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Resistance mods for limiting amp volume

J

John Burgess

Nov 28, 2011
79
42
Australia
#1
Hi I am trying to work out a solution for school amplifiers that get abused, ie the volume turned all the way up, resulting in blown speakers.

The idea occurred to me that resistors could be added to the volume potentiometer so that there is always a base resistance, meaning that even when the volume is turned all the way up, you may only be at 60% volume, or whatever is desired.

Is something that has been tried? Would resistors simply be added in series to the outer legs of the potentiometer?
 
#3
B-string said:
Signing out equipment with the statement that damages WILL be the responsibility of the student and/or student's parents is more effective. If the student and student's parents don't sign then they need to find a new elective.
Click to expand...

yeah, that's ok if students actually have an amp checked out, but what about the situation where amps are just in the music room, and there are 3 or 4 bassists in the school (or guitarists....whatever kind of amp it is), and at the end of the day, the teacher comes back to find a blown speaker....

how ya gonna know who did it?

don't know, but how about a physical block on the volume knob so it can't go above 6 (or whatever)

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#5
B-string said:
One good OD pedal will render your efforts pretty much useless. Amps and cabs should not be "just sitting" in the band room. If not signed out they should be locked in an equipment room.
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well, maybe, in a perfect world....but at my son's school, they have a couple of classrooms with guitar/bass amps in them, and the teacher is not there all the time....they certainly do not have provision to check out a particular amp to a particular student

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#7
B-string said:
Then who is responsible for the equipment? I know real world things get ignored and the old "we never had a problem" comes in. If you don't teach responsibility at home and/or in the school (which equates to a working situation) where is it to be learned?
Click to expand...

DUDE!....it's a Nashville public school and this is America circa 2013....i think they are teaching them exactly what they WANT to be teaching them...:D

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#8
B-string said:
Then who is responsible for the equipment? I know real world things get ignored and the old "we never had a problem" comes in. If you don't teach responsibility at home and/or in the school (which equates to a working situation) where is it to be learned?
Click to expand...

I appreciate the angle that you're coming from, though my skills are mainly in the musical and technical realm. There's finite supervision for students and even if all students are aware of damaging the amps, all it takes is one student to break the amp for everyone.

I like the idea of a physical gate on the amp. A different shaped knob and a stopper on the plate could work.
 
#10
John Burgess said:
I appreciate the angle that you're coming from, though my skills are mainly in the musical and technical realm. There's finite supervision for students and even if all students are aware of damaging the amps, all it takes is one student to break the amp for everyone.

I like the idea of a physical gate on the amp. A different shaped knob and a stopper on the plate could work.
Click to expand...

except you have to be sure that they couldn't just pop the knob off and turn the little metal stub....those kids are smarter than you think....:D

maybe a dab of epoxy or Gorilla Glue?

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#11
John Burgess said:
I appreciate the angle that you're coming from, though my skills are mainly in the musical and technical realm. There's finite supervision for students and even if all students are aware of damaging the amps, all it takes is one student to break the amp for everyone.

I like the idea of a physical gate on the amp. A different shaped knob and a stopper on the plate could work.
Click to expand...

They could always just pull the knob off and set it higher if so inclined. A resistor in series with the wiper might help. Like I said though an OD pedal will render that useless.
That one student can also poke a pencil or pen into the speaker cones to see if it will "make the pencil move". ;)

Choosing a safer amp power to cab input power is a more effective plan.
 
#13
B-string said:
They could always just pull the knob off and set it higher if so inclined. A resistor in series with the wiper might help. Like I said though an OD pedal will render that useless.
That one student can also poke a pencil or pen into the speaker cones to see if it will "make the pencil move". ;)

Choosing a safer amp power to cab input power is a more effective plan.
Click to expand...

read my post immediately above yours...i've taken care of the "popping the knob off" problem....:D

i also like Chaos's idea...but, Chaos, you have to remember the BUDGET...it is one thing to say "buy over spec'ed speakers"....it is another to actually have the money to do it.....better to keep them from blowing it in the first place

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#14
When I was in school it was like b-string described.... If there was a teacher around everything was behind lock and key..... Gym equipment an instruments were in cages.. If it were something in a room, the room was locked..

Why do the kids NEED access when a teacher or supervision is not present?

And also I agree again with b... The year is irrelevant... If they can't learn how to use equipment properly, they have no need to be around it..
 
#16
I was a repair tech at a music store that services over 100 school systems. Students abuse band equipment. A limiter might help, be it dynamic or fixed resistor, but any adjustments should be internal and not available to the kids.

Peavey's DDT compression and many amplifier's limit circuits that are not defeatable would be recommended. High wattage speakers are a great idea but you might as well wait till the original is blown, or if the original speaker is a really decent speaker, using less expensive, high wattage/excursion replacements would be an excellent idea. MCM Electronics has a bunch. I use a pair of 375 watt, 7mm excursion MCM 12" bass drivers in my bass rig. They were $31 a piece. I can't get them to break up with 500 watts at my gigs.

Repairs of school instruments has it's moments. I had a Kasino bass combo come in from a middle school back in the early 90's. Besides the repairs I found a used florescent condom behind the speaker grill. I added "removed used condom from behind speaker grill" to the service slip.

A Bassman combo...silverface with four 10's came in that had tumbled end over end down a marble staircase. I had to strip the chassis and beat it back into shape with a 3lb hammer on the concrete floor. All finger joints came apart, but the tolex held the cabinet together.

It went back to the school looking like new. I always restored amps cosmetically, hoping that if the equipment looked new...the students might take better care of it.

I can hope...can't I?
 
#18
A pot shaft rotation limiter can be put on a pot inside the chassis. It would require some custom machining and maybe changing the pots. It would be easier to modify the amp to decrease the gain. Getting a speaker that can't be blown would be nice but expensive. You can get amps that won't tax the speakers, again an expensive alternative.

Maybe if the students were using their own amps or paying for them through fundraisers, the amps would be treated with more respect. When the speakers blow, could they be motivated to raise money to pay for the repairs? How about offering a speaker re-coning workshop to a few students. It isn't difficult to do, you just need to do it properly. DIY can be more cost effective. Otherwise, blown speakers are going to be the cost of doing business.
 
#20
Put whatever knobs/blocks you want on there and some teenager will either find a work-around or just break it off.

The answer is brickwall/hard limiters, just like you use in PA systems to limit excursion on the subs. That would mean purchasing compressor/limiters, having someone who knows what they're doing set them to clamp down at some voltage that is pretty much guarantied the speakers can handle, and somehow building/locking all that into a case so the player only has access to a place to plug in, the eq, and a volume knob.

Personally, I like the concept of teaching responsibility, and adding in a little training session to teach these kids proper care and nurturing of equipment and how it works. Example, a high gain effects pedal means the amp can be running full tilt even though it's volume knob is set low.
 

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