Monday, September 17, 2012

Getting the rig together--FX loop tube

So, I actually have a growing need for a working and/or more permanent guitar rig. For recording I've been able to hack things together as a kind of one-off, but most of the tones I got were things that I wouldn't be able to easily reproduce again, especially live, with the equipment I have now.

Anyway, one part of this is due to the fact that I rely on a (cheap) mic tube pre-amp to make my (cheap) solid-state combo amp sounds like an (expensive) tube guitar amp.

The problem with this is that to get the nice tone coloration out of a tube, you have to drive it hot, and it ends up being driven so hot that the signal level would be unsafe. So I just keep the volume as low as possible. I just nudge it up from zero until it sounds at all--and that's still usually too loud. I feel like if I turned it up any higher than that I'd blow my power amp or speaker for sure.

The combo I'm using is a Peavey Transtube Studio Pro 112, and the mic pre is an ART Tube MP Studio. Based on the specs, the amp nominally sends and receives -10dBV through the effect loop. The Tube MP has a maximum gain of 44dB, and a maximum output of about 20dBV. While it looks like I'd need a 30dB attenuator, I'd rather it be adjustable, so I'll probably end up testing several levels before committing to one.
Unlike a guitar amp preamp, the Tube MP also lacks any tone controls. I've been wanting to implement an idea for a new passive tone stack anyway, so I've decided to use it here. It consists of two Big Muff tone stacks, each with flat mids, but who have different cutoff frequencies. This would allow a wide range of mid cut and mid boost options in addition to regular Big Muff tone operation.

Both the attenuator and tone controls can be 100% passive, and since they're intended for the same device, I'm going to consider them the same project and put them in the same box, which with the ART TubeMP I'll hopefully be able to velcro somewhere on my amp.

Here's a diagram of how it would be.

rig Without the FX loop, the signal goes straight from the internal preamp to the power amp.

Next post I'll record a video of what it sounds like without the attenuator and tone stack (although I think I've done that before, but without really talking about it), and show what would have to hook up to what.


  1. What would happen if you bought a more expensive pre-amp and used it with your other equipment? No change?

    1. Well, it's a mic preamp. In theory, at a certain point of expense, it would cost the same, but sound better, to just upgrade the amp. Guitar amps usually come with the preamp and power amp bundled though, so buying one intended for guitar is only common at the very highest price range.

      But yeah, more expensive in general is better. Most mic-pres, at this price level, add features such as extra voicings or a compressor, rather than any real increase in sound quality.

      In general, any tube pre is going to sound better than a solid-state pre, no matter what it was intended for, so that's what I'm really considering here.

      I guess I could have put the prices in the post, for comparison ...