Jawari + Discrete FET Preamp

[Cyeos]

Hi all,

After fooling with Tim Escobedo's Jawari pedal for a week now, I decided the low volume when the gain ("timbre") pot is far down wasn't going to work for me.  Conversely, the volume boost I got when it was far up was not good either.
SO, not to completely go against Mr. Escobedo's "most result for fewest parts" method or anything, I decided to add a simple audio taper pot to the end to give a level control, and a preamp at the front to increase the minimum volume.
Since I already had J201 FETs around for the Jawari, I figured I'd use J. Tillman's popular "Discrete FET Guitar Preamp" and slap it on the front of the Jawari.
This gave me the following:


Now, since I'm sticking the two together, I did not put the 10uF cap on the power supply for the FET Preamp, and instead just came off of the Jawari's 22uF that was already there.
I also put a 1uF cap bypassing the preamp's 2.2k FET source pin, to get more gain.

Anyway, I wanted to submit this to the group for direction or advice.  In essence it is working, but I think it could be better.
I am specifically curious if I can get rid of the red-circled 51K resistor on the preamp, because it is made redundant by the Jawari's 1M resistor right next to it.
Secondly, I wonder if I even need the red and yellow-circled 1M/51K resistors at all because the two circuits are now connected permanently(?)
Thirdly, does the original 100K resistor to ground on the Jawari, circled in green, serve a purpose anymore, or should my 10K level control pot be different?

Or maybe the entire idea is bad? 

[Quackzed]

yes you can lose the 100k to ground in green , your 10k volume is doing the job now.
as for the 51k and 1m resistors in yellow and red, you really only need one or the other
right now the 1m resistor isnt doing much, the 51k is overpowering it, so you could cut out the 1m and the circuit will sound the same as now. if you cut out the 51k and leave in the 1m then youll be shunting less signal to ground and it'll feed the 2nd jfet more signal and may be better or worse... you might get away with no resistor but maybee not it depends... 

[Mark Hammer]

I've made a couple of these, and it always struck me that, while we're never going to get it to sound like one of those EHX Ravish pedals, the sitar-iness of it might be improved upon by means of blending some clean signal in, and tone/gain shaping the "unstable-octave" generating part.  Certainly variable gain on the front end is a good head start.

[Cyeos]

I've made a couple of these, and it always struck me that, while we're never going to get it to sound like one of those EHX Ravish pedals, the sitar-iness of it might be improved upon by means of blending some clean signal in, and tone/gain shaping the "unstable-octave" generating part.  Certainly variable gain on the front end is a good head start.

Thanks guys!
Since I'm after a stronger signal in general, I'm going to try leaving the 1M to ground in the center, and drop the 51k.

Mark, do you suggest connecting the 1uF capacitor on the preamp stage to a pot to make it variable (as on the Jawari)?
I actually thought it could use a little more gain than I get as it is; should I change to a different cap value?

Very cool - the other ideas - what direction would you take to get a clean signal mix?
Some sort of mixer on the end, kind of like Tim has on the Jawari w/ Drones?

Do you suggest a sort of low-pass filter for the Jawari section to control the tone?

[Mark Hammer]

Well, first off consider that the Jawari  does not want a stronger signal.  It wants a signal that is juuuuusssst strong enough to produce some diode action.  More than that and you lose the drone quality.  Indeed, you can get a sitar like sound if you use any octave-fuzz, pick very near the bridge, and don't pick to strongly.  This circuit just simplifies matters, so you don't want to work against it.  There are a few versions of the Jawari, the second one (V6.3) having a 10k pot so you can reduce the gain.  That the circuit was improved by being able to reduce the gain says a lot, I think.

Perhaps the best experiment to try would be to insert the Jawari into a buff-n-blend, like this one:

You'd drop the part in red in the Buff-n-blend, as well as the 100k resistor after it, because the Jawari has that already.  You'd also drop the Jawari volume pot.  Since the drone part is in the mids, you'll want to thin out the Jawari side a bit by making the .1uf cap a smaller value, like 2200pf-3600pf (low cut starts around 480hz with 3300pf) .  You'll want the variable gain on the Jawari side to set it right with respect to sensitivity, but the pan control in the Buff-n-blend will set the the drone level.

If you attempt it, let us know how it works out.

[Cyeos]

Thanks Mark.
I don't see how I can resist trying the blend, since it uses almost all of the same current parts on my breadboard!  (Happy coincidence?)
Does the Buff 'N Blend J201 have unity gain, or is it that you don't think it is going to spoil the Jawari sound at its level?
V6.3 Jawari with the variable gain 10k pot is what I was working with, btw.

It's not really gain I am after, but just volume overall!  I'm after a level control, like on most Boss distortions and overdrives that goes from basically silent to much louder than the clean guitar.  The Jawari by itself - at least how I have it - goes from significantly quieter than dry signal when gain is low, to a little louder than dry, when gain is up.  Bleh.
Maybe my approach is wrong to begin with, and it should be an OUTPUT buffer I'm adding???

If anyone is curious, for the schem. above, dropping the original 100k to ground on the end, and leaving my A10K pot, seemed fine (no surprise).
I took off the 51k after the preamp stage and heard no difference, but then I also took off the 1M and heard no difference, so now I have none!
(Those would be "pull down resistors" there, correct?  Do they serve any purpose the way I have it wired?)
I can't hear any difference myself, but it might be because of how the Jawari is reacting to having the extra gain in the first place.

I'll give the Buff 'N Blend a try after going back to standard Jawari V6.3 first (sans Mark's capacitor swap).
We'll see if I still feel the same way about the volume level...

[Cyeos]

Well, first off consider that the Jawari  does not want a stronger signal.  It wants a signal that is juuuuusssst strong enough to produce some diode action.  More than that and you lose the drone quality.  Indeed, you can get a sitar like sound if you use any octave-fuzz, pick very near the bridge, and don't pick to strongly.  This circuit just simplifies matters, so you don't want to work against it.  There are a few versions of the Jawari, the second one (V6.3) having a 10k pot so you can reduce the gain.  That the circuit was improved by being able to reduce the gain says a lot, I think.

Perhaps the best experiment to try would be to insert the Jawari into a buff-n-blend, like this one:

You'd drop the part in red in the Buff-n-blend, as well as the 100k resistor after it, because the Jawari has that already.  You'd also drop the Jawari volume pot.  Since the drone part is in the mids, you'll want to thin out the Jawari side a bit by making the .1uf cap a smaller value, like 2200pf-3600pf (low cut starts around 480hz with 3300pf) .  You'll want the variable gain on the Jawari side to set it right with respect to sensitivity, but the pan control in the Buff-n-blend will set the the drone level.

If you attempt it, let us know how it works out.

I have indeed now tried the Buff 'N Blend with the Jawari effect!
The 0.1uF output cap has been replaced with a 0.022 uF film cap.
Currently I have the 1M pull-down resistor still at the front of the Jawari circuit - this should be removed now, though, maybe?

The blending is very cool and effective, but my original problem basically still remains!
Past about 3/4" gain on the Jawari "timbre" pot, and the signal becomes significantly hotter than the clean signal going to the blender.
It would be fine if the sound of it at the lower gains is what I always wanted, but that is not the case.
The way it is now, if you have the Jawari all the way up, but the blend 50/50, the Jawari will be much louder.

Maybe I do, in fact, need the red resistor on the Buff 'N Blend schematic?  A pot?

[Mark Hammer]

Yeah, I guess with gain applied to the Jawari side but not the clean side, it may be more difficult than I first thought to nail a decent blend of clean and effect.  The simple thing to do is stick something like a 33k-100k fixed resistor between the output cap of the Jawari and the junction of the 100k ground resistor and outside lug of the blend pot.  That will attenuate the Jawari signal about 30%-50% or so, to make more of the blend control useful to you.

[Cyeos]

Thanks again Mark.
With a resistor in series after the Jawari output cap (ended up with 270k, actually) the levels are about equal between clean and Jawari sound at full gain - when at 50/50 on the Buff 'N Blend.

Blend is definitely an improvement.
Any other ideas?
Or maybe I should just put it in an enclosure finally...

Out of curiosity: why is a series resistor there preferable to a pot bleeding to ground to control the Jawari level?

[Mark Hammer]

Thanks again Mark.
With a resistor in series after the Jawari output cap (ended up with 270k, actually) the levels are about equal between clean and Jawari sound at full gain - when at 50/50 on the Buff 'N Blend.

Blend is definitely an improvement.
Any other ideas?
Or maybe I should just put it in an enclosure finally...

Out of curiosity: why is a series resistor there preferable to a pot bleeding to ground to control the Jawari level?

Because the blend pot actually does the level adjustment, so you want something fixed.  If the "blend" consisted of two fixed resistors mixing clean and effect signals in equal proportion, then YES a level pot like you describe would be entirely appopriate.  But since we already have a variable blend, then all that was required was a simple compensation to let the blend control work better. 

[Gurner]

Whether you use a 51k resistor,or a 1M resistor won't make squat difference to the volume level (IMHO) as there's no potential divider vibe going on there.

[Cyeos]

Whether you use a 51k resistor,or a 1M resistor won't make squat difference to the volume level (IMHO) as there's no potential divider vibe going on there.

Hi there,
You are referring to the earlier questions about the pull-down resistor on the Jawari?
If so, yeah you are correct    Indeed there was no difference.

I have left it at 1M on my current Buff 'N Blend setup, as led to by Mark.
Seems to work.
I don't know if it is needed anymore with the buffer in front...but it doesn't seem to cause any problems being there that I can tell.

[Cyeos]

Because the blend pot actually does the level adjustment, so you want something fixed.  If the "blend" consisted of two fixed resistors mixing clean and effect signals in equal proportion, then YES a level pot like you describe would be entirely appopriate.  But since we already have a variable blend, then all that was required was a simple compensation to let the blend control work better. 

I gotcha.
The only reason I thought something variable might still be useful is the fact that the Jawari varies so much between the low and high gain settings for the "Timbre" pot.
Like right now with the 270K resistor, the Jawari is about equal to clean on roughly the last 30% of the knob, but any lower and it would be quieter compared to clean at 50/50 mix.
But then, I suppose, the reasoning would be that you would just blend more towards the Jawari to compensate, right?  Right.

I think I'll have this in a case by next weekend!
Gonna try a henna-style etch on a 1590B.
Muah hah hah.

[Mark Hammer]

Given your success, I'm obviously going to have to follow suit.  I have a Jawari unit in my modular setup, but the clean/effect blend will definitely improve it from where I'm standing, and allow it to provide a certain swirl or animation, rather than just sitting at the edge of garbled all the time.

As well, it and other rectifier-based octave-up units tend to only "deliver the goods" when picking near the bridge with the bridge pickup on.  My gut tells me that use of a clean signal blended in, and appropriate hi-pass filtering of what goes into the Jawari (and comes ut of it), may be able to provide a little more latitude to the player with respect to where they're "allowed" to pick.

[Cyeos]

Awesome.
Yeah, let me know what you end up going with.  I don't have a wide selection of smaller film caps to try for the hi-pass filter, so have just stuck with the 0.022uF (sorry, I insist on only listing caps in microfarads).  Also, I'm using the cheapo Radio Shack resistor pack still...4 years later.  Thankfully, I don't think they make much difference.  Also, this is only around my 3rd pedal, 2nd from scratch.

The blend circuit was so easy, I'm left wondering why it isn't very common on other effects - particularly ones that are kind-of extreme, like the Jawari.

On another note; I never did care that it didn't really sound like a sitar...

[Cyeos]

This is what I ended up with:


Getting ready to do a layout, but first I got some alternate capacitors coming to see if any sound better than 0.022uF.

I'm curious if anybody else has tried this yet?