Wednesday, September 13, 2017

Novation Bass Station Schematic

It seems that no one has a schematic of the original Bass Station, so I drew one up. This is from the keyboard version with board markings "Novation Bass Station SM, Issue 4, 1995".

DCO

At the beginning of the signal chain is the DCO. There are two identical DCOs, so we'll just look at one I've dubbed "OSCA".

DCO

At the top is an exponential current source that charges capacitor C10/2. It's built around a transistor pair marked "FMA1". Based on that marking I believe this is the correct datasheet.

At the bottom left is the sync pulse generator. When a pulse or square wave is fed into the "OSCA_SYNC" net a short pulse is output at pin 4 on U20B. The width of this pulse is determined by the RC network formed by R29 and C9. Together they cause a small delay between pins 5 and 6 changing logical state. While these inputs are unequal the output will be high.

This sync pulse enables transistor Q2 to sink the charge stored in C10/2 thereby "resetting" it to VSS. The capacitor is then able to charge back up via the exponential current source. This cycle results in a sawtooth wave that is present on pin 5 of U18B.

U18B serves as a buffer for the sawtooth, but can also be switched to generate a squarewave. Nets OSCA_WF_SW and OSCA can be connected or disconnected via multiplexer U12. If connected the opamp is configured as a noninverting amplifier outputting the sawtooth. If unconnected the opamp is configured as a comparator, comparing the pulse width CV, OSCA_PWM_CV, on pin 6 and the sawtooth on pin 5. This results in a PWM squarewave as pictured below.


Multiplexer
PWM CV

Mixer

Next in the chain is the mixer. The mixer is made of two simple VCAs, one for each oscillator. Each VCA works off of a single linear CV. The mixers serves only to change the relative volume of the oscillators, not to apply the volume envelope.
Oscillator Mixer

VCF

After the mixer is the filter. It's closely related to the OSCar filter that is, in turn, based off of the Wasp filter. It should be noted that the inverting stage present in the OSCar has been removed from the Bass Station. This stage allowed the filter to be switched into a high-pass mode. Without it, the Bass Station is stuck in lowpass mode.

Bass Station VCF
OSCar VCF
I find it interesting that the resonance is under CV control, but cannot be modulated. It does respond to MIDI though.

VCA

Last in the chain is the main VCA. It's another simple, one-OTA VCA. Unlike the mixer VCAs it includes an exponential current source and responds to modulation from one of the envelopes. It also has a trimmer to adjust the offset voltage.
VCA

CV Header

The final thing of note is an unlabeled header. It breaks out most of the internal CV and audio outputs. Almost all of them tap directly after a buffer and, with the addition of a 1K resistor, are safe to connect to other devices.

Unfortunately none of them are really suited to take a signal as input. Nearly every signal would have to be disconnected from its destination and fed through a summing-amp instead. With this summing-amp an external CV signal could then be mixed in with the existing CV.
CV Header

Full Schematic

Here is the majority of the analog section of the Bass Station. I've omitted the dull CV multiplexer and buffers.



Bass Station Schematic




67 comments:

  1. Great job !
    Thank you.
    I am looking for insert a new VCF SSM2044 based.

    ReplyDelete
  2. Hello,
    great job!
    I have a problem with my old bass station keyboard,
    the envelope amp don't work,
    you know the schematic of this part??

    ReplyDelete
    Replies
    1. Hi,
      Thank you!
      I'm not totally sure what you mean by envelope amp. The envelopes are digital and get generated inside the CPU. I don't think you will find a replacement for that.
      The VCA, at the end of the signal chain, is made from a LM3080 and a TLC274. Either one can be found easily.

      Delete
    2. Thank you for you response!
      No work the envelope (ADSR) for the amp, but work perfectly the ADSR of the filter.

      I thought the envelope was analog.

      I replaced u36 (lm3080) and U24 (TLC274) but no work.
      I only get sound, if I bridge the CV Header pins 12 and 14 (VCA CV and B_VOL_CV) but it does not work ADSR of amp, yes adsr of filter.

      If I remove the bridge there is no sound.
      Do you have any clues to follow?
      Thank you very much for your help!

      Regards,
      Jof

      Delete
    3. Jof,

      I understand you now.

      The problem may be in the exponential converter/current source made from U24 and Q4.
      VCA_CV is after it, so applying a voltage there bypasses it.

      I would also test VCA_CV_LIN. This is the envelope that comes from the CPU. If you don't see a voltage here, the CPU might be damaged.

      Let me know what you find!

      - Zack

      Delete
    4. Hello Zack,
      I made some measurements on pin 20 VCA_CV_LIN

      4.95 v DC (note off)
      4.87 v DC (note on)

      0.055 v AC (note off)
      0.135 v AC (note off)

      Do you think these values are normal or do you think the CPU is damaged?

      Thanks and Regards,
      Jof

      Delete
    5. Hi Jof,

      That does not sound normal. I would expect a much larger swing in votage. I'll test my Bass Station once I get a chance.

      The CPU is still suspect.

      Delete
    6. Hi Zack,

      Thanks for helping me!

      I have also made measurements in pin 12 (VCA_CV)

      0.490v DC note off
      0.500v DC note on

      0.011v AC note off
      0.008v AC note on

      I need to check transistor Q4
      (to see if I find an old transistor tester, which I have somewhere)

      Regards,
      Jof

      Delete
    7. No problem, Jof.

      VCA_CV_LIN should span 0.1-5.1V relative to VSS. The response is inverted, .8v at full volume.
      VCA_CV should span .3-3V relative to VSS. Response is normal.

      I did some more poking around and found that U16(LM324) is a unity buffer for the CPU signal. It goes through some passives and then into another unity buffer, U12(TLC274). The signals at both of those buffers should be very close to VCA_CV_LIN.

      Let me know what you find at those points!

      Delete
    8. Hi Zack,
      I have made some measurements

      Transistor Q4 works correctly (checked with transistor tester).

      U16 (st324):
      pin 1 (out 1) 3 VDC note on
      pin 1 (out 1) 2.6 VDC note off

      pin 7 (out 2) 5 VDC note on
      pin 7 (out 2) 4.96 VDC note off

      pin 8 (out 3) 0 VDC? note on
      pin 8 (out 3) 0.03 VDC? note off

      pin 14 (out 4) 3 VDC note on
      pin 14 (out 4) 2.6 VDC note off

      4 VDC pin 5.8 VDC


      U12 (TLC274):
      pin 1 (out 1) 3.5 VDC note on
      pin 1 (out 1) 3.5 VDC note off

      pin 7 (out 2) 4.5 VDC note on
      pin 7 (out 2) 2.8 VDC note off

      pin 8 (out 3) 3.7 VDC note on
      pin 8 (out 3) 3.7 VDC note off

      pin 14 (out 4) 4.7 VDC note on
      pin 14 (out 4) 4.5 VDC note off

      4 VDC pin 5.7 VDC

      Do you seem normal?

      Thanks and Regards,
      Jof

      Delete
    9. Jof,

      You should be seeing approx .1 and 5.1V at pins 5,6,7 of U16 and pins 12,13,14 of U12.
      Pin 5 of U16 connects directly to the CPU, so if you aren't seeing the correct value there, the issue is in the CPU.

      Things like the sustain level, and velocity can affect this voltage. Maybe try experimenting with them.
      See if it responds to MIDI velocity differently than the keybed.

      - Zack

      Delete
    10. Hi Zack,
      I have some voltage variation on pin 5 of u16,
      but I do not know if it's enough.

      These are the measures:

      U16
      pin 5 - 4.8 vdc (note off) - 2.2 vdc (note on)
      pin 6 - 4.9 vdc (note off) - 4.9 vdc (note on)
      pin 7 - 5 vdc (note off) - 4.9 vdc (note on)

      U12
      pin 12 - 4.92 vdc (note off) - 4.88 vdc (note on)
      pin 13 - 4.75 vdc (note off) - 4.56 vdc (note on)
      pin 14 - 4.75 vdc (note off) - 4.56 vdc (note on)

      I have tried with an external keyboard with different velocitys, there is little difference.

      Regards,
      Jof

      Delete
  3. Hi Zack,
    thanks for your help!

    I have tried to make a bridge in pin 20 VCA_CV_LIN to pin 14 B_VOL_CV and I have sound but without ADSR amp.

    I will test the double transistor Q4, since I replaced U24 and it did not make a difference.

    Regards,
    Jof

    ReplyDelete
  4. Hi Zac.... I have a bassstation keyboard with a non functioning modwheel.. I replaced the pot and resoldered the connections from the pot to the pcb.. I also checked the mod switch pitch/off/filter for continuity and seems to check out ok.. The pitch bend wheel works fine.. Not sure where that leaves me... I can see that the mod wheel seems to feed into a quad opamp, but cant trace the pitch wheel.. I would have assumed they were also feeding into the same quad amp, as the leads all terminate around this IC... But im thinking if the pitch wheel works then so should the mod wheel if it is operating on the same quad opamp.... I dunno ,Ive reached a dead end now!!

    You wouldn't by any chance have a schematic of the pitch and mod section laying around ?

    Cheers

    Paddy

    ReplyDelete
    Replies
    1. Hi Paddy,

      I did partially draw the CV routing. There's almost nothing to the pitch and mod wheels though. They both go into U5(?) that quad opamp, then straight out into the CPU. I believe it has two ADC channels.

      See if you get the pitch/mod signals boosted on pins 1 & 7. If not, I'd replace the opamp. Otherwise, it's the CPU and you're out of luck.

      Delete
  5. Thanks for the quick reply Mate... Much appreciated ;]
    Ok ill have a look again at the quad opamp..and check the outs..
    ill let you know the results !!

    Thanks again

    Paddy

    ReplyDelete
  6. No joy Im afraid..the Opamp seems fine ;[
    Funny how the pitch bender works ok though !!

    Cheers

    Paddy

    ReplyDelete
    Replies
    1. That's a disappointment. Any chance the bend range is turned to 0 semitones? I forget how, but there's a way to change it.

      Delete
  7. Not totally sure about that one... I have since given the synth back to a friend.. he actually owned it..
    I suppose a factory reset couldn't hurt... Like you were saying, its such a simple circuit that its odd for it to just not work.. I would have thought that if the Cpu was damaged then so would the pitch bender..
    I would imagine the routing for the mod pitch and bender pitch head to the same destination.. Then again because ive not been able to use the mod section.. Is the pitch mod destination possibly just lfo to pitch ammount ? That would make it a slightly different routing I would think..

    ReplyDelete
    Replies
    1. They go to different pins on the CPU, but they're probably inputs to the same internal ADC. Hard to say what could go wrong inside the CPU.

      I think the mod wheel controls the LFO > Pitch amount, but it's done digitally.

      Delete
  8. hi Zack.
    first of all, GREAT JOB!
    I got an answer about a bass station rack I recently bought. the module works well , sometimes some note stay ON... but it has the original Power supply and I read that there are problems about it (though I tested it and I've found a fierce 9.02 V). Anyway, the problem is another one. I noticed there's a little background noise that seems a modulation-lfo , hangin somewhere. I opened the rack and I saw only one trimmer. I read that it adjust VCA offset voltage. near there are some Test points. do you know the refereces values (P-P Voltage)? thx a lot. Marco

    ReplyDelete
    Replies
    1. Sorry, I don't have any documentation or calibration info. Would love to find a service manual!

      Delete
    2. THX anyway Zack. Another question. I tried another power supply but... nothing changes. after playing some sequence , one random note remains ON and stay on until i change preset. I've already read about this problem. MIDI optoisolator problem? Suggestions?

      Delete
    3. Are you playing it over MIDI? An optoisolator issue would explain that.

      Delete
    4. hi Zack. sorry... just a suggestion. I'm not an electronic but I've done some easy fix in the past. the question is... In your opinion what is the chip I have to replace? I think that the chip is the 6N138 (and I hope that's the right one, it's the only one easy to remove...). thx again !

      Delete
    5. Yes, 6N138 would be an optoisolator. If you have access to an oscilloscope, you can view the output to see if it's working.
      If not, just be careful desoldering the chip. Since it's a very cheap/common chip, you can cut the legs from the body to make it easier.

      Delete
  9. Hi Zack and Unknown,

    Zach, thank you very much for reverse engineering!

    Unknown, are you probably talking about a problem in the Super Bass Station?

    Best regards,
    Andrew

    ReplyDelete
  10. Hi Zack,
    Novation BassStation schematic is available from NOVATION support under NDA.

    ReplyDelete
    Replies
    1. Thanks for the tip. I can confirm this. If anyone needs the schematics in the future just email novation tech support and they will release it if you sign an NDA.

      Delete
  11. Could you by chance tell me the value of R5 on the board? Mine appears to have popped off

    ReplyDelete
  12. @astribble: On the scheme (BassStation V1), R5 (27K) and R6 (68K) are the gain divider bridge of U5(A) that controls Pitch Wheel input signal throw JP4 (3.5mm Ext. Cont. jack).

    ReplyDelete
  13. This comment has been removed by the author.

    ReplyDelete
  14. Hello Zack,
    First of all, thank you for working with this synthesizer!
    Please help me. Please tell me what the U5 part is. My Bass Station Keyboard does not use all the memory. I can save only 1, 3, 5, 7 memory slots. I bought it used. I see someone fixed it. He soldered a transistor to U5. Sign maybe 1381 3.8 S.
    Sorry for the bad English!
    Thank you!
    Best regards!
    Daniel

    ReplyDelete
    Replies
    1. I don't have the keyboard any more, and I never drew the full schematic.
      If my parts designation is correct, U5 is a TLC274 opamp that buffers the CV from the pitch and mod wheels. It wouldn't be related to the memory slots.

      Delete
    2. Thanks for the quick response!
      Ok. I will continue to look for a solution.

      Delete
  15. Hi Zack. I am working on a Bass Sation with a faulty Oscillator2 I suspect Q6 (FMA1) is faulty as the signal out on pin1 is half wave. If you agree, any idea where I can get this part? I eagerly await your reply! Thank you for your time, Graham

    ReplyDelete
    Replies
    1. Hi Graham. You should be able to learn more by swapping that transistor pair with the one from Oscillator 1. If the issues transfer with the suspect transistor, that's your culprit.
      FMA1s are still available at Mouser for less than $0.50.

      Delete
    2. Thanks for your prompt reply. I was concerned about swapping as smt's are so fiddly! Mouser was probably the one place I didn't look! Will let you know if it was the FMA1.......

      Delete
    3. I recommend a cheap hot air rework station. It makes it very easy to work with SMD. Just be mindful of what you're heating up.

      Delete
    4. I was wondering if à damage cpu vould be "arranged" somehow ,with hot air . I am suspecting that there have been a corrosion damage, even if I see no water damage really .the bass station was in a basement ,not very dry...

      Delete
  16. hi,

    do you know how the memory patches are saved on bassstation kb? does it use a battery or something else? thanks in advance.

    ReplyDelete
    Replies
    1. There's no battery or external memory chips. As far as I remember anyway. I believe they're all stored within the microcontroller. It probably has a small amount of EEPROM onboard.

      Delete
  17. Hello,

    at that point a grand THANK YOU . AT least I will be able to check VCC routing my Bassstation (old model) does not light up, only ask for 0.02A when powered, I am not electronician, but I have equipment to test signals abd values (and some chipsets) so I will try to find something that is out . I will try RESET first (I have a manual, but if someone can give me the key sequence fopr reset I will appreciate it)

    Thank you again. Isaac

    ReplyDelete
  18. Btw I did not see any "test point" . Only the connectors can be tested ?
    I did follow the ground somehow, the switches does not look as if their body is grounded. Are there well visible VCC and ground "rails " ? I am amazed on your reverse engineering work . There is no circuitry in the middle of the CI, all is "semi apparent" you had to get rid of thé projective chat to makr the sketch ? Just curious .. best regards .

    ReplyDelete
    Replies
    1. Hi Olek,

      There are no test points. Yes, the header is likely the easiest thing to attach a probe to.

      The power rails are the thicker traces that run longways under/beside the ICs.

      Thank you! I didn't modify the board in any way to make the schematic. I took photos of what was visible, and measurements of what wasn't.

      Good luck with your troubleshooting.

      Delete
  19. Protective coat, sorry, french orthographe corrector ..

    ReplyDelete
  20. hello, I gladly received a complete 10 pages electronic sketch. It shows 65 Test points . The after sale guy from focusrite/novation, is really helpful.

    I will let you know if anything of interest

    Regards

    ReplyDelete
  21. Hello guys ! Now I wanted to apologize, as the sketch I received was showing a BassStation II , rack model, much more complex than my 1995 model. I asked if by chance they have the original sketch, but now anyone seem to be on holidays
    In the mean time I have "repaired" my instrument
    First I used a lot of flux and refreshed all the soldering
    THen I did put a good quantity of the specific ammoniaqued product (for jewels, brass, electronics) in my classical Ultra Sonic Tank (not an expensive model for electronics with sweeping frequencies) , and in warm water 46° I made numeous baths, until I saw an ameliorations on pins of the jeyboard ribbon, that where oxidized. about 1 hour with 8 minuts baths, changing the orientation of the circuit board - my tank is only 6 liters when totally full so about half of the circuit is covered with the water.

    THen I rinced with hot tap water, waited a few minutes in an hot air flow , dry whatever i could with paper towel, then sprayed isopropyl alcohol 99.99% everywhere to get rid of the water, , again hot air flow (hot gun) . THen I sprayed generously in all potentiometers and switches with WD40 "specialist" contact cleaner (wich is also used to get rid of the flux after soldering )

    I was lucky enough to restore many false contacts that way. I did check with the binocular how the CPU was soldered, and did make new solder all around. NOw the keyboard seem to work with minimal false contacts. I am about to dismount it , but wait to undertand if I can clean the supple contacts without creating trouble (eventually I will use the US bath too)

    Best regards to all. I am really not an electronician, but I have some equipment and I could see that some tensions where present on all composants , that I could see waves out of the CPU and some CI too, and that the midi was playing on a DAW, so it was not a desesperate situation. (also noticed that I had a false contact , as when bowing a little the CI I had the Leds starting - probably many of the switches where corroded, and did work once in a while.

    I think that the first thing to be done on old circuitry like those is to refresh all solder points, with enough flux and a good cleaning. A friend that helped me with basics at some point did the same when an old electronic equipment did not function. Often doing the soldering again is a source of amelioration.

    A happy new year to all

    ReplyDelete
  22. Hi Olek,
    I have been struggling with my bass station keyboard for a long time to make it work and sound correctly, but I have not succeeded yet ... could you send me an email with the notes, electronic sketch, you have, even if they are from BSII? Glad your BS is coming back to life Thank you very much in advance and Happy New Year everyone.
    retrovision@telefonica.net

    ReplyDelete
  23. HelloJof, I will let you know if I receive thé good sketch for my BassStation. What id your model ? I did sign an agreement not to disclose thé sketch of the rock version I received but it is really straightforward to obtain from Novation not only the sketch but some help with testing ,( anyway I was proposed that, I can tell about you and yours so you will have thé contact ) Best regards . Send à pic of the label if possible. my mail isaacdotolegatgmail, etc

    ReplyDelete
    Replies
    1. Hi Olek, my model is the orinal BassStation Keyboard.

      Regards

      Delete
    2. OK , let's wait january for answers from Novation. my BassStation is serial 7820 - 2 octaves - 1995

      Regards

      Delete
  24. BTW I dismounted the keys little by little, and cleaned under the soft contact with isopropyl. The rubber contacts are on a few ribbons, but they are easily attacked by solvents (lighter fluid, contact sprauy) that seem to make the rubber softer and cause deformation easily.

    SO I suggest use a air can spry to clean between rubber and board, then srpay isopropyl alcohol and push it under the contacts with the sair spray.
    To dismount keys it is very easy, but one have to dismount white keys to have an easy dismounting (and back) of the sharps.

    Now all false contats are gone, the keys work fine, their dynamic seem to be consistent.
    I only had to push back in place a few rubbers (they hold on the board with small studs, that can be pushed back in place with some pressure applied with a tool.
    Cleaning of the keys was no luxury too ;)

    Regards

    ReplyDelete
  25. This comment has been removed by the author.

    ReplyDelete
  26. Hi there,
    i have had a bass station which has not worked properly for 15 years, i saw this thread and i thought i would ask if you know where i should be looking to fix the switches, none of the front panel switches work, however the soft rubber keys work and the knobs, just cant get the switches to do anything, any help on this would be awesome.
    regards

    chris

    ReplyDelete
  27. Hey Zack
    Firstly, I just wanted to say a big thanks for the work you've done here.
    I have a BassStation that is working, but it has this strange distortion in the square waves. The sync lines emanating from the CPU (U1 Pins 38 and 65) are jittery when looking at the output on the CRO. The unit works perfectly otherwise. I'm have a funny feeling that X1 (Im assuming this is a crystal clock for the CPU) is playing up. I was wondering, do you happen to know the value of X1? My next step is to contact Novation for a schematic but I was just hoping you may be able to quickly check this value on your schem?

    Kindest Regards
    Brett ;)

    ReplyDelete
    Replies
    1. Hi Brett,

      Unfortunately, I didn't draw the digital portion of the schematic, and I don't have the unit anymore.
      I would be surprised if the crystal died. Is MIDI still working? That would probably be the first to go if the crystal is on the fritz.

      Delete
    2. Thanks for the reply mate.
      Yes, everything (midi and all) is working perfectly, other than this strange noise. It almost sounds like the both OSCs are being modulated by Sample and hold. Ive swapped out all the non SMD caps, but no difference. But its happening on the sync output of the CPU itself. Not after the 4070d. so the OSC stage is working, its just being fed a bum sync signal. It also gets worse over time (temp rising, changing the Crystal freq? Long shot, I know, lol). I just thought, hey, X1 shouldn't be expensive, lets change it and see what happens. I have seen crystals go before, but I certainly agree that this is more bizarre. Not to worry, Ill give Novation a try and see if I can sign an NDA for the schematic.
      Thanks heaps mate, youre a legend!

      Delete
    3. Hi. Have you found the issue? My Bassstation is showing the same behaviour. Both square waves sound like the pulse width is slightly modulated with noise. Not a clean but jittery square. Sawtooth sounds fine however. Thank you very much

      Delete
  28. Hi,

    Do you by any chance remember the type of the rotary switch used for memory patch selection on bass station keyboard. I believe it is a plastic 8 position 1 pole rotary switch. But size or model i have no idea. For some reason i tend to have a habit of twisting it beyond the limit. Once I even thought it was stuck even though it was at the end position so of course i tried to turn it more and more until I realized the fact.

    ReplyDelete
  29. No the switch is not broken. But I am a bit anxious about the whole issue so would like to have a spare part.

    ReplyDelete
  30. Hello friend, I'm late for this post, do you know if NV released the service manual or similar for this synthesizer? Could you send me your full schematic in higher resolution. I have a fault in the filter and to start I would like to know the voltage of the lm317. Thanks mate

    ReplyDelete
    Replies
    1. I've reuploaded the last image in higher resolution. It contains everything I've drawn.

      Delete
    2. thanks mate .
      I appreciate very much . Great person .

      Delete
    3. Another silly question, do you remember what is the VDD of the 317 that feeds 3080 etc etc? I have 6.51v, do you remember the voltage? Regards

      Delete
    4. Sorry, I didn't measure that before selling the keyboard.

      Delete
  31. HI! I have a superbass station, It worked with a charm, but I did not used it for years. I turn it on and output volume is quite low, headphones is a bit better, but it cannot be really used. Tried with midi volume also, pot is ok. Anyway what do you suggest to investigate? capacitors or TLC274c (there are 7). I do have basic eletronic skills on smd sadly. Thanks

    ReplyDelete