Substituted the OPA627, biased into class A with JFETS (2n3819 with 2SK170) with an unbiased AD8610 in my pavel macura style pre-amp (OPA627 into BUF634) which feeds a NIGC). After 24 hour run-in, I could not really tell the difference in sound. Maybe biasing the AD8610 will shift it to another level?
Note that I am using a Theta dac with OA627 in both IV and filter positions. Also note that I am runningthe AD8610 at +-15V and it is well.
Time to try the biasing or AD825/AD8065....
Note that I am using a Theta dac with OA627 in both IV and filter positions. Also note that I am runningthe AD8610 at +-15V and it is well.
Time to try the biasing or AD825/AD8065....
Not to squander this class A bias thingy, but those opamps your talking about have such low distortion anyway biasing into class A aint really gonna do anything more then make an unhearable thing even more unhearable if you get me lol.
Plus doesnt the buffer have greater distorsion then the opamps anyway, so the low distortion of the opamps is going to be swamped by the higher dist of the buffer. So putting it into class A isnt really going to do anything. Or have I missed the point of class A biasing in opamps?
Plus doesnt the buffer have greater distorsion then the opamps anyway, so the low distortion of the opamps is going to be swamped by the higher dist of the buffer. So putting it into class A isnt really going to do anything. Or have I missed the point of class A biasing in opamps?
Analog SA,
So you agree with my observation then: A biased OPA627 and unbiased AD8610 sound similar. And also, biasing the AD8610 leads to very little improvement over the unbiased AD8610. So to conclude, dont buy the OPA627 (which needs biasing to sound good-my observation as well, dark and compressed without biasing), rather buy the AD8610, unless of course you have serious allergies to SMT.
Any thoughts on AD8650? I'll be trying those tonight.
So you agree with my observation then: A biased OPA627 and unbiased AD8610 sound similar. And also, biasing the AD8610 leads to very little improvement over the unbiased AD8610. So to conclude, dont buy the OPA627 (which needs biasing to sound good-my observation as well, dark and compressed without biasing), rather buy the AD8610, unless of course you have serious allergies to SMT.
Any thoughts on AD8650? I'll be trying those tonight.
Alone they are quite different.
P-A also said that with the BUF634 he didn't notice any difference between those two.
I only compared alone, in this case the AD8620 against the OPA2132, on a preamp (buffer input of my NI LM4780 GC).
I've put back the OPA2132, much better.
But that was at +/-15v and people say that the new ADs work better at +/-12v (+/-15 is over the top for them anyway).
I also tried AD8066, it worked well, but not to my taste, and I had to get it out, that thing got quite warm.
Don't try this one at +/-15v!
I only have initial impressions on these AD op-amps.
Testing conditions were not the ideal for them.
Someday I'll make a better test.
P-A also said that with the BUF634 he didn't notice any difference between those two.
I only compared alone, in this case the AD8620 against the OPA2132, on a preamp (buffer input of my NI LM4780 GC).
I've put back the OPA2132, much better.
But that was at +/-15v and people say that the new ADs work better at +/-12v (+/-15 is over the top for them anyway).
I also tried AD8066, it worked well, but not to my taste, and I had to get it out, that thing got quite warm.
Don't try this one at +/-15v!
I only have initial impressions on these AD op-amps.
Testing conditions were not the ideal for them.
Someday I'll make a better test.
Time to try the biasing or AD825/AD8065.... [/B][/QUOTE]
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There are quite a few posts on biasing in the headphone forum. Biasing the AD825 to 3 mA with fets is certainly worthwhile - tames the slightly splashy treble.
I find the 8065 a little mechanical, too close to the 627 for my liking. The LM 6171 suitably bypassed bewteen V+ and V- also sound s very good without biasing!
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There are quite a few posts on biasing in the headphone forum. Biasing the AD825 to 3 mA with fets is certainly worthwhile - tames the slightly splashy treble.
I find the 8065 a little mechanical, too close to the 627 for my liking. The LM 6171 suitably bypassed bewteen V+ and V- also sound s very good without biasing!
Another listen
Well, listened again last night to AD8610 (unbiased) vs OPA627 (biased into Class A, 2mA, with a JFET) and there is a difference.
The AD8610 seems to present a more open window, especially in the highs, on music, transients and realism of highs being enhanced.
I would say though that on some CD's it can come across as a bit bright. I will be bypassing using the Goudreau triplet and will post results here.
Well, listened again last night to AD8610 (unbiased) vs OPA627 (biased into Class A, 2mA, with a JFET) and there is a difference.
The AD8610 seems to present a more open window, especially in the highs, on music, transients and realism of highs being enhanced.
I would say though that on some CD's it can come across as a bit bright. I will be bypassing using the Goudreau triplet and will post results here.
Dr.H said:
Not at all, definitely.
It seams to me that people have very different reactions (and results) to this op-amp.
It's very picky with layout and PSU bypassing.
It can easilly sound as you describe, and also with a flappy, dominant, untight bass.
Do it properly, and it really shines.
Search if you want, I've posted several times about this.
The first impressions I've got from testing the AD8620 (a quick test) was the brighter treble (not better, not neutral), and, very important, comparing to the OPA2132 (inferior to the OPA627 by a small margin), I noticed mainly on the midband that with the AD harmonics, air, space were much worse, not on the same league.
The breathing of the voice, the resonance of the room, the AD just doesn't get it.
So, my (I repeat) initial tests made me think that the AD8610 seamed like hi-fi, and not like the real thing.
BTW, bias into class-A if you have a good (clean) PSU, or else you're injecting ripple on the signal.
Hi,
Could someone post a simple schematic to indicate what we are talking about with biasing, using jfets.
I thought biasing an opamp was using a constant current source to pull current to either the +ve or -ve rail. Alternativly, a single resistor does well.
Is this what we are talking about??
Adrian
Could someone post a simple schematic to indicate what we are talking about with biasing, using jfets.
I thought biasing an opamp was using a constant current source to pull current to either the +ve or -ve rail. Alternativly, a single resistor does well.
Is this what we are talking about??
Adrian
analog_sa said:Carlos
We have never been in more agreement. Provided of course, you transpose OPA627 and AD8610 in your text
Obviously personal preference and system context may lead to diametrically opposed views.
Personal preferences aside (I understand them), do you think that the OPA627 has a brigter, more incisive treble than the AD8610?
Really?
Yes, well... it's useless to talk about this.
Tastes are very different form person to person, and systems too.
Try both, everyone, and decide.
BTW I tested the AD825 in my Audio Alchemy DDE v3.0 dac a year ago, in place of the OPA627, and I just can't understand what the fuss is that all about.
The AD825 has a very recessed midband, no life, voices are muted. Everything else is fine.
That tells me that people who like it are trying to solve their system's imprefections and lack of neutrablity (usually it's the speakers).
Fine for me.
No i don't think so. I just find it very dead.
Agreed.
You are again hinting that you system and specifically speakers are a benchmark for neutrality and perfection. A bit childish, dont you think? Maybe you're fighting the brightness of your speakers with dead sounding opamps. I can also recommend vintage paper in oil caps.
analog_sa said:
Did I say that?
Did I talk about any of my several systems?
Did I talk about listening tests at other people's homes and systems, including op-amp comparisons?
Did I?
analog_sa said:
No, again, who speaks is exactly who is, as you misunderstood everything I said.
Don't bother' I'm getting used to that.
analog_sa said:Maybe you're fighting the brightness of your speakers with dead sounding opamps. I can also recommend vintage paper in oil caps.
Look, I didn't talk of my speakers here. Read above.
AND, last but not least, as I said too many times, it's easy to kill the sound of the OPAs, so easy, very very easy.
You may be a speciallist.
Forget it, if you don't come with childish attacks, we can be in peace here.
Please just give your oppinion, as I gave mine.
I admit other oppinions, but it seams that you like to pick on me.
Go back to your valves.
They are neutral.
5th element said:
It depends on application but I can definately say that OPA627
benefits from class A OP biasing even into light loads (50k).
We tried pull up & pull down 5mA and 10mA. PU vs PD is
pretty similar. 10mA is better than 5mA by a small marging,
which is better than nothing by a bigger margin.
I also suggest balancing IP impedances into the + & - inputs,
this goes for both capacitive and resistive elements.
When all these factors are taken care of including PS
the 627 is a very good OPA.
Cheers,
Terry
carlosfm said:
BTW I tested the AD825 in my Audio Alchemy DDE v3.0 dac a year ago, in place of the OPA627, and I just can't understand what the fuss is that all about.
The AD825 has a very recessed midband, no life, voices are muted. Everything else is fine.
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May be your own system has a problem. The AD825, like others, need to burn in.
You are always so definite about being right that others feel motivated to answer you!!
fmak said:
The AD825s were inside my AA dac for more than a week.
When I change something I leave it playing.
I think this should be enough.
fmak said:You are always so definite about being right that others feel motivated to answer you!!
I gave my oppinion about this op-amp.
Just that.
If I always have to post all the details, the colour of the resistors, the system, the cables used, the PSU,
-in time, just to give a simple oppinion to a simple question, then forget it, I won't bother to post anymore about op-amps.People can even say that the NE5534 rules, who cares?
Not me.
Instead of giving my oppinion and trying to help, I should shut my mouth.
Thanks for helping me figuring this out.
Go on...
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