Miguel and Carlos,
You guys should try biasing the opas into class a. I have made various tries and you can really get a class a type of sound with this tweak.Plus you can tune this effect by adjusting the bias.The difference is mainly in the midrange and soundstage where you can have a more open sound and deeper soundstage.
You guys should try biasing the opas into class a. I have made various tries and you can really get a class a type of sound with this tweak.Plus you can tune this effect by adjusting the bias.The difference is mainly in the midrange and soundstage where you can have a more open sound and deeper soundstage.
The gain of the pre is 1. Is the opamp unity gain stable? It may be that what you measure is do to noise and not actual dc at the output of the GC. Can you check it with a scope?
Is you pot connected before the input cap of the pre or after. It has to be infront of C1. If it is after it'll affect the DC offset of the preamp.
What kind of cap do you use between the pre and GC? If it's polar, is it connected properly polarity wise?
Is you pot connected before the input cap of the pre or after. It has to be infront of C1. If it is after it'll affect the DC offset of the preamp.
What kind of cap do you use between the pre and GC? If it's polar, is it connected properly polarity wise?
Yes.
No. Only DMM.
I do not use C1 because my source has no DC.
Film (poliester I guess, a BC orange one)
Miguel
OK, Just answered some of my questions. It is unity gain stable and it has FET in.
The way you have buf634 connected extends the freq band to 180 MHz. I suspect that you have a lot of HF interference happening there. If you remore R11 it'll tame it a bit. Have you tried that?
The way you have buf634 connected extends the freq band to 180 MHz. I suspect that you have a lot of HF interference happening there. If you remore R11 it'll tame it a bit. Have you tried that?
miguel2 said:
If you don't use C1 increase R1 to 3.3k. This way you'll decrease the pot interference to the in res to gnd. Mind you I don't expect much there because it's a fet input.
Make R1 10k and for 100k Pot put 100pF in paralel with R2 and see if that will solve the problem.
protos said:
Yes, but the OPA627 is not alone...
Anyway the sound I have is uterly top class, I don't feel anything missing.
And the guy is having trouble, does he care about class A now?
miguel2 said:
That's even worse. No connection at all/ Pin 1 should not be connected at all for lower bandwith.
So R1 goes to 10K and R2 bypassed with 100p. Got it. I´ll give results later on. Thanks.
Carlos, are you using the 200p cap between the output of the opa627 and the -in, as in the buf634 datasheet?
Miguel
Carlos, are you using the 200p cap between the output of the opa627 and the -in, as in the buf634 datasheet?
Miguel
miguel2 said:
It is, but before the regulators you should have at least 2 or 3 volts more voltage than the regulators you're going to use.
To use those regs you should have a +/-18v trafo, or a bigger +/-15v trafo, as you only have +/-19v and you should have around +/-21v with that one.
This indicates that your trafo is weak, and you should regulate at a lower voltage.
Pay attention to my initial posts, my pre has a gain of around 2.4x, it's not unity gain!
As for your problems, post some pics, it may help.
miguel2 said:
As Carlos said The cap is good to decrease the gain of the opam for HF. Yours is already at 1.
Tel us what the result of the HF filter at the front is, please.
I can't stop wondering, why do you have to have the preamp on the first place? You take the 22K in impedance of the GC and feed it with 50Ohm preamp, that has Input impedance of 47K. What's the point of it all? Just ading extra stuff on the way of the signal. If you need higher impedance, increase the res connected from +In to GND to 47k from 22k. The offset may change a bit, but so what. And all the preamp stuf will be redundant.
GregGC said:
Let the man have the pre.
At least he can put a pair of pre outs to drive another GC, even at the other end of the house.😎
carlosfm said:
Let the man have the pre.
At least he can put a pair of pre outs to drive another GC, even at the other end of the house.😎
I'm not stooping him to play with electronics if that's his goal. I'm concerned about the end result. If he wants to drive another GC I just gave him a solution in my prev. post above yours.
GregGC, I am using to non-os dac using passive I/V. I really need a pre.
And I have to say that even with all these flaws, the sound of my system improved with this pre. I just want to keep listening to it (opposed to having 22VDC in the speakers
)
I have to buy the caps and mount them before giving you guys some (I hope good) news.
And I am going to change the gain too. just to check if this has anything to do with the strange behaviour.
Miguel
And I have to say that even with all these flaws, the sound of my system improved with this pre. I just want to keep listening to it (opposed to having 22VDC in the speakers
)I have to buy the caps and mount them before giving you guys some (I hope good) news.
And I am going to change the gain too. just to check if this has anything to do with the strange behaviour.
Miguel
miguel2 said:GregGC, I am using to non-os dac using passive I/V. I really need a pre.
And I have to say that even with all these flaws, the sound of my system improved with this pre. I just want to keep listening to it (opposed to having 22VDC in the speakers
I have to buy the caps and mount them before giving you guys some (I hope good) news.
And I am going to change the gain too. just to check if this has anything to do with the strange behaviour.
Miguel
I edited my post:
http://www.diyaudio.com/forums/showthread.php?postid=268643#post268643
Read it and you'll see what I mean.
But at the end what's valid is whatever sounds good to you. And I totaly respect that.
Greg
GregGC said:
Your solution is for an integrated amp and I agree.
I ask the same question.
But to drive another GC it's better to go active.
And if the power amp is far away (mine is at 5m), you really need a pre like this one.😉
No way a passive pre would work fine in these conditions.
And I do have a phono pre that need some active stage after it. And I am liking the new sound signature of the system...
Miguel
Miguel
miguel2 said:
Yessssss!!!😀
I made several different GCs (different chips, with and without buffer...) and this is still the best combination of all the ones I made.
And it was the first one.😱
This is ultra-high-end.
Sounds s'beautiful.
Just put that 200pf cap, you NEED it.
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