What are the reasons for ...

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andrew Ivimey
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#1 What are the reasons for ...

Post by andrew Ivimey »

a click/surge/nasty spike in the loudspeakers when I switch off the amplifier


and what are the cures, please?
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pre65
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#2

Post by pre65 »

What amp ?

Have you tried switching the preamp off first ?
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andrew Ivimey
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#3

Post by andrew Ivimey »

amps not amp ... (earthing issues?)

Yes, that can give an amplified spike through the amplifier so can be even worse.
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#4

Post by Neal »

Maybe the on/off switch is arcing over when you switch off, try a X class cap across the contacts
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#5

Post by ed »

may or may not be relevent.....

I had a kt88 pp amp which was triode/ul switchable. When the amp was switched off there was always an audible click. I investigated and found that the UL/triode switch was on a solenoid so it was switching modes whenever it was turned off.......Among other things I removed this and hard wired it in triode mode, and all was well.....

I was almost certain it was the reason for frying one of my electrostatic transformers.....trixy little chaps these clicks and pops....
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#6

Post by andrew Ivimey »

It's a good example of this Ed, thanks. My vague understanding is that some sort of DC 'spike' is getting through to the secondary windings of the output transformer, but how!? Clever stuff this electricity.

With a solid state amp a DC 'spike' is getting through the circuitry also able to present itself at the speaker connection in a very unsatisfactory and very damaging manner; its the tweeters that take the brunt of this.

But why oh why oh why etc etc.
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#7

Post by Mike H »

Ed's is a very special case example, sounds like; I'd go with Neal, switching off makes an arc across the switch contacts which is then amplified by the amplifier. The amplifier is not going into any special 'mode', it is just amplifying the electro-magnetically induced pulse while it's still got some juice left.

My germanioum amp did this mucho huge-io, cure was an 220nF X2 cap effectively across the mains transformer primary (2 pole mains switch). In parallel with a mains transient suppressor (VDR). The big pulse spike is generated by the transformer primary when the current is cut, i.e. by back EMF. It's very basic stuff. Kill the spike, no more switch-off pops.

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#8

Post by andrew Ivimey »

aha! I hadn't seen Neal's comment - that makes sense and Mike, your addition is the icing on the cake, surely. I have seen this sort of setup. I need X2 caps and suppressors, bring them on!

Maplin's ???

Because it isn't just one amp that does this and it isn't just one valve amp.

Could it have something to do with the crap mains supply (I think) I have?
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#9

Post by pre65 »

Perhaps you use the same "crap" mains switch on each amp ? :wink:

I use a Lorlin rotary type 4A DPST switch on all my amps and don't suffer the problems you describe.

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http://www.hificollective.co.uk/compone ... eters.html
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#10

Post by Ali Tait »

Go for a balanced power supply also if you're mains aren't too good Mr I.
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#11

Post by andrew Ivimey »

Been there, done it Ali, it changed the sound of the system but I don't think for the better. It wasn't my usual slapdash style either. It was a very interesting experiment and it may be a way of getting a purer mains supply.

I am thoughtful about this.
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#12

Post by Greg »

andrew Ivimey wrote:Been there, done it Ali, it changed the sound of the system but I don't think for the better. It wasn't my usual slapdash style either. It was a very interesting experiment and it may be a way of getting a purer mains supply.
Yep, I recall Noel Keywood writing an article on this very subject several years ago and after trying it, he also concluded he didn't enjoy the sound compared with standard supply.
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#13

Post by Nick »

Well, for the transformer, given that the voltage out is proportional to the rate of change of the voltage in, if the switch (as most do) just stops the voltage dead, then you would expect near infinite voltage out. Thats why you need the caps across the switch.
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#14

Post by Ali Tait »

andrew Ivimey wrote:Been there, done it Ali, it changed the sound of the system but I don't think for the better. It wasn't my usual slapdash style either. It was a very interesting experiment and it may be a way of getting a purer mains supply.

I am thoughtful about this.
Interesting Mr I, I've found it well worthwhile. Be good to try it on different gear at Owston.
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#15

Post by andrew Ivimey »

indeed it would!
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