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power attenuator schematics?


 
4/8/2003 3:43 PM
josh camp
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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
BWilliamson
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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:  
 
http://www.webervst.com/mass.gif  
 
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.  
 
bwilliamson  
boxerboards.com
 
 
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4/9/2003 11:47 AM
pef
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Here:  
 
http://www.lalena.com/audio/calculator/lpad/help.shtml  
 
http://www.lalena.com/audio/calculator/lpad/
 
4/9/2003 12:28 PM
Todd Hepler
Spend some time here :  
 
http://www.aikenamps.com/spkrload.html  
 
and here :  
 
http://www.blueguitar.org/new/schem/marshall/powerbrk.zip  
 
 
RE weber mass attenuators - There are several folks here that have these.  
 
 
-T
 
4/9/2003 7:40 PM
pef
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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 :  
http://www.blueguitar.org/new/schem/misc_mod/power_sk.jpg  
 
http://www.blueguitar.org/new/schem/misc_mod/volreduc.gif  
 
 
 
-T
 
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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