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.

 

[ZaphodB]

Just to follow up on this now completed repair.....

Once I scanned over the circuit I realised whoever had 'modified' the amp prior to me seeing it, hadn't understood the input circuitry at all !!

I've replaced the butchered 3position 4pole input select switch with a new Lorlin and reinstated all input and output wiring to original scheme , and the amp is 100% back to normal.
Lastly to say both outer valves are a bit microphonic is an understatement

 

[Jameson]

I had a Smash amp years and years ago prior to our family acquiring the company. I absolutely loved it but spent a good deal of time trying to solve the microphonics. I think I ended up on a thick rubber pad underneath with some Herbie's tube dampers on the 4P1Ls.

You can tell your client that the Moreplay and the BeePre2 don't have the microphonic issues and sound incredible

 

[Kris]

I had a Smash amp years and years ago...

Do you mean like... five years ago?

 

[Jameson]

Do you mean like... five years ago?

Six!