Acoustic Image Clarus fault finding

[Bilbo]

Can anyone explain this? The amp has developed a fault that two people have been unable to identify. The amp has developed a n intermittent fault where it 'howls' for a few seconds at a time. When it is howling, there is no instrument signal getting through. When it is not howling, it sounds perfect, not the slightest hum. Here is a video of the howl. It happens on both channels with an instrument plugged in or not. It's not the instrument, the leads or the speaker. The fault is definitely in the amp.

 

Acoustic Image are no longer operating so I can't go back to the source although there is an email address on the website I have contacted and am waiting for a response.

 

Any ideas?

[Chienmortbb]

A question, why are all the EQ knobs a fully anticlockwise?

[Bilbo]

That's just how the repair bloke left them. Ironically, even with the EQ set like that, it still sounds brilliant with my brother's Ibanez SDGR bass plugged in. Until the howl kicks in. Another thing is that the howl volume is not louder or quieter depending on where the volume is on the amp.

[chyc]

I cannot offer anything concrete, but I noticed that on TalkBass the estate of Rick Jones does seem to be giving out schematics of the AI heads to repair companies. I don't know under what circumstances they do this. Also in the same thread there's someone who replaced the Ice Power module of a Clarus head.

 

Good luck with it all. I love AI stuff

 

URL: https://www.talkbass.com/threads/acoustic-image-amp-repair.1612863/

[Pea Turgh]

Sounds like the sample from Cypress Hill “Insane in the membrane”.

[Chienmortbb]

Does the noise happen with mute engaged on both channels?

[Bilbo]

I will check and let you know. I am watching Asia as we speak!

[Bilbo]

I got a reply from the son of the manufacturer with some snagging documents I have shared with my repair bloke. I will let you know if we get an outcome.

[Chienmortbb]

Thanks. Looking at the block diagram, it appears that the Mute is achieved in the preamp, that means that the power amp is always operational. Most manufacturers use the internal mute function in the power module.