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I just bought a Bugera 333XL-212 Titanium (combo, 120 Watts) which is awesome for small venues but is really too loud for practising at home. I can't set the master volume to more than 1 without taking the risk of disturbing my neighbours.

A solution would be to buy another amp, less powerfull, but before falling out with my bank and losing more space, I'd like to know if there is any way to reduce the power of the amp or the output volume, which would allow me to practise with a decent distortion, at a decent volume.

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Is it to late to trade for one of their "Bugera Magician-Infinium Amps?" bugera-amps.com/en/products/MAGICIAN-INFINIUM.aspx I notice they're Multi-class (triode class A being less watts), and also have a built in "Varipower" (1W - 85W output), I don't know if it's a traditional power soak like a Hot Plate, or more like that company up in Canada (can't remember the name off-hand); I just remember looking at some schematics that seemed different and allowed a post power-tube section output adjustment (not an attenuator, I think it was some sort of current adjustment). –  David Axtell Moore II Jun 30 '13 at 6:03
    
Yes, probably :). And my shop doesn't sell this one. –  Julien N Jul 1 '13 at 9:26

2 Answers 2

up vote 7 down vote accepted

You have to use a power attenuator such as the THD Hot plate.

This reduces your amp's volume without affecting (too much) its tone.

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Interesting gadget. Sure looks like something that could be built from scratch for more like $75 USD. Anyone know if there's a MakerShed or similar source for plans? –  Carl Witthoft Jun 25 '13 at 14:25
    
Attentuators are very subjective just like tube amps. Some people love them, some hate them etc... –  JimR Jun 25 '13 at 23:05
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@JimR And some people either resist them or react to them (cheap joke) –  Carl Witthoft Jun 26 '13 at 11:34
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@CarlWitthoft: Carl, I'm going to resist my inclination to get a little hot under the collar over your little joke. :) –  JimR Jun 26 '13 at 11:43
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How on earth have I never heard of these? I don't want one, as I like playing loud, but it is very smart. –  Dr Mayhem Jun 28 '13 at 13:20

Before spending $350 a THD hotplate per Lucas answer, which is basically just a high-powered volume control (variable resistor) between the amp and speaker, I would do the following:

  1. Buy a high powered fixed resistor from an electronics components store, of a resistance (ohms) about 2-4 times the impedance (ohms) of the speaker.

  2. Install the resistor in one of the leads from the amp to the speaker (in series.)

  3. Depending on the setup I wanted, I might install a bypass wire and switch around the resistor (in order to not have to remove it completely)

This would cost about $10, maximum.

If the electronics store does not have sufficiently powerful resistors, you can make one up by adding resistors in series. Provided you connect in series you cannot damage your amp. But NEVER connect anything in parallel (don't ever connect an additional speaker across the terminals of your amp, you will blow the amp.)

Here's a typical circuit. Assuming a 100W, 4 ohm speaker, the theoretical performance is as follows:

    One 8 ohm resistor: Impedance increases from 4 ohm to 4+8=12 ohm. 
    Total power from amp: 100W x 4/12 = 33W
    Power to speaker 33W x 4/12 = 11W
    Resistor sizing: 33W-11W=22W (though a 33W resistor is preferable)
    Power reduction: 9 times (approx 10dB)

    Two 8 ohm resistors: Impedance increases from 4 ohm to 4+8+8=20 ohm
    Total power from amp: 100W x 4/20 = 20W
    Power to speaker 20W x 4/20 = 4W
    Power reduction 25 times (approx 15dB)  
    Resistor sizing: 20W-4W=16W total, 8W each. 

enter image description here

Fixed high powered resistors are cheap and can look pretty good, see example in the link below. They do run pretty hot though. Variable high powered resistors are EXPENSIVE. If this is just for practicing at home, just have a fixed resistor (and possibly a switch) and use your master volume for fine control.

http://uk.rs-online.com/web/c/passive-components/fixed-resistors/panel-mount-fixed-resistors/?applied-dimensions=4294877032,4294875272&esid=cl_4294967294,cl_4294956717,cl_4294956547,cl_4294956056,cl_4294956957,cl_4294956191&m=1&aaaExp=Y

EDIT

There are other chatboards on the internet that discuss this solution, but nobody talking seems to have actually tried it. They theorise that damping factor (the ability of the amp to damp speaker resonances) may be an issue. But they say that tube amps already have lower damping factor than transistor amps because there is a transformer between the speaker and the electronics. So they expect less difference in tone when applying this modification to a tube amp than to a transistor amp.

I've now tried connecting a 10 ohm resistor in series with the 4 ohm speaker of my (transistor) combo and perceived no difference in tone. There was, however, virtually no difference in volume. I expect that the nominal 4 ohms of the speaker is in fact a worst-case value, and the true impedance of the speaker in the useful frequency range is much higher. I will try again later with a higher value resistor, or a potential divider circuit. Curiosity is a wonderful thing.

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Ooh, a downvote. Care to say why? Is it a belief that expensive is always better? (Valves ARE better than transistors, but there's also a lot of marketing gimmicks to help you part with your money.) Or is it because I admitted that my experiment did not go as planned? I'm obviously going to try again and edit my answer with the results. At least I'm now publishing real experience, not just the theories I've seen others expressing on the subject. –  steve verrill Sep 5 at 22:17

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