Fetzer Valve Revisited/Deluxe build report

[stm]

I simply wanted to share my experience with the Fetzer Valve Revisited/Deluxe. I hope my comments don't appear biased since I was involved in the development of this device.

I started with a 2N5457 JFET with Vp=-1.54V and Idss=2.94mA. I decided to use 18V to have more gain, since I wanted to make a booster. Using the calculator I get Rs as 435 ohms, so I used a standard 430R, 5% tolerance.  Rd appears close to 4500 ohms, so I used 2k7 in series with a 5k trimpot (I didn't have a 10k trimpot).  I tuned Rd for Vd=11.88V as indicated by the online calculator, which happened pretty close to the trimpot's mid rotation. The suggested presence capacitor was very close to 390nF, but since I didn't have anything close to this value I ended up using 150n+150n+100n=400n poliester caps.

The effect of this booster is wonderful to my guitar and SS amp, specially with the presence cap engaged. This extra presence touch is what was missing from my gear to have a relatively decent clean tone.

As an additional tuning, I reduced the 47n output cap to 6n8, which was perhaps too thin. I finally settled with 18nF which cut a bit the 6th string level and evened out the overall sound. The stock 47n cap is still usable, so I'll have a switch to select between these two values, just as with the presence cap.

The unity gain is obtained near 1 o'clock with a 100kA volume pot, and there is plenty of extra volume if desired. Since my amp is SS, I can't really take advantage of this boost capability, however I'll pass this little circuit to my brother so he can put it to the test at the recording studio.

As for the magic harmonics, I'm not sure if they are there or not. I have to blame my tin ears. Nevertheless the extra presence and slight bass thinning are enough to fix my clean tone up to a point where I can't play without this unit anymore.

Finally, I have to say that the tonestack controls in my amp now are set around 12 o'clock, thus having control range in both directions, while before I always used the Treble dimed and the Bass control near 9 o'clock, but still couldn't get close to what I wanted.  The effect of the Presence capacitor cannot be obtained just by diming the Treble control.

Cheers.

[RDV]

Have we tried to run a few of these in series to see about distortion characteristics?

RDV

[stm]

Ricky,

I attemped an AC-30 Vox emulation with such stages before the Fetzer Revisited was published, but applying its principles. It failed miserably because I used 9V supply and 2N5457 FETs which gave way too little gain (around 2.5 times per stage, instead of around 50 times). This is when I realized the low voltage supply and Vp of the JFET did matter for the gain sake. I tried then with J201's and gain increased but still not enough.

Then the Fetzer Revisited/Deluxe article came in. I know Brian did try some ideas with two of such stages in series which I tried in the sim. Looks promising, but this is still subject to investigation and *eventually* part of a new ROG release.

My feeling is to either go with higher supplies (up to 30V), or use two Fetzer Revisited stages in series per valve. Just at the theoretical level yet.

Cheers.

[MartyMart]

I;ve just tried perfing a "deluxe" Fetzer.
I set it up with a 100k trim for Rd and a 10k trim for Rs, socketed the presence cap
and choose a j201, Vp -0.81 Idss 0.67
Output cap left @ 47n

Having control of Rd and Rs is fantastic !
I tuned it "by ear" first and ended up quite close to the calculated Vd/Vs values of 5.97 and 0.31
I tried the recommended presence cap of around 150n down to 47n and liked the tone at about 82n.
Using the calculator, it will be very easy to set "optimum" fixed value resistors, in this case that would
have been Drain 10k ( closest to 9913ohms) and Source 1k ( closest to 1003 ohms)

Superb, and a very interesting way to set up a Jfet "valve" emu

I think I may re-visit some of my other builds and include the ROG calculation data on a couple of the
amp sims ....
Do yourself a favour and try a deluxe, I dont think you'll regret it !

MM.

[markm]

Ya know,
This one's been on my list too, which BTW keeps getting bigger 
I thinks it's time for me to take a vaction and build stompers the whole time!

[mutant_guitar]

i keep hearing about how everybody loves the new booster, but i haven't actually heard any sound samples of the new booster. i have the old version i built, and i have a TC based off the same idea, and they sound wonderful, which makes me very eager to hear how this updated version will sound. i'd really appreciate it if someone could post a clip sometime.