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 Documentation

I thought that it may be helpful to list where to find documentation for the 2720 and 4700 synthesizer. I'm going to link to the pages that the manuals/schematics are stored on and not the direct download.

2720-1 VCA (schematic only)
2720-2a VCO (schematic only)
2720-3B Band Pass Filter (schematic only)
2720-3L Low Pass Filter (schematic only)
2720-4 Function Generator (schematic only)
2720-5 Control Oscillator / Noise Source
2720-6 controller Vinyl Strip/S&H
2720-7 Power Supply
2720-8 Keyboard manual (13.6 MB)
2720-8 Illustrations Supplement (5.7 MB)
2720-9 Glide manual (5.9 MB)
2720-11 Envelope Follower
2720-11 Envelope Follower (schematic only)
2720-12 Inverter/Buffer
2720-12 Inv. Buffer (schematic only)
2720-14 Sine Converter/PWM (schematic only)

For documentation regarding building the 2720 modules read: Building the 2720 series modular.

Also:
Using the PAiA 2720 Synthesizer


4710 Balanced Modulator/VCA
4711 Mixer
4712 Reverb
4720A Voltage Controlled Oscillator
4730 Multi-Modal Filter
4740 Envelope Generator
4750 Control Oscillator/Noise (see PAiA 2720-5)
4761 Road Case
4762 /4782 Road Keyboard
4770 Watt/Power Block
4771 Regulated Power Supply
4780 Sequencer
4783 Joystick
4786 Velocity Touch Controller

Also:
Using the 4700S

Additional:
8781 Quad Addressable Sample and Hold (QUASH)
8785 Linear Digital to Analog Converter

If anybody has links to the scans of the manuals that I don't have please provide a link and I'll post them here.

PAiA 2720-2 VCO Tests

I ran into an individual online who was having some problems with his 2720-2 PAiA VCO. Among the problems with his VCO was that it was not tracking at all and was incredibly high pitched (even when adjusting the internal range trimmer). So I agreed to help him in any way I could.










The first thing we did was compare VCOs. In examining our VCOs, we judged that there appears to be at least two revs of 2720 VCOs. One, of course, is detailed in the PAiA 2720 VCO schematic which is widely available online (and pictured to the left).




Another rev seems to be detailed in Brice Ward's (1975) Electronic Music Circuit Guidebook. There's a few subtle differences between the two and it appears that our VCOs were closer to Ward's schematic (on the left) than the one that came from PAiA.

The red numbers are areas of the circuit, which were labeled by the owner of the faulty 2720-2, that I am going to test so we can do some comparative troubleshooting.



To help in troubleshooting, I was given a spreadsheet with some test values. The numbers correspond to the areas marked on Ward's schematic (pictured above). The VCO in question is on the left side of the spreadsheet and my VCO's readings are on the right side (and in red). You can see that there's a bit of a difference at D3 and D4. Well, the infamous Scott Lee was asked about this and he confirmed that these should be nearer to 5v.


After the diode swap, I'm told that the VCO functions better but is still very high pitched. I'm guessing that this is a capacitor issue. Perhaps one is leaking or damaged. Hopefully this individual gets his issue sorted out soon so he can enjoy the oddness that is the PAiA 2720 VCO.

My PAiA Modular and its Power Consumption

I was doing a little work on my PAiA modular today as I wait for the FaderLube to come for the ARP Axxe. I was rearranging the cabinet and making an auxiliary cabinet when I realized it would be very handy for me to make a list of the modules that I'm using in the PAiA system and how much voltage they need to be powered. Here's what my list looks like right now:

PAiA 2720 VCA: +18v, +9v
PAiA 2720-2A VCO: +/-9v
PAiA 2720-3L LPF: +18v
PAiA 2720-4 Function Generator: +18v
PAiA 2720-11 Envelope Follower: +/- 9v

PAiA 4710 Modulator/VCA: +18v, +/-9v
PAiA 4711 Mixer: +/- 9v
PAiA 4720 VCO (x2): 9v
PAiA 4730 VCF: +/-9v
PAiA 4740 Envelope Generator (x2) +18v
PAiA 4750 Control Oscillator: +18v
PAiA 4771 Regualted Power +/-9v, +18v

CGS04 DC Mixer: +/- 15v
CGS03 Psycho LFO: +/-15v
CGS30 BPF: +/- 15v
CGS35 Steiner VCF: +/-15v
CGS52 Simple Wave Folder +/-15V
MFOS Sample & Hold w/ White Noise: +/-15v

CGSRR Real Ring Modulator: Passive
Multiples (x2): Passive

PAiA 2720 Transformers

I recently acquired two original 2720 power transformers. I haven't been able to find out too much information about them. I haven't tested them out but they are center-tapped 120v/12.6v (@, I think, 100ma).










An article written by John Simonton (1979) from Radio Electronics Magazine (October), briefly mentions the transformers and how to mount them.

Re-Wiring the PAiA 4771 Regulated Power

As some might remember from my two previous posts on 11/1/2009 and 6/1/2009 I had re-appropriated the 4771 Regulated Power panel after pulling the PCB. After using my own power source, I had decided to remove the 4771 PCB, which had some badly leaking electrolytic caps, and replace it with a MFOS Sample and Hold which was wired to a René Schmitz white noise circuit.

After reading through Brice Ward's (1975) book, I saw the value in the way PAiA distributed potential power to other modules. It's kind of quirky, yet useful. Therefore I've decided to re-hook up the board and replace all of the caps.

I'm not sure what I'm going to do with the Sample and Hold circuit. It's a really handy circuit to have in the synth. Originally PAiA had s Sample and Hold on their keyboard interface. Perhaps I'll include one on the interface device I'm planning now..

2720-1 PAiA VCA Arrives

I got the 2720-1 VCA in the mail today and snapped a few picks. I haven't been able to test it as I'm busy with other projects at the moment and I'm playing with a buddy this weekend at the Eugene Noise Festival.

The schematics are posted here. They were originally grabbed at the Free Information Society (a very cool site).

Anyway, here's some pics.





































Nothing too complex on the bottom. Decent soldering job. Some traces may have been repaired. All and all it looks pretty good.

2720-1 VCA

Okay, I really need to stop, I know. I bought a 2720-1 VCA off of Ebay today for $20.00, which, truth be told, is probably too much for the world's worst VCA. Still, I wanted it because it gives me a fully functioning 2720 synth (although not 100% complete). By functioning I mean I'll have one 2720 VCO, one Function Generator, one VCA, and one LPF. It's not a complete system, like I said, but it is a very simplistic functioning DIY synth from the early 1970s. It really is a horrible VCA, I'm a sucker..

E(vil)bay Pics:




















All hail the LM748

Paia 2720-1 VCO and 2720-3L LPF Arrive

Right now I have more panels than space. This is confounded by the fact I've made another trade and that I bought a 2720-3L VCF and 2720-1 VCO for cheap on the E(vil)Bay. I got them both for less tham $45 combined so I figured what the hell and pulled the trigger.

As crazy as it sounds, I'm going to build another cabinet and keep building in this format. I like the real simple 2x4 and 4x4 panels. It works well for my DIY skills and needs. I'll build bigger panels for my "real" DIY modular but I'm going to keep going this direction for a while, especially now that there's other great (and easy) DIY Hz/Oct. projects out there. I actually have quite a few Hz/Oct. instruments and am investigating to see if I can make my MiniKorg 2 a master keyboard.

Something that's real cool about this VCO and VCF (as well as many other early Paia modules) is that they are mostly discrete. The LPF is completely discrete and the VCO only has one or two op-amps. I personally think discrete technology is pretty damn cool and I'll never buy another synth that is reliant on obsolete chips.

The 2720-3L LPF is cool but it needs some modding to be brought up to specs. I'm really looking to play and enjoy this synth (see previous posts) so I'll do any appropriate mods as long as it keeps with the general spirit of the synth. I'm going to replace the paper caps and make this into more of a BPF. I'm also looking at some easy ways to add resonance to it.

Here's a look at the new old modules:
































Here's the schematics. It's shocking how simplistic that LPF is. I like the VCO quite a bit although it's not the most stable beast around..



















Here's an image of the VCO from Brice Ward's book. As you can see it's very similar to the 2700 VCO design.

Nice Older DIY Synth Books (That Don't Use SSM & CEM Chips)

I’ve been reading through two really amazing books on building analog synthesizers recently that I got out of inter-library loan. The first is Brice Ward' s (1975) Electronic music circuit guidebook. This book has a bunch of good information about the Paia 2720 and Gnome as well as many original circuits. The GF was actually kind enough to scan much of this book for me at her work.

The second book is Delton Horn's (1984) Music synthesizers: A manual of design and construction. This book is absolutely great. Many very interesting ideas and circuits that you can still build. I actually found a good deal on this book online and bought it outright.

The great thing about these books, as opposed to Barry Klein's (1982) Electronic Music Circuits, is that most of the designs are either completely discrete or utilize something easy to find (and not CEM or SSM chips).

Be sure to check out this great thread at Muff about good modular synth books

Also, I cannot express enough how much I want to join the Electronotes secret society. These people seem really really cool and I'd love to gander at that "stack of papers" they send you.

The Paia 4771 Regulated Power Supply and Distribution

Although I can see some advantages to the original Paia power distribution method the caps in the distro and PSU are leaking badly. If you look closely you can see some pretty electrolytic crystals.

Therefore, I got a Condor +/- 15V PSU and a DIY +/- 9V PSU and some CGS distribution boards. This should make things a bit more manageable. The 2720 and 4700 systems will run fine on 15V.

The power module panel will still serve as a great bias.

The 4700 distribution method












Power regulator which is leaking electrolytic fluid badly.















Most of the brown stuff on the side of these caps is the glue that was used to secure them into the cabinet. The reddish brown stuff on the top of the caps is not glue..


















Here's how the 4771 works..

About Pin Jacks (and Bananas)

I debated with myself (and others) quite a bit about keeping or losing the original Paia pins. On one hand its cool to preserve the integrity and original aesthetic of the synth (not to mention the time removing all the little buggers). On the other hand, they're the same size as banana plugs, they do look somewhat similar, and banana plugs are more useful to me in regards to my previous builds. Plus, bananas can be stacked so I can remove the pins and have more real estate to be creative with mods..

Finally I decided to go with bananas. Function over form. So I got down to the nitty gritty and removed these pins.

FYI There are adapters for Banana to pin plug that Mouser sells.


Here's a pic of a pin plug.





















Here's a comparison of bananas and pins. As you can see the holes are quite different in size but the jacks are similar.






















Here's what the legendary Scott Lee from Paia says (taken from the Paia Talk forums):

"The pin plugs aren't as readily available as the 1/8" phone plugs, but Mouser 800-346-6873 has them (stk #530-105-0302-1) but they describe them as tip plugs. Mouser has the rubberized test cable too. Solid, 14ga insulated wire wire with about an inch stripped off at each end can be used for the cv patches. Test leads as used on inexpensive multi-testers are often the right size. Since everything in the 2720 or 4700 series systems is on the same power supply, they already have a common ground, so the cables need only be a single conductor wire. When patching to the external equipment, or between a 4700 series analog keyboard controller, one cord will need to be patched between a ground circuit jack (could be a black one?) on the synth and the device ground to establish a common ground between them."

A Look At the Paia 4700

Here's a look at the Paia 4700