Stefan Vorkoetter's Web Site

Rejuvenating and Expanding a PAiA 1550 Stringz'n'Thingz Synthesizer

Mon, 05 Jul 2010 22:49:49 GMT

When I was in the 8th grade, I was nuts about analog synthesizers. I'm not talking about the "analog revival" here, but the original heyday of analog synthesis. Although I'd read about Moogs and Buchlas and ARPs, those were clearly out of my league. Instead, I had my sights set on a PAiA 2720 system, and I spent a lot of time looking through the 1977 PAiA catalog.

Radio-Electronics February 1979 In 1979, I picked up a copy of Radio-Electronics magazine featuring PAiA's new model 1550 Stringz'n'Thingz. Unlike the monophonic 2720 system, the 1550 was fully polyphonic. It's internal architecture was more like an organ than a synthesizer, but it specialized in the production of the rich orchestral string sounds common in pop music at that time. It could also do a reasonable piano imitation.

Fast-forward to late 2009. The analog days had come and gone, and come back. A lot of old analog gear was showing up on eBay, and the prices were slowly rising. I'd been watching for old PAiA gear to find a small synth to supplement my 1962 Hammond organ. 1550s showed up from time to time, but the price always rose beyond my budget. Whenever a promising one turned up, I'd place a bid and hope for the best. I finally got lucky and got my Stringz'n'Thingz for $249.

New Low Self-Discharge Battery Test Results

Wed, 17 Feb 2010 01:53:59 GMT

I've just completed the tests on another brand of AA batteries (E8GE) and posted these to my low self-discharge battery review page. I've also posted my test results for three brands of the smaller AAA size (Sanyo, Powerex, and E8GE) and added a section for these to the page.

Hammond Organ Tonewheel Generator Capacitor Replacement and Calibration

Mon, 28 Dec 2009 19:58:35 GMT

The Hammond M-series organ service manual describes the operation of Hammond's tonewheel generator this way:

Electrical impulses of various frequencies are produced in the "tone generator", which contains a number of "tone wheels" driven at predetermined speeds by a motor and gear arrangement. Each tone wheel is a steel disc similar to a gear, with high and low spots, or teeth, on its edge (see figure 12). As the wheel rotates, these teeth pass near a permanent magnet, and the resulting variations in the magnetic field induce a voltage in a coil wound on the magnet. This small voltage, when suitably filtered, produces one note of the musical scale, its pitch or frequency depending on the number of teeth passing the magnet each second.

The phrase, "when suitably filtered", is key here. Unlike those organs which produce complex tones and then use filtering to achieve the sounds of traditional instruments (subtractive synthesis), the Hammond organ produces nearly pure sine wave tones and then combines these to create instrument sounds (additive synthesis). The relative proportions in which these are combined are controlled by the organist using the Hammond organ's harmonic drawbars.

Overhauling the AO-29 Amplifier in the Hammond M-100 Series

Thu, 24 Dec 2009 16:43:10 GMT

Well built vintage electronic circuitry can last a very long time, as evidenced by the number of Hammond organs that are still working, some from as far back as the 1930s. Hammond's engineers designed their vacuum tube (valve) amplifiers conservatively, putting minimal stress on the components. All but one of the tubes in my 1962 Hammond M-111 is original and I have no intention of replacing them unless one fails.

However, one type of component that is prone to wearing out, regardless of how little or how much a piece of equipment was used, is the electrolytic capacitor.

Panasonic and EasyPix Low Self-discharge Battery Results

Tue, 20 Oct 2009 02:44:38 GMT

I've recently completed the full suite of tests on the Panasonic and EasyPix low self-discharge battery offerings. The results are included in my battery comparison article.

Window Seat Bookcase Tone Cabinets for a Hammond Organ

Tue, 20 Oct 2009 02:42:00 GMT

The Hammond M-100 series of spinet organs is equipped with a 15W internal amplifier driving two 12" speakers, and a separate 15W reverb amplifier driving an 8" speaker. My own 1962 Hammond M-111 is missing the reverb amp and speaker. The amp was not working, and rather than repair it, I removed it and its speaker to make room for a rotary speaker powered by the main amp through a passive crossover. This gave me a Leslie-like sound, but still with only 15W total output power.

Of course, 15W from 1962 is 15 real Watts, so it's fairly loud, but it doesn't really fill the room the way I'd like. Furthermore, the bass response is not all that good. The usual solution to this is to add one or more external tone cabinets such as a Hammond PR-20 or PR-40, or one of the many Leslie rotary speaker cabinets. Finding one of these in good working order, good physical condition, and at a reasonable price can be quite challenging. Since I'm a DIY-er at heart, and the room that the organ is in was newly renovated but still in need of some built-in furniture, I decided to combine the two projects, producing a wall-to-wall window-seat bookcase with two integrated tone cabinets.

Updated Low Self-Discharge Battery Tests

Tue, 30 Jun 2009 19:13:08 GMT

I've just completed a full set of tests on a new set of Sanyo Eneloop batteries and updated the Sanyo results in my comparison (the old tests were done two years ago, using different equipment than all the other battereies tested).

I've also started tests on Panasonic and EasyPix low self-discharge batteries, and have posted the fresh-from-the-package and freshly-charged results. The one-week and seven-week results will appear one week and eight weeks from now respectively.

Retronome - A Versatile Analog Drum Machine for my Hammond Organ

Tue, 26 May 2009 18:31:43 GMT

When I purchased my 1962 Hammond M-111 organ back in 2008, it was a vast improvement over my mid-1970s Yamaha BK-20B. The drawbar controlled tonewheel sound, augmented by the warmth of the vacuum tube amplifier, made the Yamaha pale in comparison. There was one feature of the BK-20B that I sorely missed though, and that was the rhythm generator (also known as a drum machine). My sense of musical timing is terrible, but I wanted more than just a simple metronome, so I set out to design one that would be suitable for my Hammond spinet.

President's Choice Brand Low Self-Discharge Battery Test Results

Thu, 07 May 2009 23:16:12 GMT

I've just completed the tests on the President's Choice brand of low self-discharge AA batteries, available at Loblaws, Zehrs, and other grocery chains under the Loblaws umbrella. The results show that they are every bit as good as the other Japanese brands (Duracell, Sanyo, and Sony), at a lower price.

Web Site Reorganization

Thu, 26 Mar 2009 13:47:59 GMT

Stefan's web site has been reorganized. Instead of a separate index for each category (aviation, calculators, electronics, and R/C stuff), all articles are now listed in a single index.

Going forward, this news feed will contain updates about all articles published on stefanv.com, not just those related to electric R/C.

Visit Stefan's new home page >>