SP-14 to Class D amplifier

I've had this preamp connected to several solid state amplifiers since building it a few years ago, but this week I tried something new for me;

I hooked it to a balanced input only, class D amplifier. It was not happy! The speakers give out a fairly loud, high pitched squeal. I tried several wiring and grounding variations to no avail. OK. Next I tried placing a buffer that I made (Kuartlotron Buffer) between the preamp and the amp. This brought the squeal amplitude down quite a bit, but it's still there.

The music sounds marvelous, despite the squeal, so I would like to resolve the issue.

I've searched for appropriate buffers, but I don't know enough to pick the right one. I'd be grateful for any suggestions.

Thank you.

I had  a similar experiance . When I built my SP14  I tried using it with  my Krell  FPB
(Class A) through the balanced  inputs , nightmare !  I tried  different cables  then
RCA to XLR jumper adapters . Both resulted in only obnoxious very loud
noises , buzzing and screeching , from the speakers for a few seconds and then the amp
shutting down and going into protection mode !
      I then tried a generic electronic balanced to unbalanced device  that was a only little
better , at least I could hear music through  one speaker now then the other , one at a time
and “less” hum and screeching  .  I think they all were creating a very bad ground loop
resulting in the noise ?
     I finally had Roy build me a balanced to unbalanced adapter box that uses lundahl
LL1527 ?  transformers in it .   Finally it works right , and sounds incredible , perfectly
quiet . I couldn’t be happier . It sounds so much better than with my old solid state Preamp  .
     I don’t know  if this would work with a class D amp for you or not ?  Give Roy a
shout  and ask him .

Thank you for the suggestion PF!!

That rings true, as I've seen a similar scenario in a couple of Don Sachs' versions when he has used XLR inputs.

I'll bug Roy now.

Fitero wrote:Thank you for the suggestion PF!!

That rings true, as I've seen a similar scenario in a couple of Don Sachs' versions when he has used XLR inputs.  

I'll bug Roy now.

Back in the day, when solid-state was 'new' a number of amplifier manufacturers used interstage transformers to prevent just what you are describing. So, the suggestion is both apt and effective.

Could it be your Dynaco pre amp is oscillating? Or perhaps that Class D power stage..

Interesting. There are cheap solutions available at the local Guitar Centers apparently, but I hate to waste money. A pair of good isolation transformers isn't to expensive if it takes away the noise.

It's a VTA SP-14 preamp. The JBL/Crown amp has no trouble connected directly via XLR cable to my Logitech Transporter. I'll know soon enough!