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Author Topic: Guitar Amp powering off?  (Read 1230 times)

frank kayser

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Re: Guitar Amp powering off?
« Reply #10 on: March 10, 2014, 12:31:54 pm »


Either the guitarist is full of it (likely scenario), his equipment is damaged, or he is incompetent - he is using some kind of gate effect, but has his final level knob cranked, etc.


The guy needs a "toaster" - drive the amp as hard as he wants to get "the sound", but limit the power to the speaker.
I'm amazed more guitarists don't utilize of that kind of device - Don't know they exist? Don't know how to hook them up?  I know, they can't dominate the band if they use one.
frank
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Steve M Smith

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Re: Guitar Amp powering off?
« Reply #11 on: March 10, 2014, 12:34:20 pm »

I have seen that exact scenario more than a few times, especially on older mixing consoles with ribbon connectors between the channels.

I have modified just about every Peavey XR600/500/400 within 30 miles of me due to this problem.  Hard wiring between the contacts solves it.

It's not the ribbon cable at fault though, it's a build up of oxidisation on the tin plating of the connector contacts.

One of my friends used to get his XR600 working by turning the channel and master volumes up full and shouting into a microphone with no speakers connected, then turn it all down and plug the speakers in!


Steve.
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Mike Sokol

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Re: Guitar Amp powering off?
« Reply #12 on: March 10, 2014, 12:51:05 pm »


The guy needs a "toaster" - drive the amp as hard as he wants to get "the sound", but limit the power to the speaker.
I'm amazed more guitarists don't utilize of that kind of device - Don't know they exist? Don't know how to hook them up?  I know, they can't dominate the band if they use one.
frank

I used to build these power-soaks back in the 70's using toaster heating elements (I worked for Corning Glass at the time) and it could tame a 100-watt Marshall down to 10 watts or whatever. But it's hard to convince some stage musicians that they're loud enough out front no matter how good it sounds on stage. IIRC before he was famous Eddie Van Halen used a VariAC on his Marshall amp in small clubs to reduce the voltage down to 90 volts or so. That way he could get output tube saturation at a lower stage volume.

Stage volume is not just a guitar problem, I went through this last month in Evans, GA with a Hammond B3 player and a Leslie. Yikes...

Here's a THD Hot-Plate which looks like a high quality power soak.

John Roberts {JR}

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Re: Guitar Amp powering off?
« Reply #13 on: March 10, 2014, 01:21:48 pm »

I have modified just about every Peavey XR600/500/400 within 30 miles of me due to this problem.  Hard wiring between the contacts solves it.

It's not the ribbon cable at fault though, it's a build up of oxidisation on the tin plating of the connector contacts.

One of my friends used to get his XR600 working by turning the channel and master volumes up full and shouting into a microphone with no speakers connected, then turn it all down and plug the speakers in!


Steve.
I don't know about the smaller powered heads but yes, the larger ones use the same switching jack as gets used on typical console inserts between the mixer section and amp. One anecdote from a decade plus ago, when those products were under my responsibility. I discovered, after the fact that an engineer at the connector company had changed the plating spec on the switch contacts, in combination with a purchasing agent pursuing some small cost saving. IIRC the cost saving change was to silver plated vs tin plated (?), and while silver should be good, as we all know silver tarnishes and turn black over time. This was brought to my attention over the cosmetic concern that black jack contacts "looked" bad to QA inspectors in the factory, while they appeared to work OK there. When I learned of this I changed it back immediately (and kicked some purchasing a**). Even when optimally plated these switches can become problematic over time if not exercised. I do not suspect that you have any of the silver plated jacks, but even if you do they would be old enough to benefit from replacement.     

Rather than jumper across them I would just replace any faulty jacks with new ones. Many millions of these switching jacks are used routinely with quite modest failure rates. Decades later stuff happens.

JR
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Don Boomer

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Re: Guitar Amp powering off?
« Reply #14 on: March 10, 2014, 02:15:58 pm »



It's not the ribbon cable at fault though, it's a build up of oxidisation on the tin plating of the connector contacts.

One of my friends used to get his XR600 working by turning the channel and master volumes up full and shouting into a microphone with no speakers connected, then turn it all down and plug the speakers in!

I have found that to be a common problem with a lot of equipment, especially if those jacks are rarely used.  When they are used more frequently that tend to be self wiping and stay problem free for a much longer period.

Shouting into a channel to get it to turn on is usually some device in the channel that is on the verge of failing.  I had a mixer that did this once.  Yell into it and it worked just fine until you turned the mixer off.  Turned out to be a bad IC.
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Steve M Smith

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Re: Guitar Amp powering off?
« Reply #15 on: March 10, 2014, 02:21:51 pm »

and while silver should be good, as we all know silver tarnishes and turn black over time

Oxidised silver is still a good conductor though.  In my boring day job, I deal with products which use screen printed silver inks to produce flexible circuits and medical products on polyester - so I know a bit about silver tarnishing!

When printed silver is exposed such as part of a connector to go into a ZIF socket, we often overprint it with carbon.  This is largely a cosmetic thing to keep customers happy as they don't like to see tarnished silver no matter how many times we tell them it's ok!

Rather than jumper across them I would just replace any faulty jacks with new ones.

It's not the jacks I hard wired, it's the inter PCB connections which are on pins and crimp sockets (Molex? - or similar).  Cut off the crimps and solder the wires straight to the pins and the problem goes away.

It makes it a bit trickier when something else needs repairing - but invariably, that would be done by me as well!


Steve.
« Last Edit: March 10, 2014, 02:25:48 pm by Steve M Smith »
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John Roberts {JR}

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Re: Guitar Amp powering off?
« Reply #16 on: March 10, 2014, 04:35:00 pm »

I have found that to be a common problem with a lot of equipment, especially if those jacks are rarely used.  When they are used more frequently that tend to be self wiping and stay problem free for a much longer period.
Unfortunately insert jacks can sit unused for the life of the product.
Quote
Shouting into a channel to get it to turn on is usually some device in the channel that is on the verge of failing.  I had a mixer that did this once.  Yell into it and it worked just fine until you turned the mixer off.  Turned out to be a bad IC.

Sorry but I must disagree... Perhaps an IC pin making a bad connection in a socket, but semiconductor devices do not fail that way. The loud sound punching through is a purely mechanical metal to metal connection, with insulating oxidation layer.

JR
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Mike Sokol

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Re: Guitar Amp powering off?
« Reply #17 on: March 10, 2014, 05:08:13 pm »

Sorry but I must disagree... Perhaps an IC pin making a bad connection in a socket, but semiconductor devices do not fail that way. The loud sound punching through is a purely mechanical metal to metal connection, with insulating oxidation layer.

JR

I agree with your disagreement. I remember something we called "thermal ratcheting" back in the 70's which allowed IC's to walk up out of their sockets due to temperature cycling. When it walked up onto an oxide pad, then you would have a high-resistance failure of some sort. Pushing the IC's back in the sockets would "wipe" the contacts and scrape through the oxide layer, so the circuit could work for another few months or so. This was in mini-computers (remember them?) so we left them on all the time to minimize the problem. The computers that were turned off daily would sometimes fail several times a year, but those that were left on all the time (and at a constant temp) could go for years without a high-resistance failure of this type. I even did a few meter tests on IC legs to confirm this high resistance hypothesis.

Bob Leonard

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Re: Guitar Amp powering off?
« Reply #18 on: March 10, 2014, 07:13:20 pm »


Either the guitarist is full of it (likely scenario), his equipment is damaged, or he is incompetent - he is using some kind of gate effect, but has his final level knob cranked, etc.

All the above, PLUS, the guy probably has an effects board the size of Ohio and 500 stomp boxes all fighting against each other. The best way to deal with players like this is to either embarrass them or just punch them in the fucking head.
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Mike Sokol

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Re: Guitar Amp powering off?
« Reply #19 on: March 10, 2014, 08:12:12 pm »


All the above, PLUS, the guy probably has an effects board the size of Ohio and 500 stomp boxes all fighting against each other.

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