Onboard bass preamp troubleshooting - 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 18th June 2012, 09:27 AM   #1
diyAudio Member
 
Join Date: Mar 2006
Location: Canadian in Australia
Default Onboard bass preamp troubleshooting

Hey guys, I'm a bass guitar builder and have run into a wiring problem on one of my customer's bass so tought I'd ask the electronics Experts over here

I've installled an Aguilar OBP-3 preamp inside of a Jazz Bass clone I built, I must have installed about a dozen of these preamps in the last couple of years without a hitch, unfortunately i'm now stuck, here's the schematic used

Click the image to open in full size.

As can be seen I added a passive tone pot to it, I've also wired a few of these with this schematic in the past without a problem, the difference this time is that i used a Fender 250k/500k dual concentric pot for both the volume and the tone controls

Click the image to open in full size.

I essentially wired all the ground wires to one star ground and sent that to the jack. Frm the tone pot drawing, i soldered the cap to one lug then the other bit of the cap to the casing (same side casing as the lugs making sure not to touch lower casing for the other part of the pot) and then sent a ground wire from there to the star ground.

Here's the problem, absolutely everything in the circuit works fine as it should work besides the tone control. From turned up full on to about 1/3 of a turn nothing happens to the sound (tone doesn't work) then once turned the pot back to that 1/3 the sound goes dead on the bass, volume shuts completely off.

The top part of the pot (volume knob) works fine, just the lower part of the pot, the tone doesn't work

Any ideas anyone? I'm at wits end here and need to send this bass back to its owner...
  Reply With Quote
Old 18th June 2012, 01:13 PM   #2
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
Sounds like a bad pot.
Have you check its function with an ohm meter?
It kind sounds like the resistance element maybe open at some part of its travel.
I have had similar situations due to bad pots on a few of my guitars.

FWIW

jer
  Reply With Quote
Old 18th June 2012, 01:27 PM   #3
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
Tie a voltage source across the element (ie. 9v battery) and measure the voltage on the wiper and V- with a VOM or a scope.
By actuating the control, the voltage should go up and down smoothly.
If it is erratic or suddenly jumps high or low then it has a bad element.

Good Luck !!

jer
  Reply With Quote
Old 20th June 2012, 06:25 PM   #4
diyAudio Member
 
Join Date: Jan 2006
Location: Poland
Phil,

There are three options:
- either bad pot,
- or bad capacitor,
- or ground wire not connected to the ground.
At least two of these three options can be asily checked with a cheap digital multimeter (set to Ohms measurement). In many cases you can also measure capacitors with such a meter.
There is one more possibility to check the pot: since this is a double pot, you can switch wires between sections (tone <-> volume) and see whether volume still works after the wires were switched (and whether tone control started working suddenly) .

Mark
  Reply With Quote
Old 21st June 2012, 05:50 AM   #5
diyAudio Member
 
Join Date: Jan 2006
Location: Poland
Even simpler test is to short the pot with a wire and listen whether this changes the tone.

Mark
  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
2-band bass guitar onboard preamp phil mailloux Instruments and Amps 77 27th April 2014 12:49 PM
Making and onboard bass guitar preamp Skywalker83 Parts 8 17th October 2012 04:28 AM
Onboard Bass compressor? Nemuikuma Instruments and Amps 3 28th March 2012 09:18 PM
bass onboard preamp circuit jasonconanan Instruments and Amps 6 29th December 2009 04:44 PM
onboard electric guitar/ bass preamp LJOE1969 Instruments and Amps 2 24th March 2005 05:33 PM


New To Site? Need Help?

All times are GMT. The time now is 06:59 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