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has anyone had any luck doing a similar mod for a Fender Twin? I'm intrigued by the idea of getting its full-blown tone without killing everyone in the room.

The short answer is no, unless you get a speaker soak.

The long answer. While master volume Marshalls get a lot of their distorted sound from their preamps, Fenders get most of their distinctive sound from power amp tube distortion. Master volumes have to come before power tubes, except for speaker soaks, which aren't really traditional master volumes at all.

You can make Fenders break up in the preamp. However, due to their gain stage voiceing and choice of coupling caps, they pass more low frequency than the average Marshall. When this low frequency clips in the Fender preamp, you get a very ugly, farty distortion. You can mod your Fender to roll off more lows in the preamp and voice your amp a bit differently. That will get you a Dumble or early Boogie kinda sound.

Another big difference is that marshalls have three gain stages first, then the tone stack, the part of the circuit where the tone shaping happens. With amps wired this way, you can shape the distorted sound with the tone controls.

In Fenders, there is a gain stagem the tone stack, then two more gain stages, so the tone controls will be much less effective when trying to shape the overall distorted sound.

If you want the cranked twin sound at a lower volume, the easiest mod is to remove the two outside power tubes and disconnect one speaker to compensate for the impedance change. You now have a 50 watt Twin pushing 1-12. If you do this and you like it, you can have the amp biased for this kind of operation and permantly remove one speaker to lighten the load. Or you can just get a good speaker soak, which may or may not sound good to you.

ben adrian

thanks benadrian.

what's a "speaker soak" exactly?

The remove tubes/unhook 1 speaker/rebias option sounds like a quality idea. I'll give that a whirl at home.

So you'd probably also say that installing a master volume on a Twin is a lousy idea because it pumps the pres not the powers?

Just want to make sure I'm reading you correctly...thanks mate

Yes, you're getting me right. Adding a master volume will cause the preamp to distort, and the heavy preamp distortion on fenders is generally not the sound people want at all.

A speaker soak is a device you put between the speaker out and the speakers. On a fender twin you'd unplug the speaker cable going to the back of the amp and plug that into the output of a speaker soak. You'd then run a new cable between the speaker out on the back of the amp and the input of the speaker soak.

The speaker soak has a knob or switch that re-routes some or all of the power to some sort of device to safely absorb the power. The marshall and other main manufacturer who I can't recall right now use what are basically big resistors. Weber speakers makes one called the Mass that contains a speaker with no cone attached, so your amp power moves a speaker motor that doesn't move any air. It's a pretty cool device.

Ben Adrian

benadrian wrote:.

The speaker soak has a knob or switch that re-routes some or all of the power to some sort of device to safely absorb the power. The marshall and other main manufacturer who I can't recall right now use what are basically big resistors.

another device, perhaps the one you are thinking of is the Hot Plate from THD Electronics.

Yes, the THD Hot Plate. That IS what I was thinking of.

Ben Adrian