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Dummy Load for Stereo Guitar Amp

Started by ErichS, September 11, 2009, 09:20:11 PM

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ErichS

Hi everyone,

I have an old (~1985) Crate G20C Stereo guitar amp that I want to troubleshoot using my oscilloscope.  The schematic provides some test parameters and voltages to check, but the test must be performed with the volume on 10.

I have a Weber Mass Lite 50W attenuator that can be used as dummy load but I'm not sure if I can hook this up to the stereo outputs of the amp.

On the Crate there are two separate 10W outputs (one for each speaker). Can I just hook both + connectors to the tip and both - connectors to the sleeve of a single 1/4" jack to send into the Mini Mass?  I read somewhere that accidentally shorting the + and - terminals might cause damage to the amp but I wasn't sure about ++ and --

Thanks
Erich

J M Fahey

Hi erichs
Short answer: ***never-ever*** join "+"/positive/hot terminals from two (or more) amps.
Many, specially guitar ones, can't stand joining the "-" terminals either , because they are not ground proper.
Going to your amp, its low power makes everything easier.
Just two 15W or more power resistors, with an ohmic value close to your regular speakers will do, and for quite a low cost, specially compared to your Weber Mass.
Of course, you can use it on one channel at a time, because leaving the other one unloaded won't hurt it.
You can also use the speakers themselves, if your neighbors can handle that.
Sounds interesting, please post your experiences, an oscilloscope is God's send but usually unavailable.

ErichS

Quote from: J M Fahey on September 11, 2009, 11:31:00 PM
Hi erichs
Short answer: ***never-ever*** join "+"/positive/hot terminals from two (or more) amps.
Many, specially guitar ones, can't stand joining the "-" terminals either , because they are not ground proper.
Going to your amp, its low power makes everything easier.
Just two 15W or more power resistors, with an ohmic value close to your regular speakers will do, and for quite a low cost, specially compared to your Weber Mass.
Of course, you can use it on one channel at a time, because leaving the other one unloaded won't hurt it.
You can also use the speakers themselves, if your neighbors can handle that.
Sounds interesting, please post your experiences, an oscilloscope is God's send but usually unavailable.


J M,

Thanks very much for the reply.  I kind of had a feeling that would be a bad idea.  I'm just getting into solid state circuits.  I've been working with tube amps up to now and only mono amps.  I just got the O-Scope a few weeks ago and am allways trying to find ways to use it more. 

The Crate has some problems with an intermittent distortion channel and I haven't played it for years so I thought this might be a good learning experience.

I'll get the resistors as you mentioned, I was just hoping to get started tonight.

Thanks again