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
  #11  
Old 28th March 2018, 07:07 AM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,620
Default Re: KEL84XL build

Richard, I would have a guess and say that the source you were connecting, has only twin mains cable, or the 0 volts are completely isolated from the ground, in which case as Phil has said, you amp. is only receiving half of the signal, the full signal is connected to the centre pin and the screen, and both must be present. BOB
Reply With Quote
  #12  
Old 28th March 2018, 07:49 AM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Thanks Bob; I'll try other sources later.

My brain is still befuddled after several nights of no sleep/aircraft/long car journey etc. I don't think I was thinking straight!
BW

Richard.
Reply With Quote
  #13  
Old 28th March 2018, 10:44 AM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,620
Default Re: KEL84XL build

Richard, just to amend my post 11, you must insert the phono plugs completely, there is nothing wrong with your source. BOB
Reply With Quote
  #14  
Old 28th March 2018, 11:34 AM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Thanks Bob.

The amp is still burning-in. At first it was rather 'thin' sounding but gradually there appears to be a bit more 'body'. Should be OK to plug into my LV speakers tomorrow.

Richard
Reply With Quote
  #15  
Old 28th March 2018, 04:15 PM
Phil Y's Avatar
Phil Y Phil Y is offline
Senior Member
 
Join Date: Jul 2006
Location: Bristol, UK
Posts: 659
Default Re: KEL84XL build

Hello Richard,

I remember when I first built my KEL84 it was a bit of a culture shock after the Leak Stereo 20 I had been using for a couple of decades. I thought it was a bit lean sounding initially but as the amp mellowed with use and my ears adjusted to the changes I realised what a great amp it was. I'm sure you will enjoy it.

Phil.
__________________
Commission for Dark Skies (CfDS)
Reply With Quote
  #16  
Old 28th March 2018, 05:04 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build

Thanks Phil; I'm sure I will...

R
Reply With Quote
  #17  
Old 29th March 2018, 05:16 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build - now Mains Hum!

Mains hum on new KEL84…BUT there is a post-script!

On both channels.
Dependent on the volume control.
Taking out the two input leads gets rid of the hum completely.
Trying another (screened) mains lead makes no difference.
The previous amps (Quad 306 and 99, Rega Brio-R) did not show this hum.
Twiddling the external wires/cables makes no difference.

So, I guess I have an earth loop. In which case am I correct in thinking that only the amp should have an earth and all other sources, pre-amp etc should have just live and neutral connected?

If so, strange I haven’t noticed this before!

Update:

I eventually traced this to my pre-amp (A Schiit Saga Valve Jobbie). I snipped off the earth lead and there is (virtually) no hum. Great!


BUT my question is …why? All my other amps did not show this problem.

I wrote earlier that I was puzzled that there was no sound coming from the amp unless the input leads were fully pushed home so that the pin AND outer screen were engaged. I have just tried a similar experiment with the Rega Brio-R amp, and, as I recalled, only the male pin of the phono plug need to make contact with its female equivalent for there to be sound.

Are all valve amps the same? Is this something peculiar to the (earthing/grounding of the) KEL84…or is it a fault with my wiring…?

Thanks,

Richard.
Reply With Quote
  #18  
Old 29th March 2018, 08:19 PM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,620
Default Re: KEL84XL build

I think we should let John try and answer this one, but my own observation with all WAD WD amplifiers using ECF80 input - phase spliters is that they all have a small amount of hum, the WD KT88 on the other hand is very quiet, almost silent. I think you should be cautious of removing the earth cable, it is there for a reason. BOB
Reply With Quote
  #19  
Old 29th March 2018, 11:09 PM
bikerhifinut bikerhifinut is offline
Senior Member
 
Join Date: Jan 2006
Location: Penrith, Cumbria
Posts: 884
Default Re: KEL84XL build - now Mains Hum!

Quote:
Originally Posted by Bonky View Post
Mains hum on new KEL84…BUT there is a post-script!

On both channels.
Dependent on the volume control.
Taking out the two input leads gets rid of the hum completely.
Trying another (screened) mains lead makes no difference.
The previous amps (Quad 306 and 99, Rega Brio-R) did not show this hum.
Twiddling the external wires/cables makes no difference.

So, I guess I have an earth loop. In which case am I correct in thinking that only the amp should have an earth and all other sources, pre-amp etc should have just live and neutral connected?

If so, strange I haven’t noticed this before!

Update:

I eventually traced this to my pre-amp (A Schiit Saga Valve Jobbie). I snipped off the earth lead and there is (virtually) no hum. Great!


BUT my question is …why? All my other amps did not show this problem.

I wrote earlier that I was puzzled that there was no sound coming from the amp unless the input leads were fully pushed home so that the pin AND outer screen were engaged. I have just tried a similar experiment with the Rega Brio-R amp, and, as I recalled, only the male pin of the phono plug need to make contact with its female equivalent for there to be sound.

Are all valve amps the same? Is this something peculiar to the (earthing/grounding of the) KEL84…or is it a fault with my wiring…?

Thanks,

Richard.
If you get a signal when only the centre pin of an RCA phono plug is connected, there MUST be a return to signal earth back to the source. It's a basic and simple rule of electrical circuits. End of.
So.... the return path must exist somewhere, this could be via the mains earth through the mains lead into the wall socket and thence back out via the wall socket and mains lead to the accompanying item of equipment. If so this is far from optimal for a number of reasons.
I find myself puzzled that you get a result with only the centre connector of a signal plug connected into a Rega amp. This is because Rega electronics as far as I know are double insulated and have no mains earth connection. certainly all my Rega gear has only 2 pin connectors in the amps dacs and cd player even though a standard 3pin IEC plug is used. What source is this?
My suspicion is that your preamp which is one I do not know, has a compatibility issue with the WD power amp. It certainly does sound like a hum loop, however disconnectinge Mains SAFETY earths is not the solution.
The WD power amp should have its safety mains earth "Lifted" by a resistor and parallel capacitor from signal earth, this is a measure to reduce or eliminate hum caused by hum loops.
So I wonder what the output impedance of your preamplifier is for starters, it may be quite high if there is no cathode follower buffer on its output and most WD power amps as designed have a 100k input Z.
The next thing that springs to mind is how far from the mains transformer of the WD amp is your preamp? Especially if it has a sensitive Phono magnetic cartridge input which would be sensitive to quite low hum fields. Try moving your preamp away from the power amp.
As you get no hum when nothing is plugged in to your KEL84 that suggests that it is working perfectly, although a good test here is to try a couple of shorting plugs in the input sockets. Perfectly safe to short the inputs on this amp.
Is this on a magnetic cartridge source or a line level source eg CD player?

You could try a simple passive volume control on the input sockets. This is simply a potentiometer wired across the input, easy to rig a lash up with a cheap pot. Unless your power amp is one with a volume pot fitted at the input as some are. In that case plug your source directly in to the amp and if no hum it points at your preamp. I am assuming line level here or output from a cartridge step up.

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.
Reply With Quote
  #20  
Old 29th March 2018, 11:43 PM
Bonky Bonky is offline
Member
 
Join Date: Feb 2018
Location: Sheffield
Posts: 58
Default Re: KEL84XL build - now Mains Hum!

Quote:
Originally Posted by bikerhifinut View Post
If you get a signal when only the centre pin of an RCA phono plug is connected, there MUST be a return to signal earth back to the source. It's a basic and simple rule of electrical circuits. End of.
So.... the return path must exist somewhere, this could be via the mains earth through the mains lead into the wall socket and thence back out via the wall socket and mains lead to the accompanying item of equipment. If so this is far from optimal for a number of reasons.
I find myself puzzled that you get a result with only the centre connector of a signal plug connected into a Rega amp. This is because Rega electronics as far as I know are double insulated and have no mains earth connection. certainly all my Rega gear has only 2 pin connectors in the amps dacs and cd player even though a standard 3pin IEC plug is used. What source is this?
My suspicion is that your preamp which is one I do not know, has a compatibility issue with the WD power amp. It certainly does sound like a hum loop, however disconnectinge Mains SAFETY earths is not the solution.
The WD power amp should have its safety mains earth "Lifted" by a resistor and parallel capacitor from signal earth, this is a measure to reduce or eliminate hum caused by hum loops.
So I wonder what the output impedance of your preamplifier is for starters, it may be quite high if there is no cathode follower buffer on its output and most WD power amps as designed have a 100k input Z.
The next thing that springs to mind is how far from the mains transformer of the WD amp is your preamp? Especially if it has a sensitive Phono magnetic cartridge input which would be sensitive to quite low hum fields. Try moving your preamp away from the power amp.
As you get no hum when nothing is plugged in to your KEL84 that suggests that it is working perfectly, although a good test here is to try a couple of shorting plugs in the input sockets. Perfectly safe to short the inputs on this amp.
Is this on a magnetic cartridge source or a line level source eg CD player?

You could try a simple passive volume control on the input sockets. This is simply a potentiometer wired across the input, easy to rig a lash up with a cheap pot. Unless your power amp is one with a volume pot fitted at the input as some are. In that case plug your source directly in to the amp and if no hum it points at your preamp. I am assuming line level here or output from a cartridge step up.

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.
Thanks for that; much appreciated. I will answer, I hope, more fully in the morning, when I can experiment a little more.

I DO appreciate the need for earthing. My understanding is/was that if the KEL84 is earthed then no other source need be - as the outer screen along the various leads carries the earthing to all other equipment. I can use another (passive) pre-amp in the morning ( a Tisbury), but as this has no mains lead at all (!) then the earthing to the source equipment, is, as I said, carried along the various cable screens.

The Saga preamp (https://schiit.eu.com/preamps/Saga) has an output impedance of 180R...

(SChiit's manual states:" I hear hum, what do I do?
You may have a ground loop. To x a ground loop, try a ground loop isolator or an EbTech HumX.")

The source of the Rega amp is: iMac to Beresford Caiman DAC (running from a 12V battery) to the amp.

Thanks again,

Richard
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 12:04 AM.


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