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  #21  
Old 30th March 2018, 12:02 AM
bikerhifinut bikerhifinut is offline
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Default Re: KEL84XL build

Looking at that preamp I reckon its probably some sort of hybrid with an octal cathode follower. 180R seems a bit low but not unfeasible from such a CF. which should match into the WD inputs just fine and with that low an output Z you can use a long interconnect.
My money's still on hum pickup from the mains transformer on the WD.
I had a KEL84 for a while, the integrated version and never had any hum issues with it at all. It was very quiet indeed. But obviously it had to be kept well away from the turntable and phono stage.

I'd get that safety earth back on all the same.

Andy.
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  #22  
Old 30th March 2018, 08:41 AM
bob orbell bob orbell is online now
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Default Re: KEL84XL build

I am a little concerned that you seem to show little or no understanding of the need for a complete electrical circuit for an input signal to reach the amp inputs and the reasons why we have mains safety chassis earths especially on high voltage equipment.

Well I came to this conclusion some time ago Andy, but did not want to offend Richard, I am sure he is trying, but the pictures of the amp assembly leave a little doubt, but, at least he is trying. BOB
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  #23  
Old 30th March 2018, 04:59 PM
John Caswell John Caswell is offline
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Default Re: KEL84XL build

Hi all,
Hum can be the very devil to sort out. This is interesting in that with all inputs removed there is no hum but with inputs from the Schiit (unfortunate name that!) there is hum.
I have had instances of this before on various amplifier/preamplifier combinations and it appears to be an input "hum loop". In pretty well all cases I have eliminated/reduced the problem by lifting the signal earth in the send item by anything from 10-100R paralleled with a 0.1f 100V capacitor. I appreciate that this may not be possible, so you may have to try lifting them at the amplifier input end the same way.
This sort of thing often happens in my workshop where I have several audio oscillators with both earthed and unearthed outputs and some amplifiers either hum like the clappers or go into violent oscillation because both their inputs and L/S outputs are earthed back to the same power line point
Having seen the pictures of the amplifier the wiring can only be described as messy. One of the first thing I would suggest is trying to keep the output transformer feeds as short as convenient and away from the input wiring, they can all bre twisted together quite safely!. The other helpful thing is to only earth the feedback screening wire at the loudspeaker terminal end to avoid an internal hum loop, this can work wonders for residual hum and noise.
Try some of the ideas here to see what the results are.

John
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  #24  
Old 30th March 2018, 08:14 PM
bob orbell bob orbell is online now
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Default Re: KEL84XL build

Hi Richard, here is a picture of my KEL that I salvaged from the WD scrap bin, it may be of some use to you, I hope you are not offended by my last post. BOB shit, it seams like it will not enlarge.
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File Type: jpg Amplifier.jpg (3.4 KB, 91 views)
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  #25  
Old 30th March 2018, 08:27 PM
Bonky Bonky is offline
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Default Re: KEL84XL build

Bob; thanks for that. Unfortunately I cannot enlarge the image.

No, not (too) insulted. The inside of my pics on my amp does look a bit of a mess as I deliberately left all the cable ties off just in case Matthew needed to do some 'adjustments'. To you and John, it does look better now but is far from perfect.

I have sent John two PMs.

I'm not quite the numpty that I have portrayed - it's just that one is more likely to get detailed help if one doesn't appear an 'expert'.

I've been busy with other things today but hope to do some more experiments tomorrow.

The mains hum has been cured by my disconnecting the earth on the preamp. Some other posts on other forums seem to agree that there is no need to replace said earth but I'd like to get as much advice as possible.

I've asked John if there's any mileage in ensuring the mains supplies to both amp and preamp come from the same 'socket'.

Thanks.

Last edited by Bonky; 30th March 2018 at 09:05 PM.
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  #26  
Old 30th March 2018, 08:27 PM
bob orbell bob orbell is online now
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Default Re: KEL84XL build

OK so if you want to see pictures of my rebuild, go to WAD GENERAL, page 2, line 12, I hope you take a look.BOB
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  #27  
Old 30th March 2018, 09:21 PM
bikerhifinut bikerhifinut is offline
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Default Re: KEL84XL build

Quote:
Originally Posted by Bonky View Post
Bob; thanks for that. Unfortunately I cannot enlarge the image.

No, not (too) insulted. The inside of my pics on my amp does look a bit of a mess as I deliberately left all the cable ties off just in case Matthew needed to do some 'adjustments'. To you and John, it does look better now but is far from perfect.

I have sent John two PMs.

I'm not quite the numpty that I have portrayed - it's just that one is more likely to get detailed help if one doesn't appear an 'expert'.

I've been busy with other things today but hope to do some more experiments tomorrow.

The mains hum has been cured by my disconnecting the earth on the preamp. Some other posts on other forums seem to agree that there is no need to replace said earth but I'd like to get as much advice as possible.

I've asked John if there's any mileage in ensuring the mains supplies to both amp and preamp come from the same 'socket'.

Thanks.
Sounds like classic hum loop to me.

You could try "semi balanced" cables to the power amp. thats using 2 core screened cable, using the inner cores for the signal circuit and connecting only one end of the screen to earth, usually at the output from preamp/source rather than input to amp. No guarantees but might do the trick............ maybe.

You can do a quick test with a resistance meter from the mains earth pin to the outer of any of the phono sockets. If you get a zero ohms reading then the signal earth isn't "Lifted" from the mains chassis safety earth. this will likely induce a hum loop into the KEL84. Some preamps used to sport an "Earth lift" switch because of this.

Sorry if I caused offence, but I have come across one or 2 individuals that really did cause me concern hence my caution. Something tells me you'll get on top of the case.

Andy.
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  #28  
Old 30th March 2018, 09:31 PM
bikerhifinut bikerhifinut is offline
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Default Re: KEL84XL build

I had an awful time solving a really bad hum issue on my Phono3S, bought used and allegedly built "Professionally".
Thanks to the patient advice from John, Richard Bob etc etc I eventually traced it to the PSU where the original constructor had wired the mains and chassis earth to the signal earth point (0V HT negative). Took me days to find it even though it was staring me in the face! one minutes work with soldering iron and with mains earth on the correct pin and right end of the lift resistor all was solved.
So I am sure you'll get there in the end.

Andy
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  #29  
Old 30th March 2018, 10:17 PM
Bonky Bonky is offline
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Default Re: KEL84XL build

Quote:
Originally Posted by bob orbell View Post
OK so if you want to see pictures of my rebuild, go to WAD GENERAL, page 2, line 12, I hope you take a look.BOB
Thanks Bob; got them.

Impressive.


R
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  #30  
Old 31st March 2018, 07:09 PM
Bonky Bonky is offline
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Default Re: KEL84XL build

Update:

Two things:
1. I've opened her up and tidied the wiring (not as good as Bob's); cable ties; shortened wiring paths etc. It looks better ...but ...is there now a bit of a hum (with all inputs disconnected)? Perhaps I'm just getting super-sensitive.

2. I've been in contact (PMs) with the Uber-guru (John C) who confirms that removing the earth from the pre-amp mains lead should be OK. I have a decent DMM so tested the earth continuity from amp mains plug all the way back and, yes, there was continuity.


Thus I'm tempted, at present, to leave well alone.

It has had about 20 hours of burn-in time and is certainly 'less lean' in its presentation, although I can't say there is that much difference (yet?) cf my DADA modded Quad 306. TBH I wasn't expecting a night-and-day difference as I rate the Quad 306 very highly, and at my age (just turned 70) my gold (plated) ears aren't quite what they were!

Thanks for everyone's civilised and helpful inputs.

BW

Richard.
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