Building a Pharaoh Fuzz on a Mudbunny board, some questions...

[schizoidman]

Hello,

I have laying around a old PCB for a big muff project, and now I want to build a Pharaoh on it.

The thing is, I'm not sure I'm planning the mods right and would appreciate if someone could give me some confirmation of my planning.

So here it goes:

This is the Big Muff schematic that came with the PCB documentation and the Pharaoh schematic I'm using as reference. The differences are highlighted.



And this is the pcb, with the differences highlighted as well.


Points 1 and 3 are easy enough, I know what to do.
In points 5 and 6, the caps change from non polarized to polarized, I marked where the positive side should go, is it right?

Regarding the clipping diodes, they appear in different order on each schematic before and after caps... I suppose that both ways are the same but if not, what are the implications of those differences?
Finally, regarding region 4 which is the thing i'm must unsure of, I understand how to put the diodes on the switch, but i'm not sure how to connect that to the board. If someone shed some light over this I would be very grateful.

Thanks in advance

[BetterOffShred]

Don't attach diodes at 4, run a wire from either end up to your rotary. One to the common lug, and then wire each set to a throw, all hooked to the other wire. 

You did notice the tone stack is completely different as well right?  I love the Pharaoh tone stack

[patrick398]

Caps look to be oriented correctly, not familiar with the circuit but that's what i'd go with

[antonis]

You don't have to worry about the order of series items..
(the're completely interchangable..)

About clipping diodes selection, what BetterOffShred said:
(he mentioned a rotary switch but, IMHO, a SPDT ON-ON switch should be more cheap & convenient..)



P.S.
You may also use the above configuration in case you want to by-pass tonestack..
(i.e. replace lower diode pair with C10/R19 node & Tone pot wiper respectively and upper diode configuration with a 100k-150k resistor, to prevent volume increase when tonestack by-passed..)

[bean]

For the diode switching, you should be able to just switch the germanium in parallel to get the same result rather than switching between the Ge and Si. Only reason to mention it is because I don't know if switching fully between both sets will cause a pop or not because of the DC on one side of the switch. Or, if you do switch fully between both sets and get the pop, you could put a 1M resistor between the outer lugs of the SPDT.

If you want to get fancy, one other mod you could do is replace that 470k resistor on the tone section with a 500kB and 47k resistor in series to ground to get some control over the bass shaping, too.

[BetterOffShred]

My suggested switching for the diodes was based off the Pharaoh supreme, which I feel is an overall improvement.  Changes the input resistor to a pot, more diodes etc. 

Let us know

[schizoidman]

Thanks for the help guys,

BetterOffShred, I'm not sure I understood your sugestions 

Antonis, thanks very much man, but you missed one detail. The schematic shows three options, Ge or Si diodes or full diode bypass. For that I'm thinking of using a on/off/on switch but the one I have is a DPDT.
Could you re-do the wiring diagram with that in mind?

Thanks very much again guys

Edit: Now I noticed the schematic I posted does not show the diode bypass, my bad. I've seen it in other schematics and somehow I confused them.

[BetterOffShred]

Something like this.   

Since the pairs on the switch are wired anti-parallel, you can just use one set of pads from the  board and leave the other diode out.

[antonis]

Antonis, thanks very much man, but you missed one detail. The schematic shows three options, Ge or Si diodes or full diode bypass. For that I'm thinking of using a on/off/on switch but the one I have is a DPDT.
Could you re-do the wiring diagram with that in mind?

Sorry, but I can't..!! 

A DPDT switch is actually 2 SPDT ON-ON paralleled switches simultaneously activated..
You can't have 3 selective options with only 2 switch positions (throws) - despite  excesive pole number..


If you only needed 2 options (selection between Si & Ge arrangement) you coud save one position (SPST switch) in case of Ge diodes forward voltage drop is less than, or marginally equal to half of Si diodes forward voltage drop..
I leave the above mentioned SPST switch wiring to you, as a test..
(hint: A SPST is actually a SPDT with one pole left open..)

As BetterOffShred already told you, a rotary switch is more appropriate for your desired diode pair selection..

[thermionix]

Here's a really bad MS Paint

[schizoidman]

Here's a really bad MS Paint

That's how I was thinking the on/off/on switch should go... my only doubt is where do i connect those wires to the pcb? It's enough to connect the switch to say D4 and leave D3 untouched?

If you only needed 2 options (selection between Si & Ge arrangement) you coud save one position (SPST switch) in case of Ge diodes forward voltage drop is less than, or marginally equal to half of Si diodes forward voltage drop..
I leave the above mentioned SPST switch wiring to you, as a test..

What? :p

I did not understand what you are sugesting... Either way, your schematic with the SPDT is enough for me to do what I want. The only thing missing is the option to do the Diode bypass, which I'm guessing I won't use that much anyway...

The rotary option is for sure interesting, but I would have to buy the rotary (and where I live, my only option is to buy online) and I do not want to wait...

Thanks very much for your help guys...

[antonis]

What? :p

Never mind.. 
(it was a suggestion for exactly the same result with SPST switch - or SPDT switch with a "defective" pole..)
Having pernanently mounted the pair of the higher forward voltage drop allows you to selectively set in parallel the other pair, resulting in second pair's clipping level..

Anyway, you still can use SPDT wiring on DPDT, leaving the extra poles of DPDT switch for an LED indicator..
(e.g. LED ON when Si pair on circuit and LED Off when Ge diodes activated or use of 2 different colour LEDs or even a bi-colour one..)
[/quote]

[thermionix]

That's how I was thinking the on/off/on switch should go... my only doubt is where do i connect those wires to the pcb? It's enough to connect the switch to say D4 and leave D3 untouched?

The switch w/ diodes replaces D3 and D4, which are in parallel normally on the board.  The 2 wires from the switch go to opposite ends of the D3 and D4 spots on the PCB.