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FDP Forum / Miscellaneous and Non-Fender Topics / Is there such a thing as impedance buildup in guitar cables?

LeftyMeister
Contributing Member
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Buckeye Country, USA

Tone is in the lingers
Apr 21st, 2019 11:42 AM   Edit   Profile  

Last night at band practice, my amp kept cutting out. It would abruptly go silent for a few seconds, or the volume would diminish noticeably, and then return. I checked a few things but couldn't find anything wrong. I was suspecting a bad tube.

This morning at practice before church, I took a backup amp just in case. While practicing, I noticed the problem correlated with my Plimsoul. It wouldn't always happen but seemed to occur after it was engaged for awhile or I increased the volume or gain. If I lowered the volume, the problem would stop. So I jiggled the jacks and the problem went away completely. I tried jiggling the jacks and cables repeatedly but couldn't get the problem to return.

Since the jacks were fully plugged in and, since I recently rebuilt my pedalboard (ie, know the cable is good), I can't figure it out. It almost seemed like an impedance buildup issue.

Having an engineering background, I know impedance is the total opposition to current in an AC circuit (ie, resistance + reactance). Since the jack was fully plugged in and the cable is fine, maybe it was a build-up of reactance because of...whatever. Is that possible?

*scratches head*

Leftee
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VA

Apr 21st, 2019 03:21 PM   Edit   Profile  

I’ve not heard of that.

Your symptom does sound like an intermittently bad connection, though. Very intermittent.

Peegoo
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Planet Peegoo

Lewd guitar player
Apr 21st, 2019 04:27 PM   Edit   Profile  

Varying resistance or impedance does occur through solid connections, but only in conductors that heat up in use. As the temperature rises, resistance increases. But that is not the case here.

Your issue is most likely due to a poor connection in a jack or just beyond it in the amp. These sorts of intermittent issues happen due to wear or corrosion on contacts or sometimes a failing solder connection on a component in the circuit. The symptom you describe--how turning up the output on the pedal "fixes" the problem--is pretty rock solid evidence this is the case.

Leftee
Contributing Member
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VA

Apr 21st, 2019 04:40 PM   Edit   Profile  

You can get mild capacitance in cables.

LeftyMeister
Contributing Member
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Buckeye Country, USA

Tone is in the lingers
Apr 21st, 2019 05:59 PM   Edit   Profile  

Peegoo, good points except turning up the pedal volume made it worse.

Eric, I thought about that too but I couldn't figure out how that would cause my symptoms.



walshb
Contributing Member
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Manchester, TN

Ask me how I know!?
Apr 25th, 2019 03:03 PM   Edit   Profile  

I'm only having this problem with 3 different amps right now! All problems where the amp suddenly loses volume, a lot of volume. I've been thinking tubes.....until I realized the problem is very similar in all 3 amps. I haven't even begun to try and troubleshoot yet....
Let us know if you figure it out!

Cal-Woody

USA/California

Why do I keep fixing things that work?
Apr 25th, 2019 05:39 PM   Edit   Profile  

Sounds like a dirty pot on the pedal. As for the amp, if it is a tubed amp then it sounds like you are losing your bias control and related parts.
I would also look into trying different cables because we step on them frequently and cause intermittent shorts in them and that can drive you crazy. Dirty, defective pots are also symptoms of this kind of issue.
For LeftyMeister I would be cleaning up the pots on your pedal then check out the cabling for shorts. Or a power supply connection that's just barely there and when you adjust the pedal it moves enough to cause an issue. Lots to check out.

Peegoo
Contributing Member
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Planet Peegoo

Rhythm & Lewd Guitarist
Apr 25th, 2019 07:48 PM   Edit   Profile  

Many ‘noiseless’ instrument cables have a carbon-impregnated cloth or polyethylene sleeve around the inner conductor’s insulation. It’s designed to prevent the woven or spiral shielding from sliding on itself and generating crackles and pops when the cable is moved around.

I mention this because I’ve had problems with this stuff. The assembler at the factory does not trim back that sleeving far enough from the center conductor’s solder connection inside the plug, and it makes contact with the solder joint.

The carbon composition acts as a resistor and drains some or all of the signal to ground. It makes the volume drop some, or it completely kills the signal.

Many noiseless cables have molded plugs and are not repairable; you have to cut the plugs off and solder on new ones.

If your cable has metal plug bodies, open them up and see if the center conductor’s insulation has a black sleeve around it. If it does—you’re the nephew of a guy named Robert :o)

If in doubt, set your meter to test Ohms and take a reading on the surface of the insulator. These partial shorts are often intermittent, so carefully trim that stuff back away from the solder connection.

(This message was last edited by Peegoo at 12:14 AM, Apr 26th, 2019)

LeftyMeister
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Buckeye Country, USA

Tone is in the lingers
Apr 25th, 2019 09:29 PM   Edit   Profile  

I use a Leem cable that's 20 years old and I've never had the first issue with it. It's been an amazing cable.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Apr 26th, 2019 02:21 AM   Edit   Profile  

Peegoo described the Mogami type of cable. They have a black carbon insulator around the inside center of the cable.

FDP Forum / Miscellaneous and Non-Fender Topics / Is there such a thing as impedance buildup in guitar cables?




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