Attenuators and wattage

[John Matrix]

My friend gave me an attenuator that he made. It's old and he didnt really remember how many watts is could handle.

I looked up the part and it says 100 watts: https://www.parts-express.com/L-Pad-100 ... I4QAvD_BwE

Anyway, my amp is 120 watts. Is this thing safe to use as long as I don't crank it? I'm not using it to get power amp distortion or anything, I still play it pretty low on the master...just trying to get it to apartment friendly levels.

[JTurbide]

I've played 100W amps into a 20W attenuator. I think as long as you don't crank it you'll be fine

[John Matrix]

oh wow 13$, what else are amp attenuators doing besides using that part that makes them worth 300$+ prices? is the rest of the build advanced?

No, there is barely anything in there. That part, and on/off switch, and like one other component. The project on this website looks pretty much just like what my friend gave me: https://guitar.com/guides/diy-workshop/ ... ttenuator/

Commercial models have a lot of other features but they are still crazy expensive for what they are in my opinion. Maybe they are sturdier in the long term, I dunno.

[JonnyAngle]

my experience with attenuators is as follows:

you should double the wattage you need if you're going to be cranking it. I smoked a 50W attenuator I built with my Mig50. it worked fine with a valve Jr.also make sure that there is plenty of ventilation available because this baby will get hot

[John Matrix]

my experience with attenuators is as follows:

you should double the wattage you need if you're going to be cranking it. I smoked a 50W attenuator I built with my Mig50. it worked fine with a valve Jr.also make sure that there is plenty of ventilation available because this baby will get hot

Was there any damage to the amp?

[PeterBregman]

Maybe this is too nerdy, but there's a big difference between a purely resistive load (like a resistor or an L-pad) and a reactive load (like a speaker or an RLC circuit). Lots of folks find that a purely resistive attenuator doesn't sound how they had hoped, because it loads the output of the amp in a very different way than it's loaded under normal conditions. A purely resistive load is also harder for the amp to drive. Most "8 ohm" speakers present something closer to 40 or 50 ohms at their resonant frequency (typically around 100-150 hz), and steadily increase in resistance above about 1khz. Resistive loads are 8 ohms at all frequencies (or near there anyway).

Reactive loads aren't that hard to design/make, but they involve more parts than just an L-pad attenuator.

[crochambeau]

Was there any damage to the amp?

In all likelihood, the failure mode of burning out an attenuator is an open circuit condition.

Driving open circuit/infinite impedance is problematic with output transformer coupled amps, due to inductive fields flowing back into the amp (similar to inductive kickback) instead of being sluiced out into a load. Tube amps, being that they operate at both high voltage and higher impedance (more primary turns on the output iron), are far more susceptible to initiating a catastrophic failure mode (output tubes arcing over to induce a short circuit path on the milder end, transformer windings arcing over and barbequing the output iron on the bad end).

Transformer coupled solid state are going to be a bit more robust, and the far more standard solid state output transformerless topologies tend to prefer higher impedance conditions over shorts so generally speaking driving open air with a modern power amp makes them run much cooler than pushing heat into speaker coils.

TL;DR it's going to hinge on your particular amplifier and to a lesser degree what music you are subjecting it to at the time.

[John Matrix]

Maybe this is too nerdy, but there's a big difference between a purely resistive load (like a resistor or an L-pad) and a reactive load (like a speaker or an RLC circuit). Lots of folks find that a purely resistive attenuator doesn't sound how they had hoped, because it loads the output of the amp in a very different way than it's loaded under normal conditions. A purely resistive load is also harder for the amp to drive. Most "8 ohm" speakers present something closer to 40 or 50 ohms at their resonant frequency (typically around 100-150 hz), and steadily increase in resistance above about 1khz. Resistive loads are 8 ohms at all frequencies (or near there anyway).

Reactive loads aren't that hard to design/make, but they involve more parts than just an L-pad attenuator.

Are these resistive load types bad for the amp or do they just sound different? I'm not really trying to do the cranked amp power tube distortion thing...I just am using it as a more high resolution volume control so I can play quietly. Naturally the volume on this amp does not really get quiet enough for the place I live. It jumps from inaudible to pretty loud really abruptly.

[PeterBregman]

Are these resistive load types bad for the amp or do they just sound different? I'm not really trying to do the cranked amp power tube distortion thing...I just am using it as a more high resolution volume control so I can play quietly. Naturally the volume on this amp does not really get quiet enough for the place I live. It jumps from inaudible to pretty loud really abruptly.

They're not really bad for the amp. I guess theoretically, if you're using a tube amp, your tubes might wear out faster due to driving more current for the same power transfer....but who knows. Probably not. The sound is the main thing. With tube amps, some people say their amps sound "choked" when driving a purely resistive load, and I've personally noticed a lack of resonance I'm used to while driving a speaker cab directly. It's probably fairly subtle though. If all you're doing is trying to make your amp quieter for practice or if you're using a solid state/class-d amp, knock your socks off. If you're trying to record the sound of a nice big tube amp, but make it quieter, you might want to consider using a reactive attenuation circuit.

[jirodreamsofdank]

oh wow 13$, what else are amp attenuators doing besides using that part that makes them worth 300$+ prices? is the rest of the build advanced?

No, there is barely anything in there. That part, and on/off switch, and like one other component. The project on this website looks pretty much just like what my friend gave me: https://guitar.com/guides/diy-workshop/ ... ttenuator/

Commercial models have a lot of other features but they are still crazy expensive for what they are in my opinion. Maybe they are sturdier in the long term, I dunno.

holy shit. eye opener, i always assumed they had lots of other stuff going on.

Most attenuators on the market now are reactive load (faking the speaker impedance) or reamping (Fryette Power Station/Waza Tube Amp thingy) so they're a bit more complicated than just a resistive load.

[John Matrix]

Well to anyone else who was curious about this...

played through this thing for about 20 min and then

133prm.jpg (22.18 KiB) Viewed 758 times

[JTurbide]

Wow integrated fog machine too!! This is a steal ! Need one ASAP !























Honestly tho, that sucks hopefully your amp is fine...

[John Matrix]

Well to anyone else who was curious about this...

played through this thing for about 20 min and then

133prm.jpg

in a good way or a bad way

def bad hahaha