Okay, slightly strange one. I have an old Tag Mclaren amp that sometimes chooses to play in mono as opposed to stereo. If i turn the volume up, the flaky channel comes back to life and will work at any volume but unless I whack the volume up, I am resigned to owning a one Channel amp.

There are no scratchy noises coming from the volume pot, and the problem is the same no matter which input I am using.

I’m thinking on taking the volume pot apart, maybe just some dirt in there, but to be honest I am shooting in the dark.

Plan B, anywhere near Glasgow that can do affordable repairs?

I’d imagine it would be more like a poor solder joint somewhere.

Turn it up to full, the board then heats up and makes the connection.

Have a look for dry joints and you may be able to fix it yourself – I woudn’t take apart the pot as I doubt it would go back together

start with some contact cleaner. Open her up, and blast a load into every pot whilst twiddling them (might as well do the lot!). Give it a visual inspection and see if any obvious cracked/broken solder/wires etc. Give this a try. If that hasn’t fixed it then it is probably the wiper in the pot. They tend not to be user serviceable and are cheap to replace, so either learn to solder for the new year or take it to any electrical repair place.

given the volume changes the pot seems the most likely candidate, but stereo/mono issues can also relate to in/outputs. so worth giving them a good check over too.

Thnx for the advice. Many of the sites I have read, suggest contact cleaner is the last thing I want near the innards of the pots, instead (if possible) take apart, clean with an eraser and reassemble.

Not much heating up required, just turn the volume right up once and then all seems okay. I’ll try this with the amp off just in case this action is cleaning the contacts.

Will report back! Cheers again.

. I’ll try this with the amp off just in case this action is cleaning the contacts.

this is a very good idea
It might be a dry joint on the pot itself. Turning it all the way up could be pushing it into the board a little. If you have a soldering iron you could just redo the joints anyway as that is easy.

For cleaning pots look at deoxit. Superb stuff and not just normal contact cleaner.

Hams around the world swear by it for cleaning all electrical contacts, pots, switches etc…

Does it start working instantly after you max the volume?
Have you tried wiggling the pot instead?
Do you know anyone who owns a soldering iron? Pot replacement will be very simple.

Im handy enough with a soldering iron, although normally soldiering wires together in wiring looms. I’ll have a practice on something I don’t care about trashing first……

Had something similar with a sony QS AVR. First problem was definitely a worn out pot as it was triggered by messing with the knob, managed to get a similar motorised ALPs pot (£10 vs £100+ for the genuine volume board) but had to take it apart and aswap in the led and hollow shaft to let the volume knob indicator light up.

Didn’t fix the problem completely and it would occasionally shut off one of the front channels after a while, presumably as it warmed up. Ended up stripping the whole amp down and resoldering all of the FETs and relays, some of which definitely looked dry, and seems okay now. It’s a bit old and tired anyway though and no HDMI so I didn’t mind if I completely trashed it.

Okay, took it to bits, couldn’t see any dry joints.

If I plug the amp into my sonos connect, I get just one channel working as explained earlier, however if I increase the volume on the sonos app, and don’t touch the volume pot on the amp, the second channel jumps back into life when we reach a decent volume and not before. Anything else worth checking?

Does the fault happen regardless of which input you plug the Sonos Connect into? Or just on one particular input?

*** Edit :

If I plug the amp into my sonos connect

I thought Sonos Connect was a source device ie provides the input but your comment suggests the opposite. The amp is providing the Sonos with the signal.

If this is correct, I’m guessing you are using a line level out from the amp? So might suggest a problem with the preamp stage.

I’m probably talking out of my ass as usual, but could it be an issue with one of the power transistors? A fault that causes it to produce power at a slower/lower rate than the other?
I’m probably not being clear enough, I know what I mean, just can’t put it down clearly.
Or maybe a power transformer? Some amps have two, could one of those be supplying a lower voltage?
Just clutching at straws, really.

How old is it? Capacitor plague?

Phil here, electronic engineer + hi if enthusiast. Also owner of a tag mclaren dac. They made these through the 90s and early noughties I think, so your amp is not that old and (was) very nice.
Hmm interesting. From your first post I was thinking totally knackered pot (track broken right at the start of the wipe). From your second post it’s far more interesting (aka harder to diagnose). I’ve read it differently than jairaj; the Sonos is your source and you’re saying if you turn that source up enough, it starts working, even if the volume pot is not at max. Is that interpreted right?
If so, it means that the channel is only switching on once the input signal is over a certain threshold. My suspicion would be it is a misbehaviour (failure) of some control or protection circuitry. We can more or less rule out both ‘capacitor plague’ (ie dried out electrolytics) and output transistor failure, because these wouldn’t give an output that either works or doesn’t, rather they’d give either no output or very distorted output.

Bottom line is, this sadly seems to me it ain’t gonna be an easy one to fix. Whoever you take it too might get lucky, but they’ll struggle without a schematic for these complex (but excellent) amps from a now defunct brand…

Ps, don’t you dare put it in the bin. If you run out of options you can send it to me and I’ll have a go 🙂

The good news is that you have one working channel to use as a reference!

So, connect both inputs (L&R) to a suitable source (i’d suggest downloading a free pc “synth” app ( or use an online one) to generate a nice fixed tone (say 1khz) then measure the voltages as you work along from the input jacks. Ideally you’d use an oscilloscope, but a simple voltmeter in “AC” mode might be enough to show the issue.

One word of warning, the amps DC power rails will be at something like 100volts, so be a bit careful where you stick your fingers / probe!!

I’d look to replace the output protective relays (if present) in case it is a switching problem. This has solved similar symptoms for me on old amps before.

Thanks all. to answer the questions, Phil, you’re bang on the money, the sonos is the source device. Once the channel comes to life, there is no distortion, crackling etc and it will work fine at any volume until the amp is switched off. I need to try leaving the amp on and see if the channel goes back to sleep. I have no plans on binning the amp, don’t worry, it have a lovely well paced sound (I primarily listen to electronic music).

I’ll see if I can run some further diagnostics, alternatively I may give the guys at Loud and Clear a buzz as they may be able to point me towards somebody willing to have a go repairing it.

There’s a specialist Audiolab “fixer” in Banbury I recall. Might be worth giving him a shout

If he’s too faraway, I’d be hunting out for local specialists, not some chain as they’ll just want you to chuck it out.

What ever you do don’t send it to these guys: http://www.mwes.co.uk/

They did a very poor job fixing my Creek amplifier and their customer service is terrible.

I’ve gone through 3 amps all failing in the same way – centre channel cutting out. Not posh stuff, just regular AV amps inc Sony and Yamaha. Reading around these are common issues and usually there is talk of dry joints. Not really electronically minded so ended up binning them (think the Yamaha is still in the loft though) as value is very low after a few years use. Now on my 4th.

My parents have a mini system that’s doing something similar also, though cuts out all channels randomly and seems to occur at a certain temperature.

Out of interest, can you hear a click when it cuts out? In every case in my experience I hear a click as some relay or something switches. Sometimes goes into rapid clicking on and off.

Rubadub, and Glasgow Sound Centre can do audio repairs. There are also some freelancers but I dont any personally. But they could be found. 🙂