EHX - Big Muff with Tone Wicker

theblackman · Post by **theblackman** » 16 Jun 2009, 04:58

from an ebay ad i saw

" Use the Wicker switch to open up three high-frequency filters for raspy, sustaining distortion with top-end bite, or flick on the Tone switch to bypass the tone control for unabated tonal slam."

Brettski · Post by **Brettski** » 18 Jun 2009, 01:49

I played through one into an orange Rockerverb 30 (NOT a fan). Though the amp sounded like poo in a blender, the pedal made it sound pretty damn good. Worth the $90? I didn't think so, but if I saw a used one, I'd probably snatch it up.

I think I'm more of a fuzz face guy anyway, so what do I know?

trad3mark · Post by **trad3mark** » 19 Jun 2009, 18:51

I'm desperate to buy one... just gotta get paid...

Cub · Post by **Cub** » 30 Jul 2014, 09:28

Bumping an old topic with a new question, to keep all the information about this one pedal in this one thread.

This shot from a Revision A board on Kitrae's page raises an interesting questions: does the Wicker switch just take out the three filter caps, or does it do a bit more ?
http://www.kitrae.net/music/IMG_4266.jpg

The low pass filters are C10, C11 and C12. The one in the input stage (C10) is 430pF instead of 470pF like the others and there are two more caps in the vicinity:
C19 - 27pF and C21 - 10pF.

Does anybody know what's the story of these two caps ?

Bernardduur · Post by **Bernardduur** » 01 Aug 2014, 11:17

Killing HF interference on the input / input stage?

Cub · Post by **Cub** » 02 Aug 2014, 20:21

Probably

I'm guessing at least one of these caps stays in the circuit when the wicker is on, to suck up some of the hiss.
But this shot of the board doesn't show all the connections, so it's just a guess.

Anybody got a shot of the other side ?

mirosol · Post by **mirosol** » 02 Aug 2014, 21:53

There are couple of shoths on my blog - http://mirosol.kapsi.fi/2014/07/ehx-big ... ne-wicker/
If anyone needs it, i can take the unit out and snap more. Once i got the box it just looked like standard BMP with CDXXXX-driven tone booster, so at that time i didn't get too excited about trying to trace it.

Cub · Post by **Cub** » 03 Aug 2014, 13:27

Hei mirosol, thank you for those shots and offering a helping hand.

Sadly, I couldn't find any answers in the shots on your blog. This might very well be because of my inexperience, though.

But if you have the time, could you please open it up again and see what's going on with C10, C19 and C21 when the Wicker switch is flipped ?

While it's open, could you also check how the tone bypass switch is working ? In the '70s and '80s transistor Muffs with a tone bypass switch, one or two additional caps permanently in the circuit and a 150k resistor between them when the tone stage is switched off (last two schematics on this page). I couldn't find any of such parts in the shots of the TW.

You don't have to trace it completely. With Kitrae's shot of the board, I've nearly completed a trace of my own already. I focused just on the bits that give the tone, I assume anybody who wants to build a clone has a preferred way of filtering or just do it as it says in the instructions of the PCB supplier.

The values of the components in that 2009 Tone Wicker Muff with EC-D47-A board are almost identical to a 2007 NYC reissue with EC3003-C board. Ignoring the tone-bypass and wicker switches out of it for a moment, I could find only one thing being different: the coupling cap after the input stage is .47µF in both, but rated for 25v in the NYC and 50v in the TW.
With your shot of the other side of the board, I found another: the Sustain pot is 100k in both, but Linear in the NYC and Logarithmic in the TW.

mirosol · Post by **mirosol** » 03 Aug 2014, 14:34

Took a few shots of the area with those caps plus, well. The whole board. But i didn't have any time to see what is happening there. Board looks like a real pain to trace... Anyway. Here you go. I could try to take a better look before i close the box up, but time.

mirosol · Post by **mirosol** » 03 Aug 2014, 21:16

Those pictures aren't helping too much. There are way too many vias in so painful places (under CD4066, under the switches etc.) that just looking at the board won't yield us any results. I did check this twice, but it still doesn't mean it's 100% error free. C19 and C21 are really a mystery to me. And all the points the CD4066 is hooked up. There are no caps for the tone bypass, which explains it's drastic behavior when that toggle is switched. Yup. There were a few WTF!? moments when tracing this. Especially for the other half of the wicker switch - which is basically a world's hugest via in the world. If you spot an error, please let me know and i'll fix the trace.

To be honest, i have no idea how that CMOS switch is affecting the circuit operation, but i do know it adds some "wicker" and noise floor to the overall sound. Wicker on and tone on bypass - might just be my second favorite BMP. Anyone care to chip in and tell me what's happening with that CMOS switch?
+m

[schematic updated below]

Cub · Post by **Cub** » 04 Aug 2014, 13:11

Wow, that's incredible ! Thank you so much for all the time and effort you put into this.

It all looks very logical like this, 467pF for the filtering in the first stage to is close enough to the 470pF used in the second and third stages. Then 27pF when the wicker switch in on to to reduce the hiss.

mirosol · Post by **mirosol** » 04 Aug 2014, 22:05

So if i understand correctly, you could get yourself a permanent "Wicker" mode by snipping all the the 470p caps off the circuit and replacing the first transistor's cap with 27p...
+m

Cub · Post by **Cub** » 05 Aug 2014, 07:55

Exactly ! But if this introduces too much hiss to the sound, you could experiment with a lager value than 27pF. Or perhaps you could put small filter caps in the two clipping stages instead of leaving those spots on the board open.

mirosol · Post by **mirosol** » 05 Aug 2014, 10:44

They could have done the same thing with a single 3PDT toggle (or 2PDT, if they had left the first stage in tact). Of course, that would have hurt the marketing pointers. But since it's out there, all diyers can now build their Triangle/Ram'sHead/CivilWar/GreenRussian w/ ToneWicker and tone bypass, using a 3PDT+2PDT toggles by addind the switches to existing layouts. :D

Cub · Post by **Cub** » 05 Aug 2014, 17:56

In my green Russian clone, I put the filter cap form the input stage on a switch to take it out of the circuit. Sort of like a "Triangle" switch that didn't make it sound anything like a Tri-Muff at all,

just a bit more fuzziness in the highs and a lot more hiss. Too much hiss to be a useful feature, really.

JoelTone · Post by **JoelTone** » 05 Aug 2014, 19:39

I'm guessing the point of using FET switching instead of a 3PDT is to reduce "pops" when switching the wicker on and off. Using a 3PDT would leave the cap floating, so it may be at a slightly different voltage when you switch it back in (thanks mainly to noise and leakage current), leading to a "pop" when the cap is switched out. Using a FET switch should significantly reduce pops.

I think something has to be wrong with the 4066 on the schematic. As it stands, S1 is always pulled high (meaning the switch does nothing), and S2/S3 are left floating when S2A is connected (meaning their behavior is undefined). I'm guessing S1 is connected to S2/S3 underneath the IC - that would make the switch properly toggle all 3 channels.

As for SW2B, I can only speculate that it also has something to do with preventing pops (assuming the schematic is correct). Although it looks like it does nothing, keep in mind that it would briefly disconnect the cap as the switch is switched (assuming the toggle has a "break-before-make" behavior).

mirosol · Post by **mirosol** » 05 Aug 2014, 20:53

If the switching is 4066 based to cure the possible pops, then why the tone bypass is mechanical? Toggling that one causes massive distruptions to tone. No chance the marketing wanted a "new" innovation?

To be honest, i'm not familiar with CMOS switches and how they tick, so errors in that department are likely. And yes, you are correct. The pins 5 and 13 are connected. I took the pedal out again and checked it. Thanks for this correction.

On SW2B, you can assume what ever you want. During the reversing process, i desoldered both of the switches to see exactly what's going on under them (i did not desolder IC1, which can partially explain possible errors around it). The three pads for SW2B are all connected together by a trace under the switch and that trace continues towards C21/C10 on the other side of the board. I'd call that a via. Too bad i didn't snap a photo before i soldered them back on. My guess for that is they bought 2 000 000 DPDT switches and none of SPDT - rather than that having anything to do with reducing anything.

Anyway. Thanks for the note on IC1. Corrected.

JoelTone · Post by **JoelTone** » 05 Aug 2014, 21:55

In the tone section, both sides of all caps involved have a path to ground when the switch is disconnected. Although there is a fairly high impedance to ground along some of these paths (for example, the left side of C9 goes through the 27k resistor, through the full 100k pot, and through the other 27k), when the switch is disconnected, that is the only voltage reference that these caps are connected to, so these will drain off any extra charge until both sides of the cap are very close to ground voltage.

This is different from the 470p caps, because if you use a mechanical switch to take them out of the circuit, the one side is left completely floating - there is no path to ground (actually, in this case, the voltage reference you want is the collector of the transistor), so there is nowhere for excess charge to go other than through the very very small leakage current of the cap. When you reconnect it, any charge on that side of the cap rushes back into the circuit until the voltage is equalized with what it should be, and you get a pop. Obviously either of these is going to cause a change in tone, but you don't want it to also cause a huge "pop".

There actually would be ways of using a mechanical switch for pop-free wicker switching, but they would require a couple extra parts. For example, put a large resistor (like, 5-10 Meg) in series with each 470p cap, and have the switches in parallel with these resistors. When the switch is closed, the new resistor is shorted, so you've got exactly the same behavior as if the resistor wasn't there. With the switch open, the 470p caps are in series with this resistor, so they can still drain off any extra charge - the caps are technically still in the circuit, but with a large enough resistor value their effect should be negligible (this cap + resistor would be in parallel with the 470k resistor, so if we choose a large enough value then the current should all travel through the 470k - hence why we want 5M or higher).

Oh, one more reason to use an IC switch: it's probably cheaper than using a 3-pole switch. 3-pole switches are relatively expensive compared to 2-pole (which matters when you're ordering them at the volumes EHX is). ICs tend to get way cheaper when you buy them in large volumes, whereas mechanical parts like switches don't get nearly the same volume discount. Plus, this way EHX can put two of exactly the same switch on the board - they both take up the same PCB footprint, and they both have exactly the same "feel".

IvIark · Post by **IvIark** » 05 Aug 2014, 22:45

Personally I really wouldn't have any concerns about potential pops from a toggle switch which by their very nature, for me at least, aren't going to be switched on the fly mid song. The same could be said about any toggle switchable caps which are often used in effects to swap input or output caps etc. So although it may be one of Mike's reasons for using the CD4066, it wouldn't dissuade me from simplifying it. For my own builds, one additional 14 pin component and the additional required space on the board is more of a negative than possible switch pops between songs when my guitar volume would be down and the effect bypassed.

JoelTone · Post by **JoelTone** » 06 Aug 2014, 00:01

Yeah, for DIY builds, that's totally reasonable. For EHX-scale mass production that's already mostly surface-mount, a 14 pin surface-mount component doesn't actually add much to the assembly cost. Plus, if it pops, people are going to say the pedal is low quality, and that would look bad for EHX.

EHX - Big Muff with Tone Wicker [schematic]