TSL Clean Channel Buzz

[PaoloJM]

I've TSL in that has annoying hiss (it's not 50 cycle but it's not really a buzz either) on the clean channel that does not appear on the overdrive or lead channels.
It is not affected by any front panel controls.
The amp had blown a few fuses, and fried a few power valves before coming in so I suspected the hiss was related bias imbalance as there was clearly a problem in the power section. Checked all the preamp valves in a known good amp and they tested fine.
As it's and issue 5 board from 2001 I've changed the grid stops to 5.6k and that has stabalised the bias, allowing me to accuratley bias an new set of EL34s. This appeared to also get rid of the hiss on the clean channel.
The customer tried it himself before taking it and he agreed that it was completely gone.
Problem is he rang today to say the buzz had reappeared and seemed to be solved by putting a patch cable in either FX Loop.
Did a search and couldn't find a similar problem.
I've pretty much ruled out dogy solder joints, or dirty jacks in the loop(s) as it doesn't affect the other channels.
Anyone got any ideas?
Rgds,
Paul.

[PaoloJM]

Bump, anyone hear of this?
Any ideas where I should be looking

[Mick Marshall]

Tsl clean channel buzz

Owner of the TSL here. Ok heres whats happening.I Plug my guitar into input, theres a very noticeable buzz/hum on the clean channel. Switch to crunch or lead channels, buzz is gone.
I've also plugged the guitar straight into the Effects Return of loop A (therefore bypassing all the preamp section and going straight to the Power Amp stage) and the buzz/hum is not present.
The buzz/hum is a bit similar sounding to that of a guitar jack not fully connected properly, although the guitar signal is fine on all 3 channels, its just on the clean the background buzz cant be ignored.
Another thing I've tried is putting the guitar jack only about half way into the amp input, so that its only semi engaged and the guitar signal is not reaching the amp input. Although the guitar signal is not reaching the input, the buzz starts on the clean channel, but is still not present on the crunch/lead channels.
Also, I found that when a cable is plugged into the Return of Effects loop A, or the Send of Effects loop B, the buzzing seemed to stop or at least get quieter.
Any ideas what it could be? Something not grounded or damaged in the Clean Channel?

[mac1amps]

'sounds to me like you may have a defective op-amp (I.C) in the preamp section of your clean channel.

[Mick Marshall]

'sounds to me like you may have a defective op-amp (I.C) in the preamp section of your clean channel.

If this is the problem, is it a easy enough repair? Is there many op-amp's in the preamp of the clean channel?

[Mick Marshall]

Also, the buzz/hum is present even with the clean channel volume at 0, and increases as the volume is turned up, and is quite loud with the volume at 4. Any help or ideas about what might be causing it would be much appreciated thanks!

[PaoloJM]

Guys,
Studying through the schematics the stuff assosiated with the clean that I suspect would be the opto isolators and FETs assosiated with the channel switching. They seem to me to be the potential noise makers assosiated with the clean channel in isolation. Have you seen these cause problems in the past?
The ICs in the amp are assosiated with the FX Loops and Reverb circuitry so I'd imagine the noise would be on all channels if there was a problem there.
The bit that's bugging me is that plugging in the loop seems to gets rid of the noise, how can this be when there is a global and overdrive loop? Surely noise from here would appear on all channels or am I missing something obvious?
Your help would be greatly appreciated as the amp does sound really good, and is in good nick apart from this annoying hiss.
Rgds,
Paul.

[sloppy95]

tsl 100 hum on clean channel only

I have the same issue with my tsl 100 it also has a horrible hum on the clean channel only not on the crunch or lead channels. I sent it in to my amp to my tech a month ago and today he just gave up he does not find the issue any help please????

[oc disorder]

Suggest changing the 4 x 3300uF 10v that smooth/filter the heater supply.
Use the best ones you can get hold of like Panasonic or similar.
I assume with cathode connections that the signal is 180deg out of phase in the other pre tubes switched for crunch
or lead thus the hum cancels. Thats the only reason I can figure out.
The hum has a "barp" sound kinda like a munted passenger cruise ship horn ,well with a little imagination !
Anyhow I had one and fitting new caps there quietened it down.
They are on the main board under the rear jack board near the bridge rectifier.
I remember this as I had a fastidious owner and had me beat for a while.

[sloppy95]

Its sounds more like touching the input cable to ground very loud.

[sloppy95]

Did not work! Changed all caps and still the same issue.

[oc disorder]

Well I'm stumped ..have you checked the crimped ground wires that run from the main board and the clean board ?
Maybe there is some oxidation or a faulty crimp connection.
I presume if you remove V1 (the first tube nearest the o/p transformer) it disappears ?

[sloppy95]

Hi, yes I connectected and checked the ground wire. The sound is definitely from the pet amp as I connected to the power amp in and did not have hum.

[sloppy95]

Removed V1 and the hum continues.