From James Meagher Sent Mon, Apr 22nd 2019, 02:03
From James Meagher Sent Mon, Apr 22nd 2019, 02:03
Thank you so much for the insights Brian. I believe I=E2=80=99ve just now fo= und an engineer to work with who=E2=80=99s familiar with the AX60 and seems e= nthusiastic. I=E2=80=99ll keep y=E2=80=99all posted of the results.=20 Sent from my iPhone > On Apr 21, 2019, at 8:52 PM, Brian Willoughby <xxxxxx@xxxxxxxxxxxx.xxx> wr= ote: >=20 > Excellent. This all looks good. Seems like you have a good handle on what y= ou=E2=80=99re after. >=20 > I take back what I said - it might be rather easy if you=E2=80=99re willin= g to add a new circuit board. I think you=E2=80=99re on the right track to l= eave the existing 13-pin input and add a second 13-pin for output. >=20 > R148 through R153 seem like good places to pull the individual voice outpu= ts. Just make sure to connect to the voice side of the resistor and not the m= ixer side. I recommend buffering the signals so that the new connections don= =E2=80=99t interfere with the existing circuitry. Op-amp followers should ha= ve 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 c= urrent flow shouldn=E2=80=99t affect existing circuits. >=20 > One issue that might pose a problem is the A.GND connection on the 13-pin j= ack. In contrast, MIDI is wonderful because it does not connect the ground b= etween 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 gr= ound circuit on the sending unit that doesn=E2=80=99t literally connect to A= .GND from one unit to the other. This will complicate the circuit, but is pr= obably worth the effort to avoid ground loops as much as possible. >=20 > Another thing to do is to match the output of the S-612. There, they have R= 132 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 o= n 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=99= s appropriate to avoid ringing when connecting to an output cable like this.= >=20 > While you=E2=80=99re making this board with the 13-pin output jack, you mi= ght as well also have individual 1/4=E2=80=9D jacks for individual voice out= puts, like the Akai S-900 shows in its schematic. Not surprisingly, the 8-vo= ice 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 p= robably compatible. Then again, you might not want to bother with making spa= ce for anything more than the one 13-pin jack. You can always create an exte= rnal breakout board that plugs into the 13-pin jack if you want individual o= utputs. I noticed that the Akai samplers don=E2=80=99t seem to have any circ= uit design features to avoid ground loops between units. >=20 > The only drawback of this whole project is that the design process will su= rely 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 f= or the whole new board from the AX-60, assuming there=E2=80=99s spare curren= t in the existing supply. I=E2=80=99ve done similar circuits for breaking ou= t 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 su= pply. In the latter case, I spent $465.51 on printed circuit boards, parts, a= nd custom panels (and I may have missed some costs). >=20 > I hope you can find someone that will go through the whole process with yo= u. >=20 > Brian Willoughby >=20 >=20 >> On Apr 21, 2019, at 3:00 PM, James Meagher <x.xxxxx.xxxxxxx@xxxxx.xxx> wr= ote: >> 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 be= lieve I=E2=80=99m referring to the AX60 that would be assuming the role of t= he S612 as the =E2=80=9Cslave=E2=80=9D unit, and the AX60 that=E2=80=99s rec= eiving and processing the incoming signal as the =E2=80=9Cmaster=E2=80=9D, w= hereas I believe you are referring to them in the opposite manner. When an A= X60 is connected to an S612, I personally think of the AX60 as the =E2=80=9C= master=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 t= wo 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 th= e 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; differen= t waveform combinations, different footage combinations, detuning ... What I= know I won=E2=80=99t get in this scenario; sync and crossmod. Wouldn=E2=80=99= t that be nice! But what I will get in this config, (that you don=E2=80=99t o= ften get with a 2nd osc), is that the (slave=E2=80=99s) 2nd osc will be subj= ect to double/series filtering, and I=E2=80=99m a fan of two filters in seri= es.=20 >>=20 >>> What you=E2=80=99ve described so far sounds like an apples versus orange= s 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 k= eyboard with both sampling and resonant filtering. The voice architecture en= ds 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 i= nput. The advantage is that the external samples can be synchronized, althou= gh this relies heavily on MIDI, which is available for non-Akai models. By c= ombining dissimilar products, you obtain something unique with features of b= oth. >>=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 c= able. You do point out that one AX60 will be a =E2=80=9Cmaster=E2=80=9D and o= ne will be a =E2=80=9Cslave.=E2=80=9D But it=E2=80=99s worth pointing out th= at turning an AX60 into a master means that you can=E2=80=99t use any of the= existing circuitry that=E2=80=99s used for the 13-pin cable as an input. Yo= ur =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 n= ot actually any easier because you have an AX60 - you could pick any 6-voice= synth as your =E2=80=9Cmaster=E2=80=9D and the circuit modifications would b= e equally difficult. In other words, I don=E2=80=99t see how choosing the AX= 60 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=9C= slave=E2=80=9D (that is the synth that=E2=80=99s feeding out its voices rath= er than the =E2=80=9Cmaster=E2=80=9D that is taking in those voice for furth= er filtering and processing). However a second AX60 is the six voice synth t= hat 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 t= ogether! >>=20 >> . . . indeed.=20 >>=20 >>> (and the hidden problem is that converting the 13-pin input on an AX60 i= nto a 13-pin output would require extensive modifications) >>=20 >> I don=E2=80=99t believe that problem is hidden. It=E2=80=99s precisely wh= y I=E2=80=99m looking to consult with someone who has synth-design/EE experi= ence.=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 w= ith the female 13 pin Voice Input already on the =E2=80=9Cslave=E2=80=9D AX6= 0=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 indivi= dual voices, and will they need subsequent boosting and/or buffering before e= ntering the =E2=80=9Cmaster=E2=80=9D AX60 ... or do those considerations alr= eady 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 i= nput of the VCF of the =E2=80=9Cslave=E2=80=9D AX60. This is not a very comm= on 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 t= he 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 som= e very interesting filter sounds.=20 >>=20 >>> The only possibility would be like buying a vintage Synton Syrinx only t= o find that the VCF RTNG knob is permanently stuck in the anti-clockwise pos= ition, when arguably the most interesting Syrinx patches use the other filte= r 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 p= ossible with an external MIDI processor that would sit between the master an= d 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> w= rote: >>>> I=E2=80=99m looking for an EE/tech who will consult with me via email i= n my attempt to connect a =E2=80=9Cslave=E2=80=9D Akai AX60 to a =E2=80=9Cma= ster=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, b= ut I don=E2=80=99t think it=E2=80=99s at all necessary for someone who has t= he electronics understanding that I lack. I am able to follow schematics (in= a rudimentary, signal-path kinda way), find components on a circuit board, a= nd my soldering skills are decent. The two AX60=E2=80=99s are recently refur= bished (all key contacts and slider pots disassembled and cleaned, all switc= hes replaced and power supplies outputting proper voltages), and are ready f= or coupling.=20 >>>>=20 >>>> I=E2=80=99ve gone over the AX60 schematics, the S612 schematics, and th= e CEM3394 datasheet, and can see numerous places from which I access the voi= ces from the =E2=80=9Cslave=E2=80=9D AX60, and numerous points to which I ca= n 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 o= ption will make the most sense (or simply work). I=E2=80=99ll save further d= etails of my thoughts for my lucky collaborator.=20 >>>>=20 >>>> Please let me know if you, or anyone you know, could be the right perso= n for the job. Feel free to share with any other group/list you think might m= ake sense - I=E2=80=99m no longer a member of sdiy or muffs for precisely th= e same reason I need help with this project. ;) >>>>=20 >>>> Cheers, >>>> James >>>=20 >>=20