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    GM40 channel switch pops

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    grimm26

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    Join date : 2018-03-07

    GM40 channel switch pops

    Post by grimm26 on Wed Mar 07, 2018 12:17 am

    I just got a GM40 today and had a chance to plug it in and start playing with it tonight. I am noticing some fairly loud pops when switching between presets that switch channels. Is this par for the course or should I get tech support?
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    JonnyNonsense

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    Join date : 2017-06-19

    Re: GM40 channel switch pops

    Post by JonnyNonsense on Wed Mar 07, 2018 10:34 am

    Mine does not do that. Try tech support.
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    grimm26

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    Re: GM40 channel switch pops

    Post by grimm26 on Wed Mar 07, 2018 8:01 pm

    After being able to actually crank it tonight, I think it was just that I had the master vol so low last night that any little extra noise from the amp seemed loud.  With master at 9 o'clock this thing is pretty damn loud and channel/patch switching was smooth.  There was a little "pop" between some of the presets but it must be something particular to those patches with a combo of channel and boost or something.
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    bordonbert

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    Re: GM40 channel switch pops

    Post by bordonbert on Fri Mar 09, 2018 7:26 pm

    It isn't normal to have a significant popping problem on changing channels in H&K gear. H&K are good engineers and they take a lot of care over the little details like adding protections to their circuitry so that does not happen. However, I suspect that what you are hearing is the change of circuitry when you select a different channel very late in the chain after the Master Volume control and just before the power amp, there is a last signal shaping stage with channel selection switching in there in the GM36 which is very similar as far as we know. That would then be at a constant level not reduced by lowering the volume settings. In other words, let's say the fault injects 5mV of signal somewhere into the power amp signal. That would be a constant 5mV regardless of whether the music signal level was set to give 50mV or 10V at the same point. Seen as a proportion of the total signal 5mV can be very small or very significant. If you had the volume way down at that time a small pop can seem to be very noticeable.

    It is usually caused by switching between two points with slightly different DC levels and can be caused by things like very small capacitor leakage currents which always exist. No you don't need to "recap" your amp, all capacitors leak a little! You may even find in time that it improves itself naturally as the amp burns in. Anyway, glad you realised it was more a psychological effect than a real one. I'm with you, don't make a mountain out of a molehill. These little things are all a normal part of playing loud music through a complex electronic unit.
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sat Mar 31, 2018 9:59 am

    I have those pops on my TM18 when I switch between clean and lead channels. And I heard it in some review on Youtube.
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    bordonbert

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    Re: GM40 channel switch pops

    Post by bordonbert on Sat Mar 31, 2018 11:44 am

    Are they significant pops KazakUralsky?  All caps will leak a little but it is usually pretty insignificant.  If these pops are very slight and don't get heard in a playing context then that is one thing.  If they are clearly audible while you are playing at a good volume then there is something which maybe should be looked into.  I know that H&K are very conscientious at putting in place all of the measures that you can to prevent these pops.  For example, high value grounding resistors are everywhere that there is an undefined voltage to keep the caps charged as they should be.
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sat Mar 31, 2018 12:28 pm

    Is it possible to put a video here?
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    bordonbert

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    Re: GM40 channel switch pops

    Post by bordonbert on Sat Mar 31, 2018 12:34 pm

    You can insert the URL of a YouTube vid if you post it there first. We only have a limited amount of space online with our setup so uploading and storing vids themselves is not possible. If you click on the Add Reply button to go into full editing mode you will see a YouTube icon in the function bar above the edit window.
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sat Mar 31, 2018 12:35 pm

    Ok. Tomorrow.
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sun Apr 01, 2018 7:34 am

    Here it is.
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    bordonbert

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    Re: GM40 channel switch pops

    Post by bordonbert on Sun Apr 01, 2018 7:52 am

    Great vid KU, thanks for posting that.  That is what I was talking about.  There will always be a detectable "tick" when the switches/relays are activated.  If there is a DC voltage being blocked by a capacitor then there is leakage and consequently a difference in DC levels at the two connections of the switch.  That will produce a "pop" which can be shown on a scope even if it cannot really be heard.  The amount of the leakage through the capacitor dictates how big the signal jump at that point will be.  What you have just demonstrated is that in a working amp it is at a level which won't interfere when you are actively playing.  I think your amp is showing this at a level we can expect any amp to produce.  It's when the cap gets really leaky that the problems occur and the pop gets to be almost a bang!

    Are your pops at this sort of level Grimm?  I did see KazakUralsky say that his Clean volume was at 9:00.  The effect can increase as volume is set higher of course, and you are using a 40W amp not an 18W.
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sun Apr 01, 2018 8:13 am

    9 oclock on the Lead channel, Clean is on 12. After playing for some time pop can be louder, but not so much.
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    bordonbert

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    Re: GM40 channel switch pops

    Post by bordonbert on Sun Apr 01, 2018 8:21 am

    Those levels sound reasonable to me.

    The fact it can get louder after playing for a short time fits in with the idea of leakage being the problem.  That could be increased by warming up.  For the record capacitors, particularly ALL electrolytics new or old, leak a little when they are first turned on as their insulating layer breaks down a little when they are not seeing a polarising voltage.  That leakage drops over the first few minutes as they "self heal" the insulating layer.  That is why it can be necessary to "reform" electrolytics after a long period without being switched on, (that is after years not weeks!)
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    KazakUralsky

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    Re: GM40 channel switch pops

    Post by KazakUralsky on Sun Apr 01, 2018 11:41 am

    I see, thanks.

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