Bass leaves after amp warms up?

Have you tried different speakers, as Kijanki thought you might have? And if so, did the same phenomenon occur with them?

I'm still suspicious of the possibility that the performance of your speakers is changing after they have been playing music for the hour.

Regards,
-- Al

I have seen cases where old switches in pre-amps or other gear cause a very significant loss of power over time as they oxidize, etc., and good contacts are lost. Same true with volume controls, balance controls, etc.

If there are any manual switches in play with your gear, next time you hear it, try twidling with controls and switches and listen for any differences. THe twidlling alone might help but if so a good cleaning is probably in order.

This happens with my old NAD 7020 receiver from 30 years ago that I still use. A few twiddles with the input switch on occasion when I notice things have faded out sets things right again until thenext cleaning of switches and controls. Not an uncommon thing...

I had PSB Synchrony twos now I have PSB Synchrony ones which are all around better when everything works.
Auditioned Thiel speakers for about a week but results were inconclusive

Could PSB being 4ohm possibly be the reason?
No one else has these symptoms & my dealer disputes this.
Ironically I keep buying PSB anyway..

I have Kimber PK 10 powerkord for the amp & Audioprism foundation II power conditioner.
I've also went direct into the wall.
None has proved to be the issue

Did the Synchrony Twos exhibit the same symptoms as the Ones?

Could PSB being 4ohm possibly be the reason?

As Mapman asked earlier, what models were the Bryston amps?

Regards,
-- Al