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power attenuator schematics?

4/8/2003 3:43 PM
josh camp
power attenuator schematics?
Does anyone know where I can get info / schematics on how to build a power attenuator like a hotplate or airbrake?
4/8/2003 3:55 PM

This interests me as well, but alas I'm too dumb.  
Weber has a interesting product I keep eyeing in the Mass unit. But I'd also like to try to build one, he has a simplified schem on his site:  
Kinda surprised a bunch of ampagers haven't run with this and came up with something yet. I'd buy his product but I don't need the DI output and would like to play with a couple of the options.  
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4/9/2003 11:47 AM

4/9/2003 12:28 PM
Todd Hepler
Spend some time here :  
and here :  
RE weber mass attenuators - There are several folks here that have these.  
4/9/2003 7:40 PM

Hey Todd, sorry but the first link is not a attenuator but a speaker load simulator...
4/9/2003 9:14 PM
Todd Hepler
Hey pef -  
I think with a few additions this would make a great load box -  
A quote from Randall's article :  
If you want to add a line out feature for recording, tap off the input of the circuit; that is, at the junction of the amplifier output and R1. Use a resistive divider to lower the signal level (make sure the divider resistance is much larger than the output or load impedance)  
The idea is that a reactive element approximates the impedance curve of a speaker much better than a resistive voltage divider.-Weber's MASS applies this concept literally by using a speaker's motor assembly to duplicate the reactive elements of a speaker/cab combo- Some of the resistive attenuator users have complained of the tone sucking capabilities of the units at higher attenuation settings.  
A couple more resistive designs from Blue Guitar :  
4/11/2003 7:04 PM
bob predaina
i would avoid the recommendations about L-pads and T-pads.  
one thing that you may want to consider is looking in a basic electronics textbook under the subject heading "Ladder Attenuators." These are devices that are specifically designed for attenuating the output of a device while maintaining the impedance seen by the devices at the driving end and receiving end of the circuit -- exactly what we want for a guitar amp application. IIRC the old Handbook for Radio Engineers had a good section on this topic.  
the airbrake and similar products may not be as good a solution to the problem as a ladder attenuator. the airbrake type of design uses a simple approach with a pair of resistors, a rheostat, a cap, and a 2-deck rotary switch. imho a real ladder attenuator would be a better option than any of the commercial options out there, but it would be a bit more expensive to build.
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