Hey all! It's good to be back! I'm trying to actually finish my first build this summer (an 18 watt build). I have this wire with this metal braiding beneath the first layer of insulation. I have a few questions:
Where do I use this? On all wire runs between the pots and components? Between all components and tubes?
Secondly, do I solder the braided wire at both ends? Or just one? If just one, which end?
Lastly, I'm using the chassis out of a blues jr., do I just solder to the chassis, or should I drill in a grouding lug to solder to?
Thanks much for your help!
Let me know if you need clarification of my questions -- I'm a newbie, so I may not have used the right terms...
Where to use shielded wire
Moderators: pompeiisneaks, Colossal
Where to use shielded wire
I find it difficult to say "that's good enough"
Re: Where to use shielded wire
Use it from:
Input jack to V1a
Preamp volume pot to V1b (or V2a...depending on what's going on...)
Master volume pot to PI input coupling cap
Solder the ground at one end only, preferably at the input jack and at the pot (i.e., NOT at the tube end).
It worked well for me....and you've heard my amp.
Input jack to V1a
Preamp volume pot to V1b (or V2a...depending on what's going on...)
Master volume pot to PI input coupling cap
Solder the ground at one end only, preferably at the input jack and at the pot (i.e., NOT at the tube end).
It worked well for me....and you've heard my amp.
Tempus edax rerum
Re: Where to use shielded wire
> Where do I use this?
In a guitar amp: Almost nowhere.
Study drawings and photos of great guitar amp guts. Many fine amps use NO shielded cable. A lot of stuff is built with plain old hookup wire.
Your layout is much more important. If you build in a row with the weak signals at one end and the strong signals and raw power at the other end, there's little call for shielding.
I don't disagree with what dehughes says. Sometimes shielded wire IS necessary. And he's hit the highlights. But very often even these runs can be unshielded. And shielding high-impedance points (specially pot wipers) tends to suck treble. Anyway: too much work.
I just built a simple Champy-thing, no shielded wire. No audible hum or fluorescent lamp hash. Squeal above 9 cured by moving one wire by ear a half inch. More complex amps do get, ah, more complex to layout and wire, true. But try "simple" first.
> do I just solder to the chassis
HOW?
Oh, sure, Fender had a 150 Watt iron, but that only makes sense for hundreds of chassis joints. For the one or a dozen chassis hoints a DIY builder will do in a decade, it's a waste of money.
> drill in a grouding lug to solder to?
You got enough holes already. My little Champy-thing is riddled with holes: transformer mount, sockets, tagboard mounts.
Anyway, chassis is NOT ground. It can be, but that's often bad. It should be connected to ground, but ground current should not flow through it.
I have exactly two chassis grounds. Input jacks (Metal Switchcraft) and AC-Green. Bus runs from input jack shell, first stage, pots, driver, then to preamp power cap negatives, then main power cap. Power tube cathode runs to main power cap negative. No chassis ground at power caps or PT secondary; power return doesn't flow in chassis, signal return only matters for the input stage which is near the input jack. (For the plastic jax used on Marshall you need another trick.) The AC-Green wire goes direct to nearest chassis... its Prime Mission is to drain fault current from broken insulation, signal reference is secondary and trivial.
In a guitar amp: Almost nowhere.
Study drawings and photos of great guitar amp guts. Many fine amps use NO shielded cable. A lot of stuff is built with plain old hookup wire.
Your layout is much more important. If you build in a row with the weak signals at one end and the strong signals and raw power at the other end, there's little call for shielding.
I don't disagree with what dehughes says. Sometimes shielded wire IS necessary. And he's hit the highlights. But very often even these runs can be unshielded. And shielding high-impedance points (specially pot wipers) tends to suck treble. Anyway: too much work.
I just built a simple Champy-thing, no shielded wire. No audible hum or fluorescent lamp hash. Squeal above 9 cured by moving one wire by ear a half inch. More complex amps do get, ah, more complex to layout and wire, true. But try "simple" first.
> do I just solder to the chassis
HOW?
Oh, sure, Fender had a 150 Watt iron, but that only makes sense for hundreds of chassis joints. For the one or a dozen chassis hoints a DIY builder will do in a decade, it's a waste of money.
> drill in a grouding lug to solder to?
You got enough holes already. My little Champy-thing is riddled with holes: transformer mount, sockets, tagboard mounts.
Anyway, chassis is NOT ground. It can be, but that's often bad. It should be connected to ground, but ground current should not flow through it.
I have exactly two chassis grounds. Input jacks (Metal Switchcraft) and AC-Green. Bus runs from input jack shell, first stage, pots, driver, then to preamp power cap negatives, then main power cap. Power tube cathode runs to main power cap negative. No chassis ground at power caps or PT secondary; power return doesn't flow in chassis, signal return only matters for the input stage which is near the input jack. (For the plastic jax used on Marshall you need another trick.) The AC-Green wire goes direct to nearest chassis... its Prime Mission is to drain fault current from broken insulation, signal reference is secondary and trivial.
Re: Where to use shielded wire
hey guys, I just wanted to say thanks to both of you for your help! I'll probably use the shielded wire in a few choice spots (like dehughes was mentioning) -- mainly because I've already got it lying around to use. Good point though, PRR, about all the amazing-sounding amps out there with nary a shielded wire to be found...
Thanks again
Now...to the soldering pencil!
Thanks again
Now...to the soldering pencil!
I find it difficult to say "that's good enough"
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Darkbluemurder
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Re: Where to use shielded wire
PRR,PRR wrote: I have exactly two chassis grounds. Input jacks (Metal Switchcraft) and AC-Green. Bus runs from input jack shell, first stage, pots, driver, then to preamp power cap negatives, then main power cap. Power tube cathode runs to main power cap negative. No chassis ground at power caps or PT secondary; power return doesn't flow in chassis, signal return only matters for the input stage which is near the input jack. (For the plastic jax used on Marshall you need another trick.) The AC-Green wire goes direct to nearest chassis... its Prime Mission is to drain fault current from broken insulation, signal reference is secondary and trivial.
Are you saying that all your grounds run to the input jack through the bus wire? I have read that only the preamp grounds should go there whereas the power amp, speaker secondary, power cap negatives should be near the PT (but not to AC-Green).
The reason I am asking is that I have one humming Marshall JTM 45 RI where no grounding scheme I tried so far got rid of it (amp has new caps, tested with several tubes) whereas I did not have such problem in any other amp I worked on.
thanks Stephan
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David Root
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Re: Where to use shielded wire
The principle is that a single chassis ground point, whether it be thru an input jack shell or direct to chassis off the buss, minimizes ground loops, and if you wire the cap grounds, OT PT and PI correctly, there is no possibility of ground looping under normal conditions.
As to that single chassis ground point being at the preamp end or the power supply end, the preamp end seems to be the best insurance. I like to balance the heater load at the preamp end too, so it works out well for me.
Having the single ground point at the power end seems intuitive (low currents run into higher currents) and I've seen this advocated, and done it myself in the past, but as PRR says the power return itself doesn't run in the chassis.
As to that single chassis ground point being at the preamp end or the power supply end, the preamp end seems to be the best insurance. I like to balance the heater load at the preamp end too, so it works out well for me.
Having the single ground point at the power end seems intuitive (low currents run into higher currents) and I've seen this advocated, and done it myself in the past, but as PRR says the power return itself doesn't run in the chassis.
Grounding
Asked in private, but I'm sure it was meant to be public where ALL would benefit:
> since I am using isolated input jacks (though they are Switchcraft). I am building a 'Wreck and planning to use your grounding technique, not having ground current go through the chassis. I will have a bus that runs behind the pots (not ON the pots) and wire all circuit grounds to this point. Will I need to run the input jack to the chassis? Will I need to run the input-jack end of the bus to the chassis? Or should I not ground ANYTHING to the chassis?
Bond ground bus to chassis at ONE point. If no other hardware (such as metal speaker or reverb jack) forces your decision, near the input jack is good.
Bond wall-outlet ground to chassis at another point.
> where do you ground the heater center tap (or artificial tap)?
Shouldn't matter. If it does, you have a problem, perhaps a tube with very leaky heater-cathode insulation.
> since I am using isolated input jacks (though they are Switchcraft). I am building a 'Wreck and planning to use your grounding technique, not having ground current go through the chassis. I will have a bus that runs behind the pots (not ON the pots) and wire all circuit grounds to this point. Will I need to run the input jack to the chassis? Will I need to run the input-jack end of the bus to the chassis? Or should I not ground ANYTHING to the chassis?
Bond ground bus to chassis at ONE point. If no other hardware (such as metal speaker or reverb jack) forces your decision, near the input jack is good.
Bond wall-outlet ground to chassis at another point.
> where do you ground the heater center tap (or artificial tap)?
Shouldn't matter. If it does, you have a problem, perhaps a tube with very leaky heater-cathode insulation.
Re: Where to use shielded wire
Let me see if I got this right, if I follow this method than I won't need the typical "ground point at the power transformer bolt", it's all basically connected to the bus wire except for the mains AC ground and the heater center tap?
PRR is this what you were describing?
[img:800:440]http://i40.photobucket.com/albums/e217/ ... ounds1.gif[/img]
thanks
PRR is this what you were describing?
[img:800:440]http://i40.photobucket.com/albums/e217/ ... ounds1.gif[/img]
thanks
Re: Where to use shielded wire
My grounds are similar to the way PRR described and I have minimal hum. Read what Aiken says about grounding http://www.aikenamps.com/. Also if you have a logon to the Dumble Discussion forum, search on grounding. Be aware also that hum can be caused by more than just bad grounding. Forum member Drz400 has some good ideas too about dc heaters if you are really fanatical about getting all the hum out. There are lots of variations on grounding.
riscado - I would not solder a buss wire across the pots. This defeats the idea of one attachment point to the chassis. You should float the buss above the pots. Attach the pot grounds to the buss with heavy guage wire and the pots will hold the buss in place, or use an insulated standoff to the chassis.
riscado - I would not solder a buss wire across the pots. This defeats the idea of one attachment point to the chassis. You should float the buss above the pots. Attach the pot grounds to the buss with heavy guage wire and the pots will hold the buss in place, or use an insulated standoff to the chassis.
Re: Where to use shielded wire
Hmm, but that's precisely what Meister Fischer did?Tonegeek wrote: riscado - I would not solder a buss wire across the pots.
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skyboltone
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Re: Where to use shielded wire
I'm just finishing up this little guy. I've had no luck at all trying to solder a buss wire to the back of a Alpha or even Clarostat pot. This is of course a point to point build but the principle should be just as simple to implement with a board build. The buss wire is supported by the connections to components. Pots, jacks, even an odd unused tube socket pin. This chassis is tiny! 5 1/4" by 10 1/2". There is NO shielded wire and NO hum or hash. It is quieter than my old Dynaco PAS 3X. The buss wire is available from Michaels crafts store for about $2 per 10 feet. It's silver plated number 14 copper. I've taken the chassis lug off at the input end. It was just there to hold things in place while I soldered it up. The important thing to remember is that signal should not cross back over itself. So, if you need to locate a component a ways from where it's characteristics are being used, run the ground back to where it belongs on the ground buss.
[img:800:600]http://i14.tinypic.com/6fzh8ix.jpg[/img]
[img:800:600]http://i14.tinypic.com/6fzh8ix.jpg[/img]
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Where to use shielded wire
Tell you the truth I'm a bit confused now...
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skyboltone
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Re: Where to use shielded wire
Build without the tone sucking shielded wire. Then, if it howls, add first to the input jack at V1, then down the line as instructed in the earlier post. The object of the game is not to use it unless the amp is unstable without it.riscado wrote:Tell you the truth I'm a bit confused now...
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Where to use shielded wire
ok maybe I didn't explain myself too well... I always build without shielded wire, I usually mess with the leadress/layout if I have a problem, and completely go over the whole amp, in case that doesn't solve it... I'm not fond of shielded wire!
With that said, I don't understand the grounding solutions presented here...
I've always seen buss wires being soldered to the back of pots, even fender and Ken Fischer did it for years, but now I read that only the jack and ac-ground wire should be connected to the chassis, so I'm trying to understand why... So could you please look at the schematic I modified from the original Hoffman "grounding for comun amps" and tell if you see any flaws (besides the buss and pots thing), and maybe explain to me a little bit better why this method is better.
This is an honest question, no pun intended, I really haven't been able to understand...
thanks for your time and patience
With that said, I don't understand the grounding solutions presented here...
I've always seen buss wires being soldered to the back of pots, even fender and Ken Fischer did it for years, but now I read that only the jack and ac-ground wire should be connected to the chassis, so I'm trying to understand why... So could you please look at the schematic I modified from the original Hoffman "grounding for comun amps" and tell if you see any flaws (besides the buss and pots thing), and maybe explain to me a little bit better why this method is better.
This is an honest question, no pun intended, I really haven't been able to understand...
thanks for your time and patience
Re: Where to use shielded wire
In what section? I tried floral and jewelry, and the best I could find was #18 for more$.skyboltone wrote:The buss wire is available from Michaels crafts store for about $2 per 10 feet. It's silver plated number 14 copper.
I've been making my own buss wire. All I could find was #24(?) silver/copper at RS, so have been twisting them, 4 in a bundle. Cut 4 pieces to 12 in or so, put one set of ends into a drill chuck. Tighten so they are bundled together in the very center. Grab the other ends with a set of pliers and let the drill do the rest. Solder flows real well into the craniliated surface.
Works great for heater wires too. Very neat.