Derek Revell's Website
Phutney Technical Info
An attempt to tidy things up on the Technical Information web page December 2014
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Tips for Phutney Builder's
I've been doing some pretty extensive changes here and on the other pages, so if you find any broken links, or errors, please let me know ASAP and I'll fix them up, thanks in advance.
I have fully populated the "X" board and it works 100% with no track errors,
Just a quick note, all the faults I've found on any of the boards I've populated, have been down to bad component selection, poor soldering, or sloppy housekeeping, i.e. solder splashes, so before powering up the board you've just finished, take 10 to 20 minutes to fully inspect the soldering and component selection. you may save yourself several hours of fault finding.
POPULATING THE "X" BOARD
1) Mounting of the four (4) Germanium AC???K transistors is done by drilling out the 4 solder pads that are not connected to any tracks, the holes on the originals are clearance for 6BA screws, which are then secured with a shakeproof washer, and a 6BA nut, which can be replaced by 2.5mm screws, so a 3mm clearance hole is good.
2) C6 should be 2.2uf 16V, not 15uf 16V as on the previous X board component value sheet.
3) On the reverb circuit 10K resistor (R14), is missing, I have corrected this omission on my MKIII boards.
POPULATING THE "Y" BOARD
1) Please be aware that there are 2 resistors marked R93 = 68K and R93X = 10K, this is a throw back to the original Deodar circuits.
2) I added a couple of through plated holes on the Filter, a 0.1uf capacitor and a 100 ohm resistor can be connected in series with SPST switch, this makes the Filter 30dB/Octave instead of 24dB/Octave, of course this can be switched, so you can mark the switch 24dB OFF and 30dB ON, wire the switch to Y9 and Y10, to avoid having wires soldered to board, or you could add a jumper type connector to the two holes provided, and before anyone shouts, the EMS designed filter was always a 4 pole filter, which is 24dB/Oct, never 18dB/Oct, OK, nuff said. Oh! and it makes a big difference to the filter sound what type of capacitors are used in the filter ladder i.e. C33 thru C36, tropical fish, ceramic types, etc, etc.
3) Q40 doesn't have a connection on the PCB to the collector (middle leg), please snip that leg off.
4) It should be noted that there are extra tracks added to this board, the first going to edge connector Y8 and the second on Y12, the Y8 connection goes to the collector of Q44 on the Envelope Shaper, you will see that this is in the Trapezoid circuit, it was my idea to pick up the opposite voltage that was being sent to the pot, well as you can see, that was a mistake, and the only way to get the inverted voltage is to do it using an inverting buffer amp, but if the experimenter wanted to do something else, at least you have a connection to B8, if nothing else, just cut the track up at Q44. The other track connection to Y12 is covered in Item 4)
5) C39 was marked as 10uf 16V, this is an error, it should be 15uf 10V, although I'm quite sure it wouldn't have made much difference.
6) I picked up some information from a techie at Lucidsounds in the UK and I quote "I spent a considerable amount of time recently researching EMS and other filter issues, and I can tell you the type of capacitors used makes a big difference to the flatness of the resonance response. For example using modern dipped poly film types caused the resonance to rise sharply with frequency. Adding the extra network was effective in compensating for this. By contrast, using the vintage ceramic types gave an almost flat resonance response. Adding the extra network to this combination causes a roll-off of resonance with frequency. I should add I used several different filter cards from very old to very modern, and the results transferred with the components.
7) The filter wouldn't oscillate on one of the boards, unless I turned the response up to nearly 10 on the pot, so I changed the 220K resistor to 68K, which moved the pot position to about 7 to commence oscillation. Upon further investigation I've found that the FET (Q26) needs to be selected for a Vp of 2.8V to 3.5V, I've found a selection of BF245B and BF245C FET transistors should be obtained, and selected for the best operation of the filter.
8) I have had some questions asked relating to the Envelope Shaper and Trapezoid circuit, I have tried to simplify the circuit as follows, the envelope circuit you can see it is basically an oscillator, the OFF pot controls whether the oscillator cycles once or recycles, the oscillator then switches ON and OFF depending on how the ATTACK pot ON pot and DECAY pot are set, this then controls a VCA (Voltage Controlled Amplifier) it is quite critical that this Q45 NFET transistor is selected for correct Vp (V=voltage, p=pinch point) if it's not oscillating with the OFF pot at zero, you could have wired this pot up backwards try setting it a 10. And adjust the preset PR12, this at least should get the env. Recycling, Q45 should be selected and should have a Vp = 3.5 To 4.0, and Q48 should also be selected and have a Vp = 2.5 to 3.0 these values are pretty critical to the correct operation of the env. shaper, it should be said that a 24V 20mA lamp has little effect on the circuit, so doesn't have to be included at the test stage, but looks good on the front panel but! I have now added some useful information on the panel POTS, as it's not well indicated on how they should be wired up, the wiper (2) is easily figured out, but LUGS (1) and (3) are less obvious, I will do some checking and add the 1, 2 & 3 idents on the wiring diagrams in due course.
POPULATING THE "Z" BOARD
1) On the 1st run of 50 boards the was a touching trace between two copper runs, which is produces a bad waveform, this trace has now been rectified on the 2nd and subsequent board runs of course, the trace shorted between C65 on Osc 2 module and R214, Q74, Q75 and the collector on Q76, it doesn't do any damage, but the wave shape is halved, so you only get the top half of the ramp wave. THE SOLUTION, take a very sharp modeling knife, or a Stanley Knife and cut the round hole from a 0 shape to a D shape, then check that the short is gone with a test meter set on resistance. Jpeg image here.
2) The waveshape adjustment Osc 1. (sine wave only) is simply done on PR17, but it's a bit of a task to set up on Oscillators 2 and 3, ideally you need an oscilloscope to get the shape 100%, but it is possible to do it by ear, the EMS service manual and schematic aren't exactly clear, I tend to use a lower than stated resistor values for R227 and R228 for Osc. 2, and R261 and R262 but not lower than 6K8, then I hook up a resistor substitution box across the resistor I want to set. The Osc 2 waveshape is properly set up by playing about with these three resistors, R227, R228 and R226, it's advisable to adjust the R227 and R228, on Osc 3. it's R261 and R262. I've just built a 3rd Z board, this time only using 2N4288 and 2N5172 transistors, I couldn't get Osc's 2 and 3 to oscillate, I'd fitted wrongly, as it turns out 10K resistors in positions R221 and R255 instead of 12K, as soon as these were correctly swapped out, the oscillators burst into life. As I've previously mentioned the waveshape adjustment on Osc's 2 and 3, I found out by trial and error that when adjusting the waveshape pot on the front panel to the extremes of the pot adjustment, that the waveshape goes to the extremes and that the oscillator stops making a sound, I then found that by increasing the value of R226 on Osc. 2 and R260 on Osc. 3 this reduced the extreme range of the Waveshape pot, which brought the waveshape pot back into range.
3) I've always wondered why there are 4 connections for each of the power rails on this board, I've looked at my original Synthi, and all the power connectors are wired individually, the wires are not looped, so they do go elsewhere in the synthi, it's just that I didn't ever want to unsolder them and trace them, they don't seem to be wired to the 3 frequency pots, as those are looped from Osc 1 to Osc 2 and then Osc 3, so I'm afraid this one is a mystery, anyone got any idea what could be going on, I've wired my frequency pots and all the pot which have +12V and -9V across them, from a central distribution point, I don't have any issues, so maybe Robin Wood knows, it certainly has me stumped, a situation which I will endeavor to rectify, and find an answer, unless you know why! Please let me know as it's bugging me. Answered by Raphael, it looks very likely that the wiring is this way, on board X terminal X3 which is the -9V power to Y16, then from Y16 to Z17 then in a loop from Z16 to VR15,VR19,VR23, VR22,VR18 and VR38 then back to Z18, and then starting on the X board +12V terminal on X4 to Y16, and then from Y16 to Z20, then in a loop from Z19 to VR15,VR19,VR23, VR22,VR18 and VR38 and then back to Z21, whilst the power on Z7 goes straight to the SKE2 (Pin 2) and from Z9 straight to SKE4, and of course SKE2 (Pin 3) is 0V and is connect to the 0V on the common line, as this is the power to the KS or DK1 or DK2, and that is why there are two chunky capacitors C76 and C77 on the board, to allow for a power surge, as there is no power switch on the KS or DK keyboard, which is why was told by EMS, never to plug the KS or DK2 keyboard into the Synthi A, with the power turned on. Good advice I think.
4) When you come to populate this board, you will find that Q63, Q78 and Q94 transistors don't have a holes in the PCB for the collector (middle leg), please snip those legs off as close as you can to the transistor body, the exception is Q106 in the Noise Generator module the middle leg should not be snipped off, but should be bent up and left sticking out vertically like an Antenna (Aerial) to help with the noise generation, I'm not sure if this true, but it's like this on the original synth.
5) I've been asked quite a number of times why there is a resistor glued to the can of the dual transistor on the two oscillator circuits (Osc. 1 and Osc. 2), due to the nature of how a voltage is used to control the frequency, there is a fairly unique circuit which is very sensitive to temperature changes, the standard circuit uses a 1K resistor to set a current through the transistor pair, so to make the circuit less prone to changing with temperature is to stabilize this circuit, is to use a special resistor with a negative temperature coefficient (NTC) and if that can be thermally attached to the transistor pair package, the circuit becomes much more stable. Why isn't Osc. 3 circuit modified in the same way, this is due to the fact that Osc3 tracks at 0.30V/Octave and not at 0.26V/Octave as do Osc. 1 and Osc. 2, so as Osc. 3 is a low frequency type, and in my opinion the modification isn't required, also a dual transistor is not pin compatible with the present track layout, so it would be necessary to crossover the legs on the dual transistor, so unless you make the Osc. 3 track the same as Osc. 1 and 2, and do a lot of circuit changes it really isn't necessary to use a dual transistor.
6) C69, although being shown as a 1uf Electrolytic capacitor on circuit diagrams, but on the original board it seems that it's a non-polarised 1uf rated at a whopping 160V, which is quite OK, as this figure is unlikely to be exceeded on the board ;-)
7). I've checked that 2C746, 2N2916 and LM194 or LM394 are all pin compatible, and will drop into my boards with the same TAB orientation, this of course only applies to Oscillators 1 and 2, as Oscillator 3 used two BC169C or 2N5172 transistors.
8) Just in case you think the NOISE generator has a fault, if you power up the synth up, you will not get any output from the NOISE generator for a least 30 seconds, this is because the transistor used Q106 (which should have been selected to give 3V pp with PR22 in the mid position), is only connected by the base and emitter, this acts like a ZENER diode, and you will see that C71 is a 15uf electrolytic capacitor, it is this capacitor that needs to fully charge up, before the circuit starts emitting random spectrum noise.
General Information on Phutney build.
1) DK10 use 1N34A OA90 germanium diode.
2) 2.5uf 64V use 2.2uf or 3.3uf 25V-100V..
3) 80uf use 100uf.
4) 16uf 10V use 15uf or 22uf 10V.
5) 5K Potentiometers use 4K7.
6) 2000uf use 2200uf.
7) 200uf use 220uf.
8) D1 marked 1N4148 use 1N4002.
9) C15 and R32 reversed on the schematic.
10) 9V1 ZD9 added on –9V Op-Amp pin 7 (positive supply).
11) Obsolete Japanese Twin Spring Reverb Tank use Accutronics 1BC2D1B.
12) Q34 and Q35 shown as 2C746, use two BC169C’s matched for Gain, and epoxied together.
13) Q74 and Q75 Osc 3 two BC169C’s epoxied together.
14) R176 and R209 should be 1K TEMPCO resistors are readily available from www.thonk.com, once obtained, these should be affixed to the 2C746, 2N2916 or LM394CH dual transistor body, and flying leads are then soldered into the board.
16) Connect Q1 and Q6 to a flying lead, and mount the transistors on a big heat sink using Mica sheet.
17) Check with a DVM set on resistance, across 0V +12V and –9V points ,ground to Pin 4 (+12V) >= 2K ohms, ground and Pin 3 (-9V) >= 2K ohms.
18) SOT = Select On Test.
SPECIFICATIONS FOR TYPE 1, 4, 8 & 9
DIGIT #1 - REVERB TYPE
DIGIT #2 - INPUT IMPEDANCE
DIGIT #3 - OUTPUT IMPEDANCE
DIGIT #4 - DECAY TIME
DIGIT #5 - CONNECTORS
DIGIT #6 - SPRING LOCK
DIGIT #7 - TANK ORIENTATION
MkIII Phutney Information
All Mk3 Circuit Diagrams in PDF under revision.
NEW Phutney Mk3 BOM (Excel format) here
TRACK ERROR REPORTED ON "Y" BOARD
Mk3 "Y" board Q21 Trace correction - Before
Mk3 "Y" board Q21 Trace correction - After
Mk3 "Y" board C47 track error - Before
Mk3 "Y" board C47 track error - After
There are two silkscreen errors reported.
1) On the X board, R77 should be marked R311, I've changed the component layout sheet to correct the error 1), 2) error I've corrected the schematic. There was a schematic error on the Reverb layout, R14 was marked as 1K, the should have been 10K, now corrected.
2) On the Z board R152 should be marked as R252, it's a 10K resistor.
3) I've incorrectly put the wrong value for R184 it should be 8K2, not 4K7 on the Z board component layout sheet.
Other General information
I've discovered that it makes quite a difference to the behaviour of the Filter what type of FET transistor is used for Q26 on the Y board, I'm currently using BF245C FET's, try a BF245B if it's not able to Oscillate.
I've found a solution that if the Envelope re-triggers even if the OFF pot is set to 10, decreasing the value of R143 to say 820K or lower prevented this effect.
Also in the Envelope Generator circuit, C46 should be a 1uf 35V tantalum capacitor.
RS Components have DIN41612 Sockets in stock here at £3.65ea.
I've posted a brief video clip of my "Phutney" in action on YouTube here.
I'll do a video clip of the Synthi Zee and the Synthi AKS soon.
The silk screen on the boards shows component ID's not values, so I've posted the X, and Z boards silkscreen overlays with component values.
The dual transistors on Osc.1 and 2, are readily available using LM394CH or 2N2916 devices.
I've added 64 holes to each of the 32 way PCB connector tracks. DIN 41612 R/A Type B connector, these should be available on Ebay, this is an alternative to the edge connectors,