Faulty bottlehead amp

[ZaphodB]

Hello there BottleHead, via emails Jameson O’Guinn suggested I first start a thread off in these forums and Bottlehead's Tech would respond.

I have a faulty BottleHead amp in front of me (see pictures) - ( it's a clients of mine and he bought it second hand already faulty), audio is present but there's also an overwhelming noise (both channels)

I have made basic supply checks, I did find an amusing fault... a 220uF/250V cap (nearest the input sockets) had a detached +ve leg (actually about a mm into the cap !!!).
I initially found that by just checking values, if I pushed it to the left ever so slightly 220uF came up on my tester, when left its usual position no capacitance at all was measured.
As I unsoldered the negative leg from the tagstrip the +ve leg (yes, just the leg) stayed in place on the tag !

I replaced it with what I had lying around (namely a 180uF/400V) but the problem remains. You'll see my temporary 180uF cap in temporary position.

Jameson O’Guinn also suggested I could purchase the circuit/manual so I can troubleshoot further....


Thanks for any pointers , Mike

 

[Jameson]

That looks like a Smash preamplifier. Is the middle tube a 0D3 and the outer two 4P1Ls? I can send an invoice for a replacement manual and get you set up to start troubleshooting.

 

[Paul Birkeland]

The LEDs used in that preamp aren't what we supplied. The ones we supply are known for being quiet, the ones I see in there might not be.

The input wiring isn't the wire we provided, isn't properly wired to the selector switch, isn't shielded, and the input grounds aren't tied to the audio ground like they are supposed to be. This will make a ton of noise, as now all of the input signal current has to go through the power transformer cover, over to the safety ground bolt on the chassis, then through the chassis up to where the rest of the signal ground is.