Author Topic: Noise help with a flanger  (Read 1832 times)

TNblueshawk

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Noise help with a flanger
« on: August 20, 2019, 08:51:17 AM »
Ok, so I've built Bean's MXR117 SAD 1024 version. It's up and running and sounds great except for the noise. While I can live with a little noise there is just too much to make this pedal usable. I'm out of my element on how to reduce it to where it's tolerable. I've tried it on a One Spot as well as my Voodoo Lab's PS and it is the exact same. It is not in a chain of pedals.

Noise wise, you hear the clock but if that was all I heard it is low enough to where I could get by and not sweat it too much. But the classic swooshing thing is just too much.

Any thoughts on how I might attack this problem would be helpful. I realize the SAD has more inherent noise however no way do I believe that all the old SAD chips were this noisy by 'design'. Now, this SAD chip could be in and of itself 'bad' but before I decide that I'd like to try a few things to bring it down some.

I have pics below to see if anyone spots anything out of whack. All the pots work however the one that jacks this pedal up is if I take the Regen past 75% there is an immediate squeal and I don't mean the kind that you go huh and it goes up when you keep turning. I mean the kind that will make you come out of your skin immediately.

Also of note the trimmer nearest the top and nearest the SAD chip is very scratchy while turning.

Thoughts from anyone?





John

madbean

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Re: Noise help with a flanger
« Reply #1 on: August 20, 2019, 09:06:16 AM »
Well it's been 8 years since I built it so I cannot remember a damn thing about it other than mine was pretty noisy too. But, I don't remember it being too much so or not. Looking at the schematic again the two caps to embiggen would be C7 (150pF stock) and C17 (10n stock). Maybe 1n and 47n resp would tame it without totally killing the top end. Or, socket and experiment.

It could be the layout itself, too. Cramming that circuit into a single sided 125B was more of a d**k measuring contest for me rather than actually being practical. And, when it comes to d**k measuring contests I come up short ADEQUATE.
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TNblueshawk

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Re: Noise help with a flanger
« Reply #2 on: August 20, 2019, 10:07:18 AM »
Well if you don't mind me saying that I thought you measured up quite well when creating this PCB  ;D Yeah, if I could tame it just a bit I could use it.

Thanks for a few tips Bean. I'll socket those this week and see what I think.
John

Govmnt_Lacky

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Re: Noise help with a flanger
« Reply #3 on: August 20, 2019, 10:42:40 AM »
I built two of these previously. Had noise issues with both. The only way I got around it was to either feed it regulated 18V or, on another build, I incorporated the same transformer that was in the originals.

And... shielded wiring. Input to PCB and PCB to output.

Good Luck  ;D

TNblueshawk

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Re: Noise help with a flanger
« Reply #4 on: August 20, 2019, 11:06:50 AM »
I built two of these previously. Had noise issues with both. The only way I got around it was to either feed it regulated 18V or, on another build, I incorporated the same transformer that was in the originals.

And... shielded wiring. Input to PCB and PCB to output.

Good Luck  ;D

Thanks Gov. I thought about shielded wiring but didn't know if it would do anything. I guess every little thing might lower it.
John

Govmnt_Lacky

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Re: Noise help with a flanger
« Reply #5 on: August 20, 2019, 12:28:07 PM »
Of note:

Do you have an oscope to verify that the clock is the proper freq's? It may help as well. Here are the proper numbers to look for:

- Set MANUAL and WIDTH pots fully CCW

Measure SAD pins 3/14 or 8/10 for 29-32KHz. Adjust the 500K pot as necessary. (the timing cap value might need to be adjusted)

Also, make sure your REGEN is properly trimmed:

- Set REGEN pot to full CW

Adjust 20K Regen trim until Feedback 'just' starts to oscilate. then, turn trimmer back until the oscillation just stops. (at full CW on REGEN pot you should NOT hear oscillation)
« Last Edit: August 20, 2019, 12:33:21 PM by Govmnt_Lacky »

TNblueshawk

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Re: Noise help with a flanger
« Reply #6 on: August 20, 2019, 12:37:10 PM »
No, I don't have a scope unfortunately. Always meant to get one. Never did like with many things.
John

Govmnt_Lacky

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Re: Noise help with a flanger
« Reply #7 on: August 20, 2019, 12:46:31 PM »
No, I don't have a scope unfortunately. Always meant to get one. Never did like with many things.

What about a multimeter with frequency measurement?

TNblueshawk

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Re: Noise help with a flanger
« Reply #8 on: August 20, 2019, 02:15:01 PM »
No, I don't have a scope unfortunately. Always meant to get one. Never did like with many things.

What about a multimeter with frequency measurement?

Well I have to admit that I've never noticed if I do. I'll check it out tonight. I want to say no on my one meter but maybe.
John

Govmnt_Lacky

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Re: Noise help with a flanger
« Reply #9 on: August 21, 2019, 08:09:15 AM »
Another item to note:

After looking over the MBP 117 project doc, I wonder if the SPEED pot is actually supposed to be a C500K pot instead of an A500K  ???

Brian???

EDIT: After looking at the Collosalus doc... it should be C500K. Is that what was used in this build?

EDIT2: What voltage are you running at? I do not see a 15VDC regulator on your Road Rage board. Are you just feeding the charge pump output voltage directly into the 117??
« Last Edit: August 21, 2019, 08:38:44 AM by Govmnt_Lacky »

TNblueshawk

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Re: Noise help with a flanger
« Reply #10 on: August 21, 2019, 08:44:06 AM »
Well, for sure all the speed pots are C rather than A on the builds I've built but i don't recall if I caught that when I built it. I built this several months ago but got into a kitchen project and didn't get back to this one for a bit. I'm at work so I'll have to look at the build.

My multimeter doesn't have Freq measurements. This is the model  https://www.circuitspecialists.com/digital-multimeter-csi2010.html
John

TNblueshawk

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Re: Noise help with a flanger
« Reply #11 on: August 22, 2019, 07:06:48 AM »
So, in my docs it calls it a Sweep pot and not Speed. But if you look in the original manual for this pedal on line it is called a Speed pot. So, I'm thinking maybe it should be C500k. I used an A500k. I'm not sure that solves anything noise related but interesting nonetheless.
« Last Edit: August 22, 2019, 07:08:29 AM by TNblueshawk »
John

Scruffie

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Re: Noise help with a flanger
« Reply #12 on: August 22, 2019, 07:59:49 AM »
Speed should be C500k, that's nearly always the case unless the pot is being used as a voltage divider but that will only help with the action of the speed pot.

Your wiring could do with being a bit neater, wont help with hiss but it will with any stray sweeping noise. Or just shield it as already discussed.

But mainly, as Lacky pointed out, where's your regulator? An unfiltered/unregulated charge pump running in to a flanger is going to be noisy, the circuit doesn't have any kind of power filtering on the audio. It would probably be worth running a 2W 10R after the regulator to the board as well to create a filter.

It should be a reasonably quiet flanger, S/N is good and there's a decent amount of audio filtering.
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TNblueshawk

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Re: Noise help with a flanger
« Reply #13 on: August 22, 2019, 10:04:19 AM »
Speed should be C500k, that's nearly always the case unless the pot is being used as a voltage divider but that will only help with the action of the speed pot.

Your wiring could do with being a bit neater, wont help with hiss but it will with any stray sweeping noise. Or just shield it as already discussed.

But mainly, as Lacky pointed out, where's your regulator? An unfiltered/unregulated charge pump running in to a flanger is going to be noisy, the circuit doesn't have any kind of power filtering on the audio. It would probably be worth running a 2W 10R after the regulator to the board as well to create a filter.

It should be a reasonably quiet flanger, S/N is good and there's a decent amount of audio filtering.

Hey Scruff, I'm using an LT1054 if I recall right on the Road Rage with a regulated 9v PS off a Voodoo Labs PS for either 15v or 18v operation. I forget what I decided to try to run it on off hand. I do plan to shield. My wiring looks worse since I've been taking it out and playing with it but I'll route things better when I shut the box up for good.

I am a little confused though with respect to the Speed pot. In the BOM for this project there is not a Speed pot. There is a Sweep along with the Manual, Regen and Width. But, I'm guessing the Sweep should maybe be a C500k?

Are you saying I should regulate more with the 2w10r in some way?
John

Scruffie

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Re: Noise help with a flanger
« Reply #14 on: August 22, 2019, 10:12:16 AM »
You need a 7815 or 78L15 regulator after the charge pump, whatever you're powering it with, put that in and see how you get on before doing anything else.

Sweep is Speed so yes it should be C500k.
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