Shruthi XT programmer, knobs and leds and assembly questions
  • I’m now a proud owner of a Shruthi XT kit from FCD72, but there’s a couple of customizations I’d like to make to the standard set of things that come with the kit.
    First of all, I’m a bit of a knob fetishist, meaning that I don’t like rubbery plastic knobs, and rather have the something more old-school. The problem is, as Frank has explained, that the pot shafts are a bit too high for most pots and hence need to be dremeld down a bit.
    Since I don’t have a dremel, nor a workshop where I can perform such an operation, and my wide already hates me enough for soldering in our living room (which is one with our kitchen, our studio and our library) I’d rather not do that.
    Does anyone know some good 6mm shaft knobs that look something like these:
    that work with the shafts, so that I don’t have to dremel them?

    Question nr.2: I’ll have to de-solder the leds on the Shruthi, since they have been soldered for the transparent case, but the programmer frontplate is opaque (with the holes). I need to raise the leds a bit to stick out into the holes. Since I always made a big mess when de-soldering leds, do you have any special tip on how to do this?

    I’m not in a hurry a friend of mine will do most of the assembly job, and neither I nor he have the time to get to it right now… but I can start sourcing the remaining parts and plan the thing properly :)

  • Once you’ve soldered the LEDs and cut the legs it’s hard to lengthen them. The kit comes with new LEDs so you use those.

    To remove the LEDs I do the following, remove as much solder as possible. Heat up one pad and push the LED to move that leg. Do the same for the other leg until it comes out.

    Or use a large soldering iron bit and try to heat both pads at once and pull out the LED.

  • yep I was thinking about removing them completely and soldering new ones. I only have to find new leds, since I really like the white ones (but the kit comes with red ones).
    btw. has anybody tried these for the leds: fresnel lenses for leds

  • @rumpelfilter: I’ve noticed those as well – should look good IMO, although might dim the LED very slightly.

  • I use opposite tactic when desoldering: i add more tin to the legs, that way tin stays liquid longer and it is possible to push/pull component out of the circuit. If there is temperature control in soldering iron it’s useful to turn it to max.
    They used special desolder tips in my old workplace but i wouldn’t buy those for home. It’s so rarely when i need to use those and many different shapes would be needed.. .

  • The opposite is right: If you have a temperature controlled Iron, turn the temperature down so you don’t damage anything. Your Strategie although is right putting that much Energy in the Solder joint that the hold Solder Mess stays liquid.

    For this you’ll need a Processor controlled Iron with high Wattage, not these old school “Turn a knob to the right to make it hoter, just don’t trust the Scale” Thing. I recently bought a 60W Iron (if you read older Posts from me i sweared on my tiny 8W thingie) and this Beast keeps the Temperature constant wether you solder a SMD Diode or seal a Tin Can.

  • the tools I use:

    spread a little soldering flux over joints then use a very hot soldering iron (750° F) and use the solder sucker to get the solder out.
    If it doesn’t get it all, I’ll use the iron to push the leads out. If I still can’t pull it out, I’ll cut the LED off and pull the remaining lead out with a pair of plyers.

    btw, I hate desoldering

  • @fcd, if worried about damaging anything, pull the IC’s out. Usually the passive components can handle it.

  • thanks for all the valuable tips! I’ll try the “add more solder then suck it away” technique :)
    I don’t have a really pro soldering station, in fact I don’t have a soldering station at all, but so far my iron has proven a valuable tool.

    About those led lenses, anybody tried those?

  • about turning the temperature down in order to not overheat components i have to disagree with you fcd72.
    i’ve had better results applying >400°C than with lower temperature. that way you don’t have to apply heat as long as you would have to with just 300 or 320°. it’s a good thing to add plenty of fresh tin, you can suck it out afterwards.
    the higher temperature could be a problem if you have a self etched board with very thin/small solder pads and copper traces that can lift easily. but with decent pads / traces or any kind of industrial produced board there should be no problem.

  • Anyone tried making a solder sucker that attaches to a vacuum cleaner? :)

  • also have to disagree re: turning heat down to de-solder - perhaps for homemade PCBs this is the case as rosch says, not to lift traces?

    I generally set my iron on the hotter side of things in general, less time spent in contact with the surface results in less heat transfer to the rest of the components and nary a cold joint - fluid soldering iron technique is important though, I wouldn't recommend an extremely hot iron to someone that hasn't soldered at least a handful of circuit boards

    have you ever soldered a battery, particularly a small disc battery for a vintage synth? same technique - you use an extremely hot iron to make sure the temperature spike is as brief and localized as possible, this way you are actually LESS likely to explode the battery, even though your iron is very hot

    need to de-solder some LEDs myself, for nearly the same reason, and have been putting it off for months now!
  • these are mostly questions to Frank, but maybe I’m not the only one with this problem, so I’m posting them here
    I’ve been checking the assembly guide for the programmer and the 4-PM, so far I get everything, but not the most basic thing… how the hell is is this to be connected to the Shruthi-1?
    according to the general guide I connect the programmer to the digital control board. But this page and your instructions state that I have to connect the digital board to the progammer and then the programmer to the filter. this makes sense, but am I missing something or do I need one more cable here? Or how am I supposed to wire it.
    Question nr.2 I can’t find any info about wiring the rotary switches, where am I supposed to attach these, I don’t even know what they are supposed to be used for? Selecting the filter modes?
    thanks a lot for your help!

  • This is what you need to know:

    Wiring it up

  • ehm… thanks but I have the 4-Pole Mission filter…
    I understood the rotary switch though… pretty useless for the 4-PM since they are to be used for the SRM-4

  • Just put in another SMR-4 ;-)
    Theres a looooong piece of Rainbow Cable in there, just take a bit of this to connect all the Boards. I recommend soldering everything directement a la Bord for maximum reliability….

  • I need advice with those basic connections too, so i don’t even get that banana level of understanding in the flickr directions… :P

    -How to connect smr-4 mkII bandpass 1 & 3 switch to the shruthi-1? (I found out how to add that LP2/4 switch, wohoo..!)
    -How to connect LED’s of those switches? Resistors was meant to be used with those LED´s?
    -What for is that male/male 2x8 connector in the bag?

    My XT packet was for SMR4mkII + Polivoks filter board.

  • I will get an SMR-4 sooner or later!
    but back to the programmer… no I don’t have a loooooong piece of rainbox cable, I have the one that goes to the filter board (the one with the header on the end) and I have the 4 cables that go to the pots. But not a big deal, I’ll make one, I have enough colored cables here. I only hope I don’t mess it up.
    Anyway, the control board gets connected to the same pins as the filter, right? Except for the yellow wire that goes directly to the shift register IC pin nr.9 but that’s only for the filter, the digital board gets connected as always right?

  • @rumpelfilter
    xactly – this way you clone the signal lines and use the “THRU” Data from the 595. Its like Polychaining Shurthis ;-)

    Less than Banana? What Fruit do you think of is your level? ;-)

    Does this make sense to you for the LEDs? :

    How to connect the Bandpass is rather at the end in the Filters Building Instructions.

    Male/Male connector? try pulling out one half, its a 1x10 female 1x10 male Connector to solder to a board or make a connection to a Rainbow cable….

  • @Fcd72 -yeah, that pic tells it clear enough. I somehow missed this in flickr… Had to google once again which leg is positive. :P How can so simple thing be so hard to remember? After that i realized that you told it in the picture, just used word ‘wire’ instead of leg.

    Still i can’t find “Filters Building Instructions”, just Filter Combinations @

  • @fcd72 thanks a lot! :)

  • @dr3tri

    You won’t find instructions on the Filter only Pages because i didn’t design it ;-)
    Look here , its at the end of the Page.

  • @Fcd72

    Oh, that explains. Thanks for the tip. :D
    I got it done. Switches and LED’s are now working.

    I built rest of it tonight as well.. i cut one MIDI cable to two pieces and connected those to connectors in XT’s case. I did the same for power and audio In/Out cables too. I guess others did it the same way as well? It makes easier to remove Shruthi-1 later if any needs arises.
    One would be when i get Polivoks filter done. I noticed that it should to be connected to digital board and SMR4 filter needs to be moved aside to 2nd filter.

    Question about connecting two filters in the case; should they both be powered on all the time? Or do i need/want to add power switch for 2nd filter?
    (There was two power switches in the packet. One which keeps its position and another which doesn’t. I don’t quite get the purpose of the later one..).

    Has anyone built XT with SMR4+Polivoks already? How they sound together if putting filters to different channels in mixer and listening those at the same time? Do Polivoks filter sound so different that it won’t work well, whether audio modulation of the filter is used or not?

  • The one Switch that doesn’t hold ON is mistakenly in there….. normally i ship mistakenly some parts to less.

    Please power both boards at the same time, or it might draw current via the other Lines – no good idea.

    The Polivoks sounds quite different, thats part of the whole fun ;-)

  • You need to power both boards, the filter boards need negative voltages to work.

    Using plugs in sockets is fine, but they may come out. You could put a dab of removable glue (glue gun) to keep them in their sockets. But the MIDI sockets are pretty tight anyway.

  • I just got a set of pot knobs from musikding. I’ve bought a couple of these to test them on the programmer:

    @fcd72 they both work fine, and I don’t have to dremel anything. The frontplate is so thick that the pot shaft does stick out just enough for the nut to fit on it so there is not so much shaft to cover.

    I really like the effect of the white ones, though they are a bit small… Not much smaller than the standard ones that come with the kit tough, these just seem larger because they have that larger base, but the actual knob you twist is more or less the same.

    as an alternative I’m considering these as well:

    Anyway, if you’re thinking about adding your own knobs to the programmer, be assured, they all fit! Or does anyone have a different experience in this regards

  • @dr3tri

    I've got the smr4 mkII polivoks combo.
    They sound very different and really nice together.
    Like the low end of the smr4 with the sharp distorted mid high
    of the polivoks when played together.
  • I suppose you could put them in series too. Put the SMR sound through the Polivoks or the reverse.

  • Btw. has anybody already used the programmer with the 4-Pole Mission filter?

  • I looked at the filter board schematic. With so many modes for the filter it isn’t so easy to create a switch matrix for.

  • yeah but I think it’s probably enough if you can control cutoff and resonance, which is what should be working “out of the box”

  • The kit isn’t advertised as being compatible with 4PM though. It says “untested”.

  • that’s why I’m asking. But I guess I’m the tester… so I should be the one to answer this question :D

  • Its untested but personally i would take a place in a SpaceShip designed by Oliver – untested or not. So don’t fear rumpelfilter, it will work; a blinkenlight 595 i attached for testing purpose worked.

  • @dr3tri

    I really like your approach and I have also been thinking that there must be some way of creating a connection system that will allow for a less-permanently wired XT system. Thank you for posting this… It has really got me puzzling over the wiring scheme…

  • >I really like your approach and I have also been thinking that there must be some way of creating a connection system that will allow for a less-permanently wired XT system.

    Just do everything over MIDI. Obviously there’s a limit to what the MIDI implementation currently supports.

  • I’ve tested two sets knobs on the frontplate:

    so far I like the small white ones better.
    The bakelite knobs are really beautiful, but the screws don’t go in far enought to fit on a d-shaft (did I ever mention that I totally hate d-shafts?) so I would have to find some workaround for that, and I don’t think I really want to…

  • White knobs are nice!

    @6851punk – I’m thinking also about the ribbon cables soldered directly to the Shruthi boards. I’d like to finesse that somehow with connectors. So the Shruthi and all the filter boards remain just as they were and can be swapped in/out at will. Only cables need to be disconnected/reconnected.

  • One of those stackable connectors will do. They have long pins. Slide through the board from the top, solder underneath and then on top you can slide in a right angle pin connector.

  • I have soldered a Rainbow cable to the upper side of the Digital Board and uses a piece of the Male Connectors to plug in to the 2nd Filter….

  • I see Frank connect the brown wire of the rainbow cable on the Max Clockwise of the pot and the blue to the Min. Clockwise of the pot.
    We must respect that ?

    And : For the other colour of the rainbow cable.
    How the board recognize what effect is change ? (excuse my perfect english)
    It should be set that after ?
  • Every parameter has an fixed position on one of the four 4051 IC's !
    It's writen that way in the firmware.
  • you can wire it the other way but then Max at the pot would be minimum Value on the Shruthi ;-)

    Look here for correct wiring:

    Best you measure if Brown or Black is +5V, depends if you soldered the Connectors right. Better measure once than desoldering 32 connections to the Pots…

  • 4051 Port1
    Pin1 Osc2 shape
    Pin2 Osc2 range
    Pin4 Osc2 detune
    Pin5 Osc2 parameter
    Pin12 Sub osc shape
    Pin13 Osc1 shape
    Pin14 Osc1 parameter
    Pin15 Osc1 range

    4051 Port2
    Pin1 Filter cutoff
    Pin2 Filter env1
    Pin4 Filter lfo2
    Pin5 Filter resonance
    Pin12 Noise volume
    Pin13 Mix operator
    Pin14 Mix balance
    Pin15 Sub volume

    4051 Port3
    Pin1 Env2 attack
    Pin2 Env2 sustain
    Pin4 Env2 release
    Pin5 Env2 decay
    Pin12 Env1 release
    Pin13 Env1 attack
    Pin14 Env1 decay
    Pin15 Env1 sustain

    4051 Port4
    Pin1 Lfo2 shape
    Pin2 Lfo2 attack
    Pin4 Lfo2 Sync
    Pin5 Lfo2 rate
    Pin12 Lfo1 sync
    Pin13 Lfo1 shape
    Pin14 Lfo1 rate
    Pin15 Lfo1 attack
  • Sorry, it's at step 8 on Frank 's flickr page !!!
    I do not look far enough

    Thx ;-)
  • This is what I have come up with to create a solderless XT. Will you guys check me on my thinking?

    To address the connections to the digital control board, I am thinking about replacing the male headers there with these:

    They are almost twice as long and should give me enough room to make a pluggable connection on both the top and bottom. Might need to bend them slightly to fit the top of the case, but I think there might be enough room to do that. What do you think?

    So basically, all of the headers in the control board get replaced with these so they are all available in two places, top and bottom. One will go into the female socket header of the second filter board too.

    Take these 12-inch female to female jumpers to make the connections to the XT board and the second filter board. Sparkfun sells 5, 6, 2 pin versions and 1 pin versons that come in a pack of 10. Between them I should be able to make removable connections.

    Then, cut a midi cable into two pieces and wire to the midi ports, wire up 4 audio jumper cables with 1/4” jacks on one end, soldered to the neutrix jacks on the other end. Same thing with the PSU. Create two barrel to wire jumper cables to connect to both filterboards without soldering.

    PSU connectors with 2-foot pigtails

    What do you think?

    Now I have to think about the filter specific connections to the switches… Should be doable with these jumpers.

  • @ Fcd72
    -Ok. Danke schön. :) I still wonder where one would need those type of switches that doesn’t hold On.. not in a music electronics i guess.. .

    @ rumpelfilter
    -Those white knobs are sweeeet. :)

    @ Titus Raindrops

    @ DMM
    -Cool tip, i have one micro mixer where i’m gonna connect all Shruthi-1’s, surely i try to listen both filters simultaneously in different situations.
    I expect interesting results when tweaking a sound from programmer and changing levels at the mixer at the same time. Have to record a track where is acid bassline which morphs from SMR4 to Polivoks while it goes.. .

    @ 6581
    -Connecting those in series is one of those have-to-experience things too!

    - – – —————- – – –

    I still have couple issues here, minor ones but i’d like to get those fixed some day.

    SMR4mk2 filters 2-pole does not give any sound unless BP1 or BP3 is activated too. If i move BP filter switch to center position, 2-pole filter get muted. When BP1/3 is on, i hear the difference between 4pole and 2pole, so it works correctly when i get audio from 2-pole. Should it work this way? I guess not.. :O

    ENV-1 decay does not go from 0 to 127. Smallest value is 4. I can live with it because i rarely use that small values anyway.. could it be caused by imperfect soldering?
    At first i got OSC-1 range behaving similarly but worse, it couldn’t go to negative values at all. I got that one fixed but i don’t remember anymore what caused it, short in the circuit or what.

    Anyone else having similar symptoms?

  • Smr4 2 pole thing is not ok....

    Env1 looks like faulty pot or ground isn't realy 0V.
  • Please swap the Wire from your faulty ENV-1 Pot with any other one and test if its ok then. Maybe its a faulty Pot?

    Have you connected the Pole switch right? The middle Pin from the Jumper goes to the middle(long) Pin on the Switch. Please Measure with a Multimeter if the Switch itself is OK. If you heat it up to ugh the internal Contacts may get burned.

    If these Parts are faulty id like to send you replacement before my holidays so deadline is Sunday ;-)

  • You will get faulty parts from time to time. I broke one of the switches trying to get the nuts off it, it just fell apart. Another switch works for one pole but the other pole doesn’t make contact in one position. If you push is back a small amount the LED comes on, but I may have burned it as mentioned above.

    Luckily for me Maplins sell the exact same switch :)

  • Shit these Switches are from the Big R in Germany, obviously they are a bad Batch. 6581punk, drop me a line for replacement/refund please.

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