ashdown bass combo 180 watt electric blue

[gadji]

hello ,can anyone offer any help with regard to my amp going distorted after about two mins playing .Switch off for few seconds then ok for short while ! my thoughts shows all signs of a dry joint ,however checked but non found tapping , pressure . no change . anyone know of any stock faults? thanks for your time.

[soundguruman]

First, check the guitar.
Does the guitar have a battery in it?
A weak battery in a guitar causes major distortion.

Second, hook the amp to a different speaker. Does the distortion still happen?

[gadji]

ashdown bass amp

thank you soundguruman will try ! post result

[Mick Bailey]

Just check the send/return loop, too. Patch between the two to make sure it's not something as simple as a contact playing up.

If you still get distortion through another speaker, you need to isolate where the problem lies with the amp itself. It could be a thermal fault; a component warms up and either shorts or goes open, or it could be a mechanical failure that's affected by heat. Not all cracked solder joints play up with movement, sometimes they need heat, too. The most likely components to suffer thermal stress are ones that get hot under normal operating conditions (or components nearby) e.g., larger resistors, power transistors, tubes.

The other reason for a component getting hot is if it's faulty. You could have a bad op-amp pulling the supply rails down, a resistor opening or some other problem. You need to isolate which section of the amp is giving the trouble. The easiest way is to connect the 'send' signal to another amp. If the fault still occurs, then you're looking at something affecting the preamp.

If it is the preamp, you'd need to check the +/- 15v supplies. If they are dropping I'd check the op-amps first. A can of freeze spray is very useful in locating thermal faults (if that's what it is). The question is, if you locate the fault, are you skilled and equipped to take off a component without damaging the board? The tracks are easily damaged.

Just a note; many Ashdown amps (if not all) do not ground the heatsinks, so there's a pretty high voltage between them.