World-Designs-Forum  

Go Back   World-Designs-Forum > World Designs > WD Amplifiers
Register FAQ Members List Calendar Gallery Today's Posts Search Today's Posts Mark Forums Read

WD Amplifiers For discusson of World Designs Amplifiers

Reply
 
Thread Tools Display Modes
  #31  
Old 31st March 2018, 10:43 PM
Greg.'s Avatar
Greg. Greg. is offline
Senior Member
 
Join Date: Dec 2005
Location: Bristol, UK
Posts: 3,135
Default Re: KEL84XL build

You’ve used those upgrade sonic caps. They need at least 100 hours of use before the amp starts to sound correctly balanced. I would expect initially the sound is a bit bass heavy and bass muddled.

The signal wire route can be very influential with regard to hum, although I note you have previously posted your problem is a mains, possibly earth loop issue. If it is down to signal wiring, with the chassis upturned, try routing the signal wires from the front of the board, both towards the chassis center and then tied together to the rear of the amp, running both left and right cables down the centre line, also at chassis base plate level. I have in the past found this good for reducing hum on KeL84 and a KaT88 I previously owned.
Reply With Quote
  #32  
Old 31st March 2018, 11:00 PM
Greg.'s Avatar
Greg. Greg. is offline
Senior Member
 
Join Date: Dec 2005
Location: Bristol, UK
Posts: 3,135
Default Re: KEL84XL build

Oh, I also note you have posted your problem on the TAS forum. Please be aware that the advise you might receive there might be very unreliable, based simply on ignorance. You will get much better advise here, especially from Richard, Andy, Bob and John that is solidly founded with electronic knowledge that is totally reliable. Only take advise from those who really do know what they are talking about. Sadly, what you get at TAS is likely to fall well short of that essential standard.
Reply With Quote
  #33  
Old 31st March 2018, 11:54 PM
pre65's Avatar
pre65 pre65 is offline
Senior Member
 
Join Date: Jan 2006
Location: Ashen- Essex/Suffolk bord
Posts: 4,376
Default Re: KEL84XL build

Just to second Gregs opinion above.
__________________
Philip.

Everything in this post is my honest opinion based on what i thought I knew at that very moment in time.
Reply With Quote
  #34  
Old 1st April 2018, 12:32 AM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Quote:
Originally Posted by pre65 View Post
Just to second Gregs opinion above.
Thanks, donít worry both. I realise that Johnís,Bobís and Matthewís et alís opinions are likely to carry more weight.

Useful advice can also be forthcoming from the Golborne Radio and Vintage Radio sites.

Matthew obviously rates Johnís views and knowledge very highly so am more than happy to learn from him.


All seems well with the amp. I hope this pleasant exchange will inspire and inform other people to try the kit.

BW
Reply With Quote
  #35  
Old 2nd April 2018, 01:02 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Quote:
Originally Posted by Greg. View Post
Youíve used those upgrade sonic caps. They need at least 100 hours of use before the amp starts to sound correctly balanced. I would expect initially the sound is a bit bass heavy and bass muddled.

The signal wire route can be very influential with regard to hum, although I note you have previously posted your problem is a mains, possibly earth loop issue. If it is down to signal wiring, with the chassis upturned, try routing the signal wires from the front of the board, both towards the chassis center and then tied together to the rear of the amp, running both left and right cables down the centre line, also at chassis base plate level. I have in the past found this good for reducing hum on KeL84 and a KaT88 I previously owned.
Greg,
Thanks for that. I don't suppose you took a picture of the inside of the amp with your preferred wiring layout did you?

BW

Richard.
Reply With Quote
  #36  
Old 2nd April 2018, 02:59 PM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,627
Default Re: KEL84XL build

Richard, if Greg can't supply his picture, follow my build, it was almost hum free, there was just a gentle hum with the ear close to the speaker, also from the off, base light it was not, now, Matthew is not going to thank me for my next comment, but, I have used those Sonics capacitors and I don't like them, I would recommend the orange drop type that comes with the standard kit, or you could and should remove them and shorten the connecting wire to as minimum length as possible, try to sit the capacitors on the PCB, to have them hanging like you have is not good practice, some constructors even hot melt glue capacitors in place to stop vibration, as they say in Tesco, every little helps. Another thing you could try is to connect a wire to both output transformers fixing bolts then to the earth post, I see you have one to the mains transformer, it may help. BOB

Last edited by bob orbell; 2nd April 2018 at 03:27 PM.
Reply With Quote
  #37  
Old 2nd April 2018, 03:47 PM
Phil Y's Avatar
Phil Y Phil Y is offline
Senior Member
 
Join Date: Jul 2006
Location: Bristol, UK
Posts: 665
Default Re: KEL84XL build

Hello Richard,

The KEL84 can be very quiet regarding hum so you should not despair. Is the hum you have equal on both channels ? If it is worse on one side or the other that may give you a clue as to where to look. Personally I would not be too concerned about the coupling caps initially. Many people, including myself, have fitted larger "audio grade" caps without it causing hum problems.

Phil.
__________________
Commission for Dark Skies (CfDS)
Reply With Quote
  #38  
Old 2nd April 2018, 03:51 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Quote:
Originally Posted by bob orbell View Post
Richard, if Greg can't supply his picture, follow my build, it was almost hum free, there was just a gentle hum with the ear close to the speaker, also from the off, base light it was not, now, Matthew is not going to thank me for my next comment, but, I have used those Sonics capacitors and I don't like them, I would recommend the orange drop type that comes with the standard kit, or you could and should remove them and shorten the connecting wire to as minimum length as possible, try to sit the capacitors on the PCB, to have them hanging like you have is not good practice, some constructors even hot melt glue capacitors in place to stop vibration, as they say in Tesco, every little helps. Another thing you could try is to connect a wire to both output transformers fixing bolts then to the earth post, I see you have one to the mains transformer, it may help. BOB
Thanks Bob, I've had another look at your pics and cannot see that much difference in the layout, but will take a pic of my own once the amp cools down.

I could easily try shortening the leads (I did with two - accidentally). I do have a hot-glue gun!

Thanks again; much appreciated as usual,

Yours,

Richard
Reply With Quote
  #39  
Old 2nd April 2018, 04:09 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Quote:
Originally Posted by Phil Y View Post
Hello Richard,

The KEL84 can be very quiet regarding hum so you should not despair. Is the hum you have equal on both channels ? If it is worse on one side or the other that may give you a clue as to where to look. Personally I would not be too concerned about the coupling caps initially. Many people, including myself, have fitted larger "audio grade" caps without it causing hum problems.

Phil.
Thanks Phil,

The main mains(!) hum has gone since I snipped the earth lead on the PS to the preamp - I must have had an earth loop.

Since I tidied-up the wiring I've noticed a slight increase in residual hum. It's the same in both speakers and is lessened when the vol pot is turned down. Perhaps a rats' nest is better after all!

It's not bad and I can live with it - but if it's simple tweak (which it probably is), I'd like to get rid of it.

I was initially a little more concerned re the safety issues concerning removing an earth lead to the pre-amp, even though I'm sure back in the '70s the mantra was 'one earth to the amp only' - and let the cable screening 'carry' it to the other sources.

Opinion seems to be divided somewhat on this, but John C has OK'd it so I'm happy. For my sins, (manifold), I also posted on another forum: (http://theaudiostandard.net/thread/4...ew-valve-amp); folk on this site have warned me off from taking in-expert advice from others, (but I must say some of the TAS guys seem well-informed and less inclined to flame wars cf other sites (However, the thread on audiophile fuses, (45 pages and counting...) - £130 a pop (literally) created a lot of acrimony - a lot of heat (appropriately), but not a lot of light)). I daren't ask peoples' opinions re such fuses on this site! (Dare I?).

Anyway, when the caps on the amp have discharged themselves to safe levels I'll dive into the giblets again. (How long do others leave theirs before diving in?).

Does anyone know if the ready-made KEL84 is CE certified? Do I really need to get my amp PAT tested?


Apologies for all the questions...but I hope any answers will inform others too.

Thanks again; much appreciated.
Reply With Quote
  #40  
Old 2nd April 2018, 08:30 PM
bikerhifinut bikerhifinut is offline
Senior Member
 
Join Date: Jan 2006
Location: Penrith, Cumbria
Posts: 888
Default Re: KEL84XL build

1. I agree with bob re the orange drops capacitors. I know it will get us hung but I never felt the need to "upgrade" the orange drops on my phono3S and Bob reckoned they were as good as the expensive ones in that application.
I changed the original grey box shaped polyester coupling caps on my WD88VA for soniqs polyprops, they are electrically better this is a proven fact. But in all honesty I felt the difference if any was so subtle that I wouldn't do it next time.
Other people are bound to disagree and I can only speak as I find. I would avoid paper in oil capacitors on principle as they seem to be unreliable and a leaky coupling cap can do huge amounts of damage. That said, the russian K40Y military jobs seem to be constructed on a different scale and I do have them in my Leak stereo20. They're only rated to 400V though and thats fine on an EL84 amp but not on the KT88 jobs.

2. Fuses. All I can say there is there's one born every minute. If gold plating or whatever really makes a difference you'll get the same effect by cleaning any corrosion of the existing fuse. In the end it's still a VERY thin bit of wire that heats up and melts.

3. Ref PSU capacitors, they will usually have discharged as the valves cool down as the valves still pass current for a few seconds or more on switch off. If you want to be certain, then I counsel a "bleed" resistor across the first capacitor in the PSU after the rectifiers. A 2W 220k to 470k will be fine 220k is only going to consume an extra 1.5mA assuming HT of 330V so you have no worries there. That resistor will "bleed off" any remaining charge after switching off. Thats worth noting if you do any tests with valves unplugged.

4. There is no legal requirement to have your DIY kit amp PAT tested. For peace of mind and the sake of your insurance then all you need do is completely disconnect it from the mains sockets when not in use. Which is good practice for any item of mains operated electronics.

5. Most hum issues tend to be layout and earthing or both related. Tidying up wiring can disturb soldered joints and also its possible to bundle a wire carrying a low level audio signal next to one carrying a high current AC voltage. Hence the very sound advice in respect of mains transformer wiring tidiness.

Hope thats all ok.

Andy

Last edited by bikerhifinut; 2nd April 2018 at 09:26 PM. Reason: grammatical error
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 09:07 AM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright World Designs