A buzz in both channels

[Skipperrik]

Yes, I measured it before inserting it (2.48KΩ) and in place (7.5KΩ). The one I pulled out measures 2.4KΩ.

The resistor on the B side measures 2.44KΩ in place. Something is different on the A side.

 

[Paul Birkeland]

Pull the 431 regulator on that side and measure again.

 

[Skipperrik]

It's still 7.5KΩ.

 

[Paul Birkeland]

I'd post some pictures of your board, something is definitely not right...

 

[Skipperrik]

The regulator is still out. I may have to replace it. On the underside, the red wire on the left broke while removing it so it will have to be replaced.

 

[Skipperrik]

Just to clarify something, in the photo of the underside of the board the black wire appears to be connected to the Kreg terminal. I had to disconnect it from the -reg terminal to remove the capacitor and it only appears to be connected at Kreg. It was connected correctly before I removed the capacitor.

Just for the heck of it I measured the resistance across the capacitors. I don’t know if this helps but here are the values:

A side (the problem side)
0.1uf 400V = 146
2.2uf 250V = 145.8

B side
0.1uf 400V = 34.2
2.2uf 250V = 35.4

That’s a pretty big difference so it should be an indication of something.

 

[Paul Birkeland]

I have no idea how the measurement of the 2.49K resistor is increased by installing it in the circuit.  Something is definitely amiss, but I have no idea what that is.  Did you end up replacing the 431 regulators? 

 

[Skipperrik]

I don’t have a replacement but the value is the same whether it’s in the circuit or out. I could swap the one from the good side if you think it would help but that’s a lot of trouble.

 

[Skipperrik]

I have a very embarrassed look on my face. I pulled the transistor out previously, not the regulator. I just pulled the regulator out and the wayward resistor now reads 2.48K ohms. I guess the regulator was allowing current to be sucked out of the leads of my ohm meter.

 

[Skipperrik]

I need to replace the transistor. Mouser has two, an MJE350 and an MJE350G. The G looks like the one that is used but I want to make sure it's the correct one since the specs differ. Should I order the 350 or the 350G?
https://www.mouser.com/c/?q=MJE350

Is this the correct regulator?
https://www.mouser.com/ProductDetail/926-LM431ACZ-LFT3

 

[Paul Birkeland]

I don't immediately see the difference between the G and the non-G, so I wouldn't sweat that.  Yes, that is an appropriate replacement for the regulator.

 

[Skipperrik]

Okay.

I just wanted to say again that I appreciate your help and your patience. I'm sure it can be frustrating to deal with newbies and I'm a great example of that. Thanks!

 

[Skipperrik]

I'm happy to report that the new parts are installed and the voltages are all within spec. The hum is still present however. I noticed that it isn't present when I turn the amp on, only after the circuits kick in. Also, immediately after switching it off the sound gets significantly louder until it fades away. Could this help in locating the cause?

 

[Paul Birkeland]

I'd be poking around with a wooden chopstick to see if you can disturb whatever connection is causing the problem, then you'll know where to focus your resoldering efforts.  A cheap-o pair of headphones plugged into the amp is a good idea for this kind of testing, as it can produce loud noises if the poked joint is particularly loose.

 

[atul.mehta6]

The hum is still present however. I noticed that it isn't present when I turn the amp on, only after the circuits kick in.

I had a similar problem in C2A..in my case, there is a noticeable hum/distortion in both channels..  But turns out to be a problem with the selector switch in the C2A.. I need to push it hard to the current selection and then the static disappears.. I am suspecting a loose wire or a bad solder joint ...you *might* be having a similar issue perhaps. worth a shot..

 

[Skipperrik]

Thanks for offering the suggestion, Happy Ghost. I have a DAC that has a volume control and I only use one input so I bypassed the selector, balance and volume controls. So far, poking and proding hasn't helped to locate the problem. I"m still searching.

 

[Skipperrik]

Hi Paul. I believe I've narrowed the problem down to the headphone jack and would like to get a replacement.

Awhile back I sent an email to Bottlehead asking if longer lengths of your power cord could be ordered. I got no response. Last week I sent an email asking for someone to call me so I could order parts. I haven't gotten a response.

Do you guys sell parts other than what's listed on your parts page?

 

[Paul Birkeland]

A tree fell on Doc B's house and they have been a bit occupied at the moment but should be getting back to the office shortly.

 

[Skipperrik]

I’m sorry to hear that. I hope there wasn’t a lot of damage.

I ordered a new locking jack so hopefully that will solve the problem.

 

[Doc B]

Yes, we have had quite a ride the past few days getting power back to our house. After a couple of false starts it looks like we have it fixed just in time for tonight's snowfall. I am back at the office for a short time today to get through as much correspondence as I can.

I'm afraid we only offer the power cord in the 6 foot length. The gauge of the wire used puts some limitation on the current capacity and we feel that a longer run might possibly degrade the performance.

Re parts - we only sell replacement parts for our customers who may need them. If you have broken or lost a part we can help you out. Best way to handle this is an email to replacementparts@bottlehead.com