Extra tube gain stage(s) on preamps

[elvis]

If you want an extra 12ax7 gain stage, run your guitar or effects into the FX return of your preamp. Run the main out into the preamp input. Run the FX send to the amp (with or without an FX unit).

You get an extra gain boost from the output tube (now the input tube) and the main volume controls the gain.

For the studio pre, make sure the LINE/LOW is set to low (or else you get a really low input impedance). For the Triaxis, disable the FX loop.

You can also use the other FX return/main out pair as another gain stage, or as a mono send to your amp.

I did this with my studio pre, and it works really well, both for rhythm (now mild overdrive with the boost) and lead (like putting a tube screamer in front).

 

[ando]

How are you getting an extra stage in this? Or are you just referring to the extra boost into the input tube? It seems like you are getting the same number of stages but in a different order. I would have thought that a guitar going straight into the output tube might not sound that great given that the output tube would normally receive a line-level signal rather than a high impedance guitar signal. Not quite grasping why you would do this. I might try it and see what the effect is. I can only do it with the Triaxis - which already has mountains of gain as it is. What do you think the benefit is in doing it on a high gain preamp like a Triaxis?

 

[elvis]

In general, that last gain stage is designed to be clean at line level, since it buffers the FX, and is well after the overdrive circuits. So you would be a bit hard-pressed to get extra drive with the last stage, unless you drive the heck out the signal in the FX loop, and that may be a problem if you are using FX due to post-FX distortion.

What you get is essentially the same thing as running a tube screamer in front of the preamp. A big clean boost. I found that with the studio pre, more lead drive tends to get muddy, where overdriving the input tube (using any sort of clean gain stage) in addition to a reduced lead drive, gives a very different tone.

Think of it like an all-tube OD808 for free. Sort of.

It also works well to bring up my guitar level when I coil tap (I have a JEM, and the output level tapped is very low compared to the 1 and 5 positions) without resorting to a compressor. And it gives a good Fender-on-8 overdrive tone (bright, not very driven, but crunchy) tone with a humbucker.

I actually switch the tube in and out using a switch matrix (built into my G System, so it was also free). You could use any sort of loop controller to do that.

 

[ando]

Interesting, thanks for the explanation Elvis. I'll try it out when I get a chance.

 

[elvis]

You're welcome. I am curious how it works out in a TA.

I expect that you will have to keep the output volume for that channel pretty low. I find with mine that it is easy to get excessive hum.

 

[crane]

I'll try that with the TA as soon as I finish my studio record session. Not the time to break something :wink: