Tubemeister 18 30A channel buffer

I've never heard of this sort of problem before Ramiro.  All of the H&K amps I've ever come across just switch instantly no matter what channel they start from or which they are going to.  Can anyone else report they have heard this happen?

The TM18 uses the same basic configuration to switch Channels and to control the Boost as all of the other TM and GM amps do.  It should be virtually instantaneous.  This sounds like you have a problem in that control area of the circuit which needs to be looked at.  The amp's own switches are working in contact with the socket for the footswitch.  I would guess this happens only when you do not have a footswitch plugged into the amp?  Try the following test.  Insert a jumper cable into the footswitch socket.  It does not matter that it is only a TS (mono) lead as the channel switching is on the tip.  The Boost which is on the ring with a TRS (stereo) plug will engage permanently and that doesn't matter.  Short out the tip and sleeve of the cable plug.  The channel should switch.  Does this way of controlling the channel show the same delay as the amp's switches do?  I am hoping this will be fine.  If so you have dirty footswitch socket contacts, (the switching wafers on the rear of the socket not the contacts the plug makes when it is inserted).

Start with the contacts on the footswitch socket and clean them.  As I said, I mean the switch wafers which are opened when a plug is inserted, not the signal contacts with the plug.  If these are dirty they will act like a resistance in series with the switching circuitry and will alter some time delays.  I can suggest a few other ways this could happen but it gets complicated very quickly and there are so many it would be best to have someone check out the switching circuitry who understands diagnostic work.  That way they can start from the beginning and progress through the circuit logically until they spot the problem.  That is much quicker (and cheaper) than just prodding about hoping to come up with the right answer by guesswork.  You only have Clean and Lead so there is only a single relay being controlled, this circuitry is simplest in the TM18.

This is not an area which goes wrong at all often.  I can't even remember ever having any reports of there being a channel switching issue before.  That's why I think it most likely to be something very simple like this.  Make sure to give that socket a really good clean using contact cleaning spray and inserting a plug in and out a good few times as the solvent is working.  Get back to us once you have done that.

I have to say Ramiro that I'm sceptical about what you have found. There is absolutely no connection whatsoever between the Attenuator Power Soak setting and the channel switching in the circuitry. You use the phrase "energy was accumulated" but there is no accumulation of energy in any way concerned with the Power Soak.

I am glad you have discovered your workaround but I would strongly advise you to try to fix this in 5W mode too. I have a horrid feeling that it may get worse and affect your 18W setting too. You have not discovered a solution in going to the 18W mode, you only have an oddity which cannot be explained at the moment.

I really recommend you try the Footswitch socket clean and see if that really fixes the problem on 5W as well as 18W even though you feel you do not need 5W at the moment.

I still think you are making a mistake ignoring this now Ramiro but I do understand your situation and the choice is yours of course. The amp is now working and that is a good thing, you can use it. Go ahead and play through it now and enjoy yourself, you deserve that after worrying about this problem. But just bear in mind a couple of points for the future.

I think you misunderstand the problem I am suggesting about the footswitch socket. The problem will only occur when there is NO footswitch inserted. Once you plug a cable into the footswitch socket the faulty switch wafers are taken out of the circuit and are no longer a problem. When you remove the cable plug from the socket they should close again making the circuit work from the front panel switches. If they have a dirty contact or a hair or piece of grit trapped in between them they will not connect correctly and the channel switching action can become faulty as you have seen. I just wanted to make that clear to you and to anyone else who comes across this with a similar problem. This problem only occurs when there is no plug inserted.

There is absolutely no way that the circuitry of the power soak can have an effect on the channel switching. It sits between the output transformer and the speaker socket with no connections anywhere else. It has no connection to the power supply. There are many other components in the channel switching circuitry which could cause the exact effect you have seen and I was worried that the problem may lie there. It may happen again in time though we must hope it does not. If it does then get back to us here and I will talk you through things a little more.

The amp is now working and that is a good thing. We are here if you need us again. Enjoy your playing.