I have stopped updating this blog but I have left a lot of information still up regarding PAiA electronics. That said, I am no longer checking for dead links. For information regarding PAiA electronics, I encourage you to visit PAiA Talk. PAiA Talk is the official home and message board of PAiA.

PAiA 4712 Spring Reverb

I do not actually have the original 4712 spring reverb but the simple design makes it easy to build on one's own. Synth DIYer Dego was kind enough to share an amazing breaboard image as well as the informative schematics for the 4712. He also gave his blessing to share these.


 The builder's manual is available for download from PAiA.

PAiA 4710 Balanced Modulator/VCA

The 4710 Balanced Modulator/VCA is one of my favorite PAiA modules and one of the reasons that the 4700 system is so fun. Here's a description of how it works via PAiA




















DESIGN ANALYSIS

The 4710 Balanced Modulator is built around a type 1496
balanced modulator integrated circuit. The internal workings
of this I.C. package are not pertinent to this discussion but
certain general points should be made.

The 1496 chip has differential inputs for both carrier and
modulation ports. Biasing for the carrier inputs (pins 8 and
10) are supplied by the voltage divider consisting of Rll and
R12 with this biasing voltage coupled to the IC through R14
and Rl5. Input signals applied to the carrier input jack J4
are capacitively coupled by C2 to input isolating resistor
R26 and finally appear across R14. Fixed resistors R13 sad
R16 along with trim pot R25 are used to supply adjustable
current into the carrier input port to balance out variations
that occur in the integrated circuit during manufacture.
With no signal applied to either of the inputs there should
be 7v +/-20% present at pins 8 and 10 sad at the junction of
Rll and Rl2.

The modulation inputs (pins 1 and 4) are similar to the
carrier inputs except that they are tied to ground through R8
sad R9 with R7, R10 and trimmer R24 supplying tolerance
compensating bias currents. Pins 1 and 4 should read
0V +/-0.1V.

R19 and R20 serve as load resistors for IC-2 with the in-
phase output coupled to output jack J5 by way of C3.
quiescent voltages at pins 6 and 12 should be 8v. +/- 20%.

The modulation input of the 47I0 module is buffered by the
748 type operational amplifier IC-1. Control voltages are
direct coupled to the inverting input of that IC by R2 and R3
while audio signals are capacitively coupled by R1 and C1.
With the modulation LEVEL control fully counter-clockwise and
no signals present at the inputs, pin 6 of IC-l should be
0V. +/- 0.1V.

Rotating the LEVEL control in a Clockwise direction causes
less of the output of the operational amplifier to appear as
feed-back at the inverting input which in turn causes the
voltage gain of this amplifier to go from approximately 4.5
to 90 (13 - 40 db.) for signals applied to the audio input
and 0.3 to 6. 3 (-10 to 16 db.) for signals applied to the
control inputs. The voltages at pins 2 and 3 of IC-l should
be 0V. +/- 0.1V and pins 7 and 4 are positive and negative
supply respectively.

The overload Light Emitting Diode becomes forward biased and
begins to conduct on negative excursions of the output of IC-
1. Because of the forward voltage drops of D1 and D2, as
well as the LED itself, conduction begins to occur at about -
2v. The output of the buffer amplifier is coupled to IC-2
through R6.

Power supply decoupling is provided by the combinations R2l,
C6; R22, C7 and R23, C8. The voltages across C6, C7 and C8
respectively should be 13V., 7V. and -8V. +/- 20%.

06/12 @ New Zone

With piles of stuff that needs to get fixed I'm hoping to do some real blog posts this week. Until then:

Lineup:
Doors at 7:00

7:30 spark applied to powder
8:00 [view]
8:40 Obsolete Synthesis
9:20 Mandom
10:00 Paintings for Animals

More PAiA

Work has been unbelievably hectic, but fortunately in a good way. Apologies for the utter lack of updates. I've been working on a few projects but for the most part I've been concentrating on other things. If interested, I put some tracks and noises up on Soundcloud. There's really no reason to rush over there and listen, but you're welcome to if interested.

Here's some more PAiA pics. The project is essentially done for now as I'm moving on to the large DIY modular which I've been planning for some time.


If interested, the modules in the pictures are:

Top Left Wood Cabinet (left to right)
CGS Psycho LFO, Envelope Follower, 2720 VCA, blank, CGS DC Mixer
Second Row: PAiA Power Wing (altered for DC power in and mults), 2720 Function (Envelope Generator), blank panel, DIY octave divider


Top Right Wood Cabinet (left to right, then down)
Mixer (not built by me), 2720 Envelope Follower, 2720 Function (Envelope) Generator, 2720 Second Row:
2720 Power (with attenuater/mults/bias) , 2720 VCO, 2720 BPF


Left Paia Cabinet:
Top left to right
4711 Mixer, 2720 VCO, DIY Clock/Square Wave Generator, power in
Second Row:
4710 Balanced mod/VCA, 4720 VCO, 4720 VCO, 4730 VCF

Right Cabinet
Top Left to right:
CGS Steiner VCF, 2720 LPF, 2720 VCA, 4740 Envelope Generator, 4740 Envelope Generator
Bottom:
CGS BPF, 4750 Control Oscillator (LFO)/Noise, 2720 Envelope Follower, MFOS Dual VCA, MFOS VC Sample and Hold and CGS Real Ring Mod

I have a Condor and MFOS Wall Wart PSU. I prefer them to the oldschool PAiA power.

PAiA 2720/4700 Quick Help

So you bought an old PAiA system. It looks cool but now what do you do with it? It seems like I've answered this question countless times on the nerd forums. Therefore, I decided to post some of my stock answers and suggestions here:

You bought it. Now what?

- Inspect the power module. How does the board look? Are there any shorts or other problems? Replace all of those capacitors (aka a "cap"). Isolate the power module and test the voltages before firing up other modules. Another option is to get a new, clean, power supply. Many people run their systems happily on the oldschool power. The system does run quieter and smoother on a nice modern PSU. I'm running my machine off of a modern medical power supply that I have tapped into the 4771 so I can still tap it for a bias. Just a tip, the system runs fine at 15V instead of 18V.

- When I get a "new" module the first things I do is recap it and check for errors. There were a lot of builders back in the day and not all of them had skills. As far the caps, some of them are pushing 40 years old. Isolate each module before testing it for the first time.


- As you see, the 4700/2720 systems use pinjacks (which I kind of loathe). I use bananas elsewhere so this is a better option for me. The extra unused pin holes also leaves spaces for mods if you'd like that sort of thing. Bananas fit in the existing holes with any additional drilling.

- Remember, the PAiA 2720/4700 has linear VCOs similar to the early Korg and Yamaha machines. This linear response is based on the Hz/Volt system and not the Volt/Octave, or exponential system used by Moog, ARP, MOTM, modern PAiA 4700 synths, etc..

- Again, these systems can be great, especially when tweaked a bit.


LINKS

- Links to all the PAiA tutorials and build documents. John Simonton wrote some great tutorials that are definitely worth looking through.

- Info about exponential versus linear responses in context of the PAiA 2720/4700, look here.

- Module current draw info.

- Scott over at PAiA talk can be a lot of help as well.