Piezo Schematics

Started by Elantric, January 24, 2008, 12:36:00 PM

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Elantric

Various Piezo  PU Schematics

http://www.midiguitar.net/group/

Brian Moore RMC Schematic

RMC Polydrive I Install sheets

GRAPHTECH GHOST/HEXPANDER SYSTEM
STRATOCASTER INSTALLATION
http://www.jimbobwan.com/guitar/hexpander.htm

Installing Piezo RMC Polydrive in Ibanez JEM Edgepro bridge
http://www.jemsite.com/forums/showthread.php?t=36762

GeePeeAxe

#1
Does anybody have schematics for a piezzo-hex-preamp?
This needs probably 6 buffer-amps with high-pass-filters for each string.
Maybe 6 BF245C transistors will do the work.
Here's a mono preamp:
http://www.scotthelmke.com/Mint-box-buffer.html
but this is for the impedance of guitar amps... VGs or Axons have other inputs?
I need this for RMC piezzos from a Strat DeLuxe.
Thanks in advance!
Djordje

Elantric

#2
There used to be several RMC schematics on the old TroubadorTech MIDiGuitar page - I'll look too.

A block diagram of RMC PolyDrive 2


This is a Gibson Chet Atkins - "Mono" piezo preamp schematic - so make six separate gain blocks instead of One .

Realize RMC tunes each String's OpAmp Gain Block filter for the expected frequency range of each string (this is the "EQ-1, EQ-2, EQ-3, etc) in the Block above)
That EQ filter is the function of the R/C network in between IC1A and IC1B below.



Here is a Barcus -Berry Piezo preamp with Tone Controls. If you clone this times 6  (one for each string) you should have a wide control, but might take up too much room inside the guitar.





Link to a 4-pole active filter design EXE for windows.

http://www.conradhoffman.com/4_pole_LP.zip


http://en.wikipedia.org/wiki/Audio_filter

GeePeeAxe

#3
Thanks a lot, Elantric!
Still don't know about the impedance that a VG needs. Hi-Z or low Z?

Elantric

#4
Stock passive Piezo pickup output impedance is extremely high - that's why you see the 5meg ohm input trimmers on the Chet Atkins Schematic.
Typical OpAmp output impedance is 100 ohms

The GK 13 pin input on VG-8 / VG-88 / VG-99  / GR-55 is typically considered low impedance approx 10k  to 20k ohms.

So using six dual OpAmps (one per string) as your piezo transducer pickup's buffer / active EQ / gain stage to feed the VG-99 / GR-55's GK-13 pin input means you should be good.

For reference, below is the typical Roland GK hex Processor circuit on the other side of the GK 13 pin Jack.
This is from the 1998 VG-8EX, but other Roland 13 pin gear is very similar in regards to Input Impedance.
https://www.vguitarforums.com/smf/index.php?action=dlattach;topic=11091.0;attach=9118
1998 Roland VG-8EX  13 pin input  Note:  See Active Input Filter section in Orange block. There are 6 Active filters, one per string.



Now compare the above circuit with the 2007 Roland VG-99 13 pin input below (sorry poor quality)
Signal tracing each string signal reveals the VG-99 has two missing OpAmp sections per string = the missing Active Input Filter. 


One element to understand is Roland in a cost saving move, deleted the six active Input filters on all the current production GK-13 Processors - thus the reason RMC had to design a line of the Piezo 13 pin Input Filter boards for the VG-99 / GR-55, because Roland went lean and mean, and lowered their cost (increase profit) by deleting these six active Input filters on the VG-99 / GR-55. Probably saved them PC board real estate, and $15 / unit.
Roland is very proud of their GK-3, and they want to encourage  / promote its sales over the competition.
These six "missing" Active filters on the VG-99 were focused specifically to satisfy users of third party hex 13 pin Piezo pickups.
Since these Active filters reduce the Piezo pickup low frequency Rumble, and are not required for GK-3 users - Roland decided to Omit them on the VG-99. 

And here is a pic of the current RMC PolyDrive-X  hex piezo preamp board in a 2012 Godin xTSA







loulea

Hi Elantric,

Great notes about the Roland interface. I've been wondering why the tracking on my GP-10 was very poor and this explains it. My GR-50, from the late 80s, with my XtsA track perfectly and that is what I use mainly for triggering my other synths when recording. The GP-10 is basically useless for triggering with the Xtsa. It is better with my GK2 pickup and the GR-50 but not as good with Xtsa.

I think that the mods to the GR-55 is not the right place to fix this problem because for the simple fact that if you have more than one GR product, then you would have to add $250 (RMC OPT-01) bucks extra for each pedal which could get expensive. The proper place for it is the guitar to avoid this problem. I bought my Xtsa in 2011 but the board has 2003 on it. I noticed the board pictured above has 2011. Does it have the subsonic filter added? From what I hear it does not.

Looking at the filter circuit from the VG-8EX, looks like a simple bandpass filter (single pole) and not what the subsonic filter (RMC-OPT-01) spec indicates. Can you provide a clearer schematics so I can calculate the cutoff frequencies? My plan is to design an active filter board and add it to the guitar. I will put it in series with the connector board and the main poly drive board. I'm using the specs of the RMC OPT-01 (50 Hz). Looking at the photos of this board, they are not using op-amps but an emitter-follower transistor, isolating the 3 cutoff frequencies (50, 75, 100) which does not give a sharp slope. probably because it has less power consumption but it does work. If you have a blown up version of that section above, it would be great.

They probably removed this section because of the GK interface for bass guitar. It requires lower frequencies for bass guitars for improved tracking.
Thanks!
Loulea
Music is in everyone!!

CodeSmart

Hi Lolulea,
I know it's fun doing projects. I'm impresed by your MIDI things with the GP-10. Anyhow you might consider the top board that I developed for my GKPX-14F. It's pretty small.
or I also have a couple of boards left for my GKFX-11 (but no enclosures left), same thing incl. GK connectors.

I think this is the thing you are planning doing. 4'th order Butterworth HP at 50,75 and 100Hz.
Either of below boards for $62 USD + postage in an envelope - Built, incl. testing protocol and using high tolerance caps and resistors.

Board without GK connectors. (its hex in-out, GND and +/- 7V at the 2mm pin distance  connector)


Board with GK connectors.


I'm just giving you a NOT DIY option. One of these guys would work right away   :)
PM me if interested.

If you want to do it yourself you probably find free filter design tools on the Internet.
But I got more gear than I need...and I like it!

loulea

Quote from: CodeSmart on January 18, 2015, 12:57:12 PM
Hi Lolulea,
I know it's fun doing projects. I'm impresed by your MIDI things with the GP-10. Anyhow you might consider the top board that I developed for my GKPX-14F. It's pretty small.
or I also have a couple of boards left for my GKFX-11 (but no enclosures left), same thing incl. GK connectors.

I think this is the thing you are planning doing. 4'th order Butterworth HP at 50,75 and 100Hz.
Either of below boards for $62 USD + postage in an envelope - Built, incl. testing protocol and using high tolerance caps and resistors.

Board without GK connectors. (its hex in-out, GND and +/- 7V at the 2mm pin distance  connector)


Board with GK connectors.


I'm just giving you a NOT DIY option. One of these guys would work right away   :)
PM me if interested.

If you want to do it yourself you probably find free filter design tools on the Internet.

Hey CodeSmart, this looks like the ticket but I still would have to do a kluge (small) to fit it inside the XTSA. I am an electrical engineer and do this stuff for a living so designing this stuff is natural for me. I have a design already and simulated it. I have ordered the parts for perf boarding it (since I'm only making one) now but I am now laying out PBA for future use. The thing is I want it to fit in the XTSA and your design definitely will but there is a 20 pin header connector that connects between the poly drive board and the 13 pin connector board. The 13 pin connector board not only carries the 13 pin connections but also the acoustic and the normal guitar output so these will be strait through. If I use your circuit, I guess I can just adapt it to make it fit but it still will be a little DIY since I would have to remove the 13 pin connectors from your board or ask for it to be removed. If I get frustrated, I will contact you and arrange for a purchase.

This is what I love about this site! Great support!
Thanks
Music is in everyone!!

CodeSmart

Quote from: loulea on January 19, 2015, 03:45:00 PM
The thing is I want it to fit in the XTSA and your design definitely will but there is a 20 pin header connector that connects between the poly drive board and the 13 pin connector board. The 13 pin connector board not only carries the 13 pin connections but also the acoustic and the normal guitar output so these will be strait through. If I use your circuit, I guess I can just adapt it to make it fit but it still will be a little DIY since I would have to remove the 13 pin connectors from your board or ask for it to be removed.
Yeah, yeah, I know how things are never small enough ::) I guess some parts of the board could be grinded away,
and the connector doesn't need to be mounted at all (I solder them as they go out).
But anyhow it seems you know what you're doing. You'll be fine!
...and Doc, it would be interesting to see a pic of the patient post surgery with the new implant  :)
But I got more gear than I need...and I like it!

Elantric

#9
http://www.diyrecordingequipment.com/blogs/news

"Filters (Podcast #12)
How do filters work?
http://www.diyrecordingequipment.com/blogs/news/16921792-explain-like-im-5-filters-podcast-12
As audio engineers, we use filters every day. We're all intimately familiar with high-pass, low-pass, band-pass, shelf, etc. filters. But how do they actually work in analog gear?

The basic operating principles of analog filters are actually very simple. In this quick (10 minute) podcast, Peterson and Chris explain the very basics of high-pass and low-pass filters so that any 5-year-old could understand.

Download the mp3 or sub

https://cdn.shopify.com/s/files/1/0698/2265/files/ep12-filters.mp3?908


https://upverter.com/eda/#tool=schematic,designId=89bcba3b40708a3f

loulea

#10
Quote from: CodeSmart on January 19, 2015, 09:43:39 PM

...and Doc, it would be interesting to see a pic of the patient post surgery with the new implant  :)

Just remembered I was to share some pictures of the circuit board I made for the XTSA. See below.

In this picture I have the populated circuit board, a bare board and a ribbon cable purchased from DigiKey for 6 bucks. This was all that was required.

https://drive.google.com/open?id=0Byf4qrn_H-ZCTXhESE1sa3VKTmM&authuser=0



Below is a picture of the XTSA connector interface board and the Piezo interface board. The ribbon cable is to be removed from the connector interface board (has the 1/4 inch and the 13 pin connector mounted to it) and connected to filter board.

https://drive.google.com/open?id=0Byf4qrn_H-ZCblNvaUx2Z3V4eEU&authuser=0




The next picture shows how I connected the board to the Piezo board. The unconnected ribbon cable connect to the interface board.

https://drive.google.com/open?id=0Byf4qrn_H-ZCdWRQZTFuVnB3SlE&authuser=0

The final picture is how it is assembled in the guitar. I've ordered stand-offs to mount it but haven't had time screw it in. for now it works. Will post final install picts later.

https://drive.google.com/file/d/0Byf4qrn_H-ZCOXZvakVNcU5JYUE/view?usp=sharing

loulea
Music is in everyone!!

CodeSmart

Quote from: loulea on February 25, 2015, 03:53:34 PM
Just remembered I was to share some pictures of the circuit board I made for the XTSA.

It looks great, well done!
Buckle up! I hope you got yourself a XTSA with no speed limits  ;D
But I got more gear than I need...and I like it!

loulea

Quote from: CodeSmart on February 25, 2015, 10:48:24 PM
It looks great, well done!
Buckle up! I hope you got yourself a XTSA with no speed limits  ;D

The only speed limit is me!  ;)
Music is in everyone!!


ricob

Quote from: Elantric on March 13, 2013, 03:49:59 PM
Stock passive Piezo pickup output impedance is extremely high - that's why you see the 5meg ohm input trimmers on the Chet Atkins Schematic.
Typical OpAmp output impedance is 100 ohms

The GK 13 pin input on VG-8 / VG-88 / VG-99  / GR-55 is typically considered low impedance approx 10k  to 20k ohms.

So using six dual OpAmps (one per string) as your piezo transducer pickup's buffer / active EQ / gain stage to feed the VG-99 / GR-55's GK-13 pin input means you should be good.

For reference, below is the typical Roland GK hex Processor circuit on the other side of the GK 13 pin Jack.
This is from the 1998 VG-8EX, but other Roland 13 pin gear is very similar in regards to Input Impedance.

1998 Roland VG-8EX  13 pin input  Note:  See Active Input Filter section in Orange block. There are 6 Active filters, one per string.



Now compare the above circuit with the 2007 Roland VG-99 13 pin input below (sorry poor quality)
Signal tracing each string signal reveals the VG-99 has two missing OpAmp sections per string = the missing Active Input Filter. 


One element to understand is Roland in a cost saving move, deleted the six active Input filters on all the current production GK-13 Processors - thus the reason RMC had to design a line of the Piezo 13 pin Input Filter boards for the VG-99 / GR-55, because Roland went lean and mean, and lowered their cost (increase profit) by deleting these six active Input filters on the VG-99 / GR-55. Probably saved them PC board real estate, and $15 / unit.
Roland is very proud of their GK-3, and they want to encourage  / promote its sales over the competition.
These six "missing" Active filters on the VG-99 were focused specifically to satisfy users of third party hex 13 pin Piezo pickups.
Since these Active filters reduce the Piezo pickup low frequency Rumble, and are not required for GK-3 users - Roland decided to Omit them on the VG-99. 

And here is a pic of the current RMC PolyDrive-X  hex piezo preamp board in a 2012 Godin xTSA




Hi, sorry To bother after so long. would you by chance have a good quality schematic on this VG-8EX Hes circuit? I have googled it, but I always come across your post.


admin

#15
Quote from: ricob on March 23, 2018, 05:15:41 PM

Hi, sorry To bother after so long. would you by chance have a good quality schematic on this VG-8EX Hes circuit? I have googled it, but I always come across your post.

https://www.vguitarforums.com/smf/index.php?action=dlattach;topic=11091.0;attach=9118


For reference, below is the typical Roland GK hex Processor circuit on the other side of the GK 13 pin Jack.
This is from the 1998 VG-8EX, but other Roland 13 pin gear is very similar in regards to Input Impedance.
https://www.vguitarforums.com/smf/index.php?action=dlattach;topic=11091.0;attach=9118
1998 Roland VG-8EX  13 pin input  Note:  See Active Input Filter section in Orange block. There are 6 Active filters, one per string.




ricob

Quote from: admsustainiac on March 23, 2018, 05:30:00 PM
https://www.vguitarforums.com/smf/index.php?action=dlattach;topic=11091.0;attach=9118


For reference, below is the typical Roland GK hex Processor circuit on the other side of the GK 13 pin Jack.
This is from the 1998 VG-8EX, but other Roland 13 pin gear is very similar in regards to Input Impedance.
https://www.vguitarforums.com/smf/index.php?action=dlattach;topic=11091.0;attach=9118
1998 Roland VG-8EX  13 pin input  Note:  See Active Input Filter section in Orange block. There are 6 Active filters, one per string.


Thank you for your help.

Some threads before you suggested that moving these dual opamps/active filters only out of each string would make The input board compatible with other 13 pin MIDI -based multi effects processors, right? Is that it? Would it be also compatible with 13 pin MIDI based softwares, such as Kontact, Komplete 10 and/or others?

admin

#17
VG-8, VG-8EX, VG-88 employed these opamp filters in front of the A/D converters

VG-99, GR-55, GP-10 do not have these filters, as this function is now performed in the DSP. -
But Piezo hex pickup users ( RMC, Graphtech) noticed many more ghost notes, and higher rumble noise when palm muting 

So I worked with Richard McClish at RMC to develop add on  4'th order Butterworth HP  sub filter boards for VG-99, GR-55
https://www.vguitarforums.com/smf/index.php?board=177.0

later others released external sub filter boxes for Gk 13 pin guitars to assist Piezo Pickup users 

https://www.vguitarforums.com/smf/index.php?board=176.0
https://www.vguitarforums.com/smf/index.php?board=178.0

QuoteWould it be also compatible with 13 pin MIDI based softwares, such as Kontact, Komplete 10 and/or others?

99% of Kontakt  / Komplete software ( hosted on a computer is used by Keyboard players  - 1% by MIDI Guitarists
These  4'th order Butterworth HP filters address eliminating rumbles which manifest as tracking errors for Piezo PU MIDi guitars, and these HP filters allow use with GK-3 Mag hex PU guitars. 

Have nothing to do with Komplete

ricob

#18
Quote"So I worked with Richard McClish at RMC to develop add on  4'th order Butterworth HP  sub filter boards for VG-99, GR-55
https://www.vguitarforums.com/smf/index.php?board=177.0"

Course Ill take a good glimpse at The thread later on, but first things first: did your job solved The issue?



Quote"None of that software is 13 pin based  - 99% is used by Keyboard players  - 1% by MIDI Guitarists
These  4'th order Butterworth HP filters address eliminating rumbles which manifest as tracking errors for Piezo PU MIDi guitars, and these HP filters allow use with GK-3 Mag hex PU guitars. "

Im kinda new(bie) To The MIDI world, but The point is: will it be possible To use The '4'th order Butterworth HP filters' modded board with any piezo-loaded saddles and/or synth?

Also, I thought these softwares were 13 pin loaded. So How many pins do they have?

CodeSmart

Quote from: ricob on March 24, 2018, 06:34:50 AM
Also, I thought these softwares were 13 pin loaded. So How many pins do they have?
Strange question. A software does not have "pins". The guitar signal (single-pup wire or six-pup wire) needs to be converted to MIDI somehow to play MIDI based synths in software.
For other non-MIDI Audio processing software you need a computer interface and software that can handle six audio signals simultaneously.

Also I can't see how this question relates to Piezo HP-filters at all. Filters are there to assist the DSP, there's no simple "success story" with them. Crap in and hopefully a little less crap out. Depends so much of the nature of the instrument, pickup system and playing skills.
But I got more gear than I need...and I like it!

vtgearhead

And, if you live in a dry climate do not shuffle across any carpeting before handling FET input OpAmps :-).

Elantric