Speaker Attenuator DIY

[ViolenceOnTheRadio]

I'm just finally getting into the appreciation of using wattage volume rather than preamp gain and clipping to produce sustain and harmonics for guitar.
The recipe most players swear by is crank the volume so you can greatly lower the need for distortion gain. The downside being not everyone likes to blare their amp.
Since I'm not about to dish out the cash for a THD hotplate or other such commercial devices, here's the idea I'm proposing.

Using a large transformer to increase impedance and absorb power. Say I get up to 32 ohms or greater, will my power amp still be drawing a lot of power? If I understand correctly of course it is and the impedance is just changing the volume produced due to it's absorbing the load. I do know the key to this method of performance is getting more fierce power driving the signal.
I'm proposing a coil mounted to a heat sink.

The bulb trick.
Wire in a high wattage light bulb in series to suck up a lot of the power, I've done this in the past just experimenting but never thought of using it for this specific purpose. I was aiming for a dampening/compressing effect.

I'm aware of the other threads addressing this issue but nothing I've found in forums or DIY pages produced a solid answer.

[DF96]

A transformer does not absorb power, it merely transforms the impedance.

If understand you correctly, you want to have clipping in the output stage instead of an earlier stage yet without increasing sound volume. You propose increasing the volume, but then stopping all this audio power reaching the loudspeaker. Have I got it right?

You could use some power resistors to attenuate the amp output, while still leaving the amp itself running under similar conditions. For example (assuming the speaker is 8ohms): add 8 ohms in series with the speaker, then add 16ohms in parallel with this lot. The result is that the amp still sees 8 ohms, but you get only a quarter as much power at the speaker. The amp won't see the speaker impedance vary so much, so it won't necessarily sound exactly the same, but it should not be far out.

I will leave the guitarists on here to say more.

[ViolenceOnTheRadio]

I realize it does not absorb power but with raising the impedance to say 32 ohms, is the power amp drawing more power when I crank the output to match the volume for when it's driving an 8 ohm speaker load?

You have the gist of it accept for the clipping part. There is a lot of confusion due to the myths of the industry, specifically those spread about tube amps but the primary desire is to use more wattage to drive the signal to produce sustain/response so you can then use less clipping be it preamp or power amp stages.
This takes you out of the saw tooth wave form and you get better definition.

I do have some high wattage resistors for altering impedance which is why I am assuming I could pull off something similar with a transformer or bulb. I've not wanted to cook those resistors is the only issue. I have 3 or 4 with each rated about 35 watts each.
I've used them in the past and they obviously get hot. I suppose I could however use them to build my own hot plate by fastening them to a heat sink. I will just have to experiment with that and the bulb concept while waiting to see if anyone has some information about using a transformer instead.

[AndrewT]

you are in the SS section, but refer to Tubes/Valves.
A valve amplifier must never drive an open circuit load.
Changing the load to a very big mismatch is moving towards that open circuit condition.
I don't know how far you can go with Tubes before impedance becomes an issue.

SS does not mind driving any impedance higher than minimum.


Have a look at soft clipping for a sound effect.

[Peckerwood]

Attenuators make your amp run REALLY hot. And the attenuator too. Too hot to touch. It seems to me like there is bound to be a serious impedance mismatch but I base that purely on the temperature of the amp when using one. For whatever reason the amp runs much hotter than it does without one, the fact that it does makes me think that it is not good for the amp to use one. I am speaking of the attenuator that I used. It is possible there might be some kind that would not behave the same way.

[DF96]

If you attenuate the signal, then wind up the volume to get the same sound level then it is obvious that the amp is working harder - it is driving the speaker and heating the attenuator. This will be true however you attenuate the signal (except possibly by using reactance, but that will be frequency sensitive so the sound will be very different too). In engineering there are no free lunches!

If you insert a transformer to convert 8ohms to 32ohms, then the amp will have to output twice the voltage (and half the current) to get the same volume. This will bring it nearer to clipping. Whether this is good or bad, and whether the amp will draw more or less power, depends on the design of the amp.

The general rule is that valve amps don't like the impedance being raised too much, while SS amps don't like it being dropped too much. That is why my suggestion leaves the impedance seen by the amp unchanged.

[ViolenceOnTheRadio]

It is indeed a solid state I'm running. The tube reference was basically due to the commonality of running an amp loud and buying devices like the THD hotplate to soak up the power so you're not frying your ears.

I had bought the sandstone resistors for this purpose a few years ago but avoided using them because of the tonal shift caused by the change of impedance. They do what I want quite well but at a price. I hunted around and found the THD Hotplate schematic and internal view.
It's nothing but some high wattage sandstone resistors and other passive components for running a line out to your mixer/recorder and compensating for the frequency shift caused by the added load.

So I was right, I can build my own with parts I have floating around and a $1.50 project box from Home Depot.
Meanwhile these suckers sell for $300+ new!
I have now found yet another tube amp related product raping the wallets of the sheople.
In fact I hunted down the parts new and it's a beginner level project with a build cost that wouldn't break $30 even with radio shack parts!

[Peckerwood]

Why use an attenuator on a SS guitar amp? That is not the kind of distortion most people want.

[ViolenceOnTheRadio]

Originally Posted by Peckerwood

Why use an attenuator on a SS guitar amp? That is not the kind of distortion most people want.

That's merely a myth.
It's about getting more power to drive your signal, not producing power amp distortion as that would just sound quite bad. The myth survives because people just repeat what they're told and don't understand what is actually going on.

Trying to explain just turns into an argument.
It's like trying to explain 2+2= 4 to a monkey.
Bottom line is more current is driving the signal and you don't have to deal with the volume shattering your skull.

I'm not a loud man.

[Peckerwood]

Obviously, nobody who uses an attenuator is a loud man. The last thing a loud man would ever want is an attenuator. I have just never seen anybody with a SS amp use one. That is not a myth either. I actually have not seen it and that is a fact. Have you seen anybody besides yourself use one with a SS amp?

This is from the Hot Plate Owners manual at http://www.thdelectronics.com/pdf/HP...l%20060405.pdf

Q. Can I use the Hot Plate with a solid state amp?
A. NO! The Hot Plate and the power section of the amp will be dam aged if the amp does not use output tubes. Thus, even if an amp has preamp tubes, it CANNOT be used with the Hot Plate if it has a solid state output section. However, an amp that has a solid-state pre-amp section but a tube output section CAN be used with the Hot Plate.

Maybe the fact that nobody on several DIY forums but you can understand it could be taken as a clue?