Good replacment for BB OPA 2604/604

[Bgt]

Carlos,

What PSU capacitors do you use for the AD815? Transformer rating?
You awoke my interest for an active.

[Hans L]

Originally posted by carlosfm
I don't use them.
Fast diodes don't need them.

From what I've heard, slow diodes are the ones that do not need a bypass capacitor, but fast dioides do because of their switching noise.

But apparently the parallel capacitor can introduce noise as well. That's why a 'soft recovery' fast diode without bypass is preferred.

This is just repeating what I've read, nothing more.

[carlosfm]

Originally posted by Bgt
Carlos,

What PSU capacitors do you use for the AD815? Transformer rating?
You awoke my interest for an active.

You mean on the PSU pins of the AD815?
Philips 68uf + 100nf film.

I use a 400ma 2x17v toroid, but anything around 2x15v at 300~500ma will do.
Regulate for +/-15V.

I must warn you that if you never worked with current-feedback op-amps this will be a tough one.

[demogorgon]

please elaborate on this carlos, after all you are responible for me ordering a pair..

[carlosfm]

Originally posted by demogorgon
please elaborate on this carlos, after all you are responible for me ordering a pair..

As you guys have problems (???) making a search, I made that for you.

Starts here:
(re)searching for a better preamp

Schematic here:
http://www.diyaudio.com/forums/showt...255#post480255

Don't ask me too many questions, because it's all there.


PS: I'm using the direct output, without the coupling caps.
It has some DC-offset, but sounds better.
I have input coupling caps on my power amps.

[demogorgon]

Carlos, like a true gentleman, i must say.

Didn't know about that thread.
time for some info diggi'n..

[Hans L]

Originally posted by Hans L

From what I've heard, slow diodes are the ones that do not need a bypass capacitor, but fast dioides do because of their switching noise.

But apparently the parallel capacitor can introduce noise as well. That's why a 'soft recovery' fast diode without bypass is preferred.

This is just repeating what I've read, nothing more.

Carlos,

could you address this post please? A few posts ago, you recommended fast diodes without bypasses because 'they don't need them'. What is your explenation for that?

Hans.

[Bgt]

Carlos,

Pity you did not use an integrator to null the offset, is far more effective(=0.1mV offset). Like they use in power amps to avoid the offset caused by the resistor to ground in the negative feedback(=gain) path.
Anyway, the AD815 has a lot of offset. This has to be dealt with to avoid the coupling caps.

[lgo51]

Originally posted by Bgt
Carlos,
Pity you did not use an integrator to null the offset, is far more effective(=0.1mV offset). Like they use in power amps to avoid the offset caused by the resistor to ground in the negative feedback(=gain) path.

Hi BGT,

How would that go? Maybe an example...

Thanks,
LarryO

[Bgt]

How would that go? Maybe an example...

Ok, because I do my schematics on a piece of paper I can only tell you the drawing.
From the output of the power amp. take a 1M resistor to the - of the opamp, + (opamp) to ground, 470nF from - (opamp)to the output(opamp), from opamp output to the + input of the poweramp through 2x 1M8 resistors in series where in the middle of the 2x 1M8 resitors is a 100Nf to ground to take all the spurious HF components away. Don't forget to put 2 prot. diodes on the - of the opamp to protect it from going to the full supply rail voltage of the power amp. Opamp can be any modern 741 like type.