Very low output Ashdown Evo II 300 bass amplifier

[henter2017]

Hi Folks,

Im trying to find out whats going on with the ashdown in the title, it has a really low output volume and the Input Meter doesnt read anything when injecting a signal, or playing trough it.
I have checked so far the power transistors:

Tested TR21,TR19,TR13
TR7,TR6,TR4

TR22 AND TR1 are not in the board, I guess they are for the 500W version of it.
they tested fine.

I have also checked voltages of the preamp magnifier module.
+15/-15 voltages points in the schematic seems correct, also checked the voltages at the ecc83 valve, which are +360V.

I think the issue resides at the preamp but cant locate where.
I have plugged the amp and read the AC over the speaker output and the peak of it is about a volt when cranked on a 8Ohm load, which is really really low.
Any points for this one please?

Thanks a lot in advance!

Preamp schematic and power amp attached.ashdown evo300 preamp.pdfashdown evo300 preamp.pdf
ashdown evo300 power amp.pdf

[52 Bill]

Have you tested the loop jacks?

Divide and conquer, take the signal from the preamp output jack and feed it to another amp. Do you get a good signal there?

Inject a signal into the power amp in jack. Do you get a good signal from the speaker?

[Enzo]

If the INPUT meter doesn't move, that is a clue the INPUT area is the issue, not the power amp. SO look at the input stage and the first op amp or two.

[henter2017]

Thanks a lot! will try and report back!, Enzo thats what I tought, as the meter is not moving issue must be on that stage, but voltages look good in there.... will try pumping in and out of the effects loop!

[Enzo]

VOltages are only part of the story - just because the battery has a charge doesn't mean the car will start. A dead JFET or dead op amp will kill your signal, even if they have voltage.

Apply a signal to the input and trace it through the amp - where does it stop?

[olddawg]

First thing I would suspect is a PCB mounted input jack. Like Enzo says. Shove some signal into it and trace it.