trinityamps.com

Hi,

I just completed 2 sIII TMB Amps, which both present the same problem.
When i push the gain/master volume controls I get a "glassy" squeal which
rides on top of the notes and quite frankly ruins the whole amp.
I already built this circuit 3 times in Hammond Chassis which are bigger
than the Smallbox chassis that I used for these builds, so I'm pretty sure
it's got something to do with wire routing.

So far I have tested reducing the gain on the TMB channel, snubber cap
over the PI plates, more shielded cable runs, moving around wires,
changing tubes and even reversed the OT primary leads and connected
the output jacks to ground even if it hasen't got a negative feedback, all to no avail ...

As of now, I'm all out of ideas, maybe someone with a little more experience
with this circuit might chime in and point me to other things I should look after.

Edit: Putting the primary and secondary leads of the Ot closer together did the trick,
the amp ist still a little on the rough side, but I guess that's normal with this kind of
gain.

cheers,
Patrick

Twist the OT primary wires together. Then twist the secondary wires together. Even without NFB the secondary has to be grounded on one side. What OT are you using BTW?

There's no real reason the amp should be rough, unless you mean it has the typical Marshall grind. The sIII has pretty low gain for a Marshall in any case.

_________________
Great tones come in small glass jars!

First off by rough I actually meant the typical Marshall Grind.
I might be a bit old school on this but I find the sIII to have plenty gain
on the TMB side
As for the grounding of the Ot secondary, I never did this before
and never had any problems so far. I'll just include it in future
builds just to make sure.

Edit: OT ist a Radiospares clone from Shinrock.

Sometimes you can get away with not grounding the secondary, but other times you can't. An amp is more likely to suffer oscillation problems if you don't ground.


Nice! I've got one of those too, in one of my amps.

_________________
Great tones come in small glass jars!