Welcome, Guest. Please Login or Register
Decware Audio Forums
09/17/14 at 08:46:10


Pages: 1 
Send Topic Print
hum problem (Read 10856 times)
Steve Deckert
Administrator
*****


If the 1st watt
sucks why continue?

Posts: 2402
hum problem
11/01/09 at 03:05:14
 
Quote:
We talked recently on the phone about hum in my zen kit1.
I am sending you pictures of my amp. Please take a look if you have a chance.
I have tried different things like changing source, changing interconnects, changing power outlets(use the same outlet/ use different outlets), changing positions of units and cables, but result stay the same - after attaching interconnects to any source hum starts and hum sound stays the same whatever I do (no hum at all without source).    
I am under impression that something happened inside my amp after a few month of work. I don’t remember this hum in the beginning.
Waiting for your advice, what should I do.

Best regards
               Serguei



Back to top
« Last Edit: 11/01/09 at 03:12:26 by Steve Deckert »  

zkit1help.jpg
WWW   IP Logged
Steve Deckert
Administrator
*****


If the 1st watt
sucks why continue?

Posts: 2402
Re: hum problem
Reply #1 - 11/01/09 at 03:19:44
 
Your board is grounded in two locations which could be causing your problem.  You have the chassis grounded to the board with the brown wire, but then you also have a wire from the left input jack ground connecting to the chassis.  Remove this wire.

Also, the wires connecting each input jack to the board should ideally be shielded with the shields connected at the input jack ground on the circuit board.
Back to top
 
 
WWW   IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #2 - 11/01/09 at 10:05:06
 
Me too!

I think the key is "after connecting interconnects" the hum starts. That is what happens with me. My amp has a single earth. A grounded shield on the input cables did not help me.

I think this means you have a ground-loop, or mains contamination of the source signal. Having done some reading diagnosing these is trickier than it sounds.

Build a ground-lifter (a plug/socket with the earth disconnected) to  use simply to diagnose the problem by breaking loops. A ground-lifter may not be 100% safe as a final solution. And try powering various components in the hifi chain unearthed to mains (as long as one component is earthed there will be a ground connection for all components through the shield of the RCAs.)

This did not work for me.

My next step is to get an electrician to check out the Ze of our household earthing and the earth-bonding (expensive equipment and know-how required). My understanding is that it is not good simply to connect your own earthiing rod, but that Incomer Earth as it is called should be formally tested and fixed if it is inadequate. Have any building contractors been working near your house recently?

Does your hum change with the volume setting? Mine does.

My sympathies - this can be a frustrating problem!
Back to top
 
« Last Edit: 11/02/09 at 17:44:07 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #3 - 11/01/09 at 14:01:46
 
Thanks Steve
But if I use shielded wire for input jacks, then my circuit board will be connected to the chassis tree times ( brown wire plus two shields for  input jacks). Is it OK?

Alan
Hum changes with volume control
Back to top
 
 
  IP Logged
Steve Deckert
Administrator
*****


If the 1st watt
sucks why continue?

Posts: 2402
Re: hum problem
Reply #4 - 11/01/09 at 23:03:48
 
Nope, the shields are only connected at one end, not both.  

Steve
Back to top
 
 
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #5 - 11/02/09 at 00:00:16
 
Thanks Steve
Does it matter which one?
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #6 - 11/02/09 at 17:33:33
 
To exclude a ground loop, lift the ground on your cd player (use a socket/plug with the earth disconnected) and attach it to your amp with RCA cable. Leave your amp earthed. Disconnect everything else from your hifi chain.

Switch both on. If the hum is still there and unchanged then it is NOT a ground loop because you have broken the signal return path through earth which might have been causing the loop.

I have tried this but for me the hum is still there. I believe this means either there is earth contamination from some other electrical device, or earth is inadequate. I have tried a few possible culprits for contamination without success (central heating boiler etc).

It seems there is no simple test for adequacy of your earth - this is a job for an electrician. I'm going to speak to the electricians at work to see what they suggest.
Back to top
 
« Last Edit: 11/02/09 at 17:34:56 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #7 - 11/03/09 at 13:58:10
 
Well Alan
Then why none of my other equipment experience this hum problem (i have Marantz receiver and i had NAD amp)?
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #8 - 11/03/09 at 18:41:19
 
None of mine either, sll: the hum doesn't show up in my T-Amps, my Push-pull valve amp, nor my solid state amp. However apparently SET topology is extremely sensitive to mains / earth borne interference. I think this is partly to do with the air-gapped output transformers, push-pull valve amps do not require these, and so are much less susceptible to hum.

One of the reasons that SETs tend to be more expensive than other amp types is the design, and component costs required to suppress this interference (and also to ensure good frequency extension).

(Info culled from lots of web searching - I am no expert!)
Back to top
 
« Last Edit: 11/03/09 at 18:43:05 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #9 - 11/03/09 at 19:23:31
 
Thanks Alan
Let's see what Steve will tell us.
Back to top
 
 
  IP Logged
Steve Deckert
Administrator
*****


If the 1st watt
sucks why continue?

Posts: 2402
Re: hum problem
Reply #10 - 11/04/09 at 02:27:09
 
There are many ways to handle grounding schemes when trying to put this kit into a chassis and remote mounting the input jacks, pot, or both.

Below is the recommended method that will work in wood or metal chassis.

It's important to understand that shielded cables must be used and that the shield must only be grounded at one end, and it must be the correct end as shown in the diagram.


Back to top
 
 
WWW   IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #11 - 11/04/09 at 18:56:25
 
Thanks Steve - that's precisely how my grounding has been done. Might be worth adding this diagram to the Kit1 assembly instructions.
Back to top
 
 

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
dank
Seasoned Member
****


pair of dual 18
Imperials

Posts: 275
Re: hum problem
Reply #12 - 11/12/09 at 16:55:43
 
I have been "tweaking" my Zkit1 for a while now, gradually coaxing more and more power out of it.  Somewhere along the way, the hum got so loud that I couldn't ignore it anymore.  Today I looked into it, and found a fix that virtually eliminated the hum I was experiencing on the bench.  Unfortunately there is still audible hum when the amp is in system, but it is substantially lower than what it use to be.


Two 14 gauge solid wires (out of a chunk of Romax) connected to the RCA input connector shields on one end and ground on the other - where the ground connects to the negative terminals of the two (3 in my case) large power supply capacitors (which is where I ground the volume controls).  The solid wire worked quite a bit better than any stranded wire I tried, and the ground point by the power supply capacitors worked much better than going straight to the earth ground connection.

I don't think this was a ground loop problem.  The hum was dependent on the volume control setting (more volume, more hum) and went away when the RCA input cable was unplugged.  On the bench, when I had my signal generator connected as the source, the hum was present when the signal generator was connected to the Zkit1 even when the signal generator was turned off and unplugged.  After installing the two solid wires there was no hum when the signal generator was connected.

Dan
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #13 - 11/13/09 at 01:43:30
 
Dank - sounds like a ground loop to me - when you unplug the RCA you break the loop (at the RCA shield) and the hum goes away.

Try just connecting the LIVE centre conductor of the RCA. If you still hear sound then you have a return path through the chassis earth rather than the RCA shield, and will therefore have a loop when the RCA is fully connected.

Whether that loop is then the source of the hum is another question.

It is possible to buy high-end RCA cables which are designed with the shield disconnected at one end. This forces the return path to earth, and will break a loop.

I do have a loop - but breaking the loop does not change the hum in any way.
Back to top
 
« Last Edit: 11/13/09 at 01:46:25 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #14 - 11/18/09 at 00:41:29
 
Thanks dank
I've solved my problem your help.
See two brown wire from RCA jacks to taper
Back to top
 

_MG_8706_sm.jpg
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #15 - 11/18/09 at 22:58:52
 
Must try that.

btw SLL, I would re-route the brown wire that is touching the black 1kohm resistor - that baby gets extremely hot in use!
Back to top
 
 

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #16 - 11/19/09 at 18:35:19
 
Thanks Alan
It doesn't touch it
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #17 - 11/19/09 at 21:43:52
 
OK SLL,

But what is going on here? Looking at the schematic, the two brown wires you have added simply parallel a trace on the board. Also, why use two when they are connected together anyway so surely one would be just as effective.

If this cured your hum, do you think the circuit board was damaged?

Just trying to reason this through. I have used one wire temporarily and the hum was still there. Strangely the sound did appear slightly clearer with this extra point-to-point wiring, but I will have to try it in/out a few times to see if that is just psychology because I seem to be a real sucker for reporting subtle/non-existent changes as improvements.

In case any readers of this thread get the wrong idea, my zkit hum is at a level which is not obtrusive, and I am absolutely loving the sound of this amp!
Back to top
 
« Last Edit: 11/19/09 at 21:48:42 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
dank
Seasoned Member
****


pair of dual 18
Imperials

Posts: 275
Re: hum problem
Reply #18 - 11/20/09 at 13:37:18
 
SLL

Glad to hear your hum problem is fixed.  Did you ever try solid wire rather than stranded?  In my case it worked much better.  I would be interested to know if solid worked different from stranded in your case.  When I first investigated the problem, I was using light guage clip on jumper wires (that look similar in size to the brown wire you are using) and found that the more jumpers I clipped on - in parallel - the more the hum was reduced.  A good size solid wire did the same job as about 6 of my jumper wires, and a single good size stranded wire did no better than a single small gage jumper wire.

DanK
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #19 - 11/20/09 at 14:47:23
 
Hi Dank,

Did this low-resistance bypass eventually reduce the hum to zero? ie Low enough to be able to run the amp fully open and control the volume  with a passive pre-amp?

I'm now wondering about bypassing that trace completely - it runs the full length of the board - and locating the RCA inputs close to the Pot, directly wiring them with very short runs of solid silver.

Alan
Back to top
 
« Last Edit: 11/20/09 at 15:05:02 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #20 - 11/20/09 at 20:16:41
 
OK - tried fully bypassing that trace. Mounted the RCAs right beside the pot, and connected them directly. Kept one of the original grounds grounded - as per schematic.

Well it certainly changed things. Now constant hum - the same at all volumes. Loud buzz if input is disconnected. Music is there.

So, plugged in soldering iron, and undid all the changes. Now back to before - hum varying with volume, acceptable level.

Will give this bypass wire thing a go I suppose. Nothing to lose.

(and soldering-iron burn on fingertip - that'll teach me to rush things)
Back to top
 
 

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
sll
Verified Member
**




Posts: 10
Re: hum problem
Reply #21 - 11/21/09 at 03:34:13
 
Alan, Dank
I used solid wire from the beginning.
Yes brown wires running in parralel with board wires.
I use two wires to separate two channels.
I don't think my board damaged.
I recognized two types of hum . first one changes with volume changel another don't. My brown wires solve first type of hum for me.
Second type been solved by eliminating ground loops.
So my picture has some ground loops and I've removed them later.
So ground from my RCA jacks connected to taper only (no connections to case or board).
So some hum left but it is audible on max volume only. Usually my volume control is around 1PM. No hum at all on this volume
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #22 - 11/21/09 at 15:06:54
 
Cheers Dank. I suspect I could get away with 1pm on the dial if my speakers weren't so flippin' sensitive! It's 11am for me ...

OK, got some solid core here - let's try ...

Did it. And yes it helps a lot - thanks guys. Still not sure why ...
Back to top
 
« Last Edit: 11/21/09 at 16:10:32 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #23 - 11/23/09 at 23:07:43
 
I have now resoldered the solid core bypass wires. What a difference!

There is now NO hum which varies with volume control. There is a small amount of background hum which is unchanging at all volume levels. This may simply be the price of tubes, and is only audible from my listening position at night (when it is very quiet), no music playing, and listening intently. So no real deal here.

Now I have the Decware permanently at full volume, and control the volume levels with my TVC. Sound is without doubt slightly more focussed this way.

I can't see why this tweak shouldn't be mentioned in the build instructions as a possible solution to try if there is hum. It's cheap, and easily reversed if it doesn't help.

Big thanks to SLL and Dank for finding and reporting this!
Back to top
 
« Last Edit: 11/23/09 at 23:12:36 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
Dean
Verified Member
**




Posts: 4
Re: hum problem
Reply #24 - 11/25/09 at 23:42:25
 
Hello Alan,

I am trying to figure out where you used the solid wire and it eliminated the minor hum when mvoing the volume above 11 o'clock?  I have the same problem.

I have to say that I really love the sound I am getting... wow.... I have recently added a ZenHead as the preamp and now I can get the volume I want .... Oh my... sooooo nice...

Thanks,
Dean
Back to top
 
« Last Edit: 11/25/09 at 23:43:53 by Dean »  
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #25 - 11/26/09 at 00:40:52
 
Hi Dean

I used wire from some solid core mains cable - fairly large gauge, and stiff copper.

Exactly where you connect these depends on how you have built your kit1. I did not use the stock RCA connectors, but put RCA connectors on the case, and wires from them to the circuit board board. So one end of each solid-core wire gets soldered to the ground of each RCA input socket.

I also used a different volume pot to stock, with wires runing to the 6 solder pads on the board. The other end of each solid-core wire goes to the two pot solder points that are at the word "taper" in the audio taper label. I actually attached them directly to the pot.

Pretty much as Dank's second photo earlier in this thread, except he used the stock pot, and attached the wires to the solder pads.

And I agree - the amp sounds fantastic!
Back to top
 
« Last Edit: 11/26/09 at 00:42:36 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
dank
Seasoned Member
****


pair of dual 18
Imperials

Posts: 275
Re: hum problem
Reply #26 - 11/26/09 at 13:57:50
 
Continued work on what's left of my hum problem reveled that the hum caused by the amp when it is in the system was indeed a "ground loop".  I was able to measure 6 mv difference between the chassis of my PC (source) and the shield of the input RCA connectors at the Zkit1.  The new 3rd solid wire in the picture reduced this to 0 mv, the lowest volt scale on my meter.  While still not totally silent, you now have to strain to hear hum from the listening chair in between songs, and this is with the Zkit1 volume set at max.  Most of the hum now is actually coming from the subwoofer amp.

The new 3rd solid wire ties the power transformer neutrals (red/yel and grn/yel) to the two other solid wires previously installed.  It did not seem to make a difference to either move the earth ground wire to the new wire (eliminating an inch or two of trace) or to jump straight to the earth connection on the AC receptacle with solid wire, so I left the earth connection unchanged.



Happy Thanksgiving

DanK
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #27 - 11/27/09 at 00:34:22
 
Tried it here, Dank. However this one made the hum very slightly louder in my amp. So I've taken it out.
Back to top
 
 

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
HT-EXT
Seasoned Member
****


NYUK NYUK NYUK

Posts: 274
Re: hum problem
Reply #28 - 12/09/09 at 20:13:30
 
I have just order a couple of these.

http://www.dcispec.com/index.html


I hope this sovles my plate amp hum but we will haft to wait and see.


HT-EXT
Back to top
 
 

" I TRY TO THINK BUT NUT'EN HAPPENS! " CURLY
  IP Logged
Evo
Senior Member
***




Posts: 53
Re: hum problem
Reply #29 - 01/10/10 at 11:56:24
 
I have just ordered this kit and wanted to check a few things before I start about the casing and how to properly ground it.

These are probably really obvious questions, but I figure it is better to ask than to go ahead and do it wrong.

1) Firstly I wanted to mount the PCB on wood. Is there any reason why I can't mount it inside a wooden chassis with the tubes poking through the wood (just like it is mounted in a metal chassis), instead of mounted on top of the wood?

2) I am planning on having the trimpot, RCA and speaker connectors connected directly to the PCB. I am thinking that the only grounding I need is i) connecting the 'GND' and the 'SHIELD' points on the circuit with a jumper, and ii) connecting the 'SHIELD' to the earth from the mains supply connection. Is this right?

3) Anything else I need to be careful about?

Cheers

Matt
Back to top
 
 
  IP Logged
Alan H
Senior Member
***




Posts: 63
Re: hum problem
Reply #30 - 01/10/10 at 13:47:45
 
Hi Evo -  re your questions

1. Would be fine - some folk have published ZKit1 pictures and have done just that. I like the scary voltages in a box.

2. Up to you - but PCB connectors mean that the force associated with connecting/disconnecting RCAs / speaker cables will be directly to the PCB. Personally I prefer to have connection forces applied to the case - some connectors are a tight fit!

Another advantage of mounting the speaker connections on the case is that this allows you to shorten the signal path: the output transformer leads can be directly attached to the speaker connections instead of having to rejoin the PCB.

For a wooden case, you only need GND to mains earth.

Let us know how you go!
Back to top
 
« Last Edit: 01/10/10 at 13:48:40 by Alan H »  

FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
WWW   IP Logged
Pages: 1 
Send Topic Print