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Earth, ground-plane, shield question (Read 3918 times)
Alan H
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Earth, ground-plane, shield question
06/26/09 at 08:58:54
 
Almost finished the kit, detailed feedback shortly .... however, I am a little confused about exactly what attaches where re the shield, ground plane and earth. Donn't want to get this wrong!!

Mounted on aluminium sheet. Plan to connect the Chassis Ground point on the circuit board to a power transformer bolt, and a second wire from the same bolt to the earth connector of my power supply.

Sound OK?
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Steve Deckert
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Re: Earth, ground-plane, shield question
Reply #1 - 06/27/09 at 00:40:43
 
Sounds OK.

-Steve
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sebrof
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Re: Earth, ground-plane, shield question
Reply #2 - 06/27/09 at 14:40:34
 
FWIW - The grounding was the most (the only, actually) confusing part of the build.
I connected the ground pin from the IEC connector to the gnd point on the circuit board. That's the only ground I did.
It works, so I guess it was the right way to do it.
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Alan H
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Re: Earth, ground-plane, shield question
Reply #3 - 06/27/09 at 16:09:12
 
Finished ... passed smoke test ... voltages within range ... music!

Heard enough (last 4 hours) to know that this amp is something special ... details later.

But constant and significant background mains hum R+L. None at zero volume, progressive rise with volume, no change when I touch the pot shaft, nor the chassis. So sounds like mains interference getting into the signal inputs. Or ? grounding.

Not sure where to start re the hum. Do I screen my input leads? These are about 8cm long and pass between the output transformers to the circuit board. They attach where the kit connectors should have been.

Or do I shorten the output leads from the mains transformer which describe a kind of loop before attaching to the circuit board.

Or do I detach my grounding from the chassis and put is straight to mains earth as per sebrof (prev poster)?

Suggestions?

Sebrof - can I presume your amp is quiet?
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« Last Edit: 06/27/09 at 16:43:46 by Alan H »  

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Steve Deckert
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Re: Earth, ground-plane, shield question
Reply #4 - 06/27/09 at 19:29:39
 
Your input wires from the input jacks to the spot on the circuit board where the jacks would have been should be shielded with the shield connected at the input jack.  The input jack ground should go to the ground point of the original jack locations on the board.  

The earth ground from the IEC connector to the ground on the board is correct.  If a chassis is metal it should be grounded at either the IEC connector or the ground point on the board, whichever gives the least noise.

Make sure the case of the volume control is grounded to it's own ground pins, or if in a metal chassis, the chassis will provide the ground for the case.  The case is actually a shield.

Steve
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Alan H
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Re: Earth, ground-plane, shield question
Reply #5 - 06/29/09 at 15:34:57
 
Chasing hum, what fun  >:(

Fitted a temporary, grounded, screen the length of my input leads. No improvement - removed it (for now).

Rewired chasis ground to chassis / iec earth pin using various arrangements. No difference.

Shortened all transformer leads to minimum length. No difference.

At this point (blush) I disconnected my inputs and switched on again. Ah - a difference. Amp silent to half volume, then sudden onset of irregular valve noise - jittery, slightly whistling sound.

The reason I had not done this before is that my other valve amp, and my T-Amps were silent, and this was just a drop in. Seems they filter out the noise somehow.

OK - external problem. Disconnected most of the chain, leaving just input from the DAC straight into the Kit1. Sounds good - but the Kit1 volume very sensitive (must check the Beresford DAC output specs, but I'm pretty sure they weren't higher than 2). Maybe just my efficient giant horns with no power-sapping crossover. Volume levels seriously staggering for 1.8 watts (8ohms) what was I worried about. My daughter just in from other side of the house complaining it was disturbing her playing Guitar Hero!

Anyway, hum now acceptable, and not intrusive from listening position. But can't go on like this, because I need more inputs, and these are on the TVC ... so major tidyup of wiring. Reconnect chain. Run things with TVC volume high and Kit1 volume low. Much better.

Must look at house earth.

Amp still burning in ... listening impressions to follow, including A/B comparison with Charlize+Auricaps. Should be interesting.
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Alan H
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Posts: 63
Re: Earth, ground-plane, shield question
Reply #6 - 07/01/09 at 00:35:48
 
Re-reading the instructions, twice it says to be sure to connect the "board ground" and the "shield" together with a short jumper wire. It says there is no specific location for this jumper.

(This is IN ADDITION to connecting the "ground plane" to the "ground lug of the power cord" - which I have done, and which was already discussed in this thread)

So I have therefore still to put in  the ground - shield jumper, and am not sure where to put this.

Help please?
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sebrof
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Re: Earth, ground-plane, shield question
Reply #7 - 07/01/09 at 03:07:41
 
Alan - Wish I could help more, I didn't have any issues with hum. To answer your question (sorry I missed it), my amp is very quiet. My 104db Klipschorns only have a slight hum at about 1:00 on the volume. That's about as quiet as one can expect from any tube amp I would suspect. More quiet than a Jolida I had when I first had the Klipsches.
My kit is not in a case, isolated from the sheet metal it sits on (may as well be sitting on wood, electrically speaking).

The only ground I did was to connect the third pin of the IEC connector to the circiut board connection (I believe was labelled gnd, the only open spot where the other power transformer wires go).
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Alan H
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Re: Earth, ground-plane, shield question
Reply #8 - 07/01/09 at 23:33:14
 
Thanks, sebrof. I am seriously looking at earthing rods now.

With the TVC full up (1:1) and using the Kit1 Pot, the hum is insignificant, and I am very happy till I get my earthing sorted out.

I am utterly delighted with the sound quality! I had expected it to struggle with presenting Massive Attack or Garbage with any authority but not a bit of it. Sorry Charlize, you have been bested - the improvement is marked across all musical genres - classical and jazz are simply enchanting. And this is NOT valve euphony (which I hate), it is transparency, imaging and speed. I thought the Charlize was good ...

On hols soon, once I am back I will put the photo record of my build on my website, and report in detail my impressions from my reference and torture tracks.

And I can already feel some Auricaps coming on.  :-/
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« Last Edit: 07/01/09 at 23:35:27 by Alan H »  

FLAC via Ethernet-over-Mains
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Hasafraker
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Re: Earth, ground-plane, shield question
Reply #9 - 07/08/09 at 16:00:16
 
Finished mine last night, at about 2 oclock on the dial if I put my ear right up to the speakers I can hear a little hum, otherwise this thing is dead silent. So far... I'm in love. Though I will need to upgrade my speakers to something more efficient. Granted my current Klipsch Synergy B2's are 92db@1w I tossed some GEM at it this morning that has some really deep bass and the amp struggled with it if I turned it up past the 2 oclock position. Down to 1 oclock no problems and reasonable volume, this thing is awesome. After I get some more hours on it, I'll have to connect it up to my pre and see how things change.
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Alan H
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Re: Earth, ground-plane, shield question
Reply #10 - 07/17/09 at 12:42:24
 
Just to wind up this thread, turns out that the newer boards do not have the full shield, so a simple ground to earth (and chassis if metal) will be sufficient. (And vol pot case grounded too) as per Steve's post early on. Thanks for all the input.
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« Last Edit: 07/17/09 at 12:43:34 by Alan H »  

FLAC via Ethernet-over-Mains
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