THE POG2 (the Prism of Gems Synthesizer 2)

the POG2 is my third (mostly) homebuilt analog modular synthesizer. my first homebuilt synth is in my basement with most of the modules taken out and used in the POG1 and 2. it will again rise like a phoenix from it's ashes and burn it's way into the collective consciousness of humanity. hmm, anyway the POG2 consists of 7 homebuilt modules and a heavily modifried old Moog Prodigy that i took in trade for a repair job a long time ago. it needed a bit of work and had a chunk of the front panel sawed off. undaunted, i was happy to get it for a simple repair. i fixed the broken OSC2, LFO, and a few other things. the keyboard was gone which matters not since i do not play keyboards. when i became somewhat dissatisfied with the POG1 ( a similar hachet job hybrid) i started to build the POG2. i constructed one of my trademark ultra ameteur wooden cases, bent the prodigy panel a bit, grabbed a few modules out of the POS ( my first synth) and made a lot of connections internal to the prodigy accesable for patching. after about a year or so i went back and reworked a good deal of the Prodigy, added some more modules, fixed all the little minor flaws*, and in general tried to make it more playable. my big interest for the last few years has been more 'playable' interfaces, 'chaos', and extracting signals from other than the usual sources. the POG2 doesn't actually address too much of this territory yet but i have been trying just to get it to a state where it makes a good sound generating platform to try some of these concepts out with.

POG2:    MOOG PRODIGY
               MIXER/VCF/VCA
               QUAD ENV GEN
            * DUAL LFO
               GATE DELAYER/SUPERLFO
            * VOLTAGE SOURCE1
            * VOLTAGE SOURCE2
            * NOISE VOICE
            * JOYSTICK/VOLTAGE WHEEL/PUSHBUTTON

***UPDATE 4/4/02: it's been a year since i wrote this and quite a bit has changed. All the modules marked with an asterisk* have been removed and installed in the POG1.***

MIXER/VCF/VCA:this module consists of 2 VCAs (SSM2024), 3 input ac coupled mixer, 2p VCF BP, 1p VCF HP. the VCFs are made with a VCF1e from Tomg's EFM. the 2 VCAs and the mixer i soldered point to point with vector board, using my own designs (rather simple ones in this case) QUAD ENVELOPE GEN: 2 ADSR envelope generators (SSM2050) and 2 AR/AD attack/release or attack/decay envelope generators (made with CMOS and op amps)

DUAL LFO: these were made from two old scrap boards from the very first almost embarissing attempts at VCOs. made with ILC8038 waveform generator chips. with a range switch, VCrate in, and a choicbetween TRI or SIN wave on one LFO and SQA or SIN on the other. someday i will bring out the RECTANGLE waves when i feel inclined and have the time. also a pot for continuos mix between the 2 LFOs

GATE DELAYER/SUPERLFO: this module has been on the bench about half of it's existence. originally, a very long time ago (1988) it was a gate generator which i triggered from foot pedals. then i added the 'superlfo' part which is loosely based on Tom Henry's SUPERCONTROLLER circuit using a SN76495. his original circuit used a SN76477. i built a modifryed version in 1992, (which was at the end of the last phase of intensive synth building for me, since that time it's been a few months on at most per year). this part of the module consists of: 2 LFOs, S&H,and a (digital) NOISE w/filter. There has been a lot of discussion and questions about this type of circuit on synth-diy in the past and i mentioned that i had built it. i do not really like the way it functions and at this point i would recommend building all separate circuits if one wanted to have these functions in one module. my specific problems with it are: very hard to get really slow frequency waves out, not enough range on the voltage control input, and just all round pain to get working as i desire it to.

VOLTAGE SOURCE 1: is a module of simple utility circuits; 1 adjustable voltage, inverters, an attenuator, a voltage comparator, and the one unusual feature- a dual random voltage generator. one RVG is a noise filtered by a 4p adjustable frequency (but not voltage controlled)LP filter. the other RVG is a noise source through 1p LP fixed filter and a very high Q (adjustable)(one op amp, slightly unstable it seems) 1p BP filter that gives an output adjustable between total noise and oscillation at the frequency of the filter, which is about 6hz. this circuit is from Electronotes Prefered Circuits Collection. the random voltage generators are very interesting, i have only just recently just taken this module out of storage, cleaned and fixed it up, and installed it in the POG2. (now it is in the POG1)

VOLTAGE SOURCE 2: has been in the POG2 for awhile. it has the circuitry for the voltage wheel and pushbutton trigger, plus two adjustable voltages, inverters, a comparator,and two attenuators.

NOISE VOICE: was part of a drum synthesizer/drum machine from quite way back in my engineering day (around 1986.) the noise source is the regular old reverse bias transistor, plus a 4P LP VCF made with an MF10 switched capacitor filter, the VCA is a simple linear CV CA3080 circuit. also included is a VCLFO and a manual control 2P HP filter which uses a dual gang potentiometer. it can select inputs between the on-board noise source or an external signal.

the (heavily modified) PRODIGY: i made the tune range quite a bit wider, then added a fine tune (a nice 10 turn pot -bought surplus), the LFO is now voltage controlled and also has its own VCA for VC depth of modulation. i reworked the stock ASR envelope generators to be ADSR. the VCF has VC resonance. i actually used the stock VCA for this function then added a SSM2024 VCA for the signal output. one other quarter of the SSM2024 became the LFO VCA, the other two quarters of the chip are brought out as a dual VCA module. i added linear CV ins to VCO 1&2. i added 2 CV ins for the VCF, 2 CV ins that go to both VCOs and the VCF, 1 CV in to the VCA plus a manual V in to the VCA, i brought out these connections:
VCO 1&2 SIG OUT
VCF sig in and sig out
VCA sig in and sig out
LFO out, CV in, and LFO amplitude CVin
ENV 1&2 out, GATE in

i like the playability of this homebuilt/hybrid synth the most of the three i've built so far.
whenever i actually have the spare time i will put up detailed notes and schematics of these mods that i did to the original PRODIGY unit. i also did similar things to a realitic MG1 ( the guts of POG1) but i like the sound of the prodigy quite a bit more. contact crystal

updated 4/4/02

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