Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: J Rindt on January 27, 2011, 04:09:46 pm
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Maybe I did not search thoroughly enough.....I know this has been discussed many times. Anybody have a link that addresses the general use (when and where) of shielded cable in a guitar amp.?
Thank You
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Most people use it from the input to the first stage. You can use it on any wire that caries signal but remember that it has capacitance and will change your tone if you get carried away. Only ground the shield on one side. Not much else to it. I would just use it from the input to the first stage unless you need to cure some parasitic problems.
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...I would just use it from the input to the first stage...
That's what I'm doing on my build just because that's what I've read around here but I'd like to know the theory behind this. Is it just because the signal level is so small at this point that it needs more protection from noise than in later stages?
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...I would just use it from the input to the first stage...
That's what I'm doing on my build just because that's what I've read around here but I'd like to know the theory behind this. Is it just because the signal level is so small at this point that it needs more protection from noise than in later stages?
Yes, but not always. A high gain design, those rules go out the window. The signal can be so large in later stages with a high gain design that the signal can be imposed on another near by grid or even on a plate wire. I always do the input and any long length of grid wire like from volume pots to a grid pin. If I can't make that grid shorter, it gets shielded.
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Thanks....I guess I am wondering if it is normally used to the grid of a tube. From the input jack to the first grid would be classic, but I was wondering about other situations, like from a volume pot to a grid.....
Thank You
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I think a good approach is to add shielded cable only when it's needed. For example, I've added it to Blackface Fender circuits for the leads to and from the reverb pot. It's a very small signal - even smaller than the guitar input IIRC. Some amp builders use shielded cable from the volume pot back to the grid of the stage following the tone stack. Again, a small signal.
I believe that some amp builders use shielded cable instead of practicing good lead dress. IOW keeping high current/voltage leads away from and perpendicular to sensitive, low voltage leads, etcetera.
Personally, I think you would have to have yards of shielded cable in an amp before you experienced loss of high end due to capacitance but a lot of guys think otherwise.
Cheers,
Chip
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I use George L cable. That pretty much takes care of the capacitance problem. If you have room, Dave Allen (Allen Amplification) takes care of the problem by putting the first tube right up be the input. That solves the problem. I never have enough real estate since my whole design criteria is "small and light". Don't laugh, when you're 61 with a bad back, you'll be doing the same thing!
Dave
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I think a good approach is to add shielded cable only when it's needed. For example, I've added it to Blackface Fender circuits for the leads to and from the reverb pot. It's a very small signal - even smaller than the guitar input IIRC. Some amp builders use shielded cable from the volume pot back to the grid of the stage following the tone stack. Again, a small signal.
I believe that some amp builders use shielded cable instead of practicing good lead dress. IOW keeping high current/voltage leads away from and perpendicular to sensitive, low voltage leads, etcetera.
Personally, I think you would have to have yards of shielded cable in an amp before you experienced loss of high end due to capacitance but a lot of guys think otherwise.
Cheers,
Chip
I hear that a lot (loss of high end), but what about the 15 feet of guitar cable.?
Is that a different story.??
Thanks
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I use George L cable. That pretty much takes care of the capacitance problem. If you have room, Dave Allen (Allen Amplification) takes care of the problem by putting the first tube right up be the input. That solves the problem. I never have enough real estate since my whole design criteria is "small and light". Don't laugh, when you're 61 with a bad back, you'll be doing the same thing!
Dave
I've got a ways to go to reach 61 but small and light is what I'm going for too. That's part of the problem in a way because with my cramped chassis I'm finding it hard to implement proper lead dress. I won't know if it's a problem until I get it up and running (very soon).
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JR - yes, you can hear loss of high end in guitar cable. That literally is "yards of cable". You don't have to pay hundreds of dollars per foot for "pure oxygen free copper with unobtanium shielding", but you will hear more high end and more clarity with a good guitar cable. I was surprised but convinced after doing some serious A/B/C testing.
Hoffman sells the George L components to roll your own - don't even need to warm up your soldering iron!
Cheers,
Chip
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I can definitely hear loss of high end in a guitar cable. Of course, I'm an audio engineer so I certainly hope I can hear things like that but I think anyone would notice the difference between plugging in with my normal guitar cable (the Whirlwind I've been using for almost 20 years) and say a good wireless unit. There is a clear difference but I don't really consider it a problem. I kind of like the high end roll-off and prefer it to the problems that can sometimes come up when going wireless.
As for George L cables - way too expensive for me. Besides, I don't think they were using them on any of the great old records that I love the guitar sounds on.
Excessive amp noise, however, I can do without so I might have to try some more shielded cable if it seems like it might help.
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...There is a clear difference but I don't really consider it a problem. I kind of like the high end roll-off and prefer it ...
So did some of the great tone masters of the past: Clarence White, SRV, Jimi Hendrix. They all used those long curly cords. Talk about added capacitance in the signal.
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Although I love the George L cable, I DON'T love those plugs! I use Switchcraft. They don't pull loose at a gig. As far as the roll-off, well, I have a treble control that works just fine. With a treble control, you get to choose. With a cheap cord, you're stuck with what you get. I don't think SRV or Jimi Hendrix really had a choice. They didn't survive long enough the reap the benefits of the technology. Also, no matter how great they were (and they were), they were just guys with opinions. Remember, like a**holes, everyone's got one!
I love a thread where I have an opinion. Facts are useful but opinions are fun!
Dave
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More opinions... I know this is 'third hand' info but this is from an interview with Cesar Diaz:
"Anyway, I took these cables we got to Stevie and he said, “I hate these things.” I asked him, “Why, man, they’re
the best cables in the world?” He said, “They pass to much electricity.” Those were his exact words, and I’ll never forget
it as long as I live. “They pass too much electricity.” Yeah, so he sent me out to the local Radio Shack and told me
to buy every gray coil cord they had – not the black ones, only the gray ones. And I thought, “Hhmm, this freakin’ hick
from Dallas is telling me this?” I got them and ran them through my capacitance meter and found out that they added
like almost .05 mfd to the signal chain. That made it sound solid – it was like having a tone control, and the brightness
and harshness that the Marshalls had was eliminated. There isn’t a single picture of Hendrix…back then they already had
high-end cables, but there isn’t a single picture of Hendrix where you see him playing with a straight cable..."
From: http://www.tonequest.com/pdf_pubs/samples/TQRDiaz.pdf (http://www.tonequest.com/pdf_pubs/samples/TQRDiaz.pdf)
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> what about the 15 feet of guitar cable.?
Is that a different story.??
Yes.
You MUST cut the top of an electric guitar. A naked steel string has nasty upper harmonics.
The speaker designer cuts everything over 3KHz or 6KHz off your output.
The pickup designer works with the cord capacitance to put a peak/drop somewhere in the 2KHz-8KHz range.
All of this is empirical. The pickup winder tries various designs, tries them at the bench, sends a few out to friends, and puts the most-accepted designs into production. Nobody seems to publish cutoff data, and it varies depending if you use a 3-foot Mr Tee fat-foam cable or Radio Shed's chokers. But on average over many players, the cut-offs come out useful.
With these two steep and ear-approved cutoffs in your chain, you generally do not want much additional treble loss inside the amp (except on distorter stages). However most nodes in an amp have 100pFd parasitic, 4 inches of coax is another 10pFd, so short lengths are a non-problem. However don't expect to send your treble pot wiper signal around the amp and back without any treble loss.