as the other BBs I've tried; the bloated bass thing doesn't happen, it just gets a little bit fuzzy in the mid-range. I do have a minor gripe; it lacks a little bit of dynamic impact or 'bass snap' but other then that it's excellent. If your a BB fan you owe it to yourself to try it.