Weird THD+N in GSSL clone ? edit: not anymore

While waiting for cases to rack them I?m measuring my GSSL clones. Everything looks good for just having populated PCBs on the bench, only with THD+N there is something going on I don?t understand. Bypassed everything is fine, switched in ? but without compression (max. Threshold, 1:10 Ratio, no MakeUp) I measure:

3,1%:evil: @ 40 Hz (bypassed = 0,05%:grin: )
4,1%:evil: @ 100 Hz (bypassed = 0,07%:grin: )
0,8%:evil: @ 997 Hz (bypassed = 0,018%:grin: )
0,1% @ 20 kHz (bypassed = 0,025%)

Removing the sidechain VCA (for no measuring signal in sidechain) changes nothing. :?:

Measuring was done with Neutrik A2, R out <15?, R in = 600?, Level = 14 dBu.

Any idears what?s going on in there ?

Try Rin = 100kΩ... 600 ohms is a lot to draw from the output drivers...

Keith

[quote author="SSLtech"]Try Rin = 100k?... 600 ohms is a lot to draw from the output drivers...
Keith[/quote]
Changes nothing ...

yeah, they would only struggle at higher levels...

Okay, in THD+N, what's the residual look like in "scope" mode... any multiples of the fundamental? -Also, what's the residual "sound" like on the speaker? -Related harsh buzz, or uncorrelated noise?

Keith

hi Keith,

I'm at home now and all the stuff is at work, will tell you tomorrow.

volker

Have you tweeked the distortion pots?

Are you sure there is no G/R voltage hitting the VCA (don't rely on the meter, measure it)

Measure to see if there is any ac feedthrough hitting the control ports of the VCA.

Any DC creeping into the VCA input?

Is the power supply ripple-free? Any hum from the unit?

Good luck!

thank you everyone, problem found: stupid me have forgotten to solder the little bridge next to the meter connector. because of this the release circuit wasn't in, and the tantalum caps seem to smooth the cv.

one good thing: now I understand the whole circuit and know all measurings / scope pictures from this beasts. :green:

when they are racked up I will do further measurings with an Audio Precision and post the results if anybody is interested.

:thumb: