Fulltone Catalyst [traced]

[CheapPedalCollector]

Hallo
and thanks for the trace.

Did you had measured the (quiet/DC) voltages on Q1 and Q2?

BS170, they are still available no problem.

[phatt]

Traced, Enjoy.

I left out the soft LED switching and the 22uf and 1n4007 reverse polarity protection on the +9V. Interesting circuit.

Fulltone_Catalyst_V1.png

Hallo
and thanks for the trace.

Did you had measured the (quiet/DC) voltages on Q1 and Q2?

I guess, this could help to be to find a proper replacement
for the BS270.

Thanks in advance

NegationOfNegation

Hi Neg O Neg
this might help,
Here is what is on my BBoard right now, with voltages.

It certainly has potential as far as the transition from clean (ish) into ODrive just by the guitar volume pot which is impressive. But (there is always a but)
Except for a big treble peak when gain pot is full up, it's great.
Not sure how to get around that issue.

I lowered the value of C8 as it helped remove the mud lows.
Also
On my sim 220nF at C1 goes down to 10Hz, so changed C1 to 22nF which raised the low roll off point.
That helps to stop it going stupid when gain is high.
The 2 tone controls don't do a lot but maybe that is a good thing.

As I had both BS170 and 2n7000 I tried both and there is little difference in the outcome but a sim reveals the wave form is slightly different.
might be just my mind playing tricks but with a 2n7000 at Q1 and BS170 at Q2 it seemed to be a tad better,, can't put my bias finger on why but some how it sounded a bit smoother.

Re the BS170 and 2n7000 pinout,, as the centre pin of both is Gate then you just turn one 180deg and it's fine.

Phil.

[phatt]

Had some time this week to poke around this circuit and here is what I've come up with.
That gain pot was unusable due to treble peak at full up.
So I shorted the gain pot, (removed)
Then adding some caps around R12 & R13 rips off excess mud for a sweeter sound.

I was loosing too much treble when lowering the volume pot on guitar so I added the extra front end and it helps to resolve that a fair bit.
Any way might give folks some ideas to work with.
Sounds good through my setup so other gear will likely give different results.

It works with both BS170 and the 2n7000 but I'm using the 2n7000 at Q1,, it seems to be just a tad better, but I doubt anyone will notice the difference in a live setup.
Phil.

[NegationOfNegation]

Hi Neg O Neg
this might help,
Here is what is on my BBoard right now, with voltages.

It certainly has potential as far as the transition from clean (ish) into ODrive just by the guitar volume pot which is impressive. But (there is always a but)
Except for a big treble peak when gain pot is full up, it's great.
Not sure how to get around that issue.

...
Phil.

High all,

thanks for answers and measurements.

Regarding BS270 vs. 2N7000:

I asked for the quiet voltages, because it looks like the BS270 and the 2N7000 differs, generally said, in the pinch off voltage parameter, which causes different operation points, for instance in the catalyst circuit.

This circuit (and the fuzz face circuit in a similiar way) works like an, regarding the quiet voltages, self adjusting system:

• Quiet voltages depend on the (necessary) Gate-Source-voltages of Q1 and Q2:

• Q1 will work just in saturation

• Difference between U_D1 and U_S1 is sum of U_GS2 and U_GS1

• Q2 is not in saturation necessarily, but:

• the higher U_S2, the lower U_D2 and (shifted from both sides) the more quiet source on the drain of Q2 goes onto saturation, or:

• the lower U_S2, the higher U_D2 and the more quiet source on the drain of Q2 goes onto cut off.

• (When output operation point is really asymmetric, it could happen, that C5 change its average voltage on clipping, which causes a change of operation point of Q1. Playing with a standard fuzz face circuit, I got the impression, that the fuzz sound becomes a little bit more "sharp defined", but in decay really "crumbly".)

It often happens, that, in overdrive circuits, BS270 would be replaced by 2N7000, but they seems to differ in that point

That's why I asked for operation points.

About the treble peak.

Did the change between "FLAME" and "SPARK" something?

Apart from that, the catalyst circuit have a source capacitor on Q1 as well as on Q2, that means, on both stages a phase shift (acceleration) up to 90° will be realized. If there is a negative feedback (from Source of Q2 to Gain of Q1 via R7), that means a feedback of 180° additionally, it may be, that the whole system could be unstable.

So on a "normal" fuzz face there is a hint to avoid trebbly sound on high gain/attack settings---putting a low resistor (47 or 100 Ohms) before C5. This is not really a solution, it prevents high gain settings, but, in catalyst circuit on breadboard, i.m.h.o it make sense to test it (putting an e.g. 1k in series with C5 or C8.

Greets

Torsten

[phatt]

Well to get around the treble peaking try the modified circuit I posted.
(the input opamp addition is not needed to get an idea of the improvement)

The same Flame/Spark effect is achieved in my *Mod Circuit* simply by lifting one end of C4 (330nF). By doing the Flame/Spark this way there is no treble peaking. Yay
I found that made for a much more user friendly circuit.

The circuit is stable with no hint of oscillation and I'm impressed at how quite it is.
There is of course the quite background fry pan fissile of electrons buzzing around but still a lot less noise prone than some dirt pedals I've used.
Before I do a build of this I'll just keep tweaking a few things to make sure it will balance well with my setup,, I have other amplifiers to run through,, just have not had time.

It's not shown on Schematic but I'm thinking of inserting the bypass switch after the opamp (wiper of VR1) so I have a buffer stage on all the time. All work in progress.

BTW, There is no *BS270* in this circuit,, *it's a BS170*.

Regards to Quiet point,,
I assume you refer to Q point or (Quiescent point)
yes I'm aware that this is a DC (Direct Coupled) circuit
so yes the DC voltage at the Drain of Q1 sets the Gate voltage (Q point) of Q2.

Hence the AC signal floats on that Q point at the Gate of Q2.
Agreed the BS170 and 2n7000 are a bit different and the DC voltages change when I use a 2n7000 in position of Q1.

Examples;

Q1 BS170
D= 4.47v
G= 2.28v
S= .71v

Q2 BS170
D= 5.76v
G= 4.47v
S= 2.29V
--------------

Q1 2n7000
D= 4.18v
G= 2v
S= .77v

Q2 BS170
D= 6.11v
G= 4.18v
S= 2.01v

Phil
Ed; forgot to mention, As the guitar volume pot can be used to control the distortion intensity I've found no real need for a gain control. YMMV.

[Manfred]

Agreed the BS170 and 2n7000 are a bit different and the DC voltages change when I use a 2n7000 in position of Q1.

If you take two 2N7000 from different production batches you will also read different voltage values.
The value variation within the same JFET batches is generally large.

[CheapPedalCollector]

I would have read the voltages for the original unit, but that's what was wrong with it, the BS170's were both destroyed. There is no antistatic protection in the circuit, which is another improvement that could be made. Also try your changes on 18V.

[phatt]

I would have read the voltages for the original unit, but that's what was wrong with it, the BS170's were both destroyed. There is no antistatic protection in the circuit, which is another improvement that could be made. Also try your changes on 18V.

Ta mate,, yep I figured the input is prone to fail which is why I added a front end.
I did run it from 18volts which gives it more clean headroom,, that maybe an advantage depending what you want to achieve but I like it on 9Volts. The output level is very big even worse on 18volts.

A couple of mods since I posted my *Rewired Mods schematic*;
1/ To balance the bypass level I had to up R3 to 330k.
2/ I've removed R9 and C13 as it's really not needed.

If you lift C4 it brings back a fatter sound but you tend to loose the clean when you roll off the guitar volume. but some may want that.
Phil.