Ambika "Pioneers" board run [all seats reserved]
  • I plan to order the boards for the “pioneers” run tonight. There are 25 seats, 2 already taken.


    Individual outputs behavior

    One “too bad…” I got from two people is that plugging a cable into an individual out does not take the signal out of the mix like on some drum machines. I hadn’t thought about that one. My thinking was that the serious guys would be using only the individual outs anyway because it’s awesome to pan each polyphony voice independently, so the “mix out” was just there for my testing and fooling around. I am changing my mind about it. Either I do a production run of the “proven” design ; or I do a run of an alternative design with the 808 behavior. What’s your opinion about it?

    SVF voicecard DAC thing

    The SVF voicecard will have one new bit of circuitry to fix an occasional envelope / VCA clickiness the protos had. It’s an extra 470R resistor and a 1uF 5mm pitched cap (can be film or ceramic). You can short the resistor and not populate the cap to get the “original” behavior. I have never built the circuit but it’s just a passive RC filter dammit!

    LCD footprint

    I have made the cutout for the LCD as large as the PCB layout allows, which seems to make it OK for the Optrex part. I cannot guarantee anything – a 1:1 print of the Optrex drawing seems to fit in a 1:1 print of my board. If you want to verify, grab the brd files.

    Please send me a private message indicating your email address and the mix of voicecards you are interested in. If you are put off by the idea of beta-testing these new bits, let me know and I will postpone the whole cycle by 3 weeks. Note that it is not uncommon for me to directly do a production run of boards with this kind of modifications without checking them with a proto (4PM v0.2, digital board v0.7, SVF v0.2 were directly ordered in volume).

  • If the Polivoks filter was an option we could be called “Young Pioneers”! :) PM’d!

  • I’d appreciate feedback on this new variant of the output stage.

    Each individual out is straight form the voicecard with a (bigger) protection resistor in case some voicecards in the future have some funky output stages. The unconnected individual outputs are routed to an inverting mixer (right side of the op-amp) and a gain of -1 to recover the same phase as the individual outputs.

  • “ Either I do a production run of the “proven” design ; or I do a run of an alternative design with the 808 behavior. What’s your opinion about it?” I thought about this and it would be nice to have voices removed from the mix out when they are routed through their independent out. It would be nice to be able to use the mix out for poly stuff and each independent out for mono stuff simultaneously. Doubt I would ever do this, but I do know a lot of people like to use the Tetra like this.

  • Looks like it should work OK-just that if you are keeping the master volume pot at 100K then the 10K input to the final opamp stage will load it a lot-either change the resistor pair across the last opamp to 100K each or reduce the value of the master vol pot, or maybe both…

    What QP said-it would give people a lot of incentive to have hybrid Ambikas ie one channel SVF for drones and 5 channels of 4P for melodic stuff, and only need 2 lines to the mixer.

    Edit: you could probably put the output resistors up to 1K without much hassle-that’s standard in modulars, and better safety margin for accidents…

  • +1 for 808-like individual output behaviour.

  • To be honest i think the ambika deserves a stereo output on a stereo jack. Three voices panned left and three voices panned right. That way you could use 2 mono channels on a mixer and use the pans to set the width of the stereo field. I imagine using the ambika in a live setup with a
    small mixer. Having to use 6 channels takes up a lot of mixer space.
    This together with 808 output behaviour.
    Just don’t wait for me as i’ll probably wait fot the kit version.

  • Taking individually connected Voicecards from the Main Mix seems to be the common behavior. As not everybody has the luxury of a big console (and maybe even wants to take the Ambika on Stage) it looks like a good idea to implement industry standard 808 behavior.
    Maybe theres the additional possibility to implement in Jumpers to solder for options with the 808 behavior as standard? (Its common for big Consoles to have Routing Options by internally wired jumpers)

  • Better to get it perfect, then there’s nothing a reviewer can complain about?

  • i agree with shiftr that a stereo mix output would be immensely cooler than mono – but i imagine that individual panning for 6 voice cards might make things rather complicated.

  • yes, that’s why i proposed the crude stereo option of 3 left 3 right. This should relatively easy to implement.

  • ah, sorry, i hadn’t got that bit.

    but then i disagree: hardwiring 3 cards to one, and 3 to another mixed output doesn’t seem to make all that much sense to me. after all, what’s so cool about the ambica is its flexibility in allocating the voice cards: sometimes you may use 4poly + mono + mono, somtimes 2 poly + 2poly + 2poly etc.

    so in my view, for the mix output it’s either real stereo with freely adjustable panning per voice (extremely cool, but probably rather complicated to implement), or just plain mono (which i find perfectly acceptable – im used to it from my multitrak).

  • How do I apply to be a pioneer? If this is it, I’ll be down to order the boards. I’ve already got the BOMs ready to be ordered.

  • @n8bit You need to PM pichenettes with your email address, letting him know you want to be a pioneer.

  • hmmm… maybe it would make things a bit weird. i still feel there must be a clever way of achieving a stereo out.
    Would it be possible using just 6 switching jacks to have this behavior :
    jack in output 1= 6 voice mono
    jack in output 1+2 = 2x 3voice mono
    jack in output 1+2+6 = 3 voice 2voice 1voice
    but this will probably make it even weirder…

  • 808 behavior looks very versatile!
    (i think passive mixer mod can be easily implemented with pots istead of 220R resistors)

  • Needs to be a simple solution, otherwise you may as well just get a little 8 channel mixer.

  • 808 behavior is nice, plus a lot of people are used to it.

  • @pichenettes I sent you a message, but I’m now thinking I’d rather wait for another version with ’808-style’ output behaviour. I think that would be more useful.
    Depends what the lead-time on that would be.


  • Wait, schmait. I sent a PM anyway. Can’t wait! 808 behavior or not.

  • One more vote for 808 behavior. Preferrably with stereo main output.

  • Hmm, reminds me, the 9090 output stage has all the individual voices somewhat panned due to funky resistor use when being routed to the stereo main out. That could be something that would somewhat placate the stereo crowd.

  • Yes, that would be cool!!

  • @placate the stereo crowd@

    hehe, i like the sound of that! :)
    if olivier finds a good stereo solution, he could henceforth use this slogan:

    @mutable instruments – placating the stereo crowd since 2012@

    i already see schrab’s logo to go with it: a platypus with two large elephant/ganesha ears. :)

    ([edit:] i’m only kidding, of course. mono mix out is perfectly fine with me. but it’s 808 single outs ftw!)

  • Linky
    Or, maybe that’s just me. Either the output jack is a dual mono, or you’d do it all in a stereo jack and retain mono compatibility by just plugging in a mono lead. Ish.

  • Firtst i think about holes for 6 optional pots.

    But i’m just understand that it’s impossible to solder pots after soldering jacks =)
    So it’s not an optional solution. And you’ll need additional holes in case.

  • +1 for 808 behaviour

  • I’ll do the “808 revision”, so if this prevented you from participating, please reconsider.

    @Gwaidan. Thanks for the tip. Regarding the protection, I remember reading 220 for TL072 at 15V on the SDIY list. I will use 470. Set last stage to 100k too – forgot that the volume pot was a 100kA instead of the 10kB I had earlier.

    To all: no stereo will happen here. It makes a lot of sense with a uniformly loaded machine, but it would sound broken for the guys mixing and matching voicecards or for those having bought an odd number of them. The next problem is how to load a 3 voicecard machines so that they don’t end up panned all to the same side. Some people will prefer filling the cards in port 1, then port 2, then port 3… Some others in port 1, port 3, port 5 ; maybe to have a thinner 3 voices machine. Also, I am a serious guy and to me “stereo” jacks are for balanced outputs (or inserts). And there’s no room for a pair of mono jacks. Note that I made the stereo and “stereo jacks” mistake in the previous revision, so I have a feeling for the kind of weirdness to expect :)

    I would appreciate to have a second pair of eyes on the revised output design. I will meditate over it today, I am confident about it :)

  • The 9090 has a panning scheme “hardwired” due to different resistors on the L&R mixing amp.

  • Dual mono would also be nice, It would be cool to be able to just plug it into a DJ mixer or a home stereo without the need for an additional line mixer.

  • Pairs of eyes connected to a brain that has slept more than 3 hours last night appreciated!

    I am sorry to make you work on this rather than take full responsibility and do another 3 weeks cycle, but this is a (small) price to pay to get early access to the beast!

  • Even when my eyes are connected to my brain, I still couldn’t tell if the new output design was good to go or no. Much as I’d love to be a pioneer and having just shelled out for roof repairs costing >£1400, I’m going to have to wait until the final kits/boards/whatever come October/whenever :’( FWIW I think 808 style jack functionality is a winner. :Humph: at least come the rainy months I’ll be able to play without getting wet!

  • Stereo out = 2 VCAs for each voice. I vote for mono…..

  • Here is an audio file with some filter comparisons

    • SMR4
    • SVF LP
    • SVF BP
    • SVF HP
    • 4P

    Note that SMR4 has a slightly higher cutoff than the other ones, so don’t be fooled by that. As you see, the SVF gets louder when resonance is increased (the two 4-poles have approximately equal loudness). The SMR4 has an extra coloration due to the use of OTA (and probably a bit of distortion from the Darlington buffers). You can hear clicks on the SVF when resonance gets high and cutoff down (= purest sinewave, no high frequency component to mask the click), this will be fixed in the production run.

  • Thèse don’t come with programmed chips, right?

  • Looks good to me. But, I haven’t slept more than 3 hours… The protection looks good, as do the TL072 pinning.

  • I can burn chips on demand for this run.

  • The output section looks solid. The audio clips are good-seems the SMR4 is the one to beat.

  • Is this for mobo + specific voicecard or can we choose a voicecard? I have the suspicion i missed some information on another thread or something. If so, can someone give me a hint?

  • it’s all in post one of this thread

  • Would it be possible to bundle the nice negative yellowy-green LCD with pioneer boards? I’d rather not get an ugly one and have to desolder it :(

  • Mobo + your choice of voicecard(s).

  • No LCD in this run.

  • From the last picture you sent, i think the behaviour is perfect. The protection of 470 ohms seems to be enough, and the output is sent to the global mixer only if the output is not connected : that’s ideal in my opinon.

    I can’t see a mistake, unless the jacks are connected the wrong way. I assume your eagle footprint is correct….

    And you save a lot of parts, this way.

    Only cons :

    • are the traces thick enough, and spread enough so there’s no bleeding from one output to the other?
    • those jacks are not always reliable, but a good contact spray should do the job if there was a problem. That’s not your deal anyway.

  • @pichenettes Still a bit confused here… will the first ‘pioneer’ run of boards have the proposed ’808 output’ or not? Or, are the ‘pioneer’ boards you’re selling to the existing spec (plugging in individual out doesn’t remove part from mixed out)? I’d prefer the former, but if there would be a significant wait for that, then I’ll go for the existing spec mainboard. I do think the ’808 spec’ is the way to go, in the long run though, for maximum flexibility.


  • The pioneer run will have the “808 outputs” – that’s why I’m asking for pairs of eyes to review it, as this is a new feature that was not there in the previous board I had made.

    @MicMicMan: will try to space the traces a bit, though the previous versions were similarly spaced and I did not run into coupling problems.

  • [edit: nevermind]

  • I was just thinking about this 808-fashion output mixer : would this cause a problem if there’s no voicecard connected?
    As I understand it, the mixer inverter would be connected to a 10k resistor, then a wire, then a 220 resistor, then a wire again with nothing at its end.
    I’m a guitar player/diyer, so I’m maybe obsessed with microphony, but I’m just trying to find out if this would cause any problem.
    Anyway, connecting it to the ground would solve the issue (if any), but should we consider that this could cause microphony issues?

  • I don’t think this would cause any problem, and at the very worst, you can ground the line with a breadboard jumper wire inserted in the voicecard slot.

  • More room, good ju-ju.
    I like the added touch of the re-routing of J3.

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