Amp shielding

Tube or solid-state, this section goes to eleven!
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sinner
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Post by sinner »

So, I'm working on an amp, it's hi-gain single channel simplified SLO, and I was thinking to use shielded wire in few spots. On what parts of the circuity I should focus on? I know input jack wire is highly recommended, but what's about the rest of the circuit? Can I connect the shield simply to chassis star grounding, or should I use specific method?

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Post by phatt »

Hi chum,,, I could try but frankly I'd just confuse the issues :block: Better if you download the *Grounding PDF* at *merlin's Valve Wizard* site.
Read it then if you don't get it read it again. :scratch:

I know a fair bit about grounding but I learned even more by reading his PDF. :thumbsup

So A big thanks to Merlin B from Me.
Phil.

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Post by KindaFuzzy »

I use Merlin's grounding scheme religiously. The most important wires are the ones attached to the grids of the preamp tubes, so anything from pins 2 or 7 of a 12ax7 to the coupling capacitor are the most vulnerable. I do the grid wires of the power tubes too if they're going to be long. Most times I just ground the shield wherever it's convenient, like on the volume pot ground, or on the turret board near where the wire is attached.

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Post by sinner »

Thanks boys! I knew Merlin site, it was linked to me many times, good read AFAIK, it must be if I understand nothing ;)

@Kindafuzzy - I've seen 2 and 7 pin connection shielded in few amp guts, specially in V1 and V3. I'll do that. Volume knob is often shielded as I've seen, so thanks for confirmation what I suspected ;)

Any of you heard about Larry star grounding method BTW? Any opinions?

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Post by Dr Tony Balls »

Im setting up for an OR120 build and was also told to shield the NFB runs by the resident Orange expert over on the Weber forum.

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Post by KindaFuzzy »

Dr Tony Balls wrote:Im setting up for an OR120 build and was also told to shield the NFB runs by the resident Orange expert over on the Weber forum.
Really, eh. I've never heard of that, but it makes sense to avoid positive feedback.

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Post by Dr Tony Balls »

KindaFuzzy wrote:
Dr Tony Balls wrote:Im setting up for an OR120 build and was also told to shield the NFB runs by the resident Orange expert over on the Weber forum.
Really, eh. I've never heard of that, but it makes sense to avoid positive feedback.

me neither, but so sayeth this dude. I might try it unshielded first just to see.

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Post by timbo_93631 »

This is what I have stuck to:
If you are going to run shielded wires on the input you need to ground the end at the jack, but not at the tube socket. Just cut the shield cleanly at the socket end and heatshrink it, something I learned from building 18 watt marshalls. Star grounding works, and is reccomended on high gain amps. I like to make a ground buss on my turret board out of bare romex (the stuff in your walls at home) and attach all grounds to it, then take one lead to the star ground where the PT and filter caps are grounded as well. Whether you are using an IEC or a regular 3-wire power cord, ground it as close as possible to where it enters the chassis, not on the star ground.
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Post by ppluis0 »

Hi Sinner,

You also need to determine where the ground star is relative the filter capacitors and especially the relation of the first cap to the rectifier.

Take a look at this link. Was always useful to me: http://www.geofex.com/article_folders/s ... targnd.htm

Cheers,
Jose

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Post by DrNomis »

That's a really good article from RG Keen, a must read.... :thumbsup
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Post by DrNomis »

phatt wrote:Hi chum,,, I could try but frankly I'd just confuse the issues :block: Better if you download the *Grounding PDF* at *merlin's Valve Wizard* site.
Read it then if you don't get it read it again. :scratch:

I know a fair bit about grounding but I learned even more by reading his PDF. :thumbsup

So A big thanks to Merlin B from Me.
Phil.

I just went to Merlin B's Valve Wizard website and bookmarked it, going to do some serious reading of the articles, cheers for the recommendation.... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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Post by timbo_93631 »

Blencowe knows his stuff.
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Post by phatt »

DrNomis wrote:
phatt wrote:Hi chum,,, I could try but frankly I'd just confuse the issues :block: Better if you download the *Grounding PDF* at *merlin's Valve Wizard* site.
Read it then if you don't get it read it again. :scratch:

I know a fair bit about grounding but I learned even more by reading his PDF. :thumbsup

So A big thanks to Merlin B from Me.
Phil.

I just went to Merlin B's Valve Wizard website and bookmarked it, going to do some serious reading of the articles, cheers for the recommendation.... :thumbsup
Turn a schematic upside down and look at the *Ground Plane as Now Being the Positive Potential* :shock: :shock: :shock: :shock:
Then Hopefully you will see just how important the Ground plane is :scratch: :hmmm: :scratch: :hmmm:

As far as the AC signal,, (stuff you actually hear) the DC positive is just another ground plane. Oh Crap now we are back to Z stuff ,,, yuk :blackeye
Phil.

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Post by DrNomis »

Yep, that's why some circuits, if they're not properly designed and laid-out, will tend to motor-boat when the gain/volume control is turned up..... :thumbsup
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Post by defaced »

Having a touch of experience with this circuit (I'm a moderator on the SLO Clone forum), the minimum you can shield is the input, and the connections to/from the gain pot. If you are including the FX loop, the wiring to/from the send/return jack is also shielded. The rest will work just fine unshielded. Now if you want to shield more, that's up to you, but you really only do much good shielding grid connections. Just remember to watch for ground loops, and the low impedance side of the shield gets grounded.

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Post by sinner »

Thanks, I'm sure SLO fanatics are the people I should talk about my little project.

I'm still reading Merlin's site, I'm going to get his books as well.

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