To get a solid central image on my system, the M7 balance control has to be set way off centre (see pic)
I had just assumed this was because of either my hearing, the room or the xovers. However, when I took the M7 to Lopwell, it was set up by others and the balance knob ended up set even further round.
Is this likely to be some sort of component deterioration/failure in the M7, or other reasons?
TIA for any advice/suggestions. 
I had a similar situation and it turned out to be a valve in the power amp that was causing the imbalance and it was partly fixed by using the balance control on the M7 but the M7 was not the cause.
Set the balance control to neutral check which channel is down on volume then swap the inputs to the power amp and see if it stays the same or not.
This will at least tell you if it is the M7 or not.
If it is the M7 the first thing I would do is after powering down liberally spray some switch cleaner to the back of all the switches. This solved a similar problem I had.
If that doesnāt cure it then I would start looking at the valves (ignore the valves in the phono section if the issue applies to all inputs)
Thanks Kev, Iāve tried the swap over to eliminate the power amp. Also it was a completely different power amp (indeed, entire system) at Lopwell, but as mentioned in my op, the issue was evident there as well.
When you say āall the switchesā do you mean all of the knobs, or just the switches, ie the input selector and on/off?
While I had the top off I did them all as some were a bit stiff
Also play music recorded in mono so you know both channels should be the same.
There are two 6072A in the line stage, swap them over if no result from previous post
As much as it is anathema to the Kondo massive, I think you need to get someone to squirt some test signals in and measure signals through with an oscilloscope.
Or just try the obvious first
I was convinced my hearing was fucked in my left ear, not least because it is - a bit - as the Audiovalve needs a handful of opposite-lock to balance the channels. I faffed-about with speaker position (the room is asymmetric), valves, then (unrelated) rebuilt the thing with new matched components throughout any part of the circut that could reasonably be inferred to contribute to the signal path: ALL of it made no difference, so I became 100% convinced it was my hearing.
Then one day I was fannying-about using a passive pre as part of a test rig and realised that channel balance was perfectā¦ Belatedly I checked the Alps Blue potentiometer in the AudioValve - yep different R on the L channelā¦ 
Havenāt been arsed to change it out yet, but might take it as an upgrade opportunity when I do, although that means losing remote volume controlā¦
Yeah, itās a nice kit, but would need mounting outside the pre as itās so ridiculously long when assembled. That, or bodged with a 1:1 pulley or gear system.
Can you not still buy the motorised Alps Blues (yes, I know, I could check if only I had the internet 
) ?
You could last time I looked, but received wisdom is that sample variability is pretty high with Alps stuff nowadays, so I could just end-up with another channel-imbalance issueā¦
This then.
Apologies for the diversion @jim, but the opportunity to spend money that @Mrs_Maureen_OPinion doesnāt have is too tempting.
Now those look nice 
Could well be. āLogarithmicā (generally 2-section linear, in practice) carbon track pots were always a bit iffy and, as with everything, low-volume manufacturers canāt afford large quality control depts.
The modern āquasi-analogā solution seems to be a resistive ladder chip. OK, you have to accept a FET or two in the signal path and you need to sort out a digital controller for it. And if youāre really fastidious youāll buy a bag full of them, measure each one and match them in pairs for L and R (Audio Research did this for the ātubeā preamp of theirs that I worked on once - it was a bit of a bugger finding a matcher to replace the blown one given that their particular chip was by then obsolete). It did give really close channel matching in the end though.
Think Iāve got one of those somewhere if you want to try it.
Thanks Dave, but being the genius I am, I didnāt make a note of the type and value of pot fitted, so will need to pull the pre to bits at some point. Difficult at the mo as my listening room is pulled to bits waiting for the damned builder to finish the work he started nearly a fortnight agoā¦ 
Thereās 5x in the phono version @Jim the line stage valves will be the two Raytheon yellow writing ones.
I hope one hasnāt gone as they are the mutts nuts.
Yes, three in the phono stage and two in the line stage
