Modified Mid Fi Random Number Generator (blend and starve)

[moid]

Hi everyone

I hope this is OK with mods; I want to make a modified version of the Mid Fi Electronics Random Number Generator (RNG) - according to the Mid Fi site this pedal is no longer in production so I believe that discussion of this pedal is allowed here? Please remove this if it isn't. I want to make a version of this pedal that has two modifications - firstly a clean blend pot so that I can mix the wet sound of the pedal with the incoming dry sound to use the RNG as a texture underneath my other guitar sounds. The second mod is to add a Starve pot to reduce the voltage going to the board, and therefore hopefully cause the RNG to make different weird noises (or just sputter like crazy; I don't mind as long as it sounds weird )

I've taken the vero layout drawn by Mirosol on Tagboard Effects http://tagboardeffects.blogspot.co.uk/2013/01/mid-fi-electronics-random-number.html and I've spent a few hours learning the basics of DIY Layout Creator to create the below visual masterpiece (don't laugh!) . I would really be grateful if someone could look over the image and say whether any of it won't work. I haven't changed the layout of anything on the stripboard itself, I've just added in the input, output and power sockets plus the potentiometers. I'm most concerned about whether I've managed to get the signal from the input socket to go to the 3DPT switch and then the board correctly, as well as also go to the blend pot. I'm also unsure if I've connected the volume pot to the blend pot correctly and also whether the output sound from the blend pot goes to the 3DPT and then to the output socket correctly. I'm fairly sure I've got the starve pot correct, but if any of the pots should be different values or in different orders please let me know.



Why did I draw this out? I'm really not great at making pedals and I find having everything drawn out lowers the amount of mistakes I can make...

Thanks very much for any advice you can offer

[Nocentelli]

The sag pot is wired ok, but I don't think it will need to the that big - 10k or 20k will sag it right down to inoperable, so the rest of a 100k pot's rotation will be pointless.The blend arrangement you've got is not ideal: The clean guitar is direct from the input and pretty low level, and you've got to fiddle with two separate controls to set the relative blend. You would probably do better with the clean portion of the split input being sent to a non-inverting clean boost, the other split going to the fuzz, connecting the outer lugs of the blend pot direct to the outputs of the clean boost and fuzz, and sending the wiper to a master volume control.

[moid]

Thanks very much for the quick reply The Sag pot was a total guess, I'll change that to 20K now.

I think I understand what you saying about fixing the blend part of the circuit; I was guessing this based on looking at the insides of a Napalm Whammy Blenda pedal I have. By non -inverting clean boost, would a Mr Black Boost Tiger be OK to use? It seems to have an opamp (which I think is what makes a boost non inverting) and Mr Black has discontinued it and gave the schematic away and I've found a vero I could use - http://tagboardeffects.blogspot.co.uk/2013/03/mr-black-boost-tiger.html.

If that looks good, please let me know and I'll redraw my first diagram with the boost as a daughter board using the connections you suggested and post it back again; I really appreciate the help, thanks again

[Nocentelli]

That should work ok, you could even use the MXR microamp which the boost tiger is based upon but is a little simpler. The boost control is not needed here, so you could replace the pot with a fixed resistor from the boost lug 2+3 row (hole B4) to the inverting input (D4), and leave off the 1k minimum boost resistor that connects from D4 to the boost 1 lug. A resistor of about 27-33k should be fine, you just need plenty of level so the clean can compete with the fuzz when they are blended. The exact level is not so important since you'll have a blend pot to tune the mix and a master volume to control the output.

I would always advise trying something like this out on a soldered breadboard first, though: Better to spend half an hour checking it works well, and doesn't have any unintended flaws before committing 2-3 hours to building veros and potentially wasting time and components on a new design you're not happy with.

[moid]

Thanks Nocentelli, that's a lot of useful information. I've found a veroboard layout of the MXR micro amp, but I'm not sure if it corresponds to your coordinates? (B4, D4 etc)
http://tagboardeffects.blogspot.co.uk/2010/10/mxr-microamp-compact-layout.html

If this is the right one I'll try to redraw the above layout to include it as a daughterboard. Thanks, hope you have a good weekend.

I see your point about breadboard; i'll have to get one and work out how to use it - might have to wait until the end of the month, I spent a bit too much on pedals on Ebay this month!

[Nocentelli]

Thanks Nocentelli, that's a lot of useful information. I've found a veroboard layout of the MXR micro amp, but I'm not sure if it corresponds to your coordinates? (B4, D4 etc)
http://tagboardeffects.blogspot.co.uk/2010/10/mxr-microamp-compact-layout.html

If this is the right one I'll try to redraw the above layout to include it as a daughterboard. Thanks,

The modifications were for the boost tiger vero: it's not as easy to do a neat mod to that MXR vero... the quick but ugly way would be to have a flying insulated jumper wire hop over the opamp from "level3" to "level1+2", leave off the pot, and replace the 2k7 with a 15-27k resistor. A more elegant solution would involve adding a column or two so you can run a couple of flat jumpers across the face of the board to short the level pot.

[moid]

Sorry I didn't mean to confuse you, I thought you were talking bout the MXR microamp. I found different veros for the Mr Black Toger Boost, and then discovered yours on FSB; so I've used yours in the below image. I think I've followed your directions but I'm a little unsure of a couple of points if you don't mind having a quick look at them please that would be lovely.

The 33K resistor overlaps with the 512K one that is already present (not a problem if this is right, I can bend them around each other).

I've put a white rectangle over the 1K resistor on the right side of the board that you said to omit.

I think I've connected the new board up correctly, but I got lost when you mentioned about different pots (sorry) to control the volumes of the two signals... it looks to me (at the moment) that I don't have control over the volume of the boost - I can mix it into the signal of the RNG, to decide how much of the final sound is dry / RNG, but I think I'd also want to adjust the volume of the Boost itself before it is mixed with the RNG in case the RNG is either too quiet or too loud in comparison... or maybe I'm just daft and the blend pot would achieve this correctly? I guess I shouldn't do this sort of thing late at night.



Thanks again for your input, it's really helping me!


EDIT: I just realised, if I build the Boost with its own pot without your modifications, I could have a combined Boost/RNG pedal and the blend pot would allow me to reduce the RNG signal to nothing if I wanted and I could have a clean boost pedal at the same time, and save space on my board! Does that sound like it would work? I apologise if it took you a long time to work out how to modify the vero for this, but I think this might be the best solution for me Thanks!

[Nocentelli]

My directions for moddng the boost tiger vero to be a fixed level boost were for IvIark's vero layout that you linked to; The co-ordinates I used (B4, D4) don't apply to my vero since the layouts are completely different, and the changes you've made to my layout will make it inoperable. The directions need to be made to IvIarks layout.

I suggested you connect the unattenuated outputs of the boost and the RNG direct to the blend pot opposite outer lugs, with the wiper (blend) going to lug 3 of a master volume pot, because it means you could set the precise blend of clean and RNG you want (both will be plenty loud enough to compete equally at 12 o'clock, but be pretty quiet with 100k resistance at the either extreme of the pot), then control the overall output level of that blended signal independently. Your layout still shows the RNG with a volume pot before the blend pot: This will mean that you have two controls (RNG volume, and clean/RNG blend) that affect the relative levels of the two sounds, but neither allow you to control the overall output of the combined effect - If you wanted it mainly clean, but with a hint of RNG in the background, you would have to dial the RNG volume right back, and set the blend over towards the clean side, but this might not be loud enough and you'll have no way of adjusting the level relative to bypass.

If you want two totally separate effects (i.e. a stock boost tiger and stock RNG, both with independent output controls and bypass switches BUT with the ability to engage a switch to put them both in parallel with blend control you're looking at some seriously complicated switching, and probably a third daughter board to do active/buffered parallel blend and switching. You could just wire them in parallel but on separate bypass switches (i.e. passive mixing), but they may well interact badly and mess with the output level when you switched between boost only, RNG only, and boost in parallel with RNG.

Here's an easy way forward: IvIark has done a layout for a simple buffer/blender pedal - It's just a handful of components and a blend pot on a scrap of vero. I'd try this out first, putting the RNG in the effects loop, to see if you even like the effect of blending crazy fuzz with clean.

[moid]

I really misunderstood you then - I used your vero because it had coordinates on it and I assumed you were referring to those. OK now I see what you mean about the order of the volume / blend pots. I'll skip the idea of two different effects in the same box; it's definitely way over my skill level for now; it was just a momentary idea that I thought would be cool. The reason for blending fuzz with clean signal is that the clean signal wouldn't actually be clean - I often run a reverb pedal before a fuzz because that creates some washes of fuzzy sound and I thought that wash going into the RNG would sound more focused in terms of arpeggios of notes rising and falling with the reverb wash behind it as an accompaniement. Two different textures that might work well due to being based on the same notes, but would be sufficiently different as to make an interesting sound.

I will redraw the diagram again using IvIark's layout (presumably the revised one from his page; he has two for the Tiger Boost) http://tagboardeffects.blogspot.co.uk/2013/03/mr-black-boost-tiger.html

Thanks for your advice, you're saving me from a lot of future disasters

[Nocentelli]

No problem, good luck with this project.

If you can't breadboard it out first, I'd certainly advise making the RNG vero first, socketing the transistors and using crocodile clips to audio test it on it's own (i.e with the standard volume pot arrangement): I tried it out on the breadboard with a view to doing a single vero with the blend on board, but I don't have all of the listed transistors - I used 2N2222 for Q1 and 2, and there was uncontrolled oscillation at all settings of the pot (pot just altered the pitch of the oscillation) so it might be sensitive to the exact transistors used. I'm guessing it's not meant to whistle constantly.

[moid]

OK I'll do that (build the RNG first) - I now socket transistors routinely (after once getting one the wrong way around - it looked right but it turned out that the CBE pins were reversed and this took me a long time to figure out). I'll definitely make sure I have the right transistors then; I do sometimes stick different ones in to see if the sound is better / different - a bit random, but it's a form of experimentation that is within my skills! Sounds like I'd better buy the exact ones, the demos I've heard of the RNG don't whistle constantly I think there might be a few days before anymore progress will be made while I make sure I've ordered everything. At the worst I should at least make an RNG with a starve pot which hopefully will make some broken glitchy noises, and if I can't blend it with another signal I can do that via splitter and blender pedals I own. Thanks again, I'll post an update once I've got some progress.

[moid]

Thread resurrection! I can happily report that the beast lives Thanks very much Nocentelli, this would not have been possible without your help. I'll post the finished diagram below in case anyone else ever wants to build one. The clean blend knob really works well with this pedal, especially if you push a lot of reverb in before the pedal; it sounds like a poor man's Industrialectric RM1 - which makes me very happy! The starve knob at 10K Log isn't strong enough for my tastes, so I'd recommend (if anyone else builds this) that you try something much stronger (50K? 100K?). I of course being stupid and enthusiastic just built it one night straight into the box without testing anything and it worked first time which made me very happy, but also made me realise that I should've tried different pots (and it will be a nightmare to get to the pots with the way I wired the box). The clean blend might work better as a Boost with a volume pot because the RNG is really incredibly loud and drowns out the clean signal quite quickly on in the blend - it still works for me, but I think I'd try a booster circuit in there if I built it again. Lastly the pedal is not quite as chaotic as I wanted it to be... maybe a stronger Starve knob would help, but I'd be tempted to to add some sort of feedback loop where part of the signal could be feed back into the earlier parts of the circuit (maybe with a pot to control this because the volume levels could get out of hand pretty quickly. Not sure where this would go, but I guess some playing with an audio probe would make some suggestions. Still even with just a blend option, this pedal is fun