Original circuit by Don Buchla (used with his kind permission); adapted by Aaron Lanterman. This is based on the timbre circuit on Board 9 and the single-vactrol "waveshape" crossfade circuit on Borad 8 of the Music Easel. You should spend some time studying the original schematics. Warning: This board is designed to be highly flexible; it can be configured in many different ways. Please read the notes below carefully and decide what options you want before building.
Demo
Note this video is of Version 0, so pay no attention to any mention I make of errors on the PCB; those comments are not relevant to Revision 1.
Schematics & layout
Notes
I am convinced that the 50K sliders marked on the original schematics (and this version of the board) should actually be 10K linear. The 120K input and shaping resistors (R102, R103, R104, R105, R108, R109, R110, and R110) are off-board in the original Easel, but included on-board in this adaptation.
The original Easel has a 13.5 V supply, created using an op amp and a transistor buffer. If you have such a supply, you may hook it to the two +13.5 pins and omit R100, R101, R106, and R107. Otherwise, leave the +13.5 pins unconnected and use R100, R101, R106, and R107, which create "soft" +13.5 V supplies (via voltage dividers made by R100 with R101, and R106 with R107.) To counteract loading I found that lowering R100 and R106 from 10K to 1K is a good idea, so I marked these as 1K on the PCB. You may want to experiment with other values.
The Q6 JFET is used as a variable resistor. It is specified as a 2N4341 in the original, but it appears to be out of production. I picked the J201 since it happened to come with the preinstalled Eagle libraries. I've tried a MPF102 here too, and didn't notice a difference. R21 is marked as 6.8K on the original Buchla schematic. I had to raise this value quite a lot in order to not get too much gain through the VCA with the offset knob at the lowest setting. I used 330K instead of 6.8K and marked R21 as such on the PCB. I recommend that as a starting point if you're using a J201 or MPF102 for Q6 (I tried both and didn't notice any difference). Your mileage may vary. Different values of R21 (even instances of the same JFET model type) may be appropriate for different choices of Q6.
I specified Q5 as a 2N3906 since I happen to have of them and it also came preinstalled in the Eagle libraries. In the original Music Easel schematic, it is specified as a 2N4248, which seems to be out of production. You might want to try other transistors here.
The circuit has been tested with RC4558s, which was deemed to be electrically similar to the original RC4136s used in the Easel. Other op amps will probably work (many will probably work better!), but they have not been tried.
D3 is a 1N457. I suspect a 1N4148s or a 1N914 will work, but I have not tested them.
D1 and D2 are not specified in the original schematic; I used 1N457s here, but my suspicions in the previous bullet point apply here too.
Connections
Front panel connections usually have a square and round pad together in a white box. The round pad is the signal, and the square pad provides a convenient ground.
TAI - Timbre Audio Input
TAO - Timbre Audio Output
TCVI - Timbre CV input; amount of influence is controlled by setting of TCV pot
WCVI - "Waveshape" crossfader CV input; amount of influence is controlled by setting of WCV pot
A1I - Alternate input 1; buffered and appears at A1B
A1B - Buffered version of A1I input; may be used connected to A1C, or not used at all, or connected to a switch
A1C - Corresponds to pin 10 of Board 8 of the original Easel schematics. It corresponds to what you get by turning the waveshape control counterclockwise. If you want to set this up like an original Easel, connect B9P4 or TOP directly A1C, so turning the waveshape control counterclockwise corresponds to the timbre circuit. If you want to always use the "waveshape" crossfader as a stand alone crossfader, you can directly hook A1B to A1C. If you'd like to switch between both options, hook A1C to the common terminal of a on-none-on SPDT switch, and hook TOP or B9P4 to one "on" terminal and A1B to another "on" terminal. (The issue of whether to use TOP or B9P4 is complex and depends on how you set the resistors OR119, OR120, OR1A, and OR47A; see below.)
TOP - Timbre Output Pin - connected to A1C, or to a switch, or not used (see options listed under the A1C description above). This is the timbre output after the gain provided by IC5B (if gain is used).
B9P4 - Corresponds to Pin 4 of Board 9 of the original Music Easel - connected to A1C, or to a switch, or not used (see options listed under the A1C description above). This is the timbre output before the gain provided by IC5B (assuming gain is used).
A2I - "Alternate" input 2; buffered and appears at B8P; used if creating a stand-alone module. This corresponds to what you get when turning the waveshape control clockwise.
B8P - Input to the Vactrol side of the "waveshape" crossfader. If you are using the A2I input, you won't need to use the B8P pad. If you are trying to build an complete Easel, B8P corresponds to pin 12 of IC 4 on the original Easel Board 8 schematic. This is the pulse, square, or triangle shape signal that you'd get by turning the waveshape control clockwise. If you hook a signal directly to B8P, you should omit IC7, R112, R113, R114, R115 (notice this also takes out the A1I, A1B functionality, but that's probably OK since you'll probably be directly hooked the timbre output to A1C anyway). Most users building stand-alone modules will probably not need to use B8P.
MXO - Mixed Output of the "waveshape" crossfader
CSW1, CSW2 - there's a capacitor that provides some filtering action on the timbre output. You can put a switch between CSW and CSW2 and experiment with switching this cap in and out. If you want it to act like an original Easel, just short CSW1 and CSW2.
Resistor options
If you are using an op amp with some build in short-circuit protection, like the specified RC4558s, then you can use the 220R resistors OR121 and OR48A, and use wires instead of 1K resistors for OR115 and OR122. If, on the other hand, you are using a different op amp capable of creating much bigger currents, I recommend using wires instead of 220R resistors for OR121 and OR48A, and installing actual 1K protection resistors in the OR115 and OR122 spots.
OK, here is where things get really complicated. OR1A and OR47A are specified as 15K and 75K; this is as things are in the original Easel. This gives the raw timbre signal at B8P4 and whatever it is mixed with at B8P a gain of 6. IC5B, OR119, OR120, OR121, and OR122 are not present in the original Easel; this is a copy of the circuitry around IC6B to give that gain of 6 at the TAO output. If you'd like your external signal input at A2I to be subject to the same gain, then you can use 15K and 75K in the OR1A and OR47A spots, respectively. However, you may prefer to take the timbre output to mixer from the TOP pin, so it already has the gain, in which case you can omit OR1A altogether, and use a wire for OR47A, which turns IC6B into a unity gain buffer; in this case, IC5B boosts the timbre output up to the level of typical signals, and will then be on an even footing with most external signals, and IC6B won't provide additional undesired gain. Think carefully about your particular desired gain structure.
Potentiometers
WOS - "Waveshape" croassfader Offset
WCV - "Waveshape" crossfader CV; controls amount of influence of the WCVI input
TOS - Timbre Offset
TCV - Timbre CV; controls amount of influence of the TCVI input
Disclaimer
These should be considered advanced projects, and should only be attempted by people with extensive knowledge and experience in electronics, particularly in terms of practical construction and debugging techniques. The boards are dense and the documentation is sparse. If you are just getting started with Synth DIY, I recommend starting with kits.
If you try to build one of these projects, you must assume that you will be on your own, and be confident enough to tackle the project under those circumstances. I am interested in learning about people's experiences in building the boards, and will try to answer questions over e-mail, but I don't have time to do any hand holding.
Any PCBs made available to the public are provided as-is, with no guarantees or warranties whatsoever. Similarly, no guarantees or warranties are made about the correctness or usefulness of the information on these webpages.
Any electronic project may present a risk of injury or death, particularly when dealing with mains voltages. It is important to follow appropriate safety practices. The author of this post, Aaron Lanterman, disclaims any liability for injury, death, or other damage caused in using the PCBs or any of the information contained on these webpages.
Original circuit by Don Buchla (used with his kind permission); adapted by Aaron Lanterman.
This is based on the pulser & inverter circuits on Board of the Music Easel. You should spend some time studying the original schematics.
Demo
Note this video is of Version 0, so pay no attention to any mention I make of errors on the PCB; those comments are not relevant to Revision 1.
Schematic & layout
Errors
There are some errors in the schematic and the silkscreen. Fortunately these only involve incorrect names and values; addressing these issues does not require any trace cutting or jumpering. First note that the "R11" and "R22" labels on the PCB are accidentally swapped; the parts themselves are in the correct place. The resistor closer to the 2N1711 transistor should be labled "R22" and the one closer to the MC14016s should be labeled "R11." Thanks to Dave Brown for catching this error.
If you look on my Eagle schematic around the 2N1711, you'll see R21, R22, and R28 are 6K8. This is a copy-and-paste error in the resistor values, since only one of them should be 6K8. R21 should be 6.8K, but R22 should be 2.2K (I think - it's hard to tell on the original Buchla schematic, it looks like it might be 22K?), and R28 should be 100R. Thanks to Dave Brown for catching these error; I never tried hooking an LED or light bulb up, so I never noticed this error before. Dave also noted that the 100R values for R28 may be specific to using an incandescent bulb.
Notes
I am convinced that the 50K sliders marked on the original schematics should actually be 10K linear. The 120K input and shaping resistors (R105, R106, R107, and R108) are off-board in the original Easel, but included on-board in this adaptation.
The original Easel has a 13.5 V supply, created using an op amp and a transistor. If you have such a supply, you may hook it to the +13.5 pin and omit R103 and R104. Otherwise, leave the +13.5 pins unconnected and use R103 and R104, which create a "soft" +13.5 V supply. I found it important to lower R103 to something like 3.3K to counteract loading, so I marked R103 as 3.3K on the PCB. You may want to experiment with other values.
The circuit has been tested with RC4558s, which was deemed to be electrically similar to the original RC4136s used in the Easel. Other op amps will probably work (many will probably work better!), but they have not been tried.
D3-D6 are 1N457s. I suspect a 1N4148s or a 1N914 will work, but I have not tested them.
Connections
Front panel connections usually have a square and round pad together in a white box. The round pad is the signal, and the square pad provides a convenient ground.PIC, PIO, FB - Pulse Input Common, Pulse Input One-Shot, and Feedback. You want to try to find a single-pole on-off-(on) switch, where the (on) indicates momentary operation. Hook PIC to the common switch terminal, hook PIO to the (on) terminal, and hook FB to the regular on terminal. This will let you do just one "pulse," or if you switch to the feedback mode quickly after doing one pulse, the pulser will drive itself and you will get repeated pulses. The middle position turns off the pulsing. If need be, you could just use a regular on-off-on switch here.
PCVA, PCVB - Pulser CV outputs A and B. A is active when AEN is set high; B is active when BEN is set high.
PPA, PPB - Pulser pulse outputs A and B. A is active when AEN is set high; B is active when BEN is set high.
Y1, Y2 - terminal of an electronic switch; connection made when BEN is set high (untested).
Z1, Z2 - terminals of an electronic switch; connection made when BEN is set high (untested).
ANOT, BNOT - logical "not" of AEN and BEN
AEN, BEN - A and B enables; see other connection instructions for details of what they enable. I plan to connect these to a switch that will let be switch between automatically-on (connect to +15 V) and connect to an external input. Most users will probably just want to tie AEN to +15 so the A outputs are always enabled. Some users may want to just ignore the B outputs entirely. Some might want to only use the "B" part of the circuit to control the Z1,Z2 and Y1,Y2 electronic switches, and ignore the pulser B outputs. Do whatever makes you happy.
INVI, INVO - inverter input and output; takes 0-10 V CV and outputs 10-0 V CV. The inverter is independent of the rest of the pulser, so you can invert whatever CV signals you want.
LED - on the Easel schematics, this is actually called "LAMP" and is shown going through a lamp-looking symbol to a +12 V supply. I haven't tried doing anything with this, since it's a low priority for me, but if someone can get something to light up I'd love to hear about it.
Potentiometers
LOS - Level (pulser rate) Offset
LCV - Level (pulser rate) CV; controls amount of influence of the LIN input
TRIM - Trims the pulser rate - set to personal taste
Disclaimer
These should be considered advanced projects, and should only be attempted by people with extensive knowledge and experience in electronics, particularly in terms of practical construction and debugging techniques. The boards are dense and the documentation is sparse. If you are just getting started with Synth DIY, I recommend starting with kits.
If you try to build one of these projects, you must assume that you will be on your own, and be confident enough to tackle the project under those circumstances. I am interested in learning about people's experiences in building the boards, and will try to answer questions over e-mail, but I don't have time to do any hand holding.
Any PCBs made available to the public are provided as-is, with no guarantees or warranties whatsoever. Similarly, no guarantees or warranties are made about the correctness or usefulness of the information on these webpages.
Any electronic project may present a risk of injury or death, particularly when dealing with mains voltages. It is important to follow appropriate safety practices. The author of this post, Aaron Lanterman, disclaims any liability for injury, death, or other damage caused in using the PCBs or any of the information contained on these webpages.
Original circuit by Don Buchla (used with his kind permission); adapted by Aaron Lanterman
This is based on the lowpass gate circuit on Board 10 and Board 11 of the Music Easel, which contains two identical LPG circuits. You should spend some time studying the original schematics.
Schematic & Layouts
Notes
The holes and traces on the Revision 1 PCBs are the same as on Version 0. The only changes I made were to the silkscreen. I forgot to put a "Rev 1" marking on the board. You can tell it is a "Rev 1" board if it says "BEAD" in the spots near the power connector; the older version said "2R2."
I have not been able to get the LED to light. I do not know why. (It appears that one of my beta testers has gotten an LED to light, though.)
I am convinced that the 50K sliders marked on the original schematics should actually be 10K linear. The 120K input and shaping resistors (R105, R106, R107, and R108) are off-board in the original Easel, but included on-board in this adaptation.
The original Easel has a 13.5 V supply, created using an op amp and a transistor. If you have such a supply, you may hook it to the +13.5 pin and omit R103 and R104. Otherwise, leave the +13.5 pin unconnected and use R103 and R104, which create a "soft" +13.5 V supply. In testing, this was found to droop to between 9 V and 11 V depending on pot settings, resulting in me being unable to open up the filter all the way using just the LOS pot. I lowered R103 to 3.3K, and found that this helped counteract the droop and I got a reasonable full-range control, so I marked R103 as 3.3K on the board. You may want to experiment with other values for R103. An alternative would be to keep the R103/R104 ratio the same but lower the overall values, such as reducing R103 to 1K and R104 to 9.1K. However, I have not tried this.
The area around the vactrols is tight; be sure to install R42 and R41 before installing the vactrols. Also, the 910 pf silver mica caps are pretty big; to get them installed I had to leave them kind of floating above most of the other parts.
Q2, the buffer JFET, is a 2N4340 in the original. I picked the J201 since it happened to come with the preinstalled Eagle libraries. I used an actual J201 in my build and it worked fine. Any JFET you have previously successfully used as an audio buffer should work fine here.
The need for R100, the 68K input resistor, was gleaned by studying other parts of the original Easel schematics.
The circuit has been tested with RC4558s. Other op amps will probably work (many will probably work better!), but they have not been tried.
The regular diode in the original is a 1N457. I suspect a 1N4148s or a 1N914 will work, but I have not tested them.
Dr. Mabuse has run into a problem with excessive current draw cooking parts - read about the problem and his solution here. I personally haven't been able to reproduce whatever the problem is. I would be very interested to see if other people do (or don't) run into this problem.
Dr. Mabuse reports that a 0.001 uf cap (i.e. 1 nf) works fine in place of the 910 pf cap around the LED-driving 2N1711 transistor; this lets you save 910 pf micas for more critical audio path applications.
Dr. Mabuse writes: "Another sub that I decided against but still yielded useful and interesting results was swapping a single VTL5C3/2 for two VTL5C3s. It works both as a filter and as a VCA but the response curve is noticeably different (not as even and smooth) and the VCA mode didn't attenuate quite as much. In a pinch it think it could be used though."
Connections
Front panel connections usually have a square and round pad together in a white box. The round pad is the signal, and the square pad provides a convenient ground.
LIN - Level CV Input; amount of influnce controlled by setting of LCV pot
AIN - Audio input
AO - Audio output
LED - Hooks to the cathode (straight line part of symbol, shorter leg of actual device) of an LED; the anode (triangle part of symbol, longer leg of actual device) of the LED is hooked to +5 V.
SWV, SWC, and SWL - Connections for the mode switch. Use a SPDT on-off-on switch. Connect SWC to the common connection, SWV to the lower connection, and SWL to the upper connection. Switching to connect SWC to SWL puts the filter in lowpass mode; switching to connect SWC to SWV puts it in VCA mode, and switching it to the "off" position puts it in "combo" mode.
CIN - Control input. CV input for mode control; amount of influence is controlled by the CCV pot. If +13.5 V is input here, then the resistance of CCV corresponds to the resistor setting on an Easel programming card, but you can put in all sorts of varying voltages here. I have not tried to puzzle out exactly what effect this has, i.e. how many volts at a given pot setting is required to change modes, etc., but I have made it switch modes. This input piles "on top of" the switch setting, so its influence will change with switch settings.
B10P1 - Analogous to Pin 1 on Board 10; maybe useful if you are using this to replace an original Easel board. Most users will not need this.
B10P9 - Analogous to Pin 9 on Board 10; maybe useful if you are using this to replace an original Easel board. Most users will not need this.
Potentiometers
LOS - Level Offset
LCV - Level CV; controls amount of influence of the LIN input
CCV - Control CV; controls amount of influence of CCV. I specified 300K here, but I largely pulled that number out of a hat. I would suggest a linear pot, but I'm really not sure if a log or linear pot would be best. If +13.5 V is put into CIN, then CCV corresponds to the resistor setting on an Easel programming card, but you can put in all sorts of changing voltages for CIN.
Disclaimer
These should be considered advanced projects, and should only be attempted by people with extensive knowledge and experience in electronics, particularly in terms of practical construction and debugging techniques. The boards are dense and the documentation is sparse. If you are just getting started with Synth DIY, I recommend starting with kits.
If you try to build one of these projects, you must assume that you will be on your own, and be confident enough to tackle the project under those circumstances. I am interested in learning about people's experiences in building the boards, and will try to answer questions over e-mail, but I don't have time to do any hand holding.
Any PCBs made available to the public are provided as-is, with no guarantees or warranties whatsoever. Similarly, no guarantees or warranties are made about the correctness or usefulness of the information on these webpages.
Any electronic project may present a risk of injury or death, particularly when dealing with mains voltages. It is important to follow appropriate safety practices. The author of this post, Aaron Lanterman, disclaims any liability for injury, death, or other damage caused in using the PCBs or any of the information contained on these webpages.
