Low Volume Tube Distortion

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I wanted to get a good tube amp sound at low volume, so I could play Like a Hurricane at home at any time of the day. I succeeded and now I am telling you how to do it.

The Amp

I bought a 5 watt tube head (Epiphone Valve Junior). It is a very basic amp with only a volume control, turn it down for clean, up for distortion. I connected it to a 6" no-name speaker that I took out of a Fender practice amp. I thought this would be good and quiet. It sounded great but it was FAR TOO LOUD. Happily I discovered that there is an easy way to lower the volume of the speaker, without having to invest hundreds of dollars in a power brake. You need to be able to solder.

The L-Pad

You can not use a standard potentiometer to fade down the signal to the speaker. They have a too low power rating. Also a tube amp needs to have a constant, matched impedence attached to its output. In other words, if you use the 8 ohm output socket on your amp, the load needs to stay at about 8 ohms or the output transformer will blow up. OK, this is not strictly true, you can mismatch the impedences if you know what you're doing. But it's a good rule of thumb.

You can buy special speaker attenuators called "L-Pads", which allow you to fade the signal going to the speaker while keeping a fixed impedence. You need an L-Pad that matches your speaker impedence, and has a sufficient power rating for your amp. So I needed to get an 8 ohm one, rated at over 5 watts. 10 watts would have been ideal. The only one I could find was rated at 50 watts and cost NZ$25. At least I don't have to worry about it getting too hot. Later I found you can get them with lower wattages for much cheaper.

Hook it up like this.

It works really well, you can fade the speaker volume right down to very quiet. Some internet nerds say that there is a loss of tone, but I don't know... It does sound a bit lacking in power when you turn it down low, but that is just because it is literally lacking power, it's not shifting much air. When you mic it up the sound you get is perfectly fine and full.

Safety

Mount the L-Pad on the speaker box, not in your amp. Don't open your amp at all! If you don't know why it's dangerous, stay out of there. I am not responsible for you getting zapped. Mounting the L-Pad on the speaker is fine though, it is safe. The only thing is triple check that everything is connected right, and test the impedence with a multimeter. This is just so that you don't power up your amp without a load, which would be bad for it. If you are already using your own speaker like me, and not a commercially produced cabinet, I guess you know this already.

An L-Pad should make an amp quiet enough for most people. But I wanted mine to be as quiet as unamplified electric guitar strings, so that I wouldn't disturb Nana. The L-Pad does this but you need to run the speaker at least at human voice level for the mic to work well, ie. to not have noise problems. So in addition to fitting an L-Pad, I put the speaker in an isolation cabinet.

The Isolation Cabinet

An isolation cabinet is just a box that you put the speaker in and seal it up with the mic inside. I am not much of a wood worker, but I already had a box of the right size, made of 1" MDF. It only had 5 sides, so I cut a new piece of MDF and painted it to make a door. Then I got some 1" rubber weather stripping from a hardware shop. I stuck this along the front edge of the mouth of the box, and attached the door with hinges and a case-clip so it squashes against the rubber and makes a seal. Then you just put the speaker in there and stick the mic in front of it, and close the door. You need some lining to cut down the reverberations, otherwise it really sounds like it's in a box. The best thing to do would be to line it with dense sound-proofing foam, but I just stuffed some old jerseys in there. It works.

In Conclusion

I think this system is a big success. The isolation box leaks out bass but really it is very quiet. The only thing you miss out on is feedback. It sometimes feels a bit strange to have huge amounts of power-tube distortion and no feedback. But you can't have everything.

If you think anything in this article is bad advice, please contact me.

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