DIY Attenuator

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DIY Attenuator

Postby caspercody » 12 Jun 2017, 17:06

I finally was able to buy my very first tube amp. I bought a Marshal DSL 40C. Now I would like to use a attenuator to be able to use this in the house.

I bought a L pad, it is a 16 ohm 100w version. It works, but after doing some reading the L pad might do damage to the amp.

So is there a easy DIY project to do a attenuator that will allow me to turn it down to low volume and not hurt the amp?

Thanks
Rob
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Re: DIY Attenuator

Postby Cub » 12 Jun 2017, 17:48

Good score ! Have you tried the pentode / triode switch on the back yet ? That may knock off enough decibels already.
If not, the Z Air Brake by Dr. Z Amplification looks like a fun, safe and relatively easy build.
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Re: DIY Attenuator

Postby caspercody » 12 Jun 2017, 20:51

I did try the switch, but still to loud in the house. Plus want to try to get best sound out of amp, which sounds like it needs to almost cranked.

I did look at the Z brake, but from what I have read, it is best to look for a attenuator with a inductive load along with the resistive. Makes the amp last longer, and sound better.

Thansk
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Re: DIY Attenuator

Postby lolablues » 16 Jun 2017, 11:02

Try a pair of Yellow Jackets or TAD Tonebones for EL84.
40w goes to 12w aprox
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Re: DIY Attenuator

Postby caspercody » 20 Jun 2017, 15:10

Looks like using a speaker voice coil might be the best way to go. But how does one determine what speaker voice coil to use?

Is there a way to use a speaker voice coil, and a L-pad together?

Has anyone tried the EMINENCE REIGnmaker speaker?

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Re: DIY Attenuator

Postby d95err » 06 Jul 2017, 14:59

If an amp is badly designed, e.g. with undersized output transformer (as is common with low-budget amps these days), it could break when running at full blast for extended times. However, it shouldn't matter if it's playing into a speaker, attenuator or dummy load. I don't see any reason why an L-pad would be worse (or better) than any other type of attenuator available. In general, a reactive load (i.e. a speaker) puts more stress on the amplifier than a purely resistive load.

If you want to use a "noiseless" speaker voice coil as a dummy load, I can recommend the Weber Mass motor. I purchased one directly from Weber, but I'm not sure they still sell them separately.

For attenuators using a speaker coil, look for schematics for the Weber Mass attenuators.
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Re: DIY Attenuator

Postby bmxguitarsbmx » 07 Jul 2017, 18:13

d95err wrote: ... In general, a reactive load (i.e. a speaker) puts more stress on the amplifier than a purely resistive load.

...


I think you mean to say the opposite. Resistive loads are notorious for blowing output transformers. The Ohms rating on the back of the speaker is the DC resistance of the coil winding. The impedance added to that nominal DC rating by the reactive elements of the speakers acts to reduce current/total wattage and is less hard on the power amplifier than a purely resistive load.

I still use resistive loads to test amplifiers, I just wouldn't push it. You'll notice your output transformer heat up if you switch from a 16 ohm speaker cabinet to a16 ohm power resistor.
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