stereo output....hummmmmm

[Eric Banjitar]

Hello everyone!

I have questions about wiring.  What I wanted was two outputs on my guitar. The first signal is from the electric side.  It has a Loller single coil and an EMG hz passive pu.  The EMG is coil-tapped from the pot. The loller also has its own volume pot. There are no tone controls. The second output is for the just installed new piezio acoustic pickup (Schatten bj02). It goes through a volume pot and then to output.  The output is a stereo cable with the electric side active when inserting a mono cable. Both signals run through the same cable to a splitter box (stereo to mono).  The electric side then goes through a vocalizer/tuner pedal and then to a Fender Hotrod deluxe.  The acoustic side goes through an a pocket rocket and sonic maximizer on its way to an acoustic (ac60) amp.

I am now having two problems:

First the acoustic side volume pot does not work well.  I have read that the 250K pot (I think that is what is in it) will not work well unless it used with a preamp/buffer circuit. I would rather not go active. Are there other options that would allow for volume control on-board the guitar? If not, the pocket rocket (way to big for a pocket, but comfortable on a mic stand in front of me) allows this.

Secondly, I am getting a hum from the electric side that is not present when I am not using the acoustic side. The hum only effects the fender amp. Could it be a difference in impedance causing this? Could the hum be caused by sharing the grounded leg of the stereo cable?

Would it be best to run two mono cables? 

Thanks for all of the support!

Eric Banjitar

 

[line6man]

It is extremely preferable to buffer a piezo signal, for two reasons.

Number one, it is a very high impedance signal. You don't want to deal with noise, and signal degradation from the parasitic capacitance of your guitar cable, nor the fact that most amps have a 1M Ohms-ish input impedance, which is a rather direct load for a high impedance signal like that of a piezo system.
Number two, you cannot combine piezo and magnetic pickups passively, as there is an extreme impedance mismatch which will likely cause the resistance of the magnetic pickups to load down the output of the piezos.

250k Ohms is far too direct of a load for a volume pot. You will likely need something several million Ohms or higher, if you want to stay passive, but as I said, that's not desirable. It is a much better idea to simply buffer both the piezo and magnetic signals, that way they can be combined without issue.

And FWIW, I've never heard of tapped EMGs. Are you sure they aren't simply four-conductor humbuckers?

 

[Eric Banjitar]

Thanks line6man!

The EMG Hz is a four wire humbucker. It is coiltapped with a push-pull volume pot.  I am not an electrician or a luthier, just a hobbiest. The coiltapping completely changes the tone, I dont know how. 

So... an onboard FET preamplifier and buffer circuit would allow for better tone.  The way it is set-up works now, and I like the tone, my only problem is the buzz made on the electric side and the lack of volume control on-board for the piezio.  The buzz is not noticable while the band is playing, only when we stop playing.

Any other ideas?

 

[line6man]

Thanks line6man!

The EMG Hz is a four wire humbucker. It is coiltapped with a push-pull volume pot.  I am not an electrician or a luthier, just a hobbiest. The coiltapping completely changes the tone, I dont know how. 

So... an onboard FET preamplifier and buffer circuit would allow for better tone.  The way it is set-up works now, and I like the tone, my only problem is the buzz made on the electric side and the lack of volume control on-board for the piezio.  The buzz is not noticable while the band is playing, only when we stop playing.

Any other ideas?

That's coil splitting. Tapping is done with pickups specially wound with taps partway into their windings. Splitting is simply changing from series or parallel to single coil, or, though less accurate to the term, to switch from series to parallel.

I don't know that a buffer would give you a better tone or not. A good buffer should be transparent. On the other hand, you will have a constant input impedance, so the piezos will always sound the same, regardless of what you combine them with, or play into, and the input impedance won't load against the piezos as much.

What sort of buzzing are you hearing? Is it a grounding issue? 60Hz hum? Electric field noise?

 

[Cagey]

It's a Lollar single coil. It's going to make some noise no matter what you do. It's not Lollar's fault; it's the nature of the beast. Your only real defense is to get to know your volume control. Knock the thing down to zero when you're not playing, and it shouldn't make any noise at all.

 

[line6man]

It's a Lollar single coil. It's going to make some noise no matter what you do. It's not Lollar's fault; it's the nature of the beast. Your only real defense is to get to know your volume control. Knock the thing down to zero when you're not playing, and it shouldn't make any noise at all.

No, since he may be buffering the pickup, perhaps it would be worthwhile to experiment with dummy coils. There would be no interaction of the coils' LCR since they would be buffered from each other.

Or, he could just get a humbucker or something if it's a serious issue. We don't know that this is 60Hz hum yet, though, it could be something else.

 

[Cagey]

I'm just talking about how it sits now. The single coil is certainly the noise source. I didn't consider adding coils or changing pickups to get away from that problem as I assumed he chose the Lollar for its particular characteristics.

If we're allowed to reconfigure the instrument, then you're right. There are numerous options.

I haven't heard them yet, but I'm holding out high hopes for GFS' latest, the "Tru-Coil" design. This video review will give you an idea of what to expect. Very single coil-ish sound.

I bought a set for the Tangerine Strat, but I'm still dinking around with it so I haven't heard them in real life.

It's obviously a stacked humbucker...

...but the second coil is smaller. I don't know if they use lighter gauge wire or less of it or what, but there it is.