Distortion+ Clone, big humming - 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 11th January 2006, 05:29 AM   #1
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
Default Distortion+ Clone, big humming

I've just built this Distortion+ from www.generalguitargadgets.com but when i tested it, its humming so loud that you won't even hear the guitar. Everything is correctly, everything necessary is connected to ground and the opamp [UA741CP] voltages are ok.
Just to say, the led indicator was left out as i could only find a DPDT switch.
Any help would be great.
  Reply With Quote
Old 11th January 2006, 06:08 AM   #2
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
A more direct link might be of some use.

http://www.generalguitargadgets.com/...d=42&Itemid=74
__________________
- Dan
  Reply With Quote
Old 11th January 2006, 06:35 AM   #3
teemuk is offline teemuk  Finland
diyAudio Member
 
Join Date: Nov 2004
Location: Suomi, Finland
Hum in DC powered circuit? I assume you are referring to oscillation instead...

Is it "humming" on high frequency: That 10pF NFB capacitor seems quite small for high gain circuit. If the oscillation is low freq instead then i'd guess you have a ground loop somewhere. Try grounding at only one point.

Teemu K
  Reply With Quote
Old 11th January 2006, 06:55 AM   #4
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
Btw. i'm using a 9v battery to power it, not a wallwart.
Everything is grounded according to the layout, so everything, except the output pot is grounded to the same point [left top corner].
I could try with changing the output pot grounding to the same spot.
i noticed that in the DOD overdrive 250 circuit [same pcb], a 25pF cap is used, so should i try swapping the 10pF for a 25pF cap?

BTW. The humming decreases more than half when i turn the distortion pot to down, and im not using a C-taper, just a regular 1Meg linear, which is wired the same way as the C-taper in the layout...this could be wrong, i'm not sure.
  Reply With Quote
Old 11th January 2006, 07:36 AM   #5
teemuk is offline teemuk  Finland
diyAudio Member
 
Join Date: Nov 2004
Location: Suomi, Finland
Batteries do not hum so you are experiencing an oscillation problem.

Quote:
Originally posted by DolbyR
i noticed that in the DOD overdrive 250 circuit [same pcb], a 25pF cap is used, so should i try swapping the 10pF for a 25pF cap?
The purpose of that capacitor is to attenuate high frequencies so adding more capacitance will also darken the tone. When selecting that capacitor I usually start from a value of about 47pF and sometimes go up to even 1nF. But, if components are good quality and the layout is good the amplifier is less prone to high frequency oscillation.

High gain amplifiers are quite tricky and the source of oscillation could be almost anything. The safest bet is to check the circuit wiring, component values and solder joints thoroughly - again. Usually when i encounter low frequency oscillation i eventually discover that i have either made a wiring mistake or have misread a resistor value. Try to keep wire lenghts as short as possible, especially check the wire lengths of potentiometer wiring. Also, check the input and output grounding: if the ground is lifted it could cause oscillation. Even component layout will matter!

High frequency oscillation (high pitched noise rather than "humming") will most likely occur in high gain circuits if they fail to replicate the original design 100%. Opamps for example can be quite picky about the circuit they're used in. This is why my first thought was that the 10pF cap is too small. HF Oscillation can be easily cured with the expense of brightness

Teemu K
  Reply With Quote
Old 11th January 2006, 07:58 AM   #6
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
Thanks, i'll remelt all the solder joints this afternoon, check the wirings [i used cat5E for the wirings, should i change them to something else..i have also some Cat5 solid core wire around, or should i just buy something better?] and then start with cap changes if necessary.
And the distortion pot, maybe i should remove for during the tests so that i'll know that its not the problem?
  Reply With Quote
Old 11th January 2006, 12:10 PM   #7
teemuk is offline teemuk  Finland
diyAudio Member
 
Join Date: Nov 2004
Location: Suomi, Finland
What kind of wire is Cat5? I guess almost any wire will do and it shouldn't make much difference whether its braided or solid. Some people like to use very thick wire but i find it clumsy and i have never experienced any degrade on performance with (even very) thin wire. This of course only applies to low current wirings.

The resistance of the potentiometer is an important part of the circuit and if you want to test whether it's faulty you can simply bypass it with wire loop to get maximum gain. You better keep the amount of working with the PCB (swapping components etc.) as minimum as possible since the foils in printed circuit boards are very fragile. n other words, it's better to know what to fix than to throw some wild guesses and ruin the board with exessive heating. However, redoing solder joints might help in case there is a cold solder joint somewhere.

You haven't told whether the oscillation is high or low frequency. Knowing that would be a great help in troubleshooting and fixing the circuit.

Teemu K
  Reply With Quote
Old 11th January 2006, 02:38 PM   #8
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
Cat5 is ethernet/lan cable, from which ive used the wires (braided), its 24AWG and very weak, i have some some from the similar ethernet cable but its solid one, also 24AWG so i'll maybe redothe wiring with it to see if it will be stronger.
I changed the 10pF cap for a 1nF one coz it was the next lowest one that i had and most of the sound disturbance is gone.
I really can't tell whether the oscillation is high or low frequence.
I guess i'd need an oscilloscope for that?
I did try with a program called oscilloscope for windows which gave me about 550hz sweep on 0.5ms/div and 5550hz on 5ms/div but i dont really know what they mean
  Reply With Quote
Old 13th January 2006, 06:35 AM   #9
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
The problem with the humming/osc. whatever, appeared to be just my second cable (dist->amp) which was probably catching up some RFI.
Now i must just change that 10pF cap back as with 1nF its definitely filtering too much highs.
I'll post some link after that how the final version sounds, thanks for all the help
  Reply With Quote
Old 21st January 2006, 10:22 AM   #10
DolbyR is offline DolbyR  Finland
diyAudio Member
 
Join Date: Oct 2005
Has anybody ever modded a Distortion+ in order to obtain cleaner sound?
Now the drive is very strong which i like but the sound is not even close to clean, its very muffy, sounds like its coming from a bass.
I can have some 3mb mp3 sample from it if anybody wants to hear.
If i cant make the sound cleaner, i guess i'll have to try a boss DS-1 clone.
  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
Humming Zen V4 Diomedian Pass Labs 4 26th April 2006 08:30 AM
Humming GC fireman Chip Amps 9 8th August 2004 06:44 PM
Non Linear Distortion testing - Harmonic Distortion JMB Multi-Way 0 20th July 2004 02:54 PM
humming amp Pumuckel Pass Labs 10 26th February 2004 12:40 AM
Question regarding ProAc 2.5 Clone and Tempo 2 Clone zoooh Multi-Way 5 11th March 2003 08:19 PM


New To Site? Need Help?

All times are GMT. The time now is 02:23 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