Boss fz-2 owner question

[imjonwain]

Does anyone on here have an original Boss FZ-2 or a hyped fuzz clone built? I have a clone running and am getting oscillation when I have the gain and Hi controls maxed in boost mode.  The oscillation starts at the high end of the audio range moves up to about 60kHz and then down to ~34kHz (aka I can't hear it and audio cuts outs).  It's pretty much square wave.

No such "problem" in the fuzz modes, which are pretty out there anyway and do semi self oscillate at max gain. The original manual actually warns about oscillation in boost mode when the "depth" is too high.

After messing with the board and components for a while the issue was wiring/my test bench setup.  I always put the ox before the damn cart....  Using a 2" long shielded input wire and short output wires to my cables solved the oscillation and instability issues.  I did also match my jfets and cherry pick my other transistors as well in the mean time but that didn't change much.   

[ahiddentableau]

Sorry about the delay, I just saw this. 

I have an original FZ-2 and the clean boost function (as far as I can recall) on my unit does not audibly oscillate.  In fact, it sounds very clean.  I've used it as a mic pre before with shockingly good results.  But I can pull it out sometime this week and see what happens with the treble jacked if that'll help.  Would that be helpful?  You didn't really ask a concrete question so I'm a little bit unsure on what you're looking for.  Could you clarify?

[imjonwain]

Hey!  Thanks for getting back to me!  If you have time and don't mind maxing the gain and tone controls to see if it will oscillate that would be helpful as I am curious if it does or not.

The problem I am having is most likely component values it seems.  I designed the PCB myself based off the schematic floating around online drawn but "Hemmo P" and referencing the pedalpcb board and the tagboard effects layout (which also apparently have similar issues).  However it seems the schematic isn't actually correct and has some incorrect values listed based on a redit thread that was sent to me. 

[BuGG]

The "Hemmo P" schematic is incorrect.

The Hyped Fuzz circuit shouldn't oscillate at any setting.... I don't have an original FZ-2 anymore, but I don't recall it oscillating either.

The guy you're referring to on Reddit is just trying to promote his own PCB. 

The difference is that the input gain stage has been converted from hard to find FETs to a similarly functioning opamp circuit.
The first version of the Hyped Fuzz was drawn from the "Hemmo P" schematic.  This is where the incorrect values came from.

The component values have all since been updated to the original Boss schematic.   Make sure you're using the most up-to-date schematic for your values.

[imjonwain]

Thanks for the verification on that!  My board is using those old incorrect values still ( I did the schematic a few years back) so that makes sense! I'll check out the hyped fuzz so I can correct those.  My layout still has the "discreet opamp" of the original and all the boss switching but when I tested the board section by section I had that boosting w/o oscillation so we'll see!  Hopefully that part of the schematic isn't too wrong.  Thanks again! 

[BuGG]

When I'm back at my computer I can send you the original schematic so you can compare.
The Hemmo P schematic can be hard to follow.

Referencing the Hyped Fuzz schematic, make sure these values are correct on your schematic:

R9   10K
R10   1K
R11   1K
R15   1K8
R19   47K
R23   27K
R25   120K
R29   10K

C13   1n
C18   10p

This is where the difference in tone came from...  The updated circuit has been A/B'd against an original FZ-2 and is basically indistinguishable.

[JackSkellington]

Could someone post the corrected schematic for clarifying?

[imjonwain]

I will once I update values on the schematic I drew up in Eagle.

[JackSkellington]

When I'm back at my computer I can send you the original schematic so you can compare.
The Hemmo P schematic can be hard to follow.

Referencing the Hyped Fuzz schematic, make sure these values are correct on your schematic:

R9   10K
R10   1K
R11   1K
R15   1K8
R19   47K
R23   27K
R25   120K
R29   10K

C13   1n
C18   10p

This is where the difference in tone came from...  The updated circuit has been A/B'd against an original FZ-2 and is basically indistinguishable.

I found the Hyped Fuzz document.
https://www.pedalpcb.com/docs/HypedFuzz.pdf
I had an old version, but the one available now has the corrected values reported above from BuGG.
The original schematic by Heppo P. has the jfet input stage: buffer and boost. While the Hyped Fuzz has a buffer and boost in opamp version.
The correction are all in the Fuzz, Scooped and Full sections looking at the Hyped Fuzz document. And just one resistor in the EQ section. If imjonwain got oscillation in the Boost Mode just that only resistor is included the the "anti-oscillation update" (From 56k to 10k). It could that only cause of the oscillation?



Veroboard layout based on Heppo P. version, with jfet input stages and wrong value parts.


I want once day to build this, but with corrections, but I hope that will be enough to avoid oscillation problem.

[BuGG]

The updated components were not specifically intended to address oscillation.   I've never personally experienced oscillation on either revision of the circuit.

The differences between the original FZ-2 circuit and the Hyped Fuzz circuit were intentional:

1) The capacitor multipler on VCC isn't particularly necessary
2) Parallel polarity protection (diode shunt to ground) is destructive... just say no.
3) M5218 SIL opamps...   
4) The differential amplifier portion of the discrete version technically should be built using a pair of matched 2SK184 JFETs

#4 is the big "gotcha", and the primary reason the discrete input stage was converted to an opamp stage...

The input stage isn't just a random opamp gain stage thrown in the place of the discrete transistors, it's a conversion of the original gain stage.... but more importantly, this is a clean boost in front of a freakin Superfuzz circuit, not a transparent crystal lettuce overdrive.   If you can hear the difference your ears are far superior to mine.   

[imjonwain]

someone needs to make a transparent crystal lettuce overdrive now though.

[ahiddentableau]

I just tested my original unit both with gain and tone controls maxxed and then with everything maxxed.  There is no oscillation on any settings that I could find on that clean boost.  Great sounding boost, too.

[Netnnk]

I just opened up my real FZ-2 and it's the only Boss pedal I've seen so far with shielded input wire from jack to PCB.

[gordo]

That's pretty wild, I've never seen that.

+1 on the crystal lettuce overdrive

[imjonwain]

I just tested my original unit both with gain and tone controls maxxed and then with everything maxxed.  There is no oscillation on any settings that I could find on that clean boost.  Great sounding boost, too.

Awesome!  Thanks for verifying that!  I assumed it wouldn't.  I just replaced all the incorrect value parts on my build and we'll see if that sorts it out. 

Netnnk is going through his original pedal and I am drawing up a schematic of the OEM pedal with ref designaters and part numbers that match the BOSS ones so there will be a correct full schematic online soonish.