Any amp guru wanna check my Trace schematic for likely trouble spot?

Downunderwonder · #1 05-14-2011, 12:06 PM

Attached pdf of schematic for Trace Elliot AH250 SMX GP12. I plugged a 1/4" lead into the footswitch and have blown the preamp.

It seems there is no power to the preamp side of things. When powering up the amp there is the usual thump and hum hiss from the speaker if plugged in, so guessing the power stage is all there.

No lights on the front panel, no juice to the valve, the power amp on switch does nada, none of the switches for preamp do anything as far as lighting up LEDs.

No burnt components as far as I can see or smell. It didn't make any nasty noises when I did the deed, just noticed all the lights were off when I returned to the front after plugging in the lead.

BassmanPaul · #2 05-14-2011, 12:45 PM

What was the other end of the signal cable connected to??

BassmanPaul · #3 05-14-2011, 01:00 PM

I'd start by checking the voltages coming from the power supply. Is the tube heater lighting?

Tracebassplayer · #4 05-14-2011, 01:17 PM

"No juice to the valve"... for us Americans, that is "no power to the tube".

In North America we say "tube", everyone else says "valve". I learned the hard way, too.!

Tracebassplayer · #5 05-14-2011, 01:19 PM

Is there a "protection diode" inline with the in foot switch jack?

Tracebassplayer · #6 05-14-2011, 01:35 PM

You may have bent one of the connectors inside the jack and effectively turned it "off" or "mute".
Tell us exactly what you did, what happened (noise, smoke, smell, etc) at the time.

sconix · #7 05-14-2011, 01:58 PM

With the valve not lit, you've lost the +15 volt supply (the filaments are fed from +15V and dropped) Also the +15V feeds the footswitch and all the preamp which also has -15V. So you need to check bridge and connectors for the +/- 15 supply, which is not shown on the pdf schematic package, only the headers are shown. If you have the 15v on the supplys, it's likely a connector/header issue. Something could be shorting the +15 rail
but it's likely the supply as the plus rail has a much higher load on it than the minus side.

Downunderwonder · #8 05-15-2011, 12:35 AM

It was connected to a Presonous multi mic input computer recording sound device which usb'd into a Mac. It may have had 48V phantom power but I doubt it.

I'm not at all confident poking around with a multi meter. I know just enough to know I shouldn't or more than likely I would short something at 300V.

I can see a plastic "model office building" with two grey (gray) wires and an orange wire looks like it is "plugged" into the preamp board from the transformer. It's a really strange arrangement but one of the grey wire ends is different to the others. Looks soldered on whereas the others are just sitting there, very strangely sort of clipped in by itty bitty little metal teeth each side of the (stll insulated)wire. Damn not having a digital camera. They would be =15V , -15V and ground methinks. Might be a symptom.

BassmanPaul · #9 05-15-2011, 10:24 AM

The connector of which you speak has teeth that when the wire is pressed down cut through the insulation and contact the wire itself. I personally hate them. They are unreliable at best. I'm guessing that someone earlier has had a problem with the connector and thus the soldered joint.

If you do not know how to use a meter with confidence it's time for a tech visit.