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Power attenuators, inductive loads, post-amp effects

How well do the following devices work to give cranked-amp tone at low room-noise levels?

o Marshall Power Brake
o THD Hot Plate
o ADA Ampulator
o Hughes & Kettner Blues Master (called Crunch Master in Europe)
o Red Box

I am also interested in hearing from people who have used:

o Demeter speaker isolation cabinet
o MicroRoom speaker isolation cabinet and inductive load
o ADA MicroCab

I would like a short description of these items too, such as what types of outputs the Hot Plate has. I'm not sure whether the Hot Plate can drive a guitar speaker, or if it only has a line-level output.

The Power Brake sounds like one of the most authentic, useful approaches. But does the speaker cabinet really sound any good at very low volumes? Isn't speaker overdrive a major part of cranked amp tone? I suspect that a genuine speaker cabinet is important, but we know that power tube saturation is important too, because a solid-state amp driving a good cabinet does not allow power-tube saturation, and thus sounds flat.

The interaction between power tubes and fast-moving speakers, with no inductive load interfering, might be indispensable for the greatest tone. If so, the only way to get a cranked amp tone at low room noise levels would be to use a semi-small amp to directly drive a speaker isolation cabinet. Even this approach has limitations: no room reverb, a claustrophobic tone, and only a single speaker, close-mic'd.

I've gotten some good ideas by categorizing this gear related to cranked-tube-amp tone at low room-noise levels, but I'd sure like to hear from people who have worked with this gear. And I'm not the only one. Many guitarists would be interested in this topic, if it got a little more exposure. There *is* a third alternative between blasting amps too loud, and relying solely on line-level preamp tone.

AX84 site: load lines - power attenuator or dummy load article (PDF pages)

>>Which power soak works the best with tube amps? Does it affect the tone? Is it bad for amplifiers?

>>Is it true that Marhsall has a disclaimer on their head/or cabinets, that says warranty invalid if used with a power attenuator?

Randall Aiken wrote:

>I recall seeing just such a tag hanging on a new Marshall a few years back, I haven't seen them on the new amps or the reissue stuff. I believe they quit putting it on when they came out with their own Power Brake, or the SE100 rack mount speaker emulator, which had a 6, 12, and 18 dB switch. I wonder how they suddenly made the amps strong enough to handle the load? :)

>I have used these things since the first Altair power attenuator came out around 1978 or so. I used it on a Fender Twin, a Fender Bassman 50, and a 50 and 100 watt Marshall with no problems. The Altair had a rotary switch that switched in different taps soldered onto a piece of nichrome heater wire. It got nice and toasty, and had a bad habit of coming unsoldered in the middle of a set, resulting in instant full volume! Nichrome wire isn't the easiest thing in the world to solder to. The thing looked pretty cool, though. :)

>After the Altair died one too many times, I got one of the Scholz power soaks, which I still have, and occasionally use with my old 50 watt non-master Marshall. It also doubles as a nice dummy load for working on amps. It is composed of several ceramic body power resistors that can be switched in or out to change the attenuation while (supposedly) keeping a constant impedance load on the amp. I've never verified that, but I've never blown up an amp with it either, so it is probably true.

>There is a new generation of power attenuators that use a reactive load; that is, it consists of more than just a resistive load. These things vary from just an inductance/resistance unit to units that simulate the complex impedance variations of a speaker cabinet. Examples of this type (or so they claim) are the Marshall Power Brake and SE100, the THD Hot Plate, and I believe the newer model Groove Tubes speaker emulators also have an attenuator output for use with a cabinet.

>As for the sound, all the resistive units I have tried sound very close to the amp tone until somewhere around -9 to -12dB attenuation; after that, they start to sound a little thin and lifeless. This is not quiet enough to tame a roaring Marshall down to bedroom volumes, but is good for stage use. I suspect the flat tone results from the constant resistance load; at lower attenuations, the speakers have less of an effect upon the amplifier load, so the amplifier sees more of a constant resistance.

>I have not used any of the newer reactive attenuators, so I cannot comment on their tone, but I have used this type of reactive circuit as a dummy load to feed a mixer for recording, and there is a big difference in the tone you get between this type load and a straight resistive load.

>Randall Aiken
>reaiken at ix.netcom.com
>rec.music.makers.guitar, alt.guitar.amps

Wayne Petersen wrote:

>I have a Mesa Boogie DC3 amp that is great, but too loud. I can't turn
>it up past three and it doesn't start to distort. Are there any simple
>solutions to this? Ax is a Les Paul.
>If this has been asked before, sorry. I'm new to the newsgroup.

Try a Marshall Power Brake or a THD Hot Plate. I think they would be perfect for this. I haven't had a chance to experiment with them myself. Anyone else?

>Playing live or practicing at home? How do you , in this situation,
>place the efx AFTER the power tubes?

> - '71 Marshall JMP 50 head into THD Hot Plate into 4x12 cab.
> - Hot Plate Adjustable Line Out into Lexicon effects processor.
> - Effects Processor into Mesa/Boogie power amp, run clean, from
> the Boogie slave amp into a separate 2x12 cab.

> OK, it's a pretty big set-up, but it works great, and you have
> total control over the wet/dry mix. And, a big plus is the dry
> tone through the 4x12 is uncontaminated by any effects processing
> artifacts resulting from A-D conversions and other crud going on
> in the processor. It allows the same setup for live playing or
> home studio or practice, with the only change being how much
> output attenuation is set on the THD Hot Plate. This THD device
> is a very good match for the old Marshall amps and cabs, and I
> wouldn't be suprised if that is what it was designed to work
> with. The attenuation "effect" is very transparent and adds no
> ugly coloration, unlike many effects devices I have tried. You
> get a great overdrive tone, only it is less loud. And, it allows
> the time-domain processing to be _after_ the power tube distortion
> of the Marshall head.

> Dave R.

I don't trust the line-level signal tapped before the speaker. I like to actually use the mic output as the signal to apply post-amp effects to. Aren't your effects overly bright? They don't have the benefit of the treble roll-off from the speaker and mic. Do you use an eq to roll off the highs from the effects?

With my appoach (fx->amp->spk->mic->fx), the echo of the guitar amp tone is identical to the initial amp tone - no drop in distortion, no treble roll-off. I think the new 2112 fx unit enables you to roll off the treble on each echo for a more natural effect.

Your setup sounds interesting and practical. I'd like to have a power attenuator, but my first emphasis is on speaker isolation cabinets, in which the power tubes communicate directly with the speaker, with no attenuator or inductive load getting involved. The more you attenuate, the worse the tone. This means either the amp doesn't really like the attenuator, or the speaker likes to be driven hard, or the amp likes to interface directly with the speaker. In any case, the setup I trust the most is the most traditional setup: power tubes directly driving a speaker, hard. I used 15 watts of power tube power, driving 25 watts of speaker power handling capacity. This is probably a good ratio to adhere to. I doubt that 100 watt speakers sound right when driven at 1/2 watt by an attenuator.

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