Half Power switch - best way?

[Mike Sulzer]

Good observations, and there have been speaker attenuators that address the inductance issue.

BUT one thing that's neglected so far, our ear's Fletcher-Munson curve. People naturally disregard frequency extremes at lower volumes. What to do? Even if you design an attenuator that perfectly tracks inductance to keep the high frequency curves matched, and resonance for the lows, it's still not enough to satisfy the human ear. You have to exaggerate hi & low boosts in the attenuator in an attempt to keep the sonic "flavor" satisfying at lower listening levels. "Loud switch" anyone?

Good point. But on the other hand, if the reason for reducing the power is to get the right level in a smaller room, then it might be right to ignore F-M.

[Leo_Gnardo]

Good point. But on the other hand, if the reason for reducing the power is to get the right level in a smaller room, then it might be right to ignore F-M.

Every time I hear the complaint "but it doesn't sound as good attenuated" my thoughts go straight to the ol' Fletcher-Munson. That's right, it sounds like soggy toast, just like the book said. You can ignore it at your peril, if you're a producer/artiste trying to record a hit, or a band trying to keep their audience happy & paycheck coming in without blowing their wigs off. No "excitement" without tipping-up the highs & lows, or no audience = no paycheck with the soggy toast tone. That's been the battle since dinosaurs roamed the earth. Well, at least since rock n roll was invented, about the same.

[Enzo]

if the reason for reducing the power is to get the right level in a smaller room, then it might be right to ignore F-M.

You can get the level down, but at the reduced level, your ears no longer hear the highs and lows - it goes all telephone on you. That is why stereos have the "loudness" button and many volume controls have a "loudness tap" with a bit of EQ on it near the low end of travel. Those things change the contour of tone to compensate for your ears.

[Gregg]

Even if you design an attenuator that perfectly tracks inductance to keep the high frequency curves matched, and resonance for the lows, it's still not enough to satisfy the human ear. You have to exaggerate hi & low boosts in the attenuator in an attempt to keep the sonic "flavor" satisfying at lower listening levels.

If you read this thread (with samples) you'll understand which components affect the frequency response and how so you can tweak it to your taste :

Aiken's Reactive Dummy Load. | The Gear Page

Also read Kempf's article (google translation):

https://translate.google.com/transla...3.0&edit-text=

[wizard333]

As long as the tone controls on the amp are sufficient to adjust for the tonal difference at different power levels/volumes, I'm not sure it's that much of a problem. It's not like you need to hot-switch it live and expect to go from full power to 1/4 power and maintain the same tone. If you need to use the lower power setting for situation, adjust knobs to compensate.

What about this: Instead of one resistor or resistor/inductor in parallel with a speaker, set up 3 along with the speaker to get the same impedance, like you would set up 4 16 ohm speakers to get a 16 ohm cabinet. Then you don't get the impedance mismatch and need to adjust the impedance selector on the amp. So say, 16 ohm speaker, or 16 ohm speaker in parallel with a 16 ohm resistor (or resistor + inductor), then in series with another pair of 16 ohm resistors (yadda) in parallel, to get 1/4 power.....

Any issues there?

[wizard333]

Why would it cause instability? The speaker does not.

I was referring to this post:

Also, IMHE, big inductors dissipating 50+W can be problematic with high gain circuits. It might be necessary to locate the "load" in a second box away from the main chassis. As to a circuit involving the second inductor, that can be problematic too. The available parts in the smaller values for high power are air core. It works fine with humbuckers. If you have SC pickups you can't get within ten feet or it sounds like a whistling pete going off. I imagine it would be impossible to put such an inductor inside the amp chassis without instability.

[J M Fahey]

As long as the tone controls on the amp are sufficient to adjust for the tonal difference at different power levels/volumes, I'm not sure it's that much of a problem.

Any issues there?

But there is a problem,: tone controls (which are pre distortion always if you clip power tubes) become very weak and ineffective and can not equalize the distorted sound.

[The Dude]

FWIW: I had a Marshall Plexi that I used to pull 2 tubes out of in the 80's. It didn't make a hell of a lot of difference. A 1/10th power switch would be of more use. Now, ...... I just buy smaller amps. :-)

[Chuck H]

As long as the tone controls on the amp are sufficient to adjust for the tonal difference at different power levels/volumes, I'm not sure it's that much of a problem.

The hitch there is that attenuators are typically used to reduce the volume of an amp that sounds "right" at a certain setting that is loud. Which usually means that headroom is already compromised. So the tone controls won't work as they would when the amp is below it's distortion threshold. In the case of a clipping amp the tone controls act more like 'distortion character' controls and the only components dictating actual EQ are the OT, speaker and cabinet.

[wizard333]

But there is a problem,: tone controls (which are pre distortion always if you clip power tubes) become very weak and ineffective and can not equalize the distorted sound.

In this case, I'm thinking of amps that derive their overdrive from the preamp, so not really an issue.

[wizard333]

FWIW: I had a Marshall Plexi that I used to pull 2 tubes out of in the 80's. It didn't make a hell of a lot of difference. A 1/10th power switch would be of more use. Now, ...... I just buy smaller amps. :-)

Yeah that's why I was thinking about using resistors to simulate 3 other speakers in a 4 speaker array and keep the impedance the same as the actual speaker; thinking I'd get more like 1/4 power.

If I were going after a Plexi sound and wanted it reasonable volume, smaller amp yeah. I have a Germino Masonette, and at the 20 ish watts its rated at, still REALLY LOUD before it gives up the plexi roar. If I were using a larger plexi, it would be for clean tones and pedals.

[Chuck H]

In this case, I'm thinking of amps that derive their overdrive from the preamp, so not really an issue.

And in that case a power cut switch is a moot point. Is the amp that is the subject of the thread such an amp?

[wizard333]

And in that case a power cut switch is a moot point. Is the amp that is the subject of the thread such an amp?

Except that it isn't. Where the gain and master knobs are, how hard you hit the power amp even if you aren't pushing it to distort affect tone and response.

[g1]

Well, you can go simple or go complicated.
If you are attuned to the tonal differences of the power section before clipping, I think you will also notice the big difference between a resistive attenuator vs. inductive (or having some L component). The inductive portion also has an effect on feel and how the instrument reacts to touch (response).
And if you can't compensate for the power section differences via tone controls, I don't think they will do it for the resistive attenuator either.
Also, some guys use the attenuator for leads only, so they can't make tonal adjustments to compensate.

[wizard333]

Well, you can go simple or go complicated.
If you are attuned to the tonal differences of the power section before clipping, I think you will also notice the big difference between a resistive attenuator vs. inductive (or having some L component). The inductive portion also has an effect on feel and how the instrument reacts to touch (response).
And if you can't compensate for the power section differences via tone controls, I don't think they will do it for the resistive attenuator either.
Also, some guys use the attenuator for leads only, so they can't make tonal adjustments to compensate.

I'm all for using a combination resistor/inductance, but as someone noted, it becomes unstable and causes high frequency oscillation. Unless someone has a suggestion to make it more stable?