Author Topic: works in bypass, hums when engaged  (Read 8210 times)

blackthumb

works in bypass, hums when engaged
« on: June 30, 2010, 06:00:03 AM »
I have recently finished the beginner project, and am experiencing some difficulties.  I dont really know where/how to start troubleshooting.  I have a DMM but i dont know exactly where to put the leads to check each component.  When its plugged in bypass mode you can hear the guitar clearly through the amp.  When the switch is engaged the LED lights but the guitar can know longer be heard, and there is a loud hum.  Thanks for any help...... i am a total newb to DIY pedals and troubleshooting

tubelectron

Re: works in bypass, hums when engaged
« Reply #1 on: June 30, 2010, 06:17:35 AM »
Hi blackthumb,

1/ re-trace on a paper your circuit directly from the PCB and wiring, ignoring the original schematic.  Check polarities, pinouts, component placement, etc... Be suspicious. Use your DMM in ohms position for continuity connection controls. Then compare to the original schematic : chances are you may find your wiring or component error..

Otherwise :

2/ check all the soldered joints : these should be nice and shiny, no "bawls", only "cones". Chances are you may find a bad/dirty soldered joint, giving a false contact...

If the mistake has not appeared :

3/ the schematic and/or layout has errors - it sometimes arrives... (You may discover it in the 1/ stage, but no necessarily)
4/ the active component (IC's, Q's) are dead - killed by the mistake or coming dead - it sometimes happen too...

These basic failure research rules are OK in any cases. It should help where to find, and drive you finally to the mistake(s).

Patience, Method, and Good luck !
I apologize for my approximative english writing and understanding !
http://guilhemamplification.jimdofree.com/

aron

Re: works in bypass, hums when engaged
« Reply #2 on: June 30, 2010, 09:02:53 PM »
Somehow you have an error and the circuit is sending DC to your amp. Check the output connections after the transistor. There must be a miswire or solder problem there.

Aron

blackthumb

Re: works in bypass, hums when engaged
« Reply #3 on: June 30, 2010, 09:38:05 PM »
thanks aron,

   sorry for the newb question, but how exactly do i check the output after the transistor? i am also fairly certain i am not getting the proper voltages at the transistor also, thanks..  i went to radioshack for some new perfboard and components, and figured i would try doing the circuit again cleaner, and make it look EXACTLY like your pictorial.  I also at radioshack i picked up a 47uF 35v instead of a 47uF 50v cap,   will this be okay?

aron

Re: works in bypass, hums when engaged
« Reply #4 on: June 30, 2010, 09:57:20 PM »
Yes, the cap is ok. You set the DMM on DC and then put the black lead on ground. Now put the red lead on the tip of your cord that would go to the amp. You will probably see voltage on there - a few volts. Try that first.

You should see only a very little voltage in the millivolts range and very low if the circuit is working correctly.

blackthumb

Re: works in bypass, hums when engaged
« Reply #5 on: June 30, 2010, 11:35:02 PM »
hey aron,    thanks again for the help..

   i must be doing something very wrong.  When i put the black lead on the ground and the red lead on the cord that would go to the amp it is showing negative volts, jumping around the -20milivolt region.  I dont really know where to check from here.   A question about the grounding wires,   do you just ground them anywhere along the 47K resistor lead?

blackthumb

Re: works in bypass, hums when engaged
« Reply #6 on: July 01, 2010, 04:35:42 AM »
I rebuilt the board and now it works with 9v battery, however I still have the same problem when i plug in with the DC jack....  i wish i had tried a nine volt battery on my first board..  i think i am wiring it according to the diagram  from thread #4 w/ the  DC jack..    how should i troubleshoot this?  thx

Hides-His-Eyes

Re: works in bypass, hums when engaged
« Reply #7 on: July 01, 2010, 08:29:58 AM »
There are good images on BeavisAudio website showing how to wire a battery with a DC jack.

blackthumb

Re: works in bypass, hums when engaged
« Reply #8 on: July 01, 2010, 04:55:43 PM »
i went to the beavis audio website and rewired using the bottom diagram from >>>> http://www.beavisaudio.com/techpages/PedalPower/....  I am still having the same issue.. works fine with 9v battery, but when the jack is plugged in and the switch is engaged, i just get a loud hum.   any suggestions?

aron

Re: works in bypass, hums when engaged
« Reply #9 on: July 02, 2010, 03:31:18 PM »
Do you hear your guitar signal or is it only hum?

blackthumb

Re: works in bypass, hums when engaged
« Reply #10 on: July 02, 2010, 04:34:29 PM »
when the dc jack is plugged in, and the footswitch is engaged, there is no guitar signal, just the loud hum....  in bypass, the guitar signal is fine.. and with a 9v battery and no dc jack, everything works fine.

aron

Re: works in bypass, hums when engaged
« Reply #11 on: July 02, 2010, 05:25:44 PM »
OK, then again, somehow when the DC jack is engaged, you are sending DC to the output somehow. When you say loud, that indicates to me that you somehow have the DC (9v) going to the output jack somehow. Measure with the meter, it will have DC on it, OR I suppose you don't have your ground set correctly somehow and the pedal/cord is not grounded.

Gus

Re: works in bypass, hums when engaged
« Reply #12 on: July 02, 2010, 05:31:42 PM »
If I understand the posts.

The boost works with a 9VDC battery

It hums with a external supply connected.




One thing could be the external supply is not regulated and has a lot of ripple

AND/OR the circuit is not wired correctly for external power, is the external power jack insulated from the case?

blackthumb

Re: works in bypass, hums when engaged
« Reply #13 on: July 02, 2010, 05:37:40 PM »
I am using the power jack that came with the parts with the beginner project, its not yet mounted in the enclosure...    when i measure the output jack, do i put the red lead on the tip of the cable going to the amp, and the black lead on ground?

blackthumb

Re: works in bypass, hums when engaged
« Reply #14 on: July 02, 2010, 05:40:01 PM »
also,   how would i know if a power supply is not regulated??    i am using the one that came with my digitech jimi hendrix experience expression pedal.

aron

Re: works in bypass, hums when engaged
« Reply #15 on: July 02, 2010, 06:28:14 PM »
It could be the power supply but since you don't hear guitar signal, it's a wiring mistake. Probably better to post a picture or something.

Gus

Re: works in bypass, hums when engaged
« Reply #16 on: July 02, 2010, 08:23:14 PM »
Is the power supply a ps0913b?  If so it is a 9VAC at 1300ma.  It is a wonder your boost works at all after being powered by the supply.

  You want a regulated 9VDC

some links
http://www.digitech.com/support/powersupplies.asp
ftp://ftp.digitech.com/pub/PDFs/Manuals/Artist/Hendrix/JimiHendrixExperience.pdf
  look at page 22 it shows a ps0913b and page 27

blackthumb

Re: works in bypass, hums when engaged
« Reply #17 on: July 03, 2010, 12:27:27 AM »
i guess that was dumb to think any power supply would work..   How do I know if a power supply is regulated?   could i build one?

blackthumb

Re: works in bypass, hums when engaged
« Reply #18 on: July 03, 2010, 12:33:49 AM »
also, what kind of current rating should i look for? wheres the best place to buy one?