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Post new topic Buffer Adds Pot Noise *UPDATED/SOLVED*
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Author Topic:  Buffer Adds Pot Noise *UPDATED/SOLVED*
Jon Light


From:
Saugerties, NY
Post  Posted 10 Apr 2017 9:45 am    
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I was going to change the (very old) pot in my pedal that was getting pretty scratchy.

But I just happened to plug direct from pedal to amp, skipping the Freeloader that I've been using forever.

All passive like this, there is a little rustling sound from the pot but not bad. When I go back to the Freeloader it's like somebody has amplified the small noise and it is dominant.
Without the buffer, I could easily keep the old pot. With it, big noise, no good.

Signal chain with Freeloader: Guitar-->Freeloader-->volume pedal-->amp.

What's happening here?


Last edited by Jon Light on 30 Jun 2017 7:16 am; edited 2 times in total
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Darrell Birtcher

 

Post  Posted 10 Apr 2017 9:58 am    
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Deleted post.

Last edited by Darrell Birtcher on 10 Apr 2017 10:27 pm; edited 1 time in total

Jon Light


From:
Saugerties, NY
Post  Posted 10 Apr 2017 10:35 am    
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I'm going to walk this back.
I seemed pretty dramatic but I went out and did some chores and now I'm working on this and it's not nearly as big a deal. I suspect that you were right, Darrell, and also that I exercised the worst of the noise out of the pot and now the difference is just not a big enough deal to sweat for the moment.
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Glenn Demichele


From:
(20mi N of) Chicago Illinois, USA
Post  Posted 10 Apr 2017 10:50 am    
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I think what you are hearing is D.C. From the buffer being applied to the amp through the pot. If there is a D.C. on the pot, and the pot is noisy, the intermittent wiper contact will cause big jumps in the output D.C. Value, thereby sounding like loud noise.
If you only have ac into the pot, it'll be dead quiet unless you are actually playing a note, and move the pedal while the note is sounding.
The buffer should have a D.C. Blocking output cap. That could be leaky, or if it's really big, you might need the leave the pedal hooked to the buffer for awhile after power up to let the D.C. Bleed down.
_________________
Franklin D10 8&5, Excel D10 8&5, homemade buffer/overdrive, Moyo pedal, GT-001 effects, 2x BAM200 for stereo. 2x GW8003 8" driver in homemade closed-box. Also NV400 etc. etc...
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Jon Light


From:
Saugerties, NY
Post  Posted 10 Apr 2017 11:18 am    
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Thanks Glenn. I had actually written a post talking about the dc leakage thing because that was the sound I was hearing (I've heard it before with some amps) but I'm just not conversant enough on the subject to even compose an intelligent post so I ditched it.

Maybe that bleed down is the difference between when I first saw the problem today and the much reduced symptoms now.
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Georg Sørtun


From:
Mandal, Agder, Norway
Post  Posted 10 Apr 2017 11:47 am    
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The usual suspect for "scratch"-noises in VP pots, is minute DC-charges in signal-coupling capacitors right before and/or after the pot, causing DC to overlay the signal going through the pot.

Pots in constant movement (like in passive VPs) are inherently weak when presented with the job of discharging DC-charges, and will (literally) develop burn-marks on the pot-track over time.

- With coupling capacitors both before (in buffer-amp or effect units) and after the VP pot (in amp-input or effect units), any tendency to DC-charge will build up higher. As a result the "scratch"-noise heard when the DC-discharge varies at/around the wear marks will be louder.

- With just the PU before the VP-pot, the PU will participate in the DC discharging process. As the average PU has less than 1/20 the resistance of a 500Kohm pot, the PU is an effective discharger compared to the usual resistor to GND found at inputs and outputs of buffers, effect units and amps. As a result of the reduced DC-charge over the pot itself, the "scratch"-noise will tend to sound much lower.

Whether it is the capacitor at the buffer-output, or the capacitor at the amp-input, that suffers from DC-charging tendencies and causes the destructive DC-charge over the pot in the first place, is impossible to say without being able to analyze and measure very, very, minute DC-charges in the actual setup. Once the VP pot is damaged by DC-discharges it cannot be saved, and should be replaced.
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Jon Light


From:
Saugerties, NY
Post  Posted 10 Apr 2017 2:14 pm    
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Thanks George. Good facts and info. Time has taught me that as much as I would like to learn and understand electronic theory and practice, I have a stunningly low aptitude. Hard to figure.
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Brad Sarno


From:
St. Louis, MO USA
Post  Posted 10 Apr 2017 2:31 pm    
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This is fairly normal. The trick is to wait a minute and any DC charge present at the output of the FreeLoader (also present at the pot) will drain off and the pot pedal will become 100% scratch-free.

The early freeloaders used a larger value output cap and took longer to drain off the DC. More recently I've put smaller value caps and they drain off much more quickly. But if the scratchyness doesn't entirely go away, then maybe need to fix that. Perhaps the output cap is leaking a tiny bit of DC. I can easily send you a new one and it's super easy to solder in.

After all, DC is one of the primary causes of scratchy pots.

B
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Jon Light


From:
Saugerties, NY
Post  Posted 10 Apr 2017 2:42 pm    
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Brad--thanks a bunch for the info. Between this and the other posts here, it's coming to me that this is not the first time I thought my pot was shot and then a little while later I said...wait, I totally forgot about the problem...it's gone away...what the...?

I can't recall ever seeing this described before which is sort of amazing.
It's great learning this. I will monitor this for a while. It's great to know that I can source a cap from you if that seems to be indicated.
Thanks!
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Brad Sarno


From:
St. Louis, MO USA
Post  Posted 20 Jun 2017 7:09 am    
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It does seem like the output capacitor on the FreeLoader may be leaking DC, and that DC on the volume pedal's pot is likely causing the scratching.

It would also be a good test to make sure that no DC is coming from the amp's input. It's not likely, but testing with another amp will rule that out.

Replacing the output cap in the FreeLoader is super easy with basic soldering skills, and I'm happy to send one to you no charge.

And this is a good reminder that sometimes any of these buffers people use can have a DC charge present when first powered-on, and then it can take a few seconds, even a minute or 2 in some cases, for that DC to drain away and let the pot get quiet again.

B
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Jon Light


From:
Saugerties, NY
Post  Posted 20 Jun 2017 7:55 am    
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For anybody wondering why Brad popped this back up, I email him this morning for a follow up (with a link to this thread as a reminder of what we were discussing).

Thanks for putting this general info out there!

I'm emailing you contact info.
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Jon Light


From:
Saugerties, NY
Post  Posted 30 Jun 2017 7:13 am    
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**IMPORTANT UPDATE**

two vital notes:

1) Brad did what many people can attest he does---he corresponded with me and followed through with a replacement cap. Thanks, Brad.

2) The problem turns out to be TOTALLY UNRELATED TO THE FREELOADER.

I am working at confirming my discovery today but it seems to be all about a tuner in the third jack of my Goodrich 120.
I've did the volume pedal "MOD" a few years ago --- a resistor installed between the output jacks. I figured that this put everything in this jack outside of the signal path so I was using an absolutely crap $.17 plastic cord that I should have trashed long ago (a freebie from some crappy ebay music store) to run out to the tuner. That's not going to happen again. With the tuner off, there was no problem. With the tuner on, problem. But I just discovered that with a decent cord, there is no problem, on or off. It was all about the Freeloader (and probably any active device?) heavily amplifying the pedal noise that for some reason this faulty tuner cord was causing. Without the Freeloader this was not an issue. And now with the Freeloader and a good cord, it is not an issue.


Who have thought of looking there? Everybody but me, maybe. I'm pretty embarrassed and I'm VERY sorry that I caused any hint that there was a problem with this buffer.
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Brad Sarno


From:
St. Louis, MO USA
Post  Posted 30 Jun 2017 7:44 am    
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Ha!

I'm glad the conversation came up, regardless. I think we all benefit from conversations around a troubleshooting process. That makes us all smarter when we see strange causes and fixes.

And just talking about the fact that DC voltage present at a volume pot causes scratchy-ness is something we all benefit from knowing. So many good pots got thrown away thinking it was the pot itself, but it was DC voltage leaking onto the pot instead.

Glad you got it cleaned up Jon!!


B
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Georg Sørtun


From:
Mandal, Agder, Norway
Post  Posted 30 Jun 2017 7:50 am    
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Yes!!
We need such "reminders" now and then... Very Happy
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Jon Light


From:
Saugerties, NY
Post  Posted 30 Jun 2017 8:00 am    
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It is so easy to think that you are smart enough that you can abandon rule number one when trouble shooting: tear it down to the most bare, basic elements.

With the random, intermittent nature of my problem, I never looked at the extra elements -- the tuner, the tuner out jack, and the tuner cord. Because smart me figured 'what does that have to do with this?'

When the tuner would sometimes be on, we would have one set of circumstances. When the tuner shut itself off automatically, we would have a different set. And I'm thinking 'discharging caps! Aha!'

*smh*
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