Wednesday, September 5, 2012

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.

Thursday, May 12, 2011

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 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.

Sunday, November 14, 2010

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.

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

Using the 4700S

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.

Sunday, May 30, 2010

Current Draw for PAiA 2720 and 4700 Modules

Below is the current draw for most early PAiA modules. An amp, as you probably know, represents the amount of energy being consumed by each module. Make sure you don't get amps and voltage confused. There's a lot of great resources out there for learning about these units of measurement.

PAiA 2720 Modular Series Synthesizer:
2720-2 (VCO): +/-9v @25ma
2720-5 (Control Osc.): 18v @ 1.75ma
2720-9 (Glide) +/-9v @1.5 (each)
2720-11 (Env. Follower): +9v @6.5ma, -9v @ 7.5ma
Keyboard +9v@ 1.5ma. -9v @3ma, 18v @ 1ma

The original PAiA transformers that I've seen are
center-tapped 120v/12.6v at (I think) 100ma.

I'm going to get around to measuring the modules that aren't listed at some point.

PAiA 4700 Series Modular Synthesizer:
4710: +18v @10ma, +9v @ 1.5ma, -9v @7ma
4711: +/-9v @ 4ma
4712: +/-9v @ 3.5ma
4720: 9v @ 20ma
4730: +9v @ 15ma, -9v @25ma
4740: +18v @ 17ma
4750: 18v @ 1.75ma
4760: +18v @ 50ma, +/-9v @ 1ma
4762: +/-9v @ 25ma, 18v @ 25ma*
4770: (Watt Block): 117v 50/60khz, +/-9v @100ma or 18v @100ma (out)
4780: +18v @50ma, +/-9v @1ma

* Includes 2720-8 and 2720-9 circuitry.

Monday, February 15, 2010

Tuesday, February 2, 2010

PAiA 2720-2 Problem Solved

Some may recall from this post that there was still a lingering problem when I had helped an individual with his 2720-2 Oscillator. Well, it turns out that the culprit was a poor solder connection at the Zero trimmer. It was invisible to the eye but apparently everything is working smoothly now.

Thursday, January 28, 2010

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.