JHS Superbolt

[johnk]

many of you may have seen that this pedal is kind of a combination of runoffgroove's Supreax and Supreax Deux. there are a few changes though, so I drew up a vero for the JHS pedal, built it and it's VERIFIED. IMO, it sounds pretty darn good.

[Geiri]

I better try this because I built the Supdreaux Deaux and it was trouble. I had to substitute the JFETs to get the right sound out of it.

[Kinski]

I dont have any LT1054 ICs on hand. would a TC1044SCPA or ICL7660SCPA work?

[johnk]

yep. i'd use the 7660S. it's a direct drop in replacement for an LT1054.

[Kinski]

Just slapped this guy together this afternoon. Used a TC1044SCPA.

You are right, it does sound nice. I was expecting a bit more gain out of it with my tele, but no big deal. Its a really nice low-mid gain overdrive, with a nice decay too. Not crackly like a lot of low-mid gainers.

I never got the ROG Supreax to work right. So I'm glad this one is running smoothly.
Tomorrow I'll put it in a 1590A.

Thanks for the layout!

[MAO]

Sounds awesome! Mine has plenty of gain.

Silverbolt: https://plus.google.com/114192188550255459199/posts/NXa9CY2mfni

Phil X just played through a Sears Silvertone in his latest video on Fretted Americana, around 2:45. This pedals nails that sound and then some!

https://www.youtube.com/watch?v=tLaatNuyxis&list=UUFzdwJs_ajtDeimeH6d3e_w

[motterpaul]

John K....

I just built this and it really rocks - wow, one of my favorites so far.

However, the tone control seems to do nothing (acts like a volume in one switch position, and does nothing in the other position).

I would really like to swap in a Baxandall or other tone stack in place of that pot - and ideas on how to do that? What would you take OFF to eliminate the tone pot in your layout above?

Thanks for a GREAT circuit.

[giudis]

I built this and I really love that sound!
However the tone control seems to do nothing for me too, like motterpaul.
What could be the problem?

[induction]

According to my sims, the filter seems to be tuned to cut everything above 200 Hz roughly equally. To get a more traditional high-cut above 1 kHz or 2 kHz, try replacing the 4n7 right next to the double link with a 1n. Or, for a stronger cut of high frequencies, leave the cap at 4n7 and replace the tone pot with a 250k or 100k.

If you just want to remove the tone control altogether, just disconnect the tone pot. You can also remove that cap, or leave it in if it's easier.

[Frank_NH]

Induction - are you using LTSpice?  I've been using it quite a bit lately to develop an amp sim and it's been a great tool.  I even have Spice models now for all my favorite JFETs (J201, 2N5457,...)!

As for the tone control, it's pretty much a simple treble cut, so as Induction says, play around with the pot/cap values.   Anything more sophisticated would be lossy, but since there's a gain stage following, you could increase the gain there to compensate.  The second order filter at the output also rolls off high end so if you want more treble, you can play with those cap/resistor values.

[giudis]

 thank you induction and Frank!
I'll try and I will leave my comment...

Did you try the original one?

[induction]

Yes, I've been using LTSpice for a few years now. I'm a big fan. It's great for verifying a circuit's response derived from theory, or for testing things that I can't calculate. And you can't beat the price. (It's free, for those of you who are unfamiliar.) A good sim is probably the second most important tool (after the breadboard) for anyone who wants to design or mod their own circuits. I use it even just for drawing schematics, though there probably better programs for that.

Good jfet models are very useful, and not always easy to find. Are you getting your parameters from measurements of your own stash?

[induction]

I didn't build it, just simmed the tone control and surrounding subcircuit.

[giudis]

Oh no, I mean if have you ever tried the original JHS

[Frank_NH]

No, I'm using models available from the internet.  These are some JFET models used by Runoffgroove (courtesy DIYStompboxes.com):

* J201 with VGSoff=-0.8V and IDSS=0.6mA
.MODEL J201 NJF (VTO=-0.8 BETA=0.94M LAMBDA=2M IS=114.5F RD=1 RS=1
+ CGD=4.667P CGS=2.992P M=.2271 PB=.5 FC=.5 VTOTC=-2.5M BETATCE=-.5
+ KF=604.2E-18)


* 2N5457 with VGSoff=-1.6V and IDSS=3.3mA
.MODEL 2N5457 NJF (VTO=-1.6 BETA=1.29M LAMBDA=2M RD=1 RS=1 CGD=6E-12
+ CGS=2.25E-12 KF=6.5E-17 AF=0.5)


* MPF102 with VGSoff=-2.5V and IDSS=6mA
.MODEL MPF102 NJF (VTO=-2.5 BETA=0.96M LAMBDA=5M RD=1 RS=1 CGD=1.54248P
+ CGS=2.567P PB=1.49 KF=7.90591F AF=499.953M)

I've also got some LED models (specifically red LEDs).  Everything else I've used from the LTSpice library.  They even have an LT1054 charge pump model, and it works really well to simulate different charge pump configurations.

My main use of LTSpice recently was to develop an amp sim circuit based on a pre-existing solid state amp schematic.  I use LTSpice to simulate both the original circuit and my sim to make sure the frequency response and wave forms are similar in different parts of the circuit.   Someday, it would be fun to simulate tube stages, but I'm not there yet...

[Frank_NH]

giudis wrote

Oh no, I mean if have you ever tried the original JHS

I've built the original ROG Supreaux and it's similar but runs at 9V rather than 18V.  It sounds great, but I found that removing the bypass cap from the first JFET tightened up the bass quite a bit, which I liked.  I didn't play around with the tone, however.

[induction]

giudis wrote

Oh no, I mean if have you ever tried the original JHS

Nope.

[motterpaul]

While I appreciate the help you guys put into your LSpice research, I think that what Giudis is saying, as I also found, is that there seems to be a problem with the circuit design in that the tone control doesn't do anything.

Not that I don't enjoy reading about Jfets & tone controls, however. I might just take my tone control off off - at least I know I can do that and not kill the signal flow. A lot of times all those pots seem to do is cut treble (and not as if the design has too much treble).

[induction]

motterpaul wrote

While I appreciate the help you guys put into your LSpice research, I think that what Giudis is saying, as I also found, is that there seems to be a problem with the circuit design in that the tone control doesn't do anything.

I believe I understood you both perfectly well. What you said previously is that, for one switch setting, it acts like a volume control (which is not quite the same thing as not doing anything), and is exactly what my sim showed that it does ("the filter seems to be tuned to cut everything above 200 Hz roughly equally"). The problem with the circuit design is exactly what I addressed, and the mods I suggested should turn it into a traditional treble-cut tone control, which is apparently what it was intended to be.

Not that I don't enjoy reading about Jfets & tone controls, however. I might just take my tone control off off - at least I know I can do that and not kill the signal flow. A lot of times all those pots seem to do is cut treble (and not as if the design has too much treble).

If treble-cut is not what you want, getting rid of the tone control is perfectly reasonable.

[Frank_NH]

Hey Paul,

Actually, I went ahead and did an LTSpice sim of the Superbolt , and it showed me that the frequency response is pretty flat from 100Hz - 2KHz and falling off thereafter.  The 12k/3.3n filters at the end roll off the treble, so try removing that those end filters and see your treble increases.  

I think your idea of using a Baxendall or similar is a good one, but you'll lose some signal in the process (not a big deal since you have a gain stage).   Perhaps a modified BigMuff tone control would do the trick with fewer parts?  See Jack Orman's different configurations for some ideas.