Piezo Film Buffer and Amp Combo for Guitar Electronics - Page 2 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th August 2013, 09:08 AM   #11
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by gingertube View Post
One thing bothers me about the Piezo Buffer design shown. The reason that a high impedance input to the buffer is required is that the Piezo is highly capacitive. Without the high impedance buffer input you loose bass. I think that the additional capacitor to 0V shown on the buffer schematic (at teh input) is only going to reduce the input signal by capacitor divider action without giving any worthwhile frequency shaping. This will just result in a noisier system.
I presumed the capacitor was to help prevent RFI?, not for any tone shaping properties.

However, I don't like the high/low attenuator at the front which halves the input impedance - if you need a high/low switch then stick another 10meg in series with the input, and put a switch across it (giving 10meg or 20meg input impedance).
__________________
Nigel Goodwin
  Reply With Quote
Old 26th August 2013, 11:22 AM   #12
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by Nigel Goodwin View Post
I presumed the capacitor was to help prevent RFI?, not for any tone shaping properties.
Bad manners to reply to your own thread , but I've just done the calculations on the 20pF - it's certainly a BAD idea to fit it, as it's reactance is 10meg at only 800Hz or so, so it will have a fairly major effect on loading of the PU.
__________________
Nigel Goodwin
  Reply With Quote
Old 26th August 2013, 03:07 PM   #13
mjf is offline mjf  Austria
diyAudio Member
 
Join Date: Jan 2009
Location: Austria
you can build in a gate stopper res (Rg ,around 1k or so) against Rf.
should be close to the gate pin of the fet.........
Attached Images
File Type: jpg fetbuffer pre1a.JPG (20.4 KB, 77 views)
  Reply With Quote
Old 26th August 2013, 04:39 PM   #14
Lid55 is offline Lid55  Canada
diyAudio Member
 
Join Date: Nov 2011
Ah I should carify. After he posted the circuit, he suggested to use 1pF instead of 20pF... to "shunt" the RF.

I've tried the circuit quickly, but haven't found enough gain for my application. I'll go over the circuit and try some things... I'll also try the opamp circuit alone, as Gingertube has suggested.
  Reply With Quote
Old 26th August 2013, 07:18 PM   #15
Lid55 is offline Lid55  Canada
diyAudio Member
 
Join Date: Nov 2011
So... I have tried the opamp circuit posted with the OPA2134... alone... without the FET buffer circuit, and it sounds pretty good. I've changed the resistor in the feedback loop to increase the gain... from 100K up to 1.2M... now I'm happy with the gain... but the high frequencies have been cut now... a kind of LPF effect... not terrible... but... I wanted to use piezos (over magnetic pickups) to INCREASE the high frequency content... not cut it.

Any ideas?
  Reply With Quote
Old 26th August 2013, 07:23 PM   #16
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by Lid55 View Post
So... I have tried the opamp circuit posted with the OPA2134... alone... without the FET buffer circuit, and it sounds pretty good. I've changed the resistor in the feedback loop to increase the gain... from 100K up to 1.2M... now I'm happy with the gain... but the high frequencies have been cut now... a kind of LPF effect... not terrible... but... I wanted to use piezos (over magnetic pickups) to INCREASE the high frequency content... not cut it.
Where is the circuit?.

If you've increased the gain too much, then you lose high frequencies - it's a basic limitation of opamps, and given in the specifications. The solution is to use more stages, with lower gain in each stage.
__________________
Nigel Goodwin
  Reply With Quote
Old 26th August 2013, 10:15 PM   #17
Lid55 is offline Lid55  Canada
diyAudio Member
 
Join Date: Nov 2011
I've just temporarily bypassed the FET buffer circuit on a breadboard... I still have it... in fact that's the next thing I'll try... adding the two circuits together again... to see how that affects the gain stages. Maybe a better solution would be to use the OPA604 as well? What about if I use ONLY the OPA2134 but use BOTH amps within it? Is this possible?

One other potentially important question I had... is it possible to use a single 9 volt for 2 simultaneous circuits such as this? Or is it better to have one 9 volt for each circuit?
  Reply With Quote
Old 27th August 2013, 08:11 AM   #18
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by Lid55 View Post
I've just temporarily bypassed the FET buffer circuit on a breadboard... I still have it... in fact that's the next thing I'll try... adding the two circuits together again... to see how that affects the gain stages. Maybe a better solution would be to use the OPA604 as well? What about if I use ONLY the OPA2134 but use BOTH amps within it? Is this possible?
That's why it has two amps inside

Quote:

One other potentially important question I had... is it possible to use a single 9 volt for 2 simultaneous circuits such as this? Or is it better to have one 9 volt for each circuit?
Easily possible, and preferable - if you're going to use 2x9V batteries, then use them as a +/-9V split supply.
__________________
Nigel Goodwin
  Reply With Quote
Old 27th August 2013, 08:14 AM   #19
diyAudio Member
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
Quote:
Originally Posted by Nigel Goodwin View Post
You are, on all counts - the LM386 isn't even an opamp, it's a small power amp. Most opamps will run off 9V without problem.



The FET is used to give a high input impedance, the opamp gives the gain - an OPA134 would be a decent choice as well, even quieter than the NE5532.
As the impedance of the FET is above 4M7 then the signal from the buffered FET is around 700mV so not a lot of gain is required. Leave the gain requirements to your mixer!
__________________
www.flyingmole.co.uk For World Wide support for Flying Mole, Class D, Refurbishment and Repairs. www.jonsnell.co.uk
  Reply With Quote
Old 27th August 2013, 10:48 AM   #20
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by JonSnell Electronic View Post
As the impedance of the FET is above 4M7 then the signal from the buffered FET is around 700mV so not a lot of gain is required. Leave the gain requirements to your mixer!
According to the OP he's had to INCREASE the gain of the opamp in order to make it work, it obviously really depends on the output level from his source. If the source is high level, then a simple FET buffer would be all that's needed.
__________________
Nigel Goodwin
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pre Amp/Buffer and Amp for a Ukulele with an under saddle Piezo pickup Rich3761 Solid State 3 28th February 2013 02:48 PM
Film Trailer: State of Electronics (aussie) col Everything Else 1 2nd November 2010 12:56 AM
guitar amp enclosure/combo cabinet Aidan135711 Multi-Way 9 6th May 2010 07:43 AM
Piezo film used in 300 degree radiated tweeters humanhuman Multi-Way 2 18th November 2007 02:28 AM
Guitar Amp Question!!!!! Adding Film Cap? zxx123 Tubes / Valves 11 29th March 2005 01:50 AM


New To Site? Need Help?

All times are GMT. The time now is 04:04 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2