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.

  • 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). Commented Jun 30, 2013 at 6:03
  • Yes, probably :). And my shop doesn't sell this one.
    – Julien N
    Commented Jul 1, 2013 at 9:26

2 Answers 2


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.

  • 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? Commented Jun 25, 2013 at 14:25
  • Attentuators are very subjective just like tube amps. Some people love them, some hate them etc...
    – JimR
    Commented Jun 25, 2013 at 23:05
  • 1
    @JimR And some people either resist them or react to them (cheap joke) Commented Jun 26, 2013 at 11:34
  • 1
    @CarlWitthoft: Carl, I'm going to resist my inclination to get a little hot under the collar over your little joke. :)
    – JimR
    Commented Jun 26, 2013 at 11:43
  • 2
    How on earth have I never heard of these? I don't want one, as I like playing loud, but it is very smart.
    – Doktor Mayhem
    Commented Jun 28, 2013 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. 

Basic series circuit (will not harm the amp)

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.



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, very little 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 higher. The difference is more noticeable with distorsion than clean, so the lack of difference is probably partly because I'm compensating by playing harder. Two 10 ohm resistors in series makes a noticeable difference, and three makes a significant difference.

As I said before, increasing the impedance by adding things in series with your speaker will reduce the load on your amp. With such a lot of load reduction you might expect to see some difference in tone (though all I have noticed is a slight reduction in punchiness that is probably due to the lower volume anyway.) Therefore another alternative is to place a bypass resistor across the terminals of the speaker (not the amp.) When you put anything in parallel with your speaker, it's vital to check that the overall impedance of the speaker/resistor network is at least as high as the speaker impedance the amp was designed for (with a good margin). If it is lower, you will overload the amp by making it supply too much current.

Impedance check

Resistor R1, 8.2 ohms in parallel with 4 ohm speaker:

network impedance: 1/( 1/8.2 + 1/4 ) = 2.7 ohms. 

Theoretically only 1/3 of the power goes to the resistor, but the impedance of the speaker might be a bit higher than nominal.

2.7 ohms in series with 8.2 ohm resistor R2: 2.7+8.2=10.9 ohms.

This is nearly three times the nominal impedance of the speaker, so it should not overload the amp.

Potential divider circuit (To avoid overloading your amp, always carefully check impedance when connecting anything in parallel with your speaker.)

enter image description here

  • 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. Commented Sep 5, 2014 at 22:17

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