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 Post subject: Noise help on a build
PostPosted: Tue Aug 20, 2019 8:44 am 
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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?


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PostPosted: Tue Aug 20, 2019 9:53 am 
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Hey John! Posting a link to the schematic could help.

Does this circuit have a blend control? Is there a way to isolate the wet and dry signals? One way to figure out the noise issue is to isolate what is causing the noise.

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PostPosted: Tue Aug 20, 2019 9:59 am 
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Hey Morgan, I don't have a pic of the schematic but I think I have it at home. It was hard to get the docs on this old one so I'll take a pic of the schematic later tonight and post it here.

The controls are Speed, Regen, Manual and Width. Based on the old manual I found on line there is no wet/dry mix/isolation knob.

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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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PostPosted: Wed Aug 21, 2019 8:47 am 
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Here is the schematic. Also a couple suggestions over at Bean's. Not sure what you would think about those and the effect it could have on the noise. http://www.madbeanpedals.com/forum/inde ... 81.new#new

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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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PostPosted: Wed Aug 21, 2019 9:13 am 
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I've got nothing constructive to add on this other than to say "Good luck!" Sounds to me like noise at some level is just part of this circuit's character. FWIW (not much, I dare say), I built Bean's "Current Lover" flanger (EHX Electric Mistress-type circuit) a few years back and couldn't dial all the background swooshing noise out of that one, either. But it's not as bad as you're describing with this one.

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PostPosted: Wed Aug 21, 2019 11:17 am 
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duhvoodooman wrote:
I've got nothing constructive to add on this other than to say "Good luck!" Sounds to me like noise at some level is just part of this circuit's character. FWIW (not much, I dare say), I built Bean's "Current Lover" flanger (EHX Electric Mistress-type circuit) a few years back and couldn't dial all the background swooshing noise out of that one, either. But it's not as bad as you're describing with this one.


Yeah, I have a feeling that might end up being the case too Bob. I have the Current Lover and while I do get the swooshing mine is so low it doesn't affect me, that or my hearing is that bad. But this one, no way could I, or would I want to play it in it's current state.

I had these old chips and just figured why not try to build something so nothing ventured nothing gained but I won't give up yet.

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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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PostPosted: Thu Aug 22, 2019 1:03 pm 
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Got some advice over at Bean's. My plan is to put some shielded wiring in, swap out the Speed pot to a C500k, the BOM had it as an A500k, and to put a 7815 regulator on the Road Rage board to see where all that puts me at and go from there.

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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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PostPosted: Fri Aug 23, 2019 9:15 am 
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Before doing all that, I'd probe the input (pin 2) and output (pins 11 & 12) to confirm that the noise is being generated from the SAD chip.

While you have your audio probe out, listen to the SAD output while you adjust the bias trimmer (T1) then also listen to IC2 pin1 while you adjust T2.

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PostPosted: Mon Aug 26, 2019 9:19 am 
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Morgan wrote:
Before doing all that, I'd probe the input (pin 2) and output (pins 11 & 12) to confirm that the noise is being generated from the SAD chip.

While you have your audio probe out, listen to the SAD output while you adjust the bias trimmer (T1) then also listen to IC2 pin1 while you adjust T2.


Well crap, I should have jumped on here first but instead I took off work Friday and dove into the pedal Sunday going off the Bean thread forgetting to pop in here. As I get older I have a focus problem apparently :roll:

I will do as you say but first I have to fix this (copy and pasted from Bean's today)

- So as it turns out, I should never rely on memory at work, I was running it at 18v and that is the reason I didn't put in a regulator. I'm using an old Road Rage board which corresponds with Bean's 2012 build doc.

So I figured let me rewire for 15, add a regulator and see what happens. Well. when I did that all I got was this huge hum and the pedal pretty much didn't work any longer or I could just barely make out an audible swoosh but he hum is so loud, even with guitar volume off, I have to shut the pedal off or something like my speaker might blow! So because of this hum and my lack of time this weekend apparently I didn't bother with shielding the wire yet. I did put in a C500k Speed pot though.

So, I ran out of time to fiddle around. How about if I punt and start from scratch here and I'll work up a new RR board to power this thing.

If you were me would you run this thing at 18v no reg per the RR BOM or 15 with reg? Also, the correct orientation of the 7815 was where the metal backing would lay flat on the RR board (I made sure it didn't so as not to touch the SAG control eyelets), correct?

Out of curiosity, would running it at 9v be such a bad idea I wonder?



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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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PostPosted: Mon Aug 26, 2019 9:57 am 
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Yeah, get it to zero first. Make sure you are supplying the circuit with the proper voltage (15 volts regulated).

Also, with that huge hum, you need to verify that the RR board is putting out 15 volts, or see if you connected something backwards. There isn't a good reason that changing the voltage from 18 volts to 15 volts would cause a massive him like that. It's usually because something got connected backwards .

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PostPosted: Wed Aug 28, 2019 6:30 am 
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Just to update the thread I replaced the Road Rage board and the pedal worked with minimal or I guess normal noise. While I can't pinpoint why in looking at the old RR board as it looks good apparently there was an issue on that board. But in a comical moment, one has to laugh at times, I had 2 of the SAD chips so I wanted to test the second one. I pulled the chip out and noticed that pin 16 of the socket pulled up. Never had that happen before. I pushed it back down wondering if the socket was buggered up. I put the chip back it and of course nothing works. Dead quiet when I kick the pedal on. I said one has to laugh right?

So I guess I'll desolder a 16 pin socket. This should be fun. Hope I don't jack up the board doing this. I suppose I could attempt to solder in the pin that is not connecting but then all kinds of bad crap could happen. I could solder it in with of course chip in there and it still doesn't work. I could burn out the chip maybe, dunno.

Who says this hobby isn't fun :?

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powerpopguy wrote:
warm places theory sounds plausible. Occasionally, I wake up and think my snake is missing too, but it turns out it's just a chilly morning. :P


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