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mr scratch 31st October 2011 02:48 PM

valve headphone pre-amp
Hi there, please can someone help.
I have been having a problem with a headphone pre-amp ready made kit that i have been playing around with.
From the beginning one of the capacitors on the right hand channel has been leaking and although it has been replaced and working for a time, when i gave it a re-hall the right hand channel now has no sound and since blown a cap in the same place as the leaking one, i am pretty sure the polarity and value is right as it is marked well on pcb but cant understand what the problem might be and how to trouble shoot, can anyone give me some insight as to what this problem may be and how to fix it.
Please consider my only experience with diy so far is building a gainclone so knowledge is very basic but i am keen to learn.
Any help would be much appreciated.

Regards, Lee

Rod Coleman 31st October 2011 05:47 PM

Lee, it's impossible to tell what's happening without some more info.

Really, we need a schematic. You might be able to look around on the web and find one.

A cap that leaks is likely to be:

- connected wrong way around;
- circuit is applying too high a voltage;
- circuit applying voltage in reverse, due to a fault.

If you can turn it on without explosions (disconnect the cap), measure the voltage across the cap. The + terminal must really be higher than the - terminal, or damage is certain.

mr scratch 31st October 2011 06:34 PM

valve headphone pre-amp
Thanks for reply rod, I dont think a schematic is possible I have tried :( not that I would know what i was looking.
Its a cheap Chinese amp off ebay with 6p1 and 6ak5 valves not that helps anyone lol.
Its a little frustrating that i have had it working and built a lovely case for it.
When i first got it the transformer said 110v on label when i need 240v but the seller assured me the label was not correct, would this have still worked on uk mains if it was indeed 110v as had it working for sometime apart from the cap problem.
Anyway will remove cap and measure when can, thanks again.



DF96 31st October 2011 07:42 PM


Originally Posted by mr scratch
can anyone give me some insight as to what this problem may be and how to fix it

Yes, find a circuit diagram. Failing that, draw the circuit yourself from the amp (i.e. reverse engineering). Failing that, at least tell us the make and model number. We are good, but even we can't diagnose an unknown fault in an unknown amp from a distance with no diagram and no measurements - we are not that good!

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