Author Topic: piezo pickup preamp with tone stack?  (Read 1265 times)

Marcos - Munky

piezo pickup preamp with tone stack?
« on: February 10, 2019, 08:37:56 PM »
A friend asked me to build him a preamp with a 3 band tone stack for a piezo pickup he'll be putting on an acoustic guitar. While I found a few projects, I don't know if they're good, since I never considered building something like that. Any suggestions?

Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #1 on: February 11, 2019, 01:30:28 AM »
I can't suggest anything but I did find some Ovation schematics while I was working on the Ovation Preamp thread recently.

http://www.ovationtribute.com/
http://www.ovationtribute.com/Schematics.html

eg,
http://www.ovationtribute.com/Catalogues/OP24+C_Owner_Manual/OP24_PlusC.pdf
http://www.ovationtribute.com/Ovation%20Schematics/Ovation_OP-24+_C_Pre-Amp_Schematic/Ovation_OP-24+_C_Pre-Amp_Schematic.pdf

Most have BMT controls, maybe a notch, some with switchable frequencies.  That OP24 is sort of a template but I can't vouch for its sound.


Another,

http://www.ovationtribute.com/Ovation%20Schematics/Ovation_OP-X_Pre-Amp_Schematic/Ovation_OP-X_Pre-Amp_Schematic.html

« Last Edit: February 11, 2019, 01:44:37 AM by Rob Strand »
The answers are out there for those who want to find them.

tonyharker

Re: piezo pickup preamp with tone stack?
« Reply #2 on: February 11, 2019, 06:17:23 AM »
As this is for an acoustic guitar you want the Baxandal/James type of tone control as they dont have the mid frequency dip the others have. 
You need a flat response for acoustic guitars.

PRR

Re: piezo pickup preamp with tone stack?
« Reply #3 on: February 12, 2019, 01:05:01 AM »
The front end of the Fender Sidekick 25 is a basic preamp plus 3-band.

Omit the "Gain" network. Raise the input resistor to suit piezos.


Ben N

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Re: piezo pickup preamp with tone stack?
« Reply #4 on: February 12, 2019, 04:53:47 AM »
Have a gander at http://www.mimf.com/old-lib/mimf_preamp.pdf, specifically Schematics #4 (Bax) and #5 (3-band). These were designed for the purpose.

Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #5 on: February 12, 2019, 06:13:21 PM »
Quote
Have a gander at http://www.mimf.com/old-lib/mimf_preamp.pdf, specifically Schematics #4 (Bax) and #5 (3-band). These were designed for the purpose.
The first stage looks better than the Ovation ckts.  The Ovation ckts like to use dividers with high impedances which can't be good for noise.
The answers are out there for those who want to find them.

Marcos - Munky

Re: piezo pickup preamp with tone stack?
« Reply #6 on: February 12, 2019, 08:07:10 PM »
Thanks for the replies. I did a little search on the last days, and thought on building this preamp:
https://www.eleccircuit.com/wp-content/uploads/2013/06/acoustic-guitar-pickup-circuit-using-tl0711-600x482.jpg

Followed by this eq:
http://sound.whsites.net/articles/eq-f7.gif

What do you guys think? It's somehow similar to the Sidekick front end, but without the opamps on the eq (are those gyrators?).

Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #7 on: February 12, 2019, 08:58:32 PM »
Quote
What do you guys think? It's somehow similar to the Sidekick front end, but without the opamps on the eq (are those gyrators?).
You might need to think about the mid control more.  The 3-band RC equalizers have a very wide bandwidth (low Q) which might have limited use.  I *have* seen those three band on acoustic amps.   The gyrators, like the Fender Sidekick 25, let you tweak the bandwidth and they often tend to have high-ish Q's. 

You could consider a separate mid control,   like one of these.

https://www.diystompboxes.com/smfforum/index.php?topic=24359.40

The Q is about 1 which tends to sound OK.   However,  I can't say how well these work on Acoustic guitar!
The answers are out there for those who want to find them.

Marcos - Munky

Re: piezo pickup preamp with tone stack?
« Reply #8 on: February 13, 2019, 03:39:30 PM »
Thanks. I was planning on going as simple as possible :icon_lol: but I guess the Sidekick is the way to go. Now I just need to get the whole schematic to figure out the power supply and then make a layout (and then buy some boards, I'm out of them).

Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #9 on: February 13, 2019, 03:59:06 PM »
Quote
Thanks. I was planning on going as simple as possible :icon_lol: but I guess the Sidekick is the way to go. Now I just need to get the whole schematic to figure out the power supply and then make a layout (and then buy some boards, I'm out of them).
The gyrator will need three opamps but the active bass+treble and (one) mid stage only needs two opamps.   Both will work.   If you go with a gyrator it will need graphic-equalizer taper pots (L for US, or G for Japan).  If you use a linear pot the control is bunched up in the 10% at the ends and doesn't do much in the middle.   You can modify the gyrator circuit to use lower *value* pot to reduce the control-bunching.
The answers are out there for those who want to find them.

Marcos - Munky

Re: piezo pickup preamp with tone stack?
« Reply #10 on: February 14, 2019, 07:24:46 PM »
I got to find the Sidekick schematic. Gonna build it as soon as I get some time from work and buy some boards. Thanks a lot for the suggestions, I'll report the results when I build it.

caspercody

Re: piezo pickup preamp with tone stack?
« Reply #11 on: February 14, 2019, 08:26:55 PM »
How about this


http://www.....org/viewtopic.php?f=1&t=22863

I made a veto layout for the filter section and it works nice. I hope to do one for the preamp section this weekend


caspercody

Re: piezo pickup preamp with tone stack?
« Reply #12 on: February 14, 2019, 08:28:04 PM »
http://www.....org/viewtopic.php?f=1&t=22863


caspercody

Re: piezo pickup preamp with tone stack?
« Reply #13 on: February 14, 2019, 08:32:03 PM »
Okay will not copy and paste

At ....org search for Acoustimax by BBE

Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #14 on: February 14, 2019, 08:37:14 PM »
Quote
I made a veto layout for the filter section and it works nice. I hope to do one for the preamp section this weekend

Do you think the treble affects the mids too much?   
The treble frequencies are quite low.

The Ovation preamp, the Fender Acoustasonics amps, the Marshall AS50, and the Fishman preamps tend to use higher frequencies.

I had a look at about 10 acoustic circuits.  The bass control frequencies were broadly similar but the treble control frequencies where all over the place.    You get the same thing on bass preamps.

Quote
Okay will not copy and paste
BTW, free st box links are removed on this forum.
The answers are out there for those who want to find them.

Eddododo

Re: piezo pickup preamp with tone stack?
« Reply #15 on: February 18, 2019, 08:00:37 PM »
My meager input- piezos need to go into a very high I put impedance. I donít know of a magic number but I use 10meg or so.. perhaps someone can elaborate.


deadastronaut

Re: piezo pickup preamp with tone stack?
« Reply #16 on: February 19, 2019, 07:26:40 AM »
I know its not diy, but i bought and fitted a few of these modules available for cheap as chips on ebay...

inbuilt tuner.

5 band eq, and mix between piezo and mic fader too..(on my model)

ive built them into classical nylons...sound great.

https://www.ebay.com/itm/LC5-Band-Acoustic-Guitar-EQ-Equalizer-Preamp-Piezo-Pickup-Tuner-Amplifier-LCD-/142800470888


i'll get my coat... :)
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Rob Strand

Re: piezo pickup preamp with tone stack?
« Reply #17 on: February 20, 2019, 04:30:49 PM »
Quote
I know its not diy, but i bought and fitted a few of these modules available for cheap as chips on ebay
A crazy price.  All in a nice neat package. 
Unless you want something which offers custom EQ points it's hard to beat.
The answers are out there for those who want to find them.

Marcos - Munky

Re: piezo pickup preamp with tone stack?
« Reply #18 on: February 21, 2019, 10:02:04 PM »
Yeah, this seems the way to go, for a very useful unit with a cheap price. I'll send the link to the friend.