[WIJGALT]

Just connected my MAR updated Melos SHA Gold to a new Bryston 3B ST amp. The result is a good deal of audible hiss - not at all present when using phones.
The hiss is constant, does not fluctuate with volume manipulation & appears on all source inputs.
Wondering: would a change to "low noise" or better tubes help the situation...currently using a pair of new JJs.
Wondering: would using the balanced or passive outputs on the Melos help, currently using the conventional active RCA output.
Any suggestions would be greatly appreciated.
BTW, aside from the hiss problem the music this combo makes is magnificent.

 

[dngl]

I was going to ask if it was a power problem, but you have filtering... This may be weird, but it might be either a) rfi from your cables, or rfi getting in through unused rca jacks (but that's a little superstitious).

 

[Hirsch]

Do you have another set of tubes you could try? One possibility is a noisy tube, and a switch might clear the noise up. Another possibility is that one tube is making poor contact with the socket, and simply removing it and putting it back might help.

The noise may not be tube related at all, though. You might want to treat it as a ground loop, and see if it goes away (float the grounds as necessary). Beyond that, I'm out of ideas.

 

[WIJGALT]

"or rfi getting in through unused rca jacks (but that's a little superstitious)."

heh, heh, heh, Jon.
A little superstitious, you say. I've already covered - literally - that possibility with Cardas caps.

Hirsch, I have a couple of older Sovteks that I might try.

 

[Budgie]

The passive output might bypass the gain stage of the preamp, so it might be quiet-er.

 

[WIJGALT]

Tried the passive outputs & yes indeedee, the hiss was gone.
So was all the power....Where I getting serious response with the Melos' volume knob at 10 o'clock', I was barely getting satisfying levels at 3 o'clock.
So, the passive outputs are out.

 

[Budgie]

To bad- but at least you know were the problem lies! Time to start swapping tubes. Let us know how it goes, please.

 

[WIJGALT]

But the question is...if the tubes are at fault would the hissing manifest itself while listening to 'phones? 'cause there is absolutely no hiss when I have my HD600s clamped to my head.

 

[Hirsch]

When hearing hissing in a tube amp, I'd try new tubes first, then worry about something else. Some tubes go noisy, particularly in the first month of regular use. It's almost certainly a tube if it's localized to one channel. Noisy tubes are common enough that it's worth ruling them out before trying anything else. Have you talking to MAR about the problem? If you just got the unit back from them, their work should still be under warranty.

 

[Budgie]

Try the balanced output on the preamp, if the Bryston has balanced inputs. The other question would be does the system have any hiss if the power amp input is not plugged into anything? (you might hear to much hum to be certain, but it is worth a try.)

 

[WIJGALT]

The Bryston does have balanced inputs but I don't currently own XLR cables - I'm trying to get my hands on a pair.
Budgie, could you elaborate on what you mean by disconnecting the amp inputs? What components should be powered up? Thanks.