[Major Tom]

There's been some guys who were putting attenuators together, and some discussion in other threads, so I thought I would post this, maybe it will help someone.

The whole purpose of the power attenuator is to achieve power tube saturation. It basically throws away a lot of the amp's speaker output, so the amp can be turned up. Many of us believe that the saturation of power tubes sounds better than that from preamp tubes and or fuzz/distortion devices that are intended to mimic cranked amp tone. YMMV. There are some principles involved with using power attenuators - if these not understood and followed, more than likely using one will result in less than satisfactory results, and a review consisting of "they suck"


1) Human ears absolutely cannot be used to judge attenuated vs. non-attenuated tone, frequency content-wise. Our hearing, our ear's frequency response, varies tremendously with SPL. Basically the lower the SPL, the more of a pronounced midrange hump in the response. At low SPL's, bass and treble freq's will be weak. This uneven response is due to the Munson-Fletcher effect, you can read lots about it on the net. Listening to an amp at 105db and then attenuating it down to 90 - no, it will not sound the same, and I think generally will be perceived as "tone suckage". A microphone does not have this problem. To really compare, you would need to utilize a mic, recording it both ways or using an iso booth for the amp, and then listening back thru the sound system at the same SPL level for attenuated and non. Furthermore, for mic'd live use or recording with an attenuated amp, you need to kinda ignore the actual amp tone reaching your ears, and only go by the results - thru the mains of the PA, or the recorded tone. You can't really have both - heavily attenuated low SPL, and tone that sounds great at your ears. You can however, get great tones recorded or thru the mains.

2) You have to re-think and re-vamp your gain structure. It took hours, weeks, years for a player to get his/her "tone" using an amp at lower levels with the power tubes still in their hi-fi reproduction zone; using the pre gain with the master volume turned down, or an OD pedal with a non-MV amp, distortion, fuzz, whatever. The gain structure of that set up has a level of saturation/compression that is being cleanly/faithfully reproduced by power tubes. Now if you just use that rig as is, hook the attenuator up, and crank it up - the power tubes are now reaching saturation. Guess what? Now you have too much saturation! Bottom line - when you add the saturation or distortion of the power tubes, you have to reduce the saturation upstream..

3) Speakers need some power to sound "right". I think speakers have a minimum threshold to sound good, and sound a bit better with more juice. Of course too much = speaker distortion which may or may not be a good thing, depending on what you like. Without enough power to sound right, well....it won't sound....right. The more speakers, the louder its going to be at a decent power threshold for them. If you're attenuating, it better to attenuate one speaker than 4. I think a heavily attenuated tone is more related to the speaker than the amp.

4) New tones - Now that the power tubes are involved, its a different tonality from the amp. At this point I think a lot of players are really hearing their amp for the first time. You may have listened to it cranked at extreme volumes in the past, but sometimes when things are too loud, you really don't hear them well - its saturating your ear drums. Now with an atenuated cranked amp, I think you can actually hear that cranked tone better. I think a lot of players won't even necessarily like what they hear at this point, but it will be differerent, and may take some getting used to.

Power attenuators are not a panacea, they can be a significant part of a low SPL amp rig strategy, but should not be used as the only strategy. Trying to get good cranked amp tones a low volumes IMO needs to start with an appropriate amp size and speaker config, and there is a threshold at which an attenuated rig will sound good. As a kinda rule of thumb, I've found that with a 1x12 it will sound pretty good to my ears at around the SPL level of a Fender Champ at 6 or 7 and above. Much below that and it doesn't sound good at my ear. There was a bro on another forum who did some testing - he recorded different levels of attenuation and then judged the recorded tone. Except for the extremly attenuated samples, he said the attenuated tones sounded the same as the non. There is just no sense in trying to take a 100 watt 4x12 amp down to "bedroom" levels; better to start with a 15 watt 1x12 and go from there.

Power attenuators - I never leave home with out one.

[Hopeful]

Thanks, Tom. And thanks for making mine!!!

[Only Alive]

Great info, Tom. Thanks for posting!

-Nick

[Brentwood Amps]

Bravo, good info

With that said on some amps and attenuators don't work well together. For example, class AB2 designs will some times blow fuses and even toast a tranny due to the high current of those designs. I personally find that a hand full of MV amps work well and sound good with attenuators and most all NMV amps work perfectly. Just depends on the amp.