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Ashdown ctm15 loud hum, no signal


MoonBassAlpha
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3 hours ago, Reggaebass said:

It’s worth giving Dave Green a call at Ashdown, really helpful guy, I’ve met him many times and I’m sure he’ll tell you what it is 

+1 for. Dave Green. Pretty much the stock answer for Ashdown problems. Speak to Ashdown, best customer service going.

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I wonder if anyone on here has a circuit diagram for this  or the guitar version 'MoFo'? My Google fu isn't working on this one.

There's a short to ground on the preamp psu -5V, present with the tl071 and 072 op amps removed and with the -5V regulator leg lifted. -5V present on the leg,  so the regulator is OK.

I'm thinking one of the smoothing caps may have gone short,  not easy to remove. There's a couple of 2n7000 fets in there too, not sure what they do, phase splitter drivers? Clipping circuit?

 

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Update,  I  sent a request for schematics last Sunday,  got a reply Monday morning 9.45 from Dave Green enclosing schematics and layout,  and a few words more  or less confirming my diagnosis,  and advising on a preventative upgrade.

The  preamp has a split +/- 5V supply,  the negative was shorted to ground,  turns out to be the filter capacitor failed short. I  was advised to upgrade all the 1000ųF 16V caps on the preamp supplies to 25V as these had failed before "and not just on this product "

Duly bought and replaced (and the little regulators) and the amp is running perfectly again. The humming sound I'd always assumed was inherent in the design is also  massively reduced,  so I  think this cap was on the way out since I  acquired the amp (second hand).

Kudos again to the  Ashdown customer support,  they have been excellent,  as many others here have noted.

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