Adding a cathode follower

[shef86]

Hey guys

I'm in the process of modifying my crate blue voodoo 50w. I'm going for a smooth distortion, similar to a bogner xtc or mesa, and would like to add a cathode follwer to the last gain stage. However, I can't think of a way of adding one without cutting traces and potentially messing up my amp.

I'll admit i'm very new to this, and it is the first amp i'm working on, so I figured there might be another way to design a cathode follower that doesn't involve cutting the traces.

Thanks in advance!

Schematic: http://www.schematicheaven.com/newam...voodoo_60w.pdf

[tubeswell]

If your crate is based on a printed circuit board, you got to cut traces etc to convert one of the triodes into a cathode follower. Or you could put in a FET cathode follower, but that still involves cutting traces.

[shef86]

somehow I knew that would be the answer ...

How big of a difference does a c.f. have?
is there anything I can do to have a similar effect?

[tubeswell]

A CF is a 'unity gain' stage, which means it doesn't have any gain (infact it has a very slight loss in gain), so if you are looking for it to give you more grunt, you are heading in the wrong direction. It will however improve the performance of your passive tone stack controls (if installed before the tonestack - which is where they are mostly found when found in pre-amp circuits), as it is a buffering stage with a very low impedance output (which basically means it gives the tone stack controls more responsiveness/x factor)

[shef86]

Thanks for the help, for some reason I thought it added more gain. I do know that it's suppose to give you some of the signal that is lost from using a tone stack.

I was basically following the xtc schematic and trying to match it with the crate, with some differences, like moving around the high and low pass filters, but generating a similar signal.

I remember reading reviews about the crate and people saying that it had an active eq, although looking at the schematic it is placed right after all the gain stages...with a really odd mid section that I don't quite understand.

[d95err]

I remember reading reviews about the crate and people saying that it had an active eq, although looking at the schematic it is placed right after all the gain stages...with a really odd mid section that I don't quite understand.

There's certainly no active tone controls in that schematic. (OK, the Presence control is technically an active EQ control...).

Just a variation of the plain old plate-fed Fender/Marshall tonestack. This one has the mid control in paralell with the bass pot. This results (I think) in a bit more mids and less interactive controls. This type of tonestack is used in Dumble amps, and I think I've seen it in some later Marshalls.

[shef86]

Thats interesting because I never had any issues dialing in a good eq setting, and it definitely doesn't seem like a mid heavy amp. It's not hard to get a scooped tone.

It was originally sponsered by marty friedman, and wikipedia claims that he used them on some megadeth albums, although it really isn't that good of an amp unmodded.

I wasn't planning on messing with the tone stack, maybe lowering the slope resistor to 33k, will this give me more bass or just make the tone controls even less responsive?

[d95err]

Go to www.duncanamps.com and download the Tone Stack Calculator application. Then you can experiment and see how changing various components affects the frequency response of different types of tonestacks.

Unfortunately this particular tonestack is not available, but for things like the slope resistor, I think you can use the regular Fender or Marshall stack.

[shef86]

I am familiar with that program, I'll have to take a look at it again.