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Re: push pull front end (again)


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12/17/2003 11:55 PM
Enzo
Re: push pull front end (again)
If you put the ground of the guitar to one of the input grids, then the entire grounded part of the guitar becomes a giant antenna for the amp. Think hum and noise.
 
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12/18/2003 5:14 AM
kalen

but the other input grid will have the same ammount of noise going to it, so it will get cancelled out. right?
 
12/18/2003 3:37 PM
kg

it won't, because the -ve lead from the guitar is used as a ground for the strings, bridge, pot cases, knobs, and shield in your cable.  
 
your noise signal will not be very common mode as a result and will not cancel.  
 
ken
 
12/18/2003 7:01 PM
andy fuchs
Re: push pull front end (again) Les Paul's Guitars
Les Paul's guitars are low impedance, but single ended. The pickups require a transformer which matched the low impedance up to a high impedance, when used with a traditional guitar amp. You can plug the guitar directly into a 600 ohm mixing console mic input (single ended) and it sounds exceptionally clean and quiet. It does have a very low output level compared to a humbucker, but is not prone to noise pickup. You run can run the guitar wire alot longer (and use the matching transformer at the amp) and have no loss in signal quality. The solid state Gibson Les Paul amps actually had a low impedance single-ended input on them. I own one of the Les Paul Recording type guitars, and it's pretty cool, although super-heavy.  
 
My guitar idea was an actual balanced coil in the pickup. A center-tap, driving a balanced input, which (it would appear) should be a really low noise way to make a pickup. It would be almost like an "active humbucker". I don't know if EMG or anyone else making active pickups does this already, but I think it would be pretty cool to try. You can't put a single ended signal into a balanced input (as mentioned in anothe post) as you don't get the noise cancellation of a truly-balanced input setup.  
 
The advantage of balanced inputs is the signals are 180 degrees out of phase, going into inputs that are also 180 degress out of phase. In theory, the noise (hum) is in-phase on both wires, while the signal is not, so you cancel the noise, and end up with only a noise-free signal.
 
12/18/2003 7:46 PM
Shea

Thanks for the info, that's interesting.  
 
Couldn't you try your idea with a common humbucker with a 4-conductor lead?  
 
Shea
 
12/18/2003 10:10 PM
Matthew Springer

Forgive me Andy, maybe I'm missing something but wouldn't the EM stuff picked up by the pickups themselves still be effectively single ended? Or is this scheme just to elminate post pickup noise?  
 
You -would- cancel out anything that's not picked up in the pickup (i.e. you wouldn't need to shield the guitar itself), but the coil itself would still be a source of noise. You actually don't need a center tap, it's probably alot easier to use two resistors to (but they'd need to be big suckers) just like a balanced center tap heater. It's a whole lot easier to make a normal pickup than a tapped pickup. long as the resistor are big relative to amp input impedance (say 600ohms), bob's your uncle.  
 
To a single coil, the string vibrating is equally valid signal as the EM coming in. Splitting the coil in the middle still wouldn't give you anything to reference the outside EM against relative to the string signal.  
 
The only true single coil pickups that have some sort of reference for noise is the double half coil where it's basically balanced for noise pickup on every other string or three and three (ala a PBass pickups).
 
12/18/2003 10:17 PM
Matthew Springer
Never mind, I'm an idiot
Andy,  
I just figured out the point. The guitar coils see a 600ohm balanced load, so they're basically low impedance which makes the effective noise go through the floor becuase they make much crappier antennas at 600ohms than they do at 1M.  
 
Does the lower impedance load affec the effective string sensitivity? I would guess not because that's a true lenz's(?) law magnetic flux problem separate from a radiation/IF issue.  
 
This is an intruiging idea after all... hyper low noise single coils....  
 
-Matthew
 

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