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Author Topic: Noisy guitar: a head-scratcher  (Read 4266 times)

Bob Leonard

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Re: Noisy guitar: a head-scratcher
« Reply #10 on: May 30, 2015, 12:08:51 AM »

No, not a magnetic field. You are experiencing RFI. Find out what that circuit powers and what else runs on the circuit in that room.
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Scott Olewiler

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Re: Noisy guitar: a head-scratcher
« Reply #11 on: May 30, 2015, 06:59:07 AM »

Quick update:

The extension cord test identified that it's the room, not the electrical.

Guitar is a Suhr Strat or fender Strat, both with Humbuckers in the bridge positions, amp is a Suhr Badger.

If  amp is connected to electrical in them questionable room, I get noise.
If I move the amp to another room and get electrical from that other room, it's nice & quiet.
If I keep the amp in the questinable room and run an extension cord to the known 'quiet room', I still get the noise.

Keeping the amp plugged in the 'bad room' and walking out the room with the guitar and amp live, the noise quickly reduces as I move away from the room.

SOMETHING is throwing a magnetic field in that direction - no plumbing closely that I'm aware of. I think I'll just shutdown everything breaker-by-breaker and see what makes it go away!

Is there an older style TV or Computer monitor in that room that's on?  I believe I remember those causing me some issues in the distant past.  Of course, I "believe" I "remember" a lot of things these days, most of them questionable.
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John Roberts {JR}

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Re: Noisy guitar: a head-scratcher
« Reply #12 on: May 30, 2015, 11:18:06 AM »

The obvious suggestion i don't play guitar in that room.  8)

Seriously you can use the guitar as a noise sniffer. Move the guitar around the room and see where it gets loudest. Perhaps lighting? Something is making the noise.

JR
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GenePink

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Re: Noisy guitar: a head-scratcher
« Reply #13 on: June 08, 2015, 05:32:59 AM »

The obvious suggestion i don't play guitar in that room.  8)

Seriously you can use the guitar as a noise sniffer. Move the guitar around the room and see where it gets loudest. Perhaps lighting? Something is making the noise.

These days, lighting dimmers are getting so cheaply made, that I wouldn't be surprised if they don't even bother with the choke noise filter. If there is light dimmer in that room, rotate it and and see if the noise changes.

I once had a problem with severe dimmer noise when playing in a band, all the guitar amps and my bass amp started buzzing like crazy in the middle of a set. Turns out the bar owner, tired of bands playing too loud, put the stage power on a wall dimmer so he could "lower the volume" from behind the bar. Let's just say, I was a bit , um, "miffed". Never mind the rest of that story, not my shining hour in the art of diplomacy. Let's just say that guy now shits in stereo.

Off topic: JR, are you interested in my household lighting dimmer mod? Change out two parts, add three more, and a 6 dollar wall dimmer preforms like a 40 dollar one, no hysteresis at all in the low end of the range.

Hint: it is based around a rather unique part found in a Peavey CS-800.

Gene

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Steve M Smith

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Re: Noisy guitar: a head-scratcher
« Reply #14 on: June 08, 2015, 06:58:39 AM »

Off topic: JR, are you interested in my household lighting dimmer mod? Change out two parts, add three more, and a 6 dollar wall dimmer preforms like a 40 dollar one, no hysteresis at all in the low end of the range.

Hint: it is based around a rather unique part found in a Peavey CS-800.
If he's not, I am.

I don't know about the CS800 but there are a few triacs in the CS1000... And an opto triac driving a larger triac.  Is that it?


Steve.
« Last Edit: June 08, 2015, 07:01:34 AM by Steve M Smith »
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GenePink

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Re: Noisy guitar: a head-scratcher
« Reply #15 on: June 21, 2015, 03:58:01 AM »


I don't know about the CS800 but there are a few triacs in the CS1000... And an opto triac driving a larger triac.  Is that it?

The device is called a Silicon Bilateral Switch (SBS) and the CS-800s use them to fire the triac crowbar circuit on the output, if DC is detected. Usually, you find a diac feeding the gate of a triac, but those take 24-32 volts to fire, where an SBS is around 8 volts. An SBS also has a third terminal, a gate, to fire it on even when the main terminals have less than 8 volts across them.  Peavey doesn't use this terminal, they are just after the 8 volt low threshold to crowbar quicker, to protect those precious 22A Spyder driver diaphragms.

This dimmer circuit uses the gate to reset the timing capacitor to a nominal consistent value each full cycle, with two diodes and a resistor, set to dump the cap through the gate of the triac.

Or something like that, I still haven't wrapped my head fully around this circuit. But it works.

The retrofit goes like this:

1) Drill out rivets in 6-dollar dimmer. (replace with screws and nuts later)

2) Ensure that you actually have a triac, not a quadrac, which has the diac built-in. If quadrac, replace with a triac, or start with another brand of dimmer. The presence of a diac connected to the gate of the triac is a good thing here.

3) Replace diac with SBS. Doesn't matter which main terminals, they are symmetrical.

4) Replace timing cap with something about 10 times the value (0.022 with 0.22, this will likely need to be tweaked later)

5) Add two diodes and a 47K resistor (the attached schematic is flat out wrong on that value, 5.1K is just retarded).

6) Connect a lightbulb and power, try. If light is too bright at the lowest setting, increase the timing capacitor value, The exact cap value is dependent on the pot value that came with the thing, so you have to tweak.

7) Once you have it to where you like it (I go for a dull red filament, like a preheat on stage cans), reassemble, install, and enjoy the lack of hysteresis.

Note that SBS's are getting a bit hard to find, I lucked out and nabbed a spool of flea-sized surface-mount ones that, with shipping, came out to about 3 cents each. Just gotta solder wires to the little nubs to make them "normal".

And if there is not a choke for noise suppression in the dimmer, please add one. Or a dual wound choke to keep common-mode noise from coming out would be better.

Gene

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John Roberts {JR}

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Re: Noisy guitar: a head-scratcher
« Reply #16 on: June 21, 2015, 11:23:08 AM »




Off topic: JR, are you interested in my household lighting dimmer mod? Change out two parts, add three more, and a 6 dollar wall dimmer preforms like a 40 dollar one, no hysteresis at all in the low end of the range.

Hint: it is based around a rather unique part found in a Peavey CS-800.

Gene
I don't even play guitar...  ;D  To be honest I am not that familiar with old-school CS800 details... I don't recall ever seeing or messing with SBS,,, I do have my own horror story about triacs.
--------
Peavey was pretty good about sharp pencil engineering and used power triacs with a small switch to commutate the gate resistor to make/break higher current levels while keeping UL happy. I inherited one such power switch circuit in a line if fixed install mixer-amps that I was responsible for. I've used triacs several times in designs over the decades and for me they were always pretty well behaved. Until this one fixed instal amp started having field failures where the amp just wouldn't turn on. The small gate resistor would generally vaporize since they are never sized to survive full mains voltage into a short.

One time is just a random incident, but after these started piling up, and fixed install customers had a bunch of very expensive service calls to complain about, I had to get involved.

Step one, I tried but could not recreate the problem on my bench. (even using known suspect parts). 

Step two I sent a handful of parts that had failed (to start) in the field back to the thyrister manufacturer to test. Of course they found nothing wrong, and had no suggestions. 

Step three... I replaced the triac with a heavier duty mechanical power switch.

It probably cost me all of $0.25 more but that failure mode remains a mystery. Apparently the triacs had one quadrant of operation where they just didn't operate sometimes. I got a little heat for the cost increase, but the field failures for that amp went to the normal near zero, and customers could return to complaining about other stuff.  8)

JR

PS: It is not unusual for vendors to not find problems with their components. I had one Japanese vendor that I was buying cassette deck transports from that would mysteriously lock up...This was actually the second time I sourced a transport from that company. The first one worked reliably.

I wrestled with that problem for a few months trying to figure out what I had done wrong. These were pretty standard transports and the vendor claimed that the exact deign was used in millions or hundreds of thousands of consumer products. Only after months of me cycle-testing and losing sleep over this, they finally admitted to using an incorrect durometer plastic in one of the internal gears and that was what was causing the jam. By then the new product using this transport had developed a horrible reputation with dealers and was all but dead. It would have been an uphill battle to re-launch the product so it quietly (but not cheaply) faded away.   
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Jamin Lynch

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Re: Noisy guitar: a head-scratcher
« Reply #17 on: June 23, 2015, 11:04:34 AM »

How many pedals does he have?

I've had problems with guitar players who walk in with the "pedal board from hell" and wonder why there's noise.
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Re: Noisy guitar: a head-scratcher
« Reply #17 on: June 23, 2015, 11:04:34 AM »


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