Noise! Quieted!

[Ivan303]

Three kinds.  Got the Hummmmm pot down to about 1-3 mV and jumping.  Hardly audible with head in the 106dB  mid-bass horns.

But, for some reason also having ground loop problems that were not audible running two of the S.E.X. amps in bi-amp mode.

Did have a problem before with my 300B monoblocks that required cutting the earth ground on each monoblock.

So... 

Decided NOT to do that with the MonAmours and instead I am using an un-grounded power cord on the tube pre-am and...

No more ground loop.  Pre-amp is now grounded through the two MonAmours and the DAC via the RCA cables.

More noise.  The MonAmours have more gain than the 300B monoblocks they replaced and as a result I was getting a fair amount of tube noise from the 6SN7's in the Preamp when running the MonAmours.

This was not a problem with the S.E.X amps as they have a 'gain' control which I normally set at about 2/3 of the way to max.  When the S.E.X amps are full tilt the tube noise in the pre-amp is quit audible.  Turning down the two S.E.X. amps solves it.

So...

Voided the warranty on the MonAmours with a series Audio Note Tantalum resistor of about 47K in series with the input and before the 100K grid to ground resistor.  Cuts the overall gain down a bit and just need to crank the pre-amp a bit to compensate but no tube noise now from the 6SN7s.

All quiet now, except for the annoying mini-fridge in the corner of the Casita/listening room.     

[Paul Birkeland]

Voided the warranty on the MonAmours with a series Audio Note Tantalum resistor of about 47K in series with the input and before the 100K grid to ground resistor.  Cuts the overall gain down a bit and just need to crank the pre-amp a bit to compensate but no tube noise now from the 6SN7s.

Is the 6SN7 noise tube rush, hum, or buzz?

I would be amazed that there is a 300B amp with less gain than the MonAmours! 

[Ivan303]

Sounds like tube rush to me (coming out of the JBL 2441 w/ Edgar Salad Bowl which is x-ed above 500 Hz).

300B amps have about the same gain as the S.E.X. amps (one per side bi-amping the horns) cranked up only about 2/3 of max.

That's the level I've been running the S.E.X. amps in order to cut down the noise floor from the pre-amp.  Plus, ain't gonna throw out those Tung Sol black glass round plats 6SN7's (other NOS 6SN7's produce the same noise).   

Easy fix as the horns are 106dB so it doesn't take much cranking on the tubed pre to make up for the padding of the MonAmours.