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DIY Stompboxes => Building your own stompbox => Topic started by: pak420 on January 12, 2021, 05:32:46 PM

Title: Power supply noise when the effect is switched off
Post by: pak420 on January 12, 2021, 05:32:46 PM
Hello all:

I'm brand new to this board.  I have tinkered with electronic projects over the years.  This is the first time that I built a design based on a schematic, made a few changes based on parts on hand, and tested on a test board to ensure everything worked as intended.  Then, I put my project (a boost pedal) in a box, added a DC jack and filtering, and plugged it in solely with a guitar and amp.  There is an incredible amount of buzz with the effect switched off (3PDT true bypass).  The input of the effect board is grounded when the switch is in the off position. 

I don't have room for a battery in the project box, but I connected one to the DC jack, and the only noise is from my pickups.  I'm using a brand new 1Spot for power.  I have used other pedals, including a Distortion Limited 001 kit that I built, and they are all dead quiet with this supply.  Even if I unplug the other effects from the daisy chain, once the DC goes into the power jack, I get the noise.

I have reflowed all solder joints, rewired grounding to ensure no loops and a single grounding point, pulled the transistor out of the socket, removed the LED, and I can't figure out how to stop the buzzy noise just from plugging in what should be a clean supply.  Any thoughts are greatly appreciated from this knowledgeable resource.

Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 12, 2021, 05:45:25 PM
I built a design based on a schematic, made a few changes based on parts on hand, and tested on a test board

How remarkable lucidity..!!  :icon_lol:

P.S.
Welcome.. :icon_wink:
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 12, 2021, 05:48:11 PM
At first I suspected a wiring error in bypass mode or oscillations caused by the wiring.  However the fact the noise disappears with an externally connected battery is strong evidence the cause of the noise is the power supply.

The 1Spot  power supplies claim to be quiet.   They look like a switch-mode type  so you can't trust they are going to be quiet under all conditions.

One big problem with switch-modes is they misbehave with light loads.   Many DIY guitar pedals present light loads to the power supply, especially the vintage ones.   I would recommend trying to connect a 1k resistor across the power rails.   Ideally this should be done on the effect PCB but for the test it's best to place the resistor at the DC input Jack.   If that doesn't work you might try a lower resistor say 220 ohm.    You can go lower but the resistors are going to get hot.  If you hear a change in the character of the noise you might be on the right track.

There's many other possibilities but I'd try that first.



Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 12, 2021, 07:09:58 PM
Thank you for the welcome, antonis!

Rob - I appreciate your response and guidance.  I will give the resistor a shot.  It should be easy to test....I'll report back the result.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 12, 2021, 09:01:59 PM
I tried the 1k resistor across the power supply rails and it did not alter the buzz.  I then tried a 200R and, sadly, there was still no change in the noise. 

Are there other ideas?  I did use the debugging page already, and used the things that seemed to apply, and I just don't have enough experience to know where else to look. 

Thank you all.
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 12, 2021, 09:09:46 PM
Quote
Are there other ideas?  I did use the debugging page already, and used the things that seemed to apply, and I just don't have enough experience to know where else to look.
OK cool.   These problems are just a process of elimination.   If one idea doesn't work you just keep moving down the list.

The next on the list would  be something relating to the grounds.

Are you sure that the grounds of both you input and output sockets are connecting through.    Sometimes touching a mains device onto a floating circuit will cause buzz.

Another ground test is to power the unit from battery then connect one lead of the power supply (the negative lead) to the circuit ground.   What this does is check the power supply isn't putting signal into the ground.

One question, when you use the power and are in effects mode, is there no noise at all?   and are you happy the unit is working correctly in effects mode?

It would help if you posted a schematic showing the filtering you added.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 13, 2021, 12:28:23 AM
Thanks for the follow up, Rob!

This is just a boost pedal, and, as you might expect, noise that goes into a booster gets boosted, so the effect only works right when battery powered.

The filtering I put in line was a 100R in series with the 9V+, followed by two 22uF electro caps in parallel (I didn't have a 47UF on hand, so I did this for now) and a diode (1N4003 that I had on hand) between the rails.  The thing is that I added these after  the fact hoping they might change or remove the noise.

I have confirmed that my grounding is sound and goes all the way through.  I'd like to try your suggestion of powering with a battery and connecting the negative of the power supply to the the circuit ground.  I have some questions about this to be sure I understand.  First, am I connecting the negative lead of the DC supply (which would not be plugged into the pedal), or tapping off of the negative lead of the battery to connect to ground of the circuit?  Also, what would expected outcomes be?  Am I looking to see if this stops the noise or alters it in some way as an indicator that power is going to ground? 

I can try to sketch out a legible copy of the overall circuit and add the filtering I've put in if it would be helpful.

Thank you for the help!!! 
Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 13, 2021, 05:20:55 AM
First, am I connecting the negative lead of the DC supply (which would not be plugged into the pedal), or tapping off of the negative lead of the battery to connect to ground of the circuit?  Also, what would expected outcomes be?

Connect battery to circuit and leave it there..
Connect power supply GND (negative lead) to circuit GND..
If it's still "quiet", your PS is "clean" from noise injection..
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 13, 2021, 05:33:18 AM
Still continue with antonis's clarifications.

Are you sure the power is getting through to the circuit?  Can you actually measure 9V at the PCB and get boost happening?   If not, a power supply short to ground might cause noise.
Title: Re: Power supply noise when the effect is switched off
Post by: deadastronaut on January 13, 2021, 06:03:58 AM
'I can try to sketch out a legible copy of the overall circuit and add the filtering'

^^^ this will help.  8)
Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 13, 2021, 07:13:17 AM
Maybe I'm confused a bit but didn't OP said that buzz occurs only on by-pass mode..??
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 13, 2021, 07:36:20 AM
Quote
Maybe I'm confused a bit but didn't OP said that buzz occurs only on by-pass mode..??
I'm a little bit confused as well that's why I'm asking the question.   I don't think he means *only* in  bypass mode.
Later on he implies it gets worse in boost/effect mode.  If there's no sound with the PSU it's a different problem to
sound + noise in effects mode.   Obviously in the second case the effect is working and there's power
getting through.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 13, 2021, 05:17:12 PM
I'm very appreciative of everyone's input.

I'm working right now (shhhh) so haven't had a chance to try the test initially described by Rob, but will do (hopefully) this evening.  I will also measure to be sure there are 9V+ getting to the effect board.

To clarify, the noise is there regardless of whether or not the effect is switched on.  It is louder with the effect switched on.

I'll also try to work up the schematic and upload a pic of it.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 13, 2021, 05:44:16 PM
Here's my sketch of the schematic:
(https://i.postimg.cc/pyYprDkV/Booster1.jpg) (https://postimg.cc/pyYprDkV)
Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 13, 2021, 05:59:39 PM
Take reverse polarity protection diode before RC filter..

P.S.
I hope that transistor ISN'T a BJT..
Title: Re: Power supply noise when the effect is switched off
Post by: iainpunk on January 13, 2021, 06:13:28 PM
i bet its a bad ground connection, re-flow the solder on all the ground connections, that might help

Take reverse polarity protection diode before RC filter..

P.S.
I hope that transistor ISN'T a BJT..
i'd say he done it right, after the resistor so the resistor acts as a fuse.
it might work if its a Ge transistor with sufficient leakage.

cheers, Iain
Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 13, 2021, 06:25:24 PM
i'd say he done it right, after the resistor so the resistor acts as a fuse.

I'd say you never heard the dictum: "Semiconductors are for fuse protection"..  :icon_lol:

Iain, transistors are by far faster from resistors or fuses in blowing up..
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 13, 2021, 08:17:59 PM
Quote
i'd say he done it right, after the resistor so the resistor acts as a fuse.
Agreed, if you are going to put in a resistor you might as well use it to limit the current.
It might not even fuse it could just get hot.
Title: Re: Power supply noise when the effect is switched off
Post by: duck_arse on January 14, 2021, 08:54:46 AM
how come 500k pot for volume? why so large?

what we like to ask for is photos of what you've built, so we can see your parts layed out as in your schematic.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 14, 2021, 11:11:58 PM
OK, so I was able to use battery power test as Rob suggested, and there was no change.  I measured and have just a hair over +9V on the power rail, and, the effect does switch on and amplify.

Other observations:  If I turn on the amp and there is a cable plugged into the input of the amp with nothing connected on the other end (pedal, guitar, etc.) then there is a buzz.  To my ear it is the same as the buzz I'm hearing with this issue.  When I plug the cable into the output of the pedal, the noise decreases considerably.  It is still audible, but barely.  There is no change when I plug the guitar cable into the input of the pedal (with the guitar on the other end of the cable).  When I add the DC supply to the pedal, the buzz gets louder, as though it is the same noise amplified.  I can't be sure, of course, and don't have a scope to measure.

duck_arse - The original schematic called for the 500K pot.  I'll work on getting a snap of the layout/internals for you all to see.  Thanks!
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 15, 2021, 05:02:16 AM
Quote
Other observations:  If I turn on the amp and there is a cable plugged into the input of the amp with nothing connected on the other end (pedal, guitar, etc.) then there is a buzz.  To my ear it is the same as the buzz I'm hearing with this issue. 
That's pretty normal.  The buzz actually comes from the mains supply in your house.    It actually couples onto the exposed tip on the connector. 

Quote
When I plug the cable into the output of the pedal, the noise decreases considerably.  It is still audible, but barely.  There is no change when I plug the guitar cable into the input of the pedal (with the guitar on the other end of the cable). 
OK that's normal too.    The enclosure of the pedal shields the tip/center core from the external noise.

Quote
When I add the DC supply to the pedal, the buzz gets louder, as though it is the same noise amplified.  I can't be sure, of course, and don't have a scope to measure.
It's still not clear why that's happening.

So my understanding so far is,
- When the pedal is powered from battery alone, the buzz does not increase in bypass mode.   The buzz may increase a bit
  in effects mode because the pedal is a booster but overall the buzz is acceptable.
- When the pedal is powered from the external DC supply, the buzz increases in bypass mode and get loader again when in effects mode (due to the boosting action of the pedal).

Next,
- After performing the test where the pedal is powered from battery but the -ve lead of the DC power supply is connected to the pedal  ground (the positive lead of the DC power supply left unconnected).   The buzz does not increase.  It pretty much behaves as if it was powered from battery.

So the only "bad" case is when the pedal is actually getting its power from the supply itself.   The pedal has filters on the DC rail so we would expect any noise on the DC supply to be filtered out.

The biggest clue is that the noise is present even in bypass mode.

At this point I'm thinking something is wrong with the wiring.   What we think is OK from looking at the schematic isn't actually like that in reality.

From your schematic it looks like the pedal is a germanium transistor.  I'm assuming the transistor is NPN and that the circuit is a negative ground circuit.     Can you confirm that?   If it's a PNP circuit with a positive ground it's going get all mixed up and we will see weird stuff like we are seeing.     Is the 1M resistor on the base actually going to ground?  (That's why I think it's a germanium transistor.)

Quote
duck_arse - The original schematic called for the 500K pot.  I'll work on getting a snap of the layout/internals for you all to see.  Thanks!
So that's probably best thing to do.  Maybe someone here can spot the issue causing the noise.   To me it's looking like a wiring issue.   Highly like to be way you have done the footswitch wiring.   Wiring the wrong terminals on the input/output sockets will cause some havoc as well.
Title: Re: Power supply noise when the effect is switched off
Post by: duck_arse on January 15, 2021, 08:15:51 AM
(https://i.postimg.cc/pyYprDkV/Booster1.jpg)

on your posted schem, can you perhaps measure your voltages and mark them on the diagram, then repost? measure the voltage on both sides of your supply filter 100R [on battery and external supply, if they differ], and on the "transistor" legs. most important, mark the "transistor" part number on the schem!

one other Q, do you get usable BOOST from the circuit, battery or external supply, and does the trimpot vary the sound at all? thank you.
Title: Re: Power supply noise when the effect is switched off
Post by: VibratoLLC on January 15, 2021, 10:08:33 AM
I have a few suggestions and hope they help:
On the 10k Pot connected to the Transistor, it appears that one leg is unconnected - I'd connect the open leg to the center wiper.
In the past, I had a circuit act glitchy and found that the potentiometer metal case needed to be grounded!
I've also discovered that circuits on my workbench have a lot of noise because of my florescent work light AND my soldering iron is unshielded. Try turning off nearby electronics.
You circuit, as is, may function perfectly, if you put it in a metal enclosure (emi/rfi shielding).
One final suggestion is to put a 1uf or 10uf electrolytic capacitor across the 1K ohm resistor at the emitter.

-Louis
Title: Re: Power supply noise when the effect is switched off
Post by: antonis on January 15, 2021, 02:34:31 PM
From another point of view, BJT Base looks like exhibiting very high impedance (due to "unorthodox" bias configuration - almost Class C (*)..) resulting into amplifying any interference of even the slightest current ability (noise)..

(*) Take voltage measuremets on transistor legs, as already suggested by Stephen.. :icon_wink:

P.S.
Just another point of view, supported by "some" glasses of red dry wine..
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 16, 2021, 02:09:00 PM
Thanks for the fantastic feedback thus far from all who have chimed in. 

I have attached photos of the insides as best I could.  You'll notice my attempt at shielding the LED supply line as one of my early efforts to see if I could find the cause of the noise by wrapping it with a lead connected to ground on one end.  It did not make a difference, but I have not bothered to remove it as yet.  I have already reflowed solder for the grounding wires.

I had initially used some old insulated jacks that I took from some other project.  I thought there might have been and issue with those, so I went to the old standard mono jacks.  I did not directly connect their grounds since they ground to the case. Again, no change in the noise/buzz issue.

The FET is a 2N5457.  The drain has a hair over 3V, .77 volts on the source, and the gate has .02 mV.  The supply coming in is 9.07V, and after the 100R it is 8.99V.


(https://i.postimg.cc/rdyx16Tz/Booster.jpg) (https://postimg.cc/rdyx16Tz)

(https://i.postimg.cc/qNT87hZs/Booster-Board-top.jpg) (https://postimg.cc/qNT87hZs)

(https://i.postimg.cc/DSP14vtt/Booster-SWJacks.jpg) (https://postimg.cc/DSP14vtt)
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 19, 2021, 05:36:14 PM
It's a long shot but try this,
- Remove the ground wire between the DC jack and the center pin of the switch.
- Wire the ground of the DC Jack to the ground of the input socket.

You might want to check the switch contacts are working in all connections.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 19, 2021, 06:20:46 PM
Thanks, Rob!  I'll test the switch out and give that a go. I'm also going to triple check for any solder shorts that may have occurred.

Results to follow.
Title: Re: Power supply noise when the effect is switched off
Post by: pak420 on January 23, 2021, 11:21:08 PM
I got an opportunity to move the DC jack ground to the "star" ground location. I was in a hurry and didn't get to play through, but when I plugged in the DC, the noise was still there in bypass, but not when the effect was turned on. 

I have a connection to a pedal company here in town with a tech that is going to look at it for me.  If he comes up with a solution, I will relay it here so that there is a record.

Thanks, again, to all who have chimed in.  What a fantastic community!!!
Title: Re: Power supply noise when the effect is switched off
Post by: DIY Bass on January 24, 2021, 03:38:56 AM
I recently had a pedal that was noisy.  In this case the external controls were not properly grounded.  The case was grounded OK, but some of the pots and footswitches were not well grounded to the case, especially the footswitches - I had accidentally made the plastic washer that they come with the thing closest to the case, so connection was dodgy
Title: Re: Power supply noise when the effect is switched off
Post by: Rob Strand on January 24, 2021, 05:16:40 PM
Quote
I got an opportunity to move the DC jack ground to the "star" ground location. I was in a hurry and didn't get to play through, but when I plugged in the DC, the noise was still there in bypass, but not when the effect was turned on.

I have a connection to a pedal company here in town with a tech that is going to look at it for me.  If he comes up with a solution, I will relay it here so that there is a record.

Well that's some progress and perhaps a hint the supply wiring has something to do with it.

It's looking like the power supply for sure.    At this point, it would be a big sanity check to try a different power supply.  It could depend not only on the PSU but you amp and your house.     


It would be good to get someone help to look over it.   I look at your pics and see no obvious problems.    The problem seems to be related the DC adaptor itself.   Perhaps a deeper nastier problem is at play.

The only idea I have left would be to move the filter parts to the DC socket,  pretty much removing any common connections between the DC in and the audio.  I'd even try adding a 10 ohm resistor between the ground of DC inlet socket (ie. the negative DC in wire) and the filter ground and circuit ground.   Try the filter ground on either side of the 10 ohm.    It's not normal to do this for a pedal.

The weird thing is the PSU doesn't produce a problem on your other pedals.   It could be your other pedals have JFET switching not true bypass.

Anyway good luck.
Title: Re: Power supply noise when the effect is switched off
Post by: bartimaeus on January 24, 2021, 05:38:36 PM
the photos show the output jack is grounded via the enclosure. are you sure it's making a solid connection to ground? and same for the input jack? sometimes you need to rough up the inside of the enclosure with sand paper.
Title: Re: Power supply noise when the effect is switched off
Post by: iainpunk on January 24, 2021, 07:55:42 PM
the photos show the output jack is grounded via the enclosure. are you sure it's making a solid connection to ground? and same for the input jack? sometimes you need to rough up the inside of the enclosure with sand paper.
wow, i totally overlooked that when looking at the pictures.

its good practice to solder in those ground lugs, even if you think its grounded through the enclosure!!!

cheers, Iain