OPA2134 and other FET input audio op-amps - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 November 2012, 08:29 AM   #1
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
Default OPA2134 and other FET input audio op-amps

Hello

I am building a guitar preamplifier and am going to use op-amps. Old style (non active) guitar pickups have a typically high resistance, being bed though a 500KOhm pot into the pre-amp. The pre-amp therefore has to have high input impedance else it will load the guitar and the sound will lose high frequencies.

I have been using an old Fender amp which is build with TL072s and was thinking I may use these or use the OPA2134 or any other PDIP8 FET input op-amp. The Fender does have a lot of noise and we cannot mic it properly with all the hiss coming out of it. I was thinking the opa2134 may eliminate the noise in my circuits, I am thinking of using it just where I need high input impedance, and use the LM4562 elsewhere.

The places where I need high input resistance are the main input and the tone control circuitry recovery amp.

One question is can I just use the LM4562 throughout, and simply add a simple FET buffer to achieve the high input resistance eg the 2N5459?

Any other comments/suggestions?

Thanks
  Reply With Quote
Old 26th November 2012, 10:30 AM   #2
diyAudio Member
 
Robert Kesh's Avatar
 
Join Date: Oct 2012
Suggest you post in the Live Sound section.

I doubt the TL072's are causing the noise. They are not noisy by guitar amp standards, just by audiophile standards.

Hi fi components like the LM4562 are pointless in electric guitar equipment.
  Reply With Quote
Old 26th November 2012, 10:50 AM   #3
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
Quote:
Originally Posted by Robert Kesh View Post
Suggest you post in the Live Sound section.

I doubt the TL072's are causing the noise. They are not noisy by guitar amp standards, just by audiophile standards.

Hi fi components like the LM4562 are pointless in electric guitar equipment.
LM4562 also does not have the sound for guitar amp. It's sound is just too smooth and refined. In guitar amps j-fet opamps sound much more valve-like. Noise problem is more likely related to ground loops somewhere.
  Reply With Quote
Old 26th November 2012, 10:54 AM   #4
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Suggets you try OPA1641.


Patrick
__________________
xen-audio.com
  Reply With Quote
Old 27th November 2012, 03:01 AM   #5
diyAudio Member
 
Join Date: Aug 2012
try 627 the high freq open sound... i didnt believe that the pre is an outstanding amp but after burnin and also dont forget to use highend input caps...
  Reply With Quote
Old 27th November 2012, 05:21 AM   #6
diyAudio Member
 
volume knob's Avatar
 
Join Date: Dec 2011
Location: North Shore
Using a bipolar input opamp in a circuit that was designed for a fet input opamp could result in a high d.c ofset, that may or may not be a problem depending on where the opamp is in the circuit
  Reply With Quote
Old 27th November 2012, 02:26 PM   #7
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
for good info on guitar pickups' electrical parameters:

UIUC Physics 498POM Guitar Pickup Measurements


I doubt there is a lot better noise performance possible with the hi R pot as source

the TL072 input noise V ~ 16 kOhm equivalent ~ 3 dB noise figure

at higher source Z the V noise of the op amp is even less important and the noise figure can at best only asymptotically approach 0 dB (eventually limited by current noise equivalent R as high as GigaOhms)

paying extra for 1/2 the input Vnoise (OPA2134 vs TL072) won't move the noise figure at 100s of kOhm or higher noise source R by audibly perceptible amounts


directly buffering the pickup coil is a little different the Rdc of many magnetic pickups is < ~ 10 kOhm and lower Vn fet op amps could improve on dynamic range at the fundamental frequencies and where the higher Z is from complex impedance instead of pure resistance

depending on coil Rdc you could see some improvements in noise with lower Vn fet op amps


so you need to examine the circuit, its capabilities, your expectations - maybe a specific TL072 has taken a esd hit - could cause increased noise while still basically functioning so swapping it out with a good TL072 could even help

maybe you could just filter for guitar there's not much above ~4 kHz, the cable C in most setups will give a low pass with the pickup anyway
  Reply With Quote
Old 27th November 2012, 07:52 PM   #8
diyAudio Member
 
Robert Kesh's Avatar
 
Join Date: Oct 2012
Quote:
maybe you could just filter – for guitar there's not much above ~4 kHz, the cable C in most setups will give a low pass with the pickup anyway
Just should add that though a guitar might not produce much over 4k, things like effects in the signal chain might.

Last edited by Robert Kesh; 27th November 2012 at 07:55 PM.
  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
Is there any better OP than OPA2134 Progg70 Solid State 96 30th July 2013 06:15 PM
Lower volume by switching from FET to BJT input op-amp? wwenze Chip Amps 5 15th December 2010 06:29 AM
Instrumentation op-amps for audio ivanlukic Analog Line Level 10 28th November 2010 12:31 PM
Burr Brown op amps,in amps,power op amps for sale magneticnorth Vendor's Bazaar 1 23rd September 2010 10:50 PM
which op-amps should I use for manipulating ubalanced audio and why?? jenks Digital Source 1 19th March 2008 01:05 PM


New To Site? Need Help?

All times are GMT. The time now is 10:34 AM.


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