Ashdown MAG300 EVO2 problem

[Enzo]

SHorting the input and getting no noise means everything after that input short is not making noise.

Does turning RV1 to zero also remove the hum?

[m1989jmp]

SHorting the input and getting no noise means everything after that input short is not making noise.

Does turning RV1 to zero also remove the hum?

Nope, all pots on zero and still hum present. I'll follow Juan's advice and also try to test that opamp between line out and power amp input.

[m1989jmp]

Also do a visual check for burnt or blown out traces (especially ground tracks).

Bingo!

I got derailed by my own false assumptions and didn't even bother to check preamp board for burned traces.

While following Juan's suggestions, I've spotted this trace going from R98 to PL3 ground.

Also, I've found some other repaired traces and a stout black wire connecting two ground points on the PCB's copper side.

[J M Fahey]

Itīs the "stupid" problems which bite you the hardest, because you donīt expect them at all.
Glad you found it

Post a full amp gut shot, to see how itīs laid out and a general idea of board to board, panel, transformer wiring.

I always see them, but from outside.

[Enzo]

I got derailed by my own false assumptions and didn't even bother to check preamp board for burned traces

Something I include in every training lecture:
"Never think up reasons not to check something."

[m1989jmp]

One more thing confuses me, though.

Voltage on TR10s C-E junction is 0V. Shouldn't it be more like 0.3V if it's in saturation or 0.7V?

[m1989jmp]

Itīs the "stupid" problems which bite you the hardest, because you donīt expect them at all.
Glad you found it

Post a full amp gut shot, to see how itīs laid out and a general idea of board to board, panel, transformer wiring.

I always see them, but from outside.

Here's the layout.

Keep in mind that the cables were neatly kept together with zip ties; I had to remove them to get the board out. Also, black/red cable was zip tied to the vent on the bottom.

Design is fine, the fan keeps heatsinks ice cold the whole time.

[J M Fahey]

Thanks, very useful.
Very clean and uncluttered insides.

[Jazz P Bass]

One more thing confuses me, though.

Voltage on TR10s C-E junction is 0V. Shouldn't it be more like 0.3V if it's in saturation or 0.7V?

Try measuring B to E.

[m1989jmp]

Try measuring B to E.

B to E is 0.8VDC

[J M Fahey]

Then itīs fully saturated and Vce can go very low.
If curent through it is minimal, you might very well have 0 volts.

But wasnīt the amp already repaired?
If so, leave as is and enjoy

[m1989jmp]

Then itīs fully saturated and Vce can go very low.
If curent through it is minimal, you might very well have 0 volts.

But wasnīt the amp already repaired?
If so, leave as is and enjoy

Yeah, I will

One more thing. If heatsink temperature reaches 120°C, relay shorts TR8's base to the ground?

Seems a bit odd, especially because there's thermal switch on only one heatsink.

Thanks again guys for every advice, I've learned a lot troubleshooting non-existent faults

[J M Fahey]

I have mixed feelings about Ashdown amps

Designer is British Genius Clive Buttons, already famous for his long association with top notch Trace Elliot amplifiers.
So much so, that:

All the products shown on this web site were 'Designed' by: Clive Button
By 'Designed' we mean the electronic design, the circuit board layouts, the front and rear panel artworks, metalwork drawings for any chassis involved, design and drawings for the wooden cabinet (in many cases) and any technical authoring that may be involved such as test procedures, service information and operating instructions.
My association with TRACE ELLIOT started late in 1985 when I was engaged on a consultancy basis by Fred Friedlein (the sole owner of the company) to design the MP11 MIDI Programmable Graphic preamplifier.
From that first meeting I was to become the sole designer of all TRACE ELLIOT products for the next 12 years. These include such well known products as:
Bass - Series 6 range, SMX range, SMC range, 7 Band range, 12 Band range, GP7 Pre-Amp, GP12 Pre-Amp, AH150, AH200, AH300, AH350, AH500, AH1000-12, Valve Series, VA350, VA400, VR400, Twin, Quatra, Hexa, Commando range, Boxer range, PPA power amplifiers, Powered Sub 15, Bass effects pedal range, MP11 etc
Acoustic - TA100R, TA50R, TA200R, TA Concert range, TA60, TA35, TA30, Acoustic Cube, TAB100 (Acoustic Bass), Acoustic PA 16 channel powered mixer system, Acoustic PA 12 channel powered mixer system, TAP1 acoustic pre-amp pedal, in fact everything that came out of Trace Elliot all the way through to 1997.
For the years 1988 to 1997 I designed exclusively for TRACE ELLIOT at their request.
From the top 25 best selling TRACE ELLIOT products of 1996, 5 were speaker cabinets, 1 was a foot switch (to go with top of the range Bass amplifiers I designed) and out of the remaining 19 products, 18 were designed by me.

BIG problem is that investors owning T.E. stock found they were not making as much money as they wanted , so decided to sell T.E. to a competitor (I think it was Fender) basically to sell remaining inventory, maybe build a few more with existing parts and dismantle it.

So former T.E. (British) owners created Ashdown , and kept him doing his thing, problem is his best ideas were sold in the package so he could not re use them (same problem Leo had when starting Music Man) so, in my personal view (and I may be very mistaken) , he had to use a few *weird* ideas.

When I see Ashdown schematics I alternatively switch between "hey!!! what a clever and excellent design" and "WTF???".

[Enzo]

Trace Elliot is a part of Peavey.

the thermal switch is ther to shunt signal off the output drive. If the amp is driven to the point of overheating, that cap siphons off the signal so it can;t be driven any more. Until it cools down. The transistor base is not shorted to ground, only the signal on the base.

[m1989jmp]

I came across this video showing the repair of the same fault.

After repair I played a guitar through it a bit and it seemed a bit quiet with both volumes on half, but the guy here plays it on same settings and it seems to be the same loudness. I guess I'm used to Marshall blasting my ears with master volume on 1

Is there anything that could cause the volume to to be low while at the same time the sound is generally good (undistorted)?

https://www.youtube.com/watch?v=fxtffi2s2TU