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GuitarPCB’s “Mini-Me” is (IMO) a mature and faithful reproduction of a Small Clone chorus circuit with some tastefully useful modifications; primary of which and part of the stock build is a “Depth” control. Herein is the story of three different approaches to building out this chorus pedal. With two different versions of the PCB, the emphasis was initially placed on the use of the MN3007 BBD chip, but the latest version of the ‘Mini-Me’ provides a means of optionally employing an MN3207 or Cool Audio’s V3207 chip instead. The clock (LFO source) in this build is a CD4047 CMOS multivibrator. (The original Small Clone used a SAD1024 BBD chip and was later modified to work with the MN3007.)
Originally designed to be housed in a 125B enclosure, this first build was instead targeted for a 1590BB enclosure to accommodate Ray Wilkinson’s ‘Mini-Me’ “Depth Range” modification. It uses a GuitarPCB “Roto-Tone” PCB for selecting one of four capacitance values to alter the range of the effect depth at C18. This mod is presented by Ray in the documentation made available on the GuitarPCB Forum website. Essentially it just changes the cap value of the “C timing” capacitor used on pin 1 of the CD4047 clock chip. A clever modification which can bring this modest chorus circuit to the verge of flanging.
My second build with the “Mini-Me” circuit was a bit more encompassing as I wanted to achieve a ‘duo-chorus’ with stereo capability (or just two choruses in series), LFO (clock) synching and still provide the ‘Depth Range’ control modifications on each one. This build went into a 1590XX, but with the intended Root-Tone daughterboard PCB’s, there was just NOT enough real estate to use the 1590XX box. So, to keep the enclosure size at the 1590XX limit, I eliminated the Roto-Tone daughterboard PCBs and simply dead-bugged the 4 different ‘Depth Range’ caps onto each of the two 4-way rotary switches for the build. The challenging part was finding the means to “sync” the two chorus circuits to either of the LFO (clocks) while still allowing for independent operation. I feared I might need some exotic circuit to manage the switching, but a close study of the circuit exposed the fact that there is a but a single entry point of the ‘Rate’ & ‘Depth’ signal to the CD4047 clock chip – at the wiper of the ‘Depth’ pot. By interrupting the junction of the ‘Depth’ pot wiper to the PCB, a tap-point could be made wherein a DPDT (On-On-On) toggle switch could be used to determine which set of ‘Rate’ & ‘Depth’ controls fed to the CD4047 clock chips. (See the toggle switch images.) And in a pleasing surprise, there is no ‘click’ or ‘pop’ when changing the sync toggle. I considered adding ‘rate indicator LEDs’ for each circuit, but lazily opted out of adding them. The only other modification used in this build was to use a 1N5817 Schottky protection diode in series instead of clamping a 1N4001 to ground. (I believe a series 1N5817 in combo with a 47µF provides superior protection & filtering while providing a smaller voltage drop on the power supply.)
In the third build, I wanted a slightly more flexible BBD chip option so I could easily test MN3007, MN3207 and V3207 BBD chips. Using the Mini-Me 2019 PCB, which has jumper wiring options for either the 3007 or 3207 BBD chip, I chose not to hard-wire the jumpers and used header pins and jumper clips so the chips could easily be swapped out for testing purposes. Also, I wanted to put this build in a smaller enclosure, selecting a sky-blue 1590B – which a bit smaller than the 125B enclosure. I spent more than a couple of days drawing, measuring, place-testing, redrawing, remeasuring and constraining the construct to within 1mm physical placement tolerances and still have top-mounted jacks. Just barely, the Mini-Me will fit into a 1590B enclosure, but without the 4-way rotary switch for the “Depth Range” mod. Instead of the 4-way rotary, I elected to use a DPDT (On-On-On) toggle switch with three different cap values (47pF, 100pF & 330pF) in dead-bug fashion. Again, this uses a series 1N5817 protection diode instead of the 1N4001 protection clamp. Also, I noted that the pots specified in the BOM (16mm right-angle PC-mount) would place the pot shafts rather close to the outer edges of the 1590B enclosure, but wanted them closer to the center of the enclosure top rather than so close to the edges. So I modified those by cutting off the pot legs and added my own shorter<span class=”Apple-converted-space”> </span>leads, using discarded 1N5817 diode leg trims. Coulda used solder-lug pots, but there were none on-hand. (See pics.)<span class=”Apple-converted-space”> </span>This allowed the pots to position closer together and with a slight bend, gained another 2mm to position the main PCB a bit lower from the top of the enclosure. This made a bit more room for the DPDT toggle switch and the DC jack. The DC jack’s positive leg was a bit long, so I bent it to 90 degrees to gain another 3mm of precious vertical positioning space. In the end, all the planning, drawing an easing paid off and I was able to get all the bits stuffed into the smaller enclosure and still provide a pleasant presentation for the candy-wrapper without any internal bits shorting to anything. I did, however, have to take a Dremel cut-off wheel to the rim-lip of the cover (near the stompswitch) where the 3PDT Wiring PCB comes in such close proximity to the lid’s seating shoulder when closed. (I said it was a tight fit.)
At any rate, thanks for reading and hope you enjoyed the circuit porn. Keep building!
MERRY CHRISTMAS!
Well, I for one, thoroughly enjoyed this dissertation. While many of Barry’s Builders (Hmm. I like the sound of that moniker. Perhaps we need t-shirts with that logo?) may be afraid to attempt such complex projects, I believe there are some great lessons contained therein.
Read carefully and you will spot several unique and clever build techniques that you may want to use at some point. Although we consider this hobby to be all about electronics, ( I like to call it “Wires and Sparks”) it also requires a good bit of mechanical skills to complete our projects.
Many thanks, Cybercow!
“a close study of the circuit exposed the fact that there is a but a single entry point of the ‘Rate’ & ‘Depth’ signal to the CD4047 clock chip – at the wiper of the ‘Depth’ pot. By interrupting the junction of the ‘Depth’ pot wiper to the PCB, a tap-point could be made wherein a DPDT (On-On-On) toggle switch could be used to determine which set of ‘Rate’ & ‘Depth’ controls fed to the CD4047 clock chips.”
Wow. Excellent. This gives me a lot of thoughts.
Thanks for the excellent build story and kudos to thinking outside the board.
Barry – thanks! I was inspired by recent PedaPCB “Duo-Phase” I’d built and thought about the 3 other Mini-Me PCBs I had in on hand. Two of them were the old style and one of them the newer style with the choice between using MN3007 and the MN3207 (or Cool Audio’s v3207). I used the two old style PCBs to attempt the dual-chorus. The newer board was used to cram into the 1590B enclosure an allow the BBD to swapped for testing. (I found a small stash of MN3007s and a few MN3207s that I wanted to test and thought the jumper clips would be easiest.)
For what it’s worth, here is the Mini-Me schematic marked up for identification of the points used in the mods so employed.
Hope everyone has a Merry Christmas!
Beautiful and inspiring work!!!
Coincidentally I was looking at the “commercial pedal” about a week ago MXR Phase 99.
It has dual phasers synced and was thinking about how cool it would be to have the Dr. Phybes and The Vibe synced. They each have a unique quality on their own but it would be very interesting to not only sync them but Blend them. The Phase 90 by itself inverts the Phase so having a dual circuit allows for them to do stereo. A Blend here would be nice also.
A Blend control is finally becoming more prevalent in commercial pedals and no doubt why my Buff N Blend Add-on Boards over the last 8 years are so popular. Blending your tone is so helpful IMHO.
Excellent as always Mark
I’ve a couple of mini me’s and a CE2 board
I’ll be studying your informative report and seeing what I can come up with
Have a great Christmas everyone
Cheers
Barry said: “was thinking about how cool it would be to have the Dr. Phybes and The Vibesynced. They each have a unique quality on their own but it would be very interesting to not only sync them but Blend them. The Phase 90 by itself inverts the Phase so having a dual circuit allows for them to do stereo. A Blend here would be nice also.”
Interesting concept indeed. I was looking at the schematics for the Dr Phybes and The Vibe and noted that each has two connection points; one for establishing the bias of the matched FETs (the junction of C10 & R30) and the other for setting the speed (@ R23) – and I’m guessing the bias settings would need to remain independent, but the ‘speed’ connection point could be toggled as one, the other or remain independent as I did in the duo-chorus. It would certainly have to be tested to verify. Considering the high resistance values of R23 & R30, using just the speed insert point seems feasible. Also, I would consider tolerance matching the LFO section passive components on each board to assure as close as possible matching.
So much potential fun!
Barry – now I’m thinking of pairing a ‘Mini-Me’ with a ‘Dr Phybes’ and synching the LFOs. Considering calling it a “Stone Clone” for a phaser\chorus combo.
I just need to suss out the LFO synch bits if possible.
Cybercow, my baited breath is waiting to see your result!
Barry W Davis – thank you!
Barry, Wilkie1 – planning and research is in progress. I need to take several measurements (scope & voltages) to see how well the two different LFOs will play together in such an endeavor. 😉
18 months later, I found my Dual Chorus in a box with several other builds and thought to pull it out and play with it. Wow! I am just amazed at how flexible this thing is. Seeing as it was plugged into my PC’s DI box, I thought to go ahead make a quick (about 6+ minutes) demo.
Here is the link for the Stereophonic Gizmotronic Symphonic Harmonic Perambulator Dual Chorus
Just for re-refernce, here is the pedal description:
Based on a pair of GuitarPCB “Mini-Me” chorus circuit boards (basically a modified Small Clone circuit), this unit uses Wilkie’s “Depth Mod” on each circuit, (and some fancy switching to link both chorus circuits to either of the LFO’s – or not), for some extreme chorusing ranges. And with two of them in one box, configurable for mono and/or stereo, it is a chorus monster.
The “Sync” switch determines which LFO is charge. When one LFO (Left or Right) each chorus can be set to different Depth settings and a nice psycho-acoustic effect ensues. It will connect as Mono (from “IN 1” to “OUT 2”), can be used as two separate chorus pedals (using “IN 1” to “OUT 1” and/or “IN 2” to “OUT 2”) or Mono in and Stereo out (using “IN 1” and both “OUT 1” & “OUT 2”)
Each circuit has its own Rate, Depth and ‘Depth Range’ controls. In any configuration, the ‘Depth’ and ‘Depth Range’ controls remain independent. When the “LFO SYNC” toggle is in the middle, the LFO’s are independent and the ‘Rate” control of each side works independently.
(9v @ ~15mA, neg. center)
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