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Author Topic: Peavey Musician Series 300  (Read 6691 times)

86warlock

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Peavey Musician Series 300
« on: September 12, 2010, 01:47:32 AM »
I have an old Peavey 300 series head that works BUT Has too much volume when the volume control is turned all the way down. Its actually pretty loud! Can anybody give advice on this? I have some electrical repair ability.

Thanks in advance!

phatt

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Re: Peavey Musician Series 300
« Reply #1 on: September 12, 2010, 09:44:51 AM »
Hi Warlock,
               Don't know the Amp but from your comment the Volume pot might have gone open circuit.
If the ground leg on the Volume pot breaks then that will be the result.

While running an audio signal Gentle pressure around that commponent on the circuit board may lead you to the offending issue. It may only be a cracked solder joint on the board but if the pot has *internal damage* then replacement is the best option. :(
Pots are touchy little things and are a moving part.
Hope you sort it out.
Phil.

86warlock

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Re: Peavey Musician Series 300
« Reply #2 on: September 12, 2010, 09:56:17 PM »
Thanks for the note. I removed to volume pot today and tested it out of circut. Its a 10K linear pot and tests 8K turned all the way to the right and 16 Ohm rolled all the way back, Shouldn't it be 0 Ohms to 10K Ohms? Thanks for the help!
« Last Edit: September 16, 2010, 08:12:40 PM by 86warlock »

DJPhil

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Re: Peavey Musician Series 300
« Reply #3 on: September 13, 2010, 02:02:00 AM »
Thanks for the note. I removed to volume pot today and tested it out of circut. Its a 10K linear pot and tests 8K turned all the way to the right and 16 Ohm rolles all the way back, Shouldn't it be ) Ohms to 10K Ohms? Thanks for the help!

In a perfect world yes, but this is a fairly common spread. Poor original tolerance and age may have taken that last 2K, which is important for your low volume operation.

However!

A linear pot you say? You might get the fine control at low volume you're after by simply replacing it with a log pot! The downside is that if there's something truly wrong you're just treating the symptoms instead of finding a cure. It's not uncommon for amp manufacturers to use a linear volume pot as a marketing strategy, as it sounds louder at low volume implying more total power (Dude, this thing is loud at 2, imagine 10!). If this is the case then you are actually treating the problem, at least in my opinion. Has it always been this way? If so, it's a good sign that there's probably nothing wrong that wasn't built in. :)

If you have a log pot handy you can test it. Ideally you should use a 10k log, but anything up to around 100k should be fine, and you could go higher. If you have a lot of choice, try a 20k. No log pots handy? You can get really close with a linear pot and a resistor. The main issues with the creative substitution of pots involve loading the circuit, but without a schematic it's hard to say if this will be an issue. This loading won't usually hurt anything at audio signal levels other than to potentially add non-linearity or distortion to the signal, and this is not often a concern with a guitar amp. Essentially, you probably won't hurt anything by experimenting (unless you have an accident or do something silly) and you can judge by your own ear to see if there's an undesirable change in tone.

The one thing to watch out for is the giant, high power pots or rheostats used to attenuate the high power output on some amps. I've seen them in schematics for older tube amps, but who knows, there may be some solid state amps that do this too. These aren't too common in my limited experience, and are easy to spot by their size. They're intended to serve as a volume control for large amps that want a low power mode for studio use while still overdriving the amp's power stage, and dissipate several to tens of watts as heat. I wouldn't suggest experimenting with one of these unless you're sure of what you're doing, as there's a lot of power flying around.

See The Secret Life of Pots for details on tapers and simulating them with a linear pot.

If in doubt, there's no harm in waiting until one of the pros stops by, I'm just a new guy. :)

Too much coffee, I hope I didn't ramble too much! :)