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Buffalo DAC (ESS Sabre 9008)

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mikelm

mikelm

Member
Joined 2003
counterpoint

Hi Guys,

I have connected up my counterpoint and it is playing music and it sounds ok but . . . .

The o/p from counterpoint to my discrete op amp has .5V ringing between each o/p leg & earth at about 10 meg hz.

I don't think this will upset my bal to unbalanced discrete op amps, I think up to about 100 meg hz is ok for them, but having said that somewhere along the line I cannot help thinking things would be better if the oscillation was eradicated.

I have just over - / +15 volts for each board from separate passively filtered supplies for each channel.

Any ideas ?

Is there a specific thread that deals with this on your forum ? I could not find one yet

mike
 
mikelm

mikelm

Member
Joined 2003
counterpoint

Hi Russ I read the thread and this is what I have learned:

The variables seem to be:

1) CC 4 & 5 100 - 1000pF

2) CC 3 higher than present value

3) R 11 & 12 from current value to 210ohms

4) only one earth connection - I only take an earth from the buffalo board so I think this is ok already for me

But I noticed that even 1000pF did not fix it for someone.

If you think you understand the issues here now could you give me some ideas about what values I should choose to avoid endless experimentation

thanks

mike
 
Russ White

Russ White

Member
Joined 2005
twistedpearaudio.com
Re: IVY Question

TV Man said:
I remember reading somewhere that to get the most out of the IVY Buffalo combination we should remove or link out C1, C2, C3, and C4. Something about the opamp not liking capacitive loads. Am I remembering this correctly?
Click to expand...


This is correct.

What we found is that would the OPA1632 behaves fine when operated from a voltage source (which requires an input resistor) with feedback caps, it does not when used from a current source.

Live and learn. We will be updating the manual to reflect the changes.

Basically what happens is anything above a certain frequency is passed directly though the feedback cap. This is not good.

Simply removing C1-4 totally resolves the issue. And the filtering provided by the caps at the input is sufficient.

Cheers!
Russ
 
Russ White

Russ White

Member
Joined 2005
twistedpearaudio.com
mikelm said:
Hi Russ

If u have a "fix" for counterpoint oscillation I would appreciate knowing what it is

thanks

mike
Click to expand...

Hi Mike.

I really can't be certain what is causing it. Did you try swapping the quad opamp? Is it the same on both boards?

All I can suggest is playing with the compensation cap values.

Also check to see if it is common mode or differential. If it's common mode then the problem is probably around the integrator that sets common mode output voltage.

If it differential it could be one of the integrators that set the input common mode voltage.

It could also just be a bad opamp.

Cheers!
Russ
 
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