From Brian Willoughby Sent Mon, Apr 22nd 2019, 01:50
From Brian Willoughby Sent Mon, Apr 22nd 2019, 01:50
Excellent. This all looks good. Seems like you have a good handle on = what you=E2=80=99re after. I take back what I said - it might be rather easy if you=E2=80=99re = willing to add a new circuit board. I think you=E2=80=99re on the right = track to leave the existing 13-pin input and add a second 13-pin for = output. R148 through R153 seem like good places to pull the individual voice = outputs. Just make sure to connect to the voice side of the resistor and = not the mixer side. I recommend buffering the signals so that the new = connections don=E2=80=99t interfere with the existing circuitry. Op-amp = followers should have really high impedance and pull very little = current. Connecting on the =E2=80=9Cvoice=E2=80=9D side of the resistors = will ensure that even the small current flow shouldn=E2=80=99t affect = existing circuits. One issue that might pose a problem is the A.GND connection on the = 13-pin jack. In contrast, MIDI is wonderful because it does not connect = the ground between multiple synths, and that significantly reduces the = chances of hum in the audio. For your added 13-pin output, I=E2=80=99d = recommend a virtual ground circuit on the sending unit that doesn=E2=80=99= t literally connect to A.GND from one unit to the other. This will = complicate the circuit, but is probably worth the effort to avoid ground = loops as much as possible. Another thing to do is to match the output of the S-612. There, they = have R132 through R137 after the TL082CP op-amps, so it=E2=80=99s = probably good to use similar series resistance. They don=E2=80=99t list = the resistor value on the schematic, and I couldn=E2=80=99t find = anything in the parts list. The exact value is probably not that = critical. You might even be able to pick a value from TL082CP data = sheets for an added output resistance that=E2=80=99s appropriate to = avoid ringing when connecting to an output cable like this. While you=E2=80=99re making this board with the 13-pin output jack, you = might as well also have individual 1/4=E2=80=9D jacks for individual = voice outputs, like the Akai S-900 shows in its schematic. Not = surprisingly, the 8-voice S-900 uses pins 2 through 9 of the 13-pin for = its 8 voices, while the S-612 uses pins 2 through 7 of the 13-pin for = its 6 voices. I suppose it=E2=80=99s possible to create a 12-voice = connection this way, although nothing is probably compatible. Then = again, you might not want to bother with making space for anything more = than the one 13-pin jack. You can always create an external breakout = board that plugs into the 13-pin jack if you want individual outputs. I = noticed that the Akai samplers don=E2=80=99t seem to have any circuit = design features to avoid ground loops between units. The only drawback of this whole project is that the design process will = surely be iterative. The first design might not work, and then it will = have to be revised. One-off PCB fab costs money, but if you don=E2=80=99t = mind that cost then it can be quick and rewarding. You can probably even = take power for the whole new board from the AX-60, assuming there=E2=80=99= s spare current in the existing supply. I=E2=80=99ve done similar = circuits for breaking out the individual string outputs on a 13-pin = guitar - mine is a Godin Freeway SA (SynthAccess) - and the most = challenging aspect was the +/-7VDC power supply. In the latter case, I = spent $465.51 on printed circuit boards, parts, and custom panels (and I = may have missed some costs). I hope you can find someone that will go through the whole process with = you. Brian Willoughby On Apr 21, 2019, at 3:00 PM, James Meagher <x.xxxxx.xxxxxxx@xxxxx.xxx> = wrote: > Brian Willoughby <xxxxxx@xxxxxxxxxxxx.xxx> wrote: >=20 >> Hi James, >=20 > Hi Brian, >=20 > To avoid confusion I think I should point out right off the bat that I = believe I=E2=80=99m referring to the AX60 that would be assuming the = role of the S612 as the =E2=80=9Cslave=E2=80=9D unit, and the AX60 = that=E2=80=99s receiving and processing the incoming signal as the = =E2=80=9Cmaster=E2=80=9D, whereas I believe you are referring to them in = the opposite manner. When an AX60 is connected to an S612, I personally = think of the AX60 as the =E2=80=9Cmaster=E2=80=9D unit and the S612 as = the =E2=80=9Cslave=E2=80=9D.=20 >=20 >> Can you explain exactly what is supposed to be the benefit of = combining two AX60 synths? What would the resulting voice architecture = look like? >=20 > In a nutshell you=E2=80=99d be getting a two osc CEM3394 synth. Of all = the CEM3394 synths that I know of, (SCI SixTrak, MultiTrak, Pro8, and = the AX60) all are single osc synths. So the usual benefits of a second = osc; different waveform combinations, different footage combinations, = detuning ... What I know I won=E2=80=99t get in this scenario; sync and = crossmod. Wouldn=E2=80=99t that be nice! But what I will get in this = config, (that you don=E2=80=99t often get with a 2nd osc), is that the = (slave=E2=80=99s) 2nd osc will be subject to double/series filtering, = and I=E2=80=99m a fan of two filters in series.=20 >=20 >> What you=E2=80=99ve described so far sounds like an apples versus = oranges comparison. >=20 > I=E2=80=99ve made a comparison? >=20 >> The Akai samplers are 6-voice and lack filter resonance. The Akai = synths are 6-voice and lack sampling. Combining the two types gives you = a 6-voice keyboard with both sampling and resonant filtering. The voice = architecture ends up being very similar to most other subtractive synth = architectures where there is an =E2=80=9Cexternal=E2=80=9D channel in = the mixer at the filter input. The advantage is that the external = samples can be synchronized, although this relies heavily on MIDI, which = is available for non-Akai models. By combining dissimilar products, you = obtain something unique with features of both. >=20 > I agree that the AX60 + Sampler is a wonderful combo.=20 >=20 >> If you were to combine two AX60 synths, I don=E2=80=99t see how it = would be a benefit, since you=E2=80=99d still only have 6 voices. >=20 > The benefit would be the voice architecture complexity of two oscs = versus a single osc ... and double/series filtering on one of those = oscs.=20 >=20 >> Consider that the Akai samplers always output their 6 voices onto the = 13-pin cable, and the Akai synths always take 6 voices as inputs on that = same cable. You do point out that one AX60 will be a =E2=80=9Cmaster=E2=80= =9D and one will be a =E2=80=9Cslave.=E2=80=9D But it=E2=80=99s worth = pointing out that turning an AX60 into a master means that you can=E2=80=99= t use any of the existing circuitry that=E2=80=99s used for the 13-pin = cable as an input. Your =E2=80=9Cmaster=E2=80=9D AX60 will need to = output 6 voices, and there=E2=80=99s no signal path in the synth for = that. At this point, your challenge is not actually any easier because = you have an AX60 - you could pick any 6-voice synth as your =E2=80=9Cmaste= r=E2=80=9D and the circuit modifications would be equally difficult. In = other words, I don=E2=80=99t see how choosing the AX60 as your master = makes anything easier. >=20 > I=E2=80=99m in no way convinced that using an AX60 as my =E2=80=9Cslave=E2= =80=9D will be any easier than using any other six voice synth as my = =E2=80=9Cslave=E2=80=9D (that is the synth that=E2=80=99s feeding out = its voices rather than the =E2=80=9Cmaster=E2=80=9D that is taking in = those voice for further filtering and processing). However a second AX60 = is the six voice synth that I want to use as my =E2=80=9Cslave=E2=80=9D.=20= >=20 >> Another way to phrase the above is this: You cannot connect two = inputs together! >=20 > . . . indeed.=20 >=20 >> (and the hidden problem is that converting the 13-pin input on an = AX60 into a 13-pin output would require extensive modifications) >=20 > I don=E2=80=99t believe that problem is hidden. It=E2=80=99s precisely = why I=E2=80=99m looking to consult with someone who has synth-design/EE = experience.=20 >=20 > FWIW I have a spare, female, 13 pin connecter that could be used for = the =E2=80=9Cslave=E2=80=99s=E2=80=9D individual voice output (not = needing to futz with the female 13 pin Voice Input already on the = =E2=80=9Cslave=E2=80=9D AX60=E2=80=99s Control Board). The big question = becomes at what point in the =E2=80=9Cslave=E2=80=9D AX60=E2=80=99s = voice circuit should I pull those individual voices, and will they need = subsequent boosting and/or buffering before entering the =E2=80=9Cmaster=E2= =80=9D AX60 ... or do those considerations already exist in the = circuitry of the =E2=80=9Cmaster=E2=80=9D AX60 between its 13 pin Voice = Input and pin 9 (EXT IN) on each individual CEM3394.=20 >=20 >> Even if you manage to pull this off, you=E2=80=99ll have the entire = VCO+VCF+VCA signal chain of the =E2=80=9Cmaster=E2=80=9D AX60 feeding = the mixer input of the VCF of the =E2=80=9Cslave=E2=80=9D AX60. This is = not a very common voice architecture. >=20 > Perhaps not, but it=E2=80=99s the voice architecture that I want.=20 >=20 >> You might be able to get some interesting filter sounds, but note = that the filters will still be in series, not in parallel. >=20 > I=E2=80=99m very much into this. And yes, I just might be able to get = some very interesting filter sounds.=20 >=20 >> The only possibility would be like buying a vintage Synton Syrinx = only to find that the VCF RTNG knob is permanently stuck in the = anti-clockwise position, when arguably the most interesting Syrinx = patches use the other filter routing options. >=20 > Luckily I=E2=80=99m not trying to outperform a Syrinx.=20 >=20 >> Anyway, if you can explain what you hope to accomplish, then maybe = I=E2=80=99ve missed an interesting combination that would make sense for = the AX60. >=20 > I don=E2=80=99t think you=E2=80=99ve missed anything, except perhaps = that I might find interesting what you do not.=20 >=20 >> Note that you won=E2=80=99t end up with a 12-voice synth. That would = be possible with an external MIDI processor that would sit between the = master and slave keyboard, and would not require any modifications. >=20 > Which is currently how I have them setup.=20 >=20 > Cheers, > James >=20 >> On Apr 21, 2019, at 9:41 AM, James Meagher = <x.xxxxx.xxxxxxx@xxxxx.xxx> wrote: >>> I=E2=80=99m looking for an EE/tech who will consult with me via = email in my attempt to connect a =E2=80=9Cslave=E2=80=9D Akai AX60 to a = =E2=80=9Cmaster=E2=80=9D AX60 in the same manner that you can run an = Akai Sampler (S612 or S700) into an AX60 to combine the sampler=E2=80=99s = voice with the AX60=E2=80=99s single osc pre-CEM3394 filtering. Of = course I=E2=80=99m happy to pay this person for their time.=20 >>>=20 >>> Of course previous knowledge of the AX60 and/or S612 would be a = bonus, but I don=E2=80=99t think it=E2=80=99s at all necessary for = someone who has the electronics understanding that I lack. I am able to = follow schematics (in a rudimentary, signal-path kinda way), find = components on a circuit board, and my soldering skills are decent. The = two AX60=E2=80=99s are recently refurbished (all key contacts and slider = pots disassembled and cleaned, all switches replaced and power supplies = outputting proper voltages), and are ready for coupling.=20 >>>=20 >>> I=E2=80=99ve gone over the AX60 schematics, the S612 schematics, and = the CEM3394 datasheet, and can see numerous places from which I access = the voices from the =E2=80=9Cslave=E2=80=9D AX60, and numerous points to = which I can introduce those voices into my =E2=80=9Cmaster=E2=80=9D = AX60, but I don=E2=80=99t have the EE understanding to make an informed = decision as to which option will make the most sense (or simply work). = I=E2=80=99ll save further details of my thoughts for my lucky = collaborator.=20 >>>=20 >>> Please let me know if you, or anyone you know, could be the right = person for the job. Feel free to share with any other group/list you = think might make sense - I=E2=80=99m no longer a member of sdiy or muffs = for precisely the same reason I need help with this project. ;) >>>=20 >>> Cheers, >>> James >>=20 >=20