Piezo with older GraphTech preamp an passive magnetic blend

[jimcorliss]

I have an older Piazo with preamp board from GraphTech (FAAS =Fat butt Acoustic Sound). I removed it from my wife’s Tele and going to install it in mine. I had connected the outputs from the passive mag pickups and had wanted to have a blend of both types. There was a push pull pot that was set so that the ground to the mag volume ran through the push pull and when the switch was pulled up it disconnected that ground and completed the circuit for Battery negative to the preamp. I don’t recall why it was wired this way but was probably from GraphTech. Anyway the magnetic vol control still worked with the piezo turned on but no piezo would be heard until the piezo volume got to about 8 which is where the piezo would be heard and overpower the magnetic sound. Essentially I could have one pickups sound or another but never did the separate volume controls give me a spot with both pickups sounds. The Piezo vol pot was 500k.

guitarnuts2.proboards.com/thread/4595/active-pickup-blender-volume-module

I found this thread searching for a solution and want to see if this buffer circuit from John will be the answer for this. It would be ideal to have 2 volume controls, one for piezo and the other for passive magnetic. I ordered some JFETs to try this out. Any help appreciated!

[sumgai]

jimcorliss,


I had a Strat with a Ghost system for several years, and the value of its Vol control was only 10K. In most Piezo control designs, 10K to 20K is par for the course. Only once have I seen that control come in at 50K, but that's pretty uncommon.

If you've got a 500K control, I'd question just why that might be so. If possible, shunt the control with a 100K resistor, or a lesser value (whatever's on hand at the moment will do for this experiment), and see what happens.

HTH





sumgai

[JohnH]

This thread was my take on mixing puckup actively

guitarnuts2.proboards.com/thread/4595/active-pickup-blender-volume-module

Best to add a buffer to a magnetic pickup before blending with an active piezo system.

[jimcorliss]

This buffer has 2 inputs but one pot … I have pots for both preamp and magnetic and don’t want to have 3 volume controls… would this perhaps replace one of the controls I have ?
Separate would seem better. 

[jimcorliss]

I found your response to an earlier thread doable where you took the magnetic volume center lug for the input to your circuit and used the blend circuit you’ve developed to add in as much piezo as you would want … in that thread you have the preamp you developed so I’m not sure which is being “buffered”. 

here is a copy of your explanation which I seem to understand and am not sure I understand where to start . 

You had responded back then : 


“What you describe should work out fine. On the circuit diagram, the signal source labelled as 'magnetic', feeding into C2 and transistor Q2, actually represents the output from the full magnetic pickups switching and volume/tone circuit. So it comes from the volume control centre lug, where it would normally be going to the jack. Any normal guitar wiring could work. So overall, you set up the magnetic tone and volume, then mix in however much peizo you want, which blends from a 0/100% mix, to 50%/50% to 100%/0. There's no overall master volume, but there is enough controls to get any blend or volume you want. eg If you only want pure piezo, then turn the magnetic volume to zero, and now the blend control is acting like a piezo volume …

so my question is with your buffer schematic there are two inputs … which gets the passive magnetic and can I take the full output from a preamp board without a pot and fed it to one of the inputs ? 

Thanks again for your work and help ! 

Jim

[JohnH]

The main intent is that the pot shown with the buffer is a blender, you can get a smooth and even mix of two very different pickups from 100%:0% to 0%:100%. So with that and another pot on your main pickup, you can set any blend, and with this tupe of blender the pickups don't meet electrically so they don't cancel each other. So you set your main puckup with its own controls, then blend in some of the other.