Brutalist JR - Clipping Diode Toggle Switch Help

[darbycrash]

Hi everyone, nice to meet y'all...

I know this general topic has been beat to death here and on just about every other DIY pedal forum, but even after combing many threads and diagrams I'm still not 100 percent sure I have the right idea so I decided to just ask here. Hopefully it's not too annoying of a question....

For the unfamiliar - the Brutalist JR is an easy PCB based kit based on the Providence Stampede pedal.

For my build, I'd like to add two SPDT on/off/on switches, one for either clipping diode position, such that a user could toggle between a total of 9 different combinations. My main issue is that I can't quite figure out exactly where I need to come in and out from the PCB. I understand that since LED's have a larger V_f they should be connected such that they are selected when the switch is in the OFF position, correct?

My hypothesis
Using an SPDT on/off/on switch, I'm assuming that I would need to have a lead from the corresponding anode position on the PCB that would connect to the anodes of two different diodes. Each of the cathodes of the aforementioned components would then connect to either outer lug of the switch separately, and the common lug of the switch would then have an LED (I'm assuming anode goes to the lug?) connected to it, with a lead connecting that to the corresponding cathode position on the PCB.

Are my instincts correct, or am I way off base here? If it turns out to be the latter, I would greatly appreciate a visual aid and an explanation of the flaws in my logic. I'm really trying to gain a solid understanding of the "why" when it comes to circuits. (I swear I don't normally need to be spoonfed this hard - I've been lurking for quite some time now). Thanx and infernal hails in advance for any help .

Schematic


Not my build but included for more reference

[idy]

Welcome!
The schematic shows a single pair of diodes, right?

You might put LEDs in the PCB where the diodes are marked, observing polarity (sometimes they call the configuration "reverse parallel.") You are right, the LEDs with higher Vf can stay in the path all the time.

Now you need a wire from each side of the LED pair. If you were to use two switches, the wires will "branch" to both switches. Each wire is connected to the "A" of one LED and the "K" of the other. Maybe better to think of it as pins 6 and 7 of the opamp. Maybe make them blue and red wires. On switch will hook up blue to "K"s, the other switch will hook up blue to "A"s.

That being said: You will *probably* find that half of the combos sound like the other half; all the assymetric pairs will sound the same, i.e. LED + ge will sound the same as ge+ LED, LED + si will sound the same as si+LED, if you get what I mean. So you will have 9 positions but only 6 sounds. (LEDs, Si, Ge, LED+Si, LED+Ge, Si+Ge.)

I would advise first auditioning combos and then commit the few you like to the switches. I at one point put a bunch of combos on a pair of rotaries in a coffee can and would stick the blue and red wire into the appropriate spots on new projects and see what worked.

Which ones sound best to you is taste and the response (gain, tones shaping) of the circuit.

[darbycrash]

Thank you for the response. I'd like to clarify a couple things if you don't mind:

Now you need a wire from each side of the LED pair. If you were to use two switches, the wires will "branch" to both switches. Each wire is connected to the "A" of one LED and the "K" of the other. Maybe better to think of it as pins 6 and 7 of the opamp. Maybe make them blue and red wires. On switch will hook up blue to "K"s, the other switch will hook up blue to "A"s.

I'm with you on leaving the LED's on the PCB, but not clear on where you're telling me to position the respective wires or the other diodes. Not entirely sure what you mean exactly by "the wires will branch to both switches". I'm assuming A represents Anode and K cathode in your example? Where then, do the diodes to be switched into the circuit go? Was my instinct correct? Do the two different diodes/combos (thinking about doing different combo numbers instead of just a single diode on each) go from Anode lead connected to the wire coming from A (anode on PCB) to the cathode leads connected to either outside lug of the switch? You didn't address that part of the question so forgive me if that was supposed to be obvious  If this is the case then the wire going from K (cathode) connects to the common lug then, correct?

Thank you again!

[idy]

The way I have drawn it calls for Double Pole center-off switches. The second pole (the terminals on the right-hand side, or "4, 5 and 6") are not part of the circuit, they are there to give you a handy place to solder your diodes, no flying leads to bend and break. Only the left and terminals (1,2 and 3) are switching. I do this a lot.

[darbycrash]

Thanks a lot for the reply! I really appreciate you taking the time to the include visual aid as well. I ended up opting for just one SPDT to switch between two diode pairs with a single LED selected in the OFF position - mainly because of space constraints that I didn't feel like dealing with since I'm just using the stock 125BB enclosure.

The two pairs I went with were the 1n914's included in the kit and some 1n4007's I had lying around. The sonic difference that I've been able to detect between those two is nearly non-existent. I plan to do an experiment ITB where I compare waveforms through the two pairs, but before I do that, I'm curious to know if there is usually a big sonic difference between those two types and perhaps the circuit isn't functioning how I intended it to?

I used the attached image as a guide - was it incorrect to wire one end of both pairs across the same lead? Should I have instead attached an additional separate lead for both pairs to the wire coming from the PCB? I didn't think it would have made a difference but since there's seemingly almost no difference between the them I just wanted to make sure.

As an aside, this pedal is an interesting sounding overdrive compared to what I'm mostly familiar with in this wheelhouse. From a test through my 50's Valco "Comet" Chicago 51, I was getting sort of higher gain Klon-ish vibes through the LED with the "Loudness" and "Distortion" pots at lower settings but it definitely started to rip as I turned them higher. Just a clear LED I had lying around, I've listened to demos of different types of them and didn't hear much difference at all but I am curious to try out an infrared as the difference in V_f seems like it might be noticeable sonically (maybe?). The pairs sound real nice too (albeit identical to each other) - definitely more hairy and aggressive, sort of like a more articulate RATish thing maybe. I just need to go back and address the volume drop issue when switching between the LED and pairs at some point.

[idy]

your drawing is fine.

[idy]

What I said. You are auditioning different diodes in your circuit. Everyone has tastes. Different circuits bring out different sounds. Most people find that a switch with lots of combos is disappointing, and maybe you only need two... or three...or...one. But everyone has to make the experiment.

Ge is so small, no dynamics. But some times "compressed" and "buzzy" are good. Schotky are kind of like Ge, but sound good in my NY Big Muff. Si is OK, fine, nothing wrong with them. LEDs are louder. Stacking more of the same doesn't do much for me, except you can get asymmetry, which I like.

MOSFETs seem to have a different mechanism in one direction and a diode in the other.  I like MOSFETs, partly because one MOSFET and one regular diode can produce two different asymetric combos, one of which has no diode clipping at all in one direction. I like asymmetry because, as I hear it, one side begins to clip while the other side stays clean so you still hear your guitar. Then you hit harder and either the other diode or then next thing in line (like the opamp, or another box, or your amp) starts to clip. So there are several plateaus.

And the volume change thing also makes vastly different combos awkward in one pedal. The only way to tame it is to have a second pole on the switch adding a resistor some place to drop the level of the LEDs (or whatever.)

And psychologically, they say "louder sounds better," i.e. it is hard to really judge the difference between pairs because bumping the volume up a tiny bit changes your perception of things like frequency response.

[darbycrash]

Thanks for all the detailed responses Idy! Judging from your answer I suppose it's likely then, that the 1n914's and the 1n4007's sound very similar and everything is indeed hooked up correctly! Appreciate your time! 

[eh la bas ma]

Hi,

I built this circuit too, did some tests (with a roto-tone board with many diode combinations), I thought I could share my results.

My favorite choices are : a pair of 3mm leds (green and red) on one side, and BAT41 (0.4V) +1N4148 (0.6V) in series, connected to an other pair in the opposite orientation, so 4 diodes total, on the other side.
I use the leds most of the time.

I also added a "fat mod" switch (3 rows like 3PDT in order to change C1, C6, C9) with some of the values suggested in the instructions. It's mostly usefull with a bass. I get a fat juicy sound with guitar but I need to set Tone control on the brightest position.

ICs are quite important to shape the character of the disrortion. I am currently using OP07 + C4558C  (NE5532 sounds good too)

[Vivek]

Different diodes clip at different Vf

This translates to clipping at different point of the incoming signal and creating different final volume

There are many Youtube that show that if many different diodes are tested while clipping at same normalised point of incoming signal and then amplified to same final volume, the differences are almost inaudible.


I mean

Take 25Vp signal, chop with 2.5V LED and amplify to 5Vp

and compare that to

6.5Vp signal, chop to 0.65V with Si diode and amplify to 5Vp


and they will practically be the same


Hence it might be better to have more control and range of gain and final volume, to get more sounds more easily.

[darbycrash]

I built this circuit too, did some tests (with a roto-tone board with many diode combinations), I thought I could share my results.

Thanks for sharing! Good point on the op amps, ill try some different ones too. You wouldn't happen to know where I could procure some of those BAT41's at a reasonable price would you? 

Hence it might be better to have more control and range of gain and final volume, to get more sounds more easily.

Thanks! That's a really good point you make and I suppose I never thought about it that way.