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-   -   Tube Amp Dummy Load questions (http://www.diyaudio.com/forums/instruments-amps/214768-tube-amp-dummy-load-questions.html)

exnomine 19th June 2012 05:23 PM

Tube Amp Dummy Load questions
 
I know there are a million forum posts regarding dummy loads, but my question has not been addresses (at least to my knowledge.)
I know that a purely resistive dummy load will affect your tone in a terrible way. However most posts I have seen are asking about a dummy load with a line out.
I like running my amp's speaker out into a DI Box (Behringer G10, which lets me either use strickly a DI signal, or color it with a 412 sim, which I actually like). The Di box has a line level out which goes to my mixer and a speaker out which usually goes to my cabinet. I just moved into an apartment and can no longer record this way, so I was wondering if a simple resistor based load box in place of the speaker would work well. In other words would it "suck" the tone from my DI box which comes in line before it. Also my amp is rated at 100 watts RMS, It is a very high gain amp. I would run the amp at half volume, maybe a little less, so would a 150 ohm resistor do the trick?

Nigel Goodwin 19th June 2012 07:19 PM

You need a high power resistor, equal to the speaker impedance - so 8 ohm if your speaker is 8 ohm. For a 100W resistor I would suggest a 150W resistor (or more likely stack of resistors).

You can buy (fairly cheaply), 1 ohm 17W wirewound resistors, and 8 of those in series would do the job. There's a lot of crap about using wirewound resistors (because of their inductance - which is only low anyway), but it should be fine, and relatively low cost.

The resistors will get HOT!!! - so need mounting in free air, and well apart - and don't touch them!.

exnomine 19th June 2012 08:34 PM

That sounds reasonable. Would this be acceptable: 8 Ohm 200W Non-Inductive Dummy Load Resistor 019-030
Also, I was wondering if I could use something like this Aura AST-2B-4 Pro Bass Shaker 299-028 as a reactive load (like the weber speaker motors) and just put it in a box of pillows?

Printer2 19th June 2012 10:34 PM

Sounds real odd but an old 1200W hair dryer or electric heater can dissipate more than any amp most have.

Enzo 19th June 2012 11:51 PM

Yes, that Parts Express item ought to work fine.


I don't think a pure resistive dummy load can fairly be called terrible. It may not be optimal tonally, but a bit of EQ tweaking usually takes care of that. The "cab emulation" that some products like your DI have is just a little EQ.

sreten 20th June 2012 12:29 AM

Quote:

Originally Posted by exnomine (Post 3065201)
I know that a purely resistive dummy load will affect your tone in a terrible way.

Hi,

That is pure myth, it simply doesn't. It loads your amplifier consistently
and creates consistent distortion. A real speaker load is barely different,
if it has an effect its less distortion around the speakers Fs and towards
the top end of the range, hardly a difference that is terrible / preferable.

rgds, sreten.

A cheap dummy load is a 1.5KW / 110VAC kettle or heating element = 8 ohms.

Loudthud 20th June 2012 02:00 AM

You didn't say if your amp is tube or solid state. If it has a tube output stage, you will likely hear a difference in the DI output. Behringer doesn't like to disclose their schematics, so what's in there is a mystery at this point.

Some 100W resistors require a heatsink and/or a fan. A 100W guitar amp will put out close to 200W when it's making a rail to rail square wave, but you probably won't be doing that on a continuous basis. If the amp is solid state, it will probably work fine without a load at all.

Enzo 20th June 2012 05:00 AM

I don't see a G10, I see a GI100. Can you verify the model number?

Now that I look, the GI100 has a rather complex emulator, four op amp stages with bunches of tone shaping, and a transformer out, which circuit can run off battery or phantom.

exnomine 20th June 2012 10:53 AM

Thanks for all the advice. Sorry, I wasn't specific. My amp is a tube amp, a Peavey JSX. The DI is the Behringer GI100. As for the resistive dummy load sounding "terrible" I am just going by what I hear. Then again, opinions are just that, opinions. I am thinking the Parts Express 200 watt 8 ohm dummy load resistor, with a jack hooked to the leads may work fine. Just gotta figure out how to mount it.

Nigel Goodwin 20th June 2012 08:37 PM

Quote:

Originally Posted by exnomine (Post 3065972)
Thanks for all the advice. Sorry, I wasn't specific. My amp is a tube amp, a Peavey JSX. The DI is the Behringer GI100. As for the resistive dummy load sounding "terrible" I am just going by what I hear. Then again, opinions are just that, opinions. I am thinking the Parts Express 200 watt 8 ohm dummy load resistor, with a jack hooked to the leads may work fine. Just gotta figure out how to mount it.

It sounds absolutely perfect - it's made for the job.


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