noise floor / grounding issues with stereo pultec / ssl

I have built a stereo gyraf pultec, I can get the noise floor,
to appear to be correct as long as I only ground one channel
at a time, but with both grounded, either to pin1 or to the
chassis at the same time, the noise floor is -70dbA or so.

but if I ground pin1 on the other channel.

and then together.

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Here's is my ssl, it seems noisy too, compared to my aphex 204 aural exciter. it's the white line..


So what is this power supply ripple or something?
I read through all the threads, tried as many of the grounding schemes several times as I could think off, including the "soft" ground with the 100r resistors, that seemed to change the response curve though, and the gain?
maybe I didn't do that right and I should re-test with rmaa.

The input is unbalacned, but not on the ssl, and I can get it to "work" one channel at a time so.
what in the beams am I doing wrong?

The noise, inbetween the two units too, the ssl and the pultec, look very very similar, I have comparted this with different da /ad combinations, does this mean that it is ground / power supply noise for sure?

> it is ground / power supply noise for sure?

Yes.

Grounding is critical and mistakes are not always obvious.