DIY piezo pickup pre-amp?

[Mark]

Hi

A friend has bought a cigar box guitar and it came with a piezo pickup. The pickup sounds terrible and it is obvious that there is no pre-amp thus the output is low and thin sounding.

Do you guys know of any good DIY pre-amps out there for piezo pickups?

Thanks in advance.

[matt h]

(deleted)

[Mark]

Thanks for your reply Matt, I did see this and while it is dumbed down, the guitar doesn't sound too bad. I'm wondring if this will be enough?

https://www.youtube.com/watch?v=AzW69IPEvys

http://www.scotthelmke.com/Mint-box-buffer.html

Agreed, a piezo without a pre-amp is a disaster.

[ToneMerc]

Hi

A friend has bought a cigar box guitar and it came with a piezo pickup. The pickup sounds terrible and it is obvious that there is no pre-amp thus the output is low and thin sounding.

Do you guys know of any good DIY pre-amps out there for piezo pickups?

Thanks in advance.

Mark, the Dumble FET circuit is basically the original 60's Barcus Berry piezo pickup preamp. Thus, I would start there.


TM

[matt h]

(deleted)

[Mark]

Thanks Matt the circuit looks good, but it is a follower circuit which means it doesn't boost the output, the output is pretty low at the moment, but that could be due to the pickup being loaded down.

Thanks TM the Dumble circuit does provide gain which is a plus, the input impedance might be low, or maybe not depending on the piezo pickup.

Finding more stuff.

http://www.buildmyelectricguitar.com/el ... pf102.html

http://www.muzique.com/schem/mosfet.htm

Thanks again it's all food for thought.

[tele_player]

Thanks Matt the circuit looks good, but it is a follower circuit which means it doesn't boost the output, the output is pretty low at the moment, but that could be due to the pickup being loaded down.

Thanks TM the Dumble circuit does provide gain which is a plus, the input impedance might be low, or maybe not depending on the piezo pickup.

Finding more stuff.

http://www.buildmyelectricguitar.com/el ... pf102.html

Thanks again it's all food for thought.

The schematic on that page is for the buffer circuit, but also mentioned it's the AMZ MOSFET Booster, which provides gain.

Robert

[Leo_Gnardo]

Hi

A friend has bought a cigar box guitar and it came with a piezo pickup. The pickup sounds terrible and it is obvious that there is no pre-amp thus the output is low and thin sounding.

Do you guys know of any good DIY pre-amps out there for piezo pickups?

Thanks in advance.

Mark, the Dumble FET circuit is basically the original 60's Barcus Berry piezo pickup preamp. Thus, I would start there.


TM

I agree with ToneMerc, also you can use an MXR MicroAmp which has a 5.6M or 6.8M input, woops I forget which, but it's up there. Lots of gain available in the MicroAmp, about 26 dB if you need all that much. For a simple single FET, Alembic StratoBlaster, they had a trimpot you could dial gain from none to 6 dB for a little boostage. Easy enough to make your own, it's just a couple of parts. A little more work to copy a MicroAmp, you'll need a TL061 op amp or more modern substitute. Or you might have the original item lurking around.

And there's no harm in changing the load R in a Fender or similar amps' pre to multi megohms. Keep in mind 60's Ampeg combos often had input loading resistors 5.6M or so.

[matt h]

(deleted)

[Leo_Gnardo]

Leo, a couple of points of healthy "au contraire mon frere!"...

By just jacking up the input grid resistor, beyond a circuit point, you get to the point where you might end up accidentally ending up in a hybrid grid-leak-bias/cathode-bias arrangement.

The other point is, and this may or may not matter for the specific pickup/instrument, but the article i linked seemed to think that 8M was the minimum (youreddatritetfokes) for signal transfer. yowza.

Ampeg's engineers/designers must have been aware. If you can't "unload" your piezo with 8 Megs while keeping a preamp tube operating in a sane way, then I don't know what to do. Seems a reasonable limit to me and thanks for the "input" (heh heh... ) The highest I ever went in an amp was 6.8 M. With a "regular" guitar plugged in the resistance of the volume control/pickup combination becomes the resistance of interest and normally a good deal lower than 1 Meg. What the "source resistance" of a piezo, straight out of the pickup is, must be approaching infinite. Pretty dam' big anyway.

Our OP seems to be looking for a preamp but yours is good advice should anyone who may want to swap the resistor at the input of their amp for a bigger one when using a piezo pickup instrument.

So this isn't the place for 22M, 39M, super high value R's. Rats, I gotta box full... what the heck am I gonna do with 'em.

[matt h]

(deleted)

[Leo_Gnardo]

So this isn't the place for 22M, 39M, super high value R's. Rats, I gotta box full... what the heck am I gonna do with 'em.

Incredibly tasteful and distributed local feedback.

Thanks for reminding, yes I seen 'em used that way in very very very x-pensive amps by you-know-whoomble.

[pops]

K&K use 1M for their preamps as it matches their pickups. Orchid also used 1M for their preamp. Baggs uses 10M which will allow anything but the 1M of the other two sound better as they match the impedance better. It should be easy enough to get a 1M input from a tube amp and not need the pre amp

[JMFahey]

Just use the simplest single FET buffer, you don't actually need *gain* but simply to stop *loss* of which you have a lot right now.

1M input impedance is fine for 90% Piezos out there and 3M3 will accomodate up to 98% .


If yours needs more, junk it and get a better one

The tinbox one is fine, just use a single 3M3 gate resistor to ground, a 10K to 22K resistor source to ground , 1uFx16V or more output capacitor and after it 220K to ground to avoid pops when plugging.

Even if the Guitar amp has 1 M input impedance (most do), they are at the far end of a 20 ft cable, the buffer main usefulness is that by driving a long cable from a low impedance you improve its interference (radio, hum, buzz) rejection.

That alone is worth the buffer slight inconvenience.

You don't even need a separate enclosure, it fits inside the cigar box guitar cavity and battery lasts forever (ok, more than a year), just wire like in pedals so when unplugging it turns off.

Or add a small switch somewhere.

[Firestorm]

The last time I had to do this (for an acoustic bass pickup) I just bootstrapped the input. 10M input impedance. Worked fine.