DIY 100W Attenuator - any easy 'How-To's' ?

[pfflam]

I want to make a 100W attenuator. I see the prices of these things and am surprised more DIY discussion or kits are not available.

Anyone know of a site of kit or whatever that would make it easy and cheap to make one for a kinda-newby?

[The Gaz]

Go over to the Amp Garage site, check out the Trainwreck files, where they have all kinds of info on the Airbrake.

[WaltC]

With the tightening restrictions on lead and lead-containing products it getting harder to get and more expensive to get the high capacity "pot" you need (L-pad or the like), and the large ceramic resistors are more costly and more expensive as well.

I like the Airbrake as well as any I've tried, but they all let you run the power tubes very hard and put much more strain on the power section (tubes, OT, PT, etc.). If you've seen an amp self-destruct because of flyback or internal power tube shorting, it can change your opinion of Attenuators in general and the value of pedals as well. At least it did for me...<G>

[Toneseeker361]

I just bought one of these and put it between the amp and the speaker and be done with it.
partsexpress.com


Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
Brand: Parts Express
Overview
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. This L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware.
Part #: 260-265 Weight: 0.42 lbs.
In Stock

Lifetime Tech Support FREE
Your Price $12.95
Buy 10-up $11.65
Part # 260-265 Qty: ea
Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. At the same time, a counter-resistance is placed in parallel with the driver(s)/speaker(s) to maintain a constant impedance which allows the original crossover design to be used. L-pads are to be placed in between the amplifier and driver(s)/speaker, or in between the crossover and driver(s)/speaker(s). This particular L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware and faceplate. Dimensions: 2-1/2" diameter, 1" depth. Note: See the Tech Drawings tab for wiring instructions.

L-Pad Instruction Diagram

[torquil]

For a very fancy DIY attenuator with detailed discussion of component types and ratings, look at this thread:

http://www.thegearpage.net/board/sho....php?t=1072793

Know that most "100W" tube amps will put amp much more when cranked, so it is wise to have a safety margin of a factor two in power handling.

I have made a resistive 200W rated attenuatur using a 100W L-pad as above, combined with some extra power resistors. It attenuates a few dB when the L-pad is set to zero. Then the L-pad makes it attenuate more as the knob is turned.

[Prairie Dawg]

Originally Posted by WaltC

I like the Airbrake as well as any I've tried, but they all let you run the power tubes very hard and put much more strain on the power section (tubes, OT, PT, etc.). If you've seen an amp self-destruct because of flyback or internal power tube shorting, it can change your opinion of Attenuators in general and the value of pedals as well. At least it did for me...<G>

What the gennelmun says, people. Resistive loads ain't the same as impedance loads. Unfortunately you get to find it out only after the bad stuff happens.

[doctorx]

Originally Posted by Toneseeker361

I just bought one of these and put it between the amp and the speaker and be done with it.
partsexpress.com


Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
Brand: Parts Express
Overview
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. This L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware.
Part #: 260-265 Weight: 0.42 lbs.
In Stock

Lifetime Tech Support FREE
Your Price $12.95
Buy 10-up $11.65
Part # 260-265 Qty: ea
Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. At the same time, a counter-resistance is placed in parallel with the driver(s)/speaker(s) to maintain a constant impedance which allows the original crossover design to be used. L-pads are to be placed in between the amplifier and driver(s)/speaker, or in between the crossover and driver(s)/speaker(s). This particular L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware and faceplate. Dimensions: 2-1/2" diameter, 1" depth. Note: See the Tech Drawings tab for wiring instructions.

L-Pad Instruction Diagram

I have built numerous attenuators using this kind of L-Pad, and can firmly testify that in no way can you use this with a 100 watt amp, either rms or peak power. Don't even think about it.

For the single ganged L-Pad, I would rate it at about 35 watts rms, and for the dual ganged L-Pad I would go 40-45 watts. This are conservative estimates but that's just me. I always put a fan on them too.

For a larger amp you can build one using fixed resistors. There is a project floating around the internet by Gerald Weber for a -6db/-12db attenuator, and I have schematics for a -3/-6/-9 and a -6/-12-/-18 attenuator.

You can get the resistors from Mouser.com.

No offense to anyone elses's opinion, but I've been using attenuators since the early eighties with all kinds of amps (Usually dimed), and have never had any kind of problem. If you use the proper impedance and use it within it's design parameters, an attenuator used with a stable healthy amp will not damage it.

I just finished building an attenuator for my AC30 using a single ganged 16 ohm L-pad, I call it my Bohemian Rhapsodyne, check it out:

[phsyconoodler]

Get a smaller amp.Attenuators are tone sucking devices that kill parts in amplifiers.

[phsyconoodler]

Get a smaller amp.Attenuators are tone sucking devices that kill parts in amplifiers.
And I would never,ever,ever put an L-pad of 100 watts between the output and speakers of a 100 watt amp!!!
You would melt that L-Pad in short order.
If you don't want to get a smaller amp then look into variable voltage regulation.
www.skipzcircuits.com

[doctorx]

Originally Posted by phsyconoodler

Get a smaller amp.Attenuators are tone sucking devices that kill parts in amplifiers.

OK. I guess the dozens of manufacturers that build commercial attenuators and the thousands of guitarists that use them on a daily basis with no problems, and my own experience of using both commercial and DIY attenuators for thirty years without issue, are all in the wrong.

[GuitarBuilder]

Originally Posted by Toneseeker361

I just bought one of these and put it between the amp and the speaker and be done with it.
partsexpress.com


Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
Brand: Parts Express
Overview
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. This L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware.
Part #: 260-265 Weight: 0.42 lbs.
In Stock

Lifetime Tech Support FREE
Your Price $12.95
Buy 10-up $11.65
Part # 260-265 Qty: ea
Speaker L-Pad Attenuator 100W Mono 1" Shaft 8 Ohm
L-pads adjust the relative volume of driver(s)/speaker(s) connected to them by placing added resistance in series. At the same time, a counter-resistance is placed in parallel with the driver(s)/speaker(s) to maintain a constant impedance which allows the original crossover design to be used. L-pads are to be placed in between the amplifier and driver(s)/speaker, or in between the crossover and driver(s)/speaker(s). This particular L-pad is rated at 100 watts RMS, is designed to be used with 8 ohm loads, features a 1" shaft length, and comes with mounting hardware and faceplate. Dimensions: 2-1/2" diameter, 1" depth. Note: See the Tech Drawings tab for wiring instructions.

L-Pad Instruction Diagram

This does indeed work well with a solid-state amp. A 100W tube amp will kill it in short order.

[GuitarBuilder]

Originally Posted by phsyconoodler

Get a smaller amp.

Good suggestions.

Originally Posted by phsyconoodler

Attenuators are tone sucking devices that kill parts in amplifiers.

The first part is partially true for some attenuators. The last part is bogus.

Originally Posted by phsyconoodler

And I would never,ever,ever put an L-pad of 100 watts between the output and speakers of a 100 watt amp!!!
You would melt that L-Pad in short order.

Very true for a tube amp; L-pads work fine with solid-state amps. This is primarily due to the difference in how power output is specified for the different technologies.

Originally Posted by phsyconoodler

If you don't want to get a smaller amp then look into variable voltage regulation.
www.skipzcircuits.com

VVR doesn't work very well with high power tube amps, it's much better for the smaller (5 - 20W) designs.

[TubeLuvr]

I built an L-Pad modeled after doctorx's.
Works great, with my 25-watt amp.

Would someone really need an attenuator with a solid state amp? What am I missing?

[GT100]

Originally Posted by Prairie Dawg

What the gennelmun says, people. Resistive loads ain't the same as impedance loads. Unfortunately you get to find it out only after the bad stuff happens.

What "bad stuff"?
Electrically resistive loads are easier on your amp-assuming you set the impedance correctly.
Because there is no fly back.
The reason amps are being damaged is because they are cranked.

The real bad stuff with resistive loads has to do with tone...

Lloyd

[PCR]

Give this a try...

http://www.thegearpage.net/board/sho...d.php?t=974159