SSL 9K Mic Pre

[G-Sun]

Which were the capacitors you changed?

It was C68 and C64 on both channels

 

[G-Sun]

Can you connect the +ve inputs (p3) of IC23 & 30 together?  This disables the earlier stages.  If the noise goes away whatever the setting of the GAIN, it means problem is in the earlier stages.

I can now turn the gain up 3/4 (3 o'clock) without noise (the vlz mixer being the noise-floor of -85db).
Then up to max gain, the noise peaks at -35db

 

[G-Sun]

A note: My pcb looks like I've spilled some sugar-water over it. Must be from the isopropanol cleaning. Is this normal?

 

[ricardo]

I can now turn the gain up 3/4 (3 o'clock) without noise (the vlz mixer being the noise-floor of -85db).
Then up to max gain, the noise peaks at -35db

Is this the same on the good channel?

It was C68 and C64 on both channels

I hope you mean C68 & C84

DC conditions tell us if a stage is working properly.  U32b is a servo that's supposed to keep the outputs of IC30 & IC23 the same regardless of GAIN setting.  I'm still trying to figure out why they are different.

 

[G-Sun]

I can now turn the gain up 3/4 (3 o'clock) without noise (the vlz mixer being the noise-floor of -85db).
Then up to max gain, the noise peaks at -35db

Is this the same on the good channel?

I'll solder a short and check

It was C68 and C64 on both channels

I hope you mean C68 & C84

Sorry, typo, yes C68 and C84

DC conditions tell us if a stage is working properly.  U32b is a servo that's supposed to keep the outputs of IC30 & IC23 the same regardless of GAIN setting.  I'm still trying to figure out why they are different.

Thanks! Cool, didn't know about the servo-design. It makes sense.

 

[G-Sun]

Can you connect the +ve inputs (p3) of IC23 & 30 together?  This disables the earlier stages.  If the noise goes away whatever the setting of the GAIN, it means problem is in the earlier stages.

I can now turn the gain up 3/4 (3 o'clock) without noise (the vlz mixer being the noise-floor of -85db).
Then up to max gain, the noise peaks at -35db

Ch2: approx the same. Max gain, noise peak at -44db (reseted meters)
(Disclaimer: When checking max gain noise on ch1, I might had get a different reading if I had reset my meters after turning the gain up. There's some crackling in turning the pots.)
So, my conclusion is: No big difference.

 

[G-Sun]

Could a bad cap cause the ch1 noise? In the IC 23 area?
And could an exposure to frost be the cause?

 

[ricardo]

Can you connect the +ve inputs (p3) of IC23 & 30 together?  This disables the earlier stages.  If the noise goes away whatever the setting of the GAIN, it means problem is in the earlier stages.

Ch2: approx the same. Max gain, noise peak at -44db (reseted meters)

If the noise is the same on both channels on this test, the fault is at an earlier point.

Do you have P48V phantom power?

 

[G-Sun]

If the noise is the same on both channels on this test, the fault is at an earlier point.

Do you have P48V phantom power?

Ok,
yes I have +48 on the GoBetween

 

[G-Sun]

What parts makes the feedback-curcuit in the scemo?

 

[G-Sun]

Bridged ch 1 in with ch 2
Removed c1 c68 an c64.
Connected ch2 c68 out with ch1 c68 out.
Same for C84.

Listened to ch1 out. Good, no noise.

So, the problem is before the coupling caps.
I'll check lo-hi-path, independently.

 

[G-Sun]

Input hi ch1 was good.

 

[G-Sun]

And ch1 lo input path was sounding good
??

 

[G-Sun]

Both channels are now working fine. Must have been something about the soldering around c68/c84.

Thanks Ricardo for all your excellent help!

 

[chefducuisine]

Glad you sorted it out with Ricardo's help.
Enjoy the pre... it is really usefull!!!

Mine was used 2 weeks ago for drum recordings - came out excellent and easy to mix.

 

[EmptyMusicBox1]

Hi everyone !

i have just finish my 9K SSl preamp and i have a problem ...

The preamp Working good with a LINE source and a Static MIC

But not working with a SM57 ....

i have a Go betwin interface how do you have Wire ?

thanks

 

[G-Sun]

Hi everyone !

i have just finish my 9K SSl preamp and i have a problem ...

The preamp Working good with a LINE source and a Static MIC

But not working with a SM57 ....

i have a Go betwin interface how do you have Wire ?

thanks

Works with a condenser? and +48V?
And not a dynamic?

The wireing is shown here:
http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=8

 

[ricardo]

Both channels are now working fine. Must have been something about the soldering around c68/c84.

Thanks Ricardo for all your excellent help!

I'm not sure I contributed anything except perhaps some idea of how to break the circuit into parts to check each one in turn.  This indeed sounds like soldering.

Another possibility is the 2 pots. .. both on the input stage and also on the 2nd stage.  Something to bear in mind in future.

On your next project, once its working, measure voltages at important points (eg outputs of all OPAs) and note them on your schematic for reference.
____________

I have to say, this close look at SSL9k doesn't inspire confidence.  It is MUCH more complex than it needs to be .. hence difficult to troubleshoot.

SSLtech & Rochey have a far better and simpler product in their new Eden boards based on TI INA163

 

[s2udio]

I have to say, this close look at SSL9k doesn't inspire confidence.  It is MUCH more complex than it needs to be .. hence difficult to troubleshoot.

Sorry to disagree here ,but......In it's defence
The 9k is a very good pre...is quite simple and is not difficult to fault find,
I have 2 x 4 channel units in almost daily use for the last 4 yrs......
The confidence is in the constructors ability to understand the circuit.....and not to blame a very good stable circuit design
For his poor construction and fault finding blunders !

 

[G-Sun]

I'm not sure I contributed anything except perhaps some idea of how to break the circuit into parts to check each one in turn.  This indeed sounds like soldering.

Another possibility is the 2 pots. .. both on the input stage and also on the 2nd stage.  Something to bear in mind in future.

On your next project, once its working, measure voltages at important points (eg outputs of all OPAs) and note them on your schematic for reference.
____________

I have to say, this close look at SSL9k doesn't inspire confidence.  It is MUCH more complex than it needs to be .. hence difficult to troubleshoot.

SSLtech & Rochey have a far better and simpler product in their new Eden boards based on TI INA163

Well, I don't think I would have proceeded with any trouble-shooting if it wasn't for your help.
And yes, you put me on a good path with you suggestions. So, many thanks!

Not knowing what caused the error is a little unsettling though.
I'll take your word for it regarding the complexity of the ssl9k. I'm surly not understanding the schemo, but that's not telling so much of the ssl9k