(re)searching for a better preamp

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darkmoebius said:
This may sound like an "amateur hour" question, but will there be a need for the buffer once you use the AD815 pre?

A buffer?
Where?
In the power amp?
Yes, the same as ever.
It sounds better with it.;)
OPA627 biased to class-A.
Inverting amp needs a buffer.
I don't want a 5 meter feedback loop.:D
Inverting + buffer sounds better than NI, with or without buffer.

EDIT:
Believe me, counting the parts of my pre and power amp, they are still very few.
The boards are very small.
The signal path inside is very small.

I've seen preamps with more parts than all my system, including the CDP and Dac.:yikes:
Like ML preamps.:dead:
 
Bom dia Carlos!

Hi Carlos,

Regarding the Jeff Rowland Coherence sound, did you ever had the chance to listen to a PLINIUS M16?

If you do, please let me know what you think about the sound not the way it is build.

Jeff Rowland Coherence is a great amp, but for the money, they are better ones IMHO. It may be, again, just a mather of taste! I love an am that makes you feel that everythin sounds just like there is no amp at all in the chain.

Obrigado,


Audiofanatic;)
 
Nuuk said:
Good morning Carlos - did you get the picture? ;)

Good morning uncle Nick.:D (c) Pedja
You didn't receive my repply?

Nuuk said:
I think that darkmoebius meant do you still need the BUF634 with the AD815.

Huh?
No, what for?
The AD815 has between 2 to 3 times the current output of a BUF634.

Nuuk said:
So, another OPA627 fan discovers that they like treble as well as bass! :D

Not at all.
Have you tried it with the BUF634?
Or alone, biased to class-A?
Very very good.
The problem is, they are very picky with layout and I've seen too many boards out there (like the Pimeta:dead: ) that are a complete murder to these chips.
:att'n: They like capacitance on the PSU pins, not just small bypass caps.:att'n:

My Dac has OPA627 on the output buffer stage (in class-A), my power amp too, and my phono pre has OPA637s (in class-A).
The preamp is in the middle of these and there was an improvement from my previous one (not night and day, as I said, but mainly the treble).

The OPA627 is not bass-and-treble.
EDIT: it's very easy to have overblown, untight bass with the 627.
A clear indication of a bad layout.

Midband is gorgeous.
Some AD op-amps that I tried are bass-and-treble, they have a recessed midband.
Not the 815.
Maby because it's for video.:D

BTW, the AD815 has an excellent pinout IMHO.
The PSU pins are just on the right place.:cool:

:att'n: Any of these preamps is much better than using a pot, as good as it may be, as a passive "pre".:att'n:
 
Re: Bom dia Carlos!

Audiofanatic said:
Regarding the Jeff Rowland Coherence sound, did you ever had the chance to listen to a PLINIUS M16?

Bom dia.:cool:
No, I haven't heard the Plinius.

Audiofanatic said:
If you do, please let me know what you think about the sound not the way it is build.

My passion is music, not boxes.:D

Audiofanatic said:
Jeff Rowland Coherence is a great amp, but for the money, they are better ones IMHO.

It can be, but I still have to hear better.
I've heard more expensive ones but my ears liked this one.

Audiofanatic said:
It may be, again, just a mather of taste!

Yes, it can be.

Audiofanatic said:
I love an am that makes you feel that everythin sounds just like there is no amp at all in the chain.

Me too.:)

Audiofanatic said:

De nada.:cool:

Oh, I knew a guy that bougt exactly the Jeff Rowland Coherence that I heard.
That pre has been on demos, affairs, and someone had stolen the display (it's separated from the chassis).:bawling:
The guy bought it for less than half the price.
He contacted the distributors here to buy the missing parts and they didn't have it, didn't care, they have a very bad service.
He sent a mail to Jeff Rowland, the company.
The new display was slightly different and it was necessary to open the pre and make a very small mod (change a resistor).
Do you know who repplied, gatthered the parts, sent them, along with some notes on how to mount it?
Jeff Rowland, the man.:cool:
 
Jennice said:
I know this may sound dumb, but how do you make a chip op-amp or buffer work in class-A? I thought it was dependent on the idle current of the output stage within the chip, and could not be influenced from outside the chip?

You can force the chip to work biased to class-A by injecting voltage (usually from the negative rail) to the output.
If you google you will find lots of stuff about this.
 
Off topic!

carlosfm said:


Next time you have to go to Azores.
9 beautiful islands.;)


Please don't make me :bawling: :bawling: :bawling:
I'm allready drooling :D :D :D

Back to the (real) world of pre amps.


Audiofanatic ;)
 

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carlosfm said:

A buffer?
Where?
In the power amp?
Yes, the same as ever.
It sounds better with it.;)
OPA627 biased to class-A.
Inverting amp needs a buffer.
I don't want a 5 meter feedback loop.:D
Inverting + buffer sounds better than NI, with or without buffer.


Let's rewind a little. The main reason for using a buffer with an IGC is to isolate the amp from the pot. A single chip, like the OPA627, can do that.

If you add feedback resistors on that buffer circuit, it becomes a lineamp.

If you add a current booster (which is what the BUF634 mainly is) you can put the preamp away from the GC.

Now you are using the AD815, which is apparently replacing your line preamp/buffer, so you certainly do not need another stage in between. Why would you use it?


Carlos
 
carlmart said:
Now you are using the AD815, which is apparently replacing your line preamp/buffer, so you certainly do not need another stage in between. Why would you use it?

Yes, I have a standalone preamp, sitting on my Target rack.
Then I have a 5 meter (shielded) interconnect that goes to the power amp, on a central position between the speakers.
This way I have shorter speaker cables, the same size for both sides, and better results.
Without an input buffer, the power amp would have 5 meters worth of feedback loop.
And it would pick (as I experienced without an input buffer) interferences.
Yes, I knew my mobile phone was going to ring some seconds before.:clown:
Tarara tarara tarara... on the speakers.:D
Independently on these issues, I make my power amp so that it can behave in any situation: near or far away from a preamp, he is always happy.
And I have the input impedance I want without compromising the power amp's chip performance.
NI buffer + I amp.

For an integrated amp, you're right, this is not necessary, because the input buffer is the pre.
But for standalone devices I do it this way.
I like to make my things "universal", to play everywhere, in most situations.
Figure out: if I had the power amp on my rack, I could have a passive pre (with short interconnects).:cool:
The gain of the amp would be lower than usual for an integrated, though...

The advantage I have in having short speaker cables is greater than making an integrated, installing it on the rack, and having a 6 meter speaker cable for one of the speakers.

I suppose this is a very common situation for people (like me) that don't have a dedicated room for the system.
 
carlosfm said:


Yes, I have a standalone preamp, sitting on my Target rack.
Then I have a 5 meter (shielded) interconnect that goes to the power amp, on a central position between the speakers.
This way I have shorter speaker cables, the same size for both sides, and better results.
Without an input buffer, the power amp would have 5 meters worth of feedback loop.
And it would pick (as I experienced without an input buffer) interferences.
Figure out: if I had the power amp on my rack, I could have a passive pre (with short interconnects).:cool:
The gain of the amp would be lower than usual for an integrated, though...

The advantage I have in having short speaker cables is greater than making an integrated, installing it on the rack, and having a 6 meter speaker cable for one of the speakers.

The principle of having shorter speaker cables is a good one, even if speaker cables are less prone to RFI than interconnect cables.

Better yet would be to have balanced interconnects, which is certainly the way out for longer than 3m runs, but I am not quite certain on the layout your propose. Let's see if I get it:

1) Standalone preamp. What's in it? It's the OPA627/BUF634 buffer?

2) IGCs close to speakers.

Is there a stage I am missing? Are you proposing another buffer on the IGCs?


Carlos
 
carlmart said:
1) Standalone preamp. What's in it? It's the OPA627/BUF634 buffer?

Huh?
It's a normal pre, Carlos.
With case, PSU, everything.
A preamp.
I have a gain of 2.8x on my pre.

carlmart said:
1)Is there a stage I am missing? Are you proposing another buffer on the IGCs?

What stage?:confused:
I use an input buffer on my (inverting) power amp.
It's absolutely normal on power amps, no?
Carlos, is my previous post confusing?

matjans said:
did you use the ad815 in differential mode or as a normal dual opamp?

Normal, dual op-amp.

matjans said:
can you post your schematics?

One more thing for my "to do" list.:magnify:
:bawling:

Sorry, I've been very busy lately.
 
carlosfm said:

It's a normal pre, Carlos.
With case, PSU, everything.
A preamp.
I have a gain of 2.8x on my pre.

OK. So the pot is on this stage? What chips do you use on this preamp?

carlosfm said:

What stage?:confused:
I use an input buffer on my (inverting) power amp.
It's absolutely normal on power amps, no?
Carlos, is my previous post confusing?

Well, it became a bit confusing now. Apparently not only for me.

Just now I realized that you seem to have two active stages between your source and power amp: your preamp and a buffer.
And I don't quite see the need for them.

It's OK to have a strong cable drive to handle the interconnects and fight RFI, instead of speaker cables. And the BUF634 (or AD815) should provide for that. But if you have another active stage close to the IGCs, then you should have another source for noise and distortion.

If there is an input buffer close to the IGC, where you are also using the 627/634 combo, then I don't see the need for the second chip then, as the drive distance is short. A single 627 would be enough.

That's the reason for my question on your arrangement.


Carlos
 
carlmart said:
OK. So the pot is on this stage? What chips do you use on this preamp?

:bawling: It's the AD815.:bawling:
My pre was OPA627+BUF634 and I changed it for an AD815.:bawling:
My pre has always had gain.
Read my posts, Carlos.

carlmart said:
Well, it became a bit confusing now. Apparently not only for me.

Who else?:D

carlmart said:
If there is an input buffer close to the IGC, where you are also using the 627/634 combo, then I don't see the need for the second chip then, as the drive distance is short. A single 627 would be enough.

What?:confused: :bawling:
Carlos, wake up.:D
I have a single OPA627 biased to class-A on each LM3886 PCB, inside the amp.
Forget the buffer, will you?.
The OPA627+BUF634 was my preamp , wich I now changed for AD815.
I removed one board and installed the other one, inside the preamp.
 
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