Hi there
2009-03-29 by Terry Garrett
Hi,
; My name is Terry Garrett and have just joined the forum, having picked up my Formant project of 30 odd years !! I started my first synthesizer in 1973 (a Dewtron module based system but not very good, so scrapped and started the Formant some years later). Basic system was stated in 1978 with 2 vco, 24dB vcf, vca and adsr plus another cut down to ar ( as ARP odyssey uses adsr and ar thought i would do the same). I retained the 3 octave keyboard from my original synth back in '73, building new wooden case for main unit and a new keyboard case - still to be completed.
I planned to later add anothe vco and await further modules as they came, LFO and ring mod plus envelope follower as in Elektor, plus RFM. A sample and hold and output amp etc plus maybe a vcLFo, didn't see the point of the Com module.
In 1980 i purchased a vco kit from Phonosonics where i had bought all the other components, at the same time i modified the vco's to accept the jfet opamps with a slight improvement to stability although they were ok as originally built.
Since restarting in March 2009 I have had problems. First was the keyboard interface resistor R25 going o/c. Not a common fault which took me some time but i should have realised the obvious but thought the cap C5 faulty first, then substituting various other components. This caused a delayed gate pulse, the LED staying on a few seconds. Now before i go on i should point out that at 58 the eyesight is not good with intricate printed cct boards. The second fault which took longer was down to a component in the sample hold circuitry, having substituting various FET's and cap's i lifted the pcb track. Drastic measures so the only thing for it was to build a small daughter board with a TL074 covering the 3 fet's T1,3 and 4 plus a BF245 for T2. The result was now a constant tone, as before the keyboard note would slide down or up.
This happily is where i am at now. The next thing will be a New pitch detector (called Legato in Elektor Jul/Aug 1980). This will incorporate also a pitch bend cct and transpose (2 octaves up / down) I originally planned the LFO in the keyboard unit but due to space for pcb's and extra connections needing more than the 2, 5-pin Din sockets this may now be installed in the main unit.
I have at several times been on the brink of giving up (as i suppose some others feel) but the buzz when something actually goes right lifts the spirit once more. But i fear the other modules will have their gremlins, I have only one vco powered up plus the vcf, which does not sound much like a vcf so something wrong there. No vca or envelopes, but gently we go. The synth has been stored in my shed for over 12 years so i cannot expect all to go well, no doubt some of the dreaded cap's will be due for change and various pot's and switches are not at their best. With exposure to high summer temperatures and feezing winters I only hope the 726's and CA3080/3084's are ok.
I close with a few useful links to synth websites including actual schematics of various Moog/ARP/Roland etc. I hope some of you will find them interesting, surprisingly some of the specs are NOT as good as the Formant.
Terry