People,
I really have to wonder sometimes. This thread is all about a preamp that is quasi identical to the one designed by PMA. See post 75. He designs his stuff very professionnally. He is sometimes opinionated like all of us, but always gives tips and gives away his findings. On his website there is plenty of info on design principles, links to the original BB/TI datasheet (where the topology comes from), discussion AND distortion measurements, comparing different op amps and the finer details of topology.
PMA is also selling PCB's.
And PMA's efforts are pretty much ignored here, ppl asking questions he already answered, designing PCB's that PMA is already offerering.
Why? Because PMA abides by the rules of this forum and doesn't beat any commercial drum.
I just say, go to his website, ckeck it out, and for crying out loud, if you buy a PCB, buy his.
I really have to wonder sometimes. This thread is all about a preamp that is quasi identical to the one designed by PMA. See post 75. He designs his stuff very professionnally. He is sometimes opinionated like all of us, but always gives tips and gives away his findings. On his website there is plenty of info on design principles, links to the original BB/TI datasheet (where the topology comes from), discussion AND distortion measurements, comparing different op amps and the finer details of topology.
PMA is also selling PCB's.
And PMA's efforts are pretty much ignored here, ppl asking questions he already answered, designing PCB's that PMA is already offerering.
Why? Because PMA abides by the rules of this forum and doesn't beat any commercial drum.
I just say, go to his website, ckeck it out, and for crying out loud, if you buy a PCB, buy his.
Re: no more 627's for me...
I use opa627/buf as a pre amp and I have found that performance, bass slam in particular, is completely dependent on the quality of the PSU. I just can't dissmiss opa627 just because you heard a pre using different opamps that sounded better.
The opa's seem to love decoupling capacitance a lot. Try using at least 200 uF for each rail. You'll notice that performance will go through the roof.
I bought the PCB from PMA. I use 200 uF (Pana FC) on the output of the PSU and 66 uF (2 x Black gate N 33 uF/16V) at both the + and - pins of each device. I can only say that bass slam is the best I ever heard.
Note that with the generally recommended values for decoupling capacitance bass slam was really poor.
Note also that I use supply voltages of 12,5 V. This lower than avarage value does not seem to affect sound.
Hope this helps
Hope this helps.
matjans said:
I use opa627/buf as a pre amp and I have found that performance, bass slam in particular, is completely dependent on the quality of the PSU. I just can't dissmiss opa627 just because you heard a pre using different opamps that sounded better.
The opa's seem to love decoupling capacitance a lot. Try using at least 200 uF for each rail. You'll notice that performance will go through the roof.
I bought the PCB from PMA. I use 200 uF (Pana FC) on the output of the PSU and 66 uF (2 x Black gate N 33 uF/16V) at both the + and - pins of each device. I can only say that bass slam is the best I ever heard.
Note that with the generally recommended values for decoupling capacitance bass slam was really poor.
Note also that I use supply voltages of 12,5 V. This lower than avarage value does not seem to affect sound.
Hope this helps
Hope this helps.
sound of single opamp?
Matjans,
Although I don't contest your listening result, remember that there is no such thing as the sound of OPA627 or ADxx
You can only talk about the sound of a particular circuit, of which the opamp is only a part. I'm sure that in your particular setup the AD sounded better. That does not mean that the latter is a better sounding opamp.
In this case it may be that the AD is not as sensitive to decoupling capacity. Perhaps there is a clue about that in its datasheet. Of course it could well be that the AD really is a better opamp for this application. I just want to make the point that opamp rolling is completely useless if you don't know what you are doing.
But something tells me that you already knew this..
Matjans,
Although I don't contest your listening result, remember that there is no such thing as the sound of OPA627 or ADxx
You can only talk about the sound of a particular circuit, of which the opamp is only a part. I'm sure that in your particular setup the AD sounded better. That does not mean that the latter is a better sounding opamp.
In this case it may be that the AD is not as sensitive to decoupling capacity. Perhaps there is a clue about that in its datasheet. Of course it could well be that the AD really is a better opamp for this application. I just want to make the point that opamp rolling is completely useless if you don't know what you are doing.
But something tells me that you already knew this..
some time ago we were modding a project phono box and the 8610 came out as best. in an earlier headamp project (cmoy) the 8610 came out best as well.
in my cdp however, i liked some other opamps better.
it's a matter of which opamp suits your circuit best, i think.
but there ARE differences, and they are very much audible, i must say.
but let's get back to the original thread...
/matti
in my cdp however, i liked some other opamps better.
it's a matter of which opamp suits your circuit best, i think.
but there ARE differences, and they are very much audible, i must say.
but let's get back to the original thread...
/matti
Alcaid said:
First thanks for the help the opa549 amp,It is working.
I have one preamp that is a combo of Esp 02 & 97, it sound pretty good. I also have a preamp with 4 sockets for dual op amps. I tried different combinations of op amps(opa2134,ne5532,412,tl072,lm353,etc). so far I like 2 ne5532 and the 2 412 the best. I had the opa2134 & buf634 and the ne5532 & 412 running for least than two days,so that might be a doesnt sound as good as it should.
jaudio said:
I built a couple of headamps to see if I could hear the differences between opamps. I found the cmoy was very sensitive to opamp selection and supply voltage, while in a $12 kit headamp it seemed to make little or no difference, so I concluded that everyone was right, in some circuits the opamp makes a big difference, in others, very little.
So using better quality opamps will make an "improvement", just the improvement may be enormous or so small you can't tell.I have to admit my testing procedure wasn't very scientific and just based on gut feeling, but it produced an answer I can live with.
Re: sound of single opamp?
It IS less sensitive to decoupling capacitance.
But used correctly the OPA627 is better.
I think Matjans knows all that, I've been telling him for a long time.
Just a final note: a good PSU decoupling will do no harm to any op-amp. The OPA627 will sound at it's best, but also most other op-amps will.
But there is not such a thing as the best op-amp for everything in audio applications.
I/V conversion, line preamp, phono preamp (MM, MC...) the implementation and component values used... there is always one op-amp that shines on one circuit and may sound less good on another.
There is no universal solution.
But if one knows where to use a good bipolar and where to use a good fet-input op-amp, that's a good starting point.
Or go more radical and step up to a good current-feedback op-amp.
I use the AD815 in my line preamp and I just love it.
ABO said:
ABO said:
It IS less sensitive to decoupling capacitance.
But used correctly the OPA627 is better.
ABO said:
I think Matjans knows all that, I've been telling him for a long time.
Just a final note: a good PSU decoupling will do no harm to any op-amp. The OPA627 will sound at it's best, but also most other op-amps will.
But there is not such a thing as the best op-amp for everything in audio applications.
I/V conversion, line preamp, phono preamp (MM, MC...) the implementation and component values used... there is always one op-amp that shines on one circuit and may sound less good on another.
There is no universal solution.
But if one knows where to use a good bipolar and where to use a good fet-input op-amp, that's a good starting point.
Or go more radical and step up to a good current-feedback op-amp.
I use the AD815 in my line preamp and I just love it.
Referring to the original cct of the thread - OPA627 and Buffer. This is a line stage with GAIN, right? Why on earth wouldn't you use a OPA637 for the same price it's 5 times the GBW and has better +PSRR by 14 dB (error on datasheet)! You don't need to compromise it with 200Pf and you don't need the buffer.
The impedance of the Noble pot? Have you centred it electrically and measured the crosstalk? I would be keeping the wiper to chip input tracks well apart and ground planed and the pot shielded.
Tim,
No need to subject the signal to any more abuse then, is there?
The impedance of the Noble pot? Have you centred it electrically and measured the crosstalk? I would be keeping the wiper to chip input tracks well apart and ground planed and the pot shielded.
Tim,
No need to subject the signal to any more abuse then, is there?
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