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Debugging NCC200s

M

mcai7et2

pfm Member
Hi all,

Les is away this week taking a well earned break, so I am going to post my query here to see if any of you audio genii can shed light on my problem.

I have wired up my NCC200 boards in my case (temporary until Les gets more stock, and then a short delay until I can face all that drilling and wiring again). The preamp supply works beautifully, gives a stable 24.2 volts out of the Din socket. The right channel has its bias set at 38.1V steady after 30 minutes of being powered on and all seems right with the world.

The left channel on the other hand has issues. The bias control does nothing to affect the quiescent current, which sticks around 24ma and trying it (carefully) with music through it produces a very distorted sound, it sounds like a very cheap portable radio turned up way too high. I am not sure why this should be, but I suspect a blown component somewhere on the board (these boards were run over voltage for several minutes recently due to me having the wrong transformer). Can anyone suggest where to look for this, or know in more detail what the problem could be.

The right channel of my setup sounds amazing, please help me get this in stereo :)

Cheers,

Ed
 
Measure the volts at all sorts of likely places and write them on the circuit diagram. This should make it clear where the current is or isn't flowing. You could post your results here perhaps. You also have an apparently working channel to compare to.

This is the type of situation where you really need an oscilloscope and signal generator. Nothing fancy required at all, just a basic 20 or 30MHz job. A PC will make a very acceptable signal generator, there must be a million simple free apps out there.

Paul
 
Thanks Les, I will bag and tag the bad channel and post it off tomorrow.

Even in mono, the amp sounds fantastic :) I cannot wait
 
Les, you're supposed to be on holiday (nag, nag).

Even in mono, the amp sounds fantastic
Click to expand...

I found a similar thing (though with both channels) - I tested mine with some £15 cruddy speakers, and a portable CD player feeding it. Sounded great!
 
Doh!

I found a dodgy connection on the 68K resistor next to the bias control on the board, so I will sort that tonight and check to see if that fixed the problem. Hopefully I will be making beautiful music very soon.

Les, I will email you if I still need your assistance.

Kind regards,

Edward
 
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