NEriks Blog

Moog Modular maintenance

Sat, 27 Feb 2010 14:17:00 GMT

I often get questions from various musicians about renting out gear from my studio. One of the most sought-after instruments that I have is my old Moog Modular system. The system is basically a standard Moog System 35 with a sequencer complement cabinet. Although the system is over 30 years old I rarely have any major issues with it. As long as the system is kept in one place and not moved around between different studios it normally stays in a functional state for a very long period of time. Occasionally the system needs to be fine-tuned but that's merely a minor issue ...

A few years back the original power-supply of my Moog system suddenly decided to give in during a tuning session of the oscillators. After troubleshooting the original power supply I finally decided to repace it with a new one from Power One.

Replacing the old power supply proved difficult because the connections of the new power supply did not fit the internal power harness of the cabinet. Rewiring the internal power harness wasn't an option since I wanted to keep the system as close to original as possible. The solution was to build a new power supply by reusing the enclosure of the original power supply. The electronics of the original power supply was removed from its enclosure to give room for the new power supply.

The new power supply was built by using four independent power supplies (NEriks PSU-1) connected and configured to supply +12V, -6V, +15V and -15V to the system.

In order to dissipate heat from the voltage regulators a heat sink was constructed from an 8 mm thick aluminum plate.

The circuit boards of the power supply was mounted on the heat sink plate which was installed in the old enclosure. The original transformer was reused as well as parts of the internal wiring and the output connector.

One of the best!

Wed, 23 Dec 2009 12:03:00 GMT

A few months ago I received a broken Moog Sonic 6 from a client in Norway. I've repaired a few Moog Sonic 6's in the past but I have never worked with an early revision of the Moog Sonic 6 before.

The Moog Sonic 6 is a duo-phonic analogue synthesizer manufactured by Moog Music in the 70's. The Sonic 6 was a result of a company merge between R.A Moog and MuSonics, which previously had been developing a synthesizer called the MuSonics Sonic 5 The early revision of the Moog Sonic 6 is equipped with the same type of diode-ladder filter used in its predecessor, the MuSonic Sonic 5. Comparing an early revision of the Moog Sonic 6 with a later revision (with a serial number above 1264) one will most certainly notice that they sound a bit different from each other.

Apart from the diode-ladder filter there are a few other details that also differs from the later revision. This made the repair process more challenging since I only had the service manual of the later revision at hand.

Having the Moog Sonic 6 in my workshop for some time I've become rather attached to it. I really like the design of the synthesizer which offers both extensive modulation capabilities and a very powerful sound. The only thing that really bothers me is the AR (ASR) type of envelope generator which sometimes feels a bit limited. All-in-all I think that the Moog Sonic 6 (especially the early revision with the diode-ladder filter) is one of the best Moog-synthesizers ever produced.

For more information about the Moog Sonic 6, please read this excellent article about the Moog Sonic 6, written by Gordon Reid.

Back to work with electronics ...

Fri, 25 Sep 2009 12:22:00 GMT

Recently I've worked a lot to get our Saab Safir airworthy but last night I finally got a chance to get back in my workshop to work with electronics again. The reason that forced me back to my workshop was that the COMM / NAV radio of the airplane suddenly decided to stop working ...

Note the frequency of Eskilstuna/Kjula (ESSU) AFIS tuned-in on the radio

It's been years since last time I worked with old analogue radio equipment so I was a bit unsure if I would be able to fix the radio. However, the fault turned out to be a bad capacitor that short-circuited the power supply to ground so I managed to repair the radio rather quickly ...

Internals of the COMM / NAV box. Note the large frequency selectors to the right in the picture ... I really love vintage electronics!

Installing an ELT406

Wed, 23 Sep 2009 15:45:00 GMT

Today we finally installed an emergency transmitter (ELT406) in our Saab Safir. Below are a few pictures from the event ...The aeroplane isn't airworthy in its current state but we hope to get it airborne again by the end of October this year.

NEriks Air

Wed, 01 Jul 2009 17:17:00 GMT

It's been a while since my last blog post so I feel it's about time to write something about the recent activities that I'm been involved in. A large part of my recent work has been focused around avionics to some extent so we recently decided to extend the business of NEriks Audio to also involve avionics. The work with avionics have been organized as a new side business to NEriks Audio called NEriks Air.

Besides working with avionics, NEriks Air recently acquired a Saab 91B Safir (SK50) who previously has been owned and used as a military trainer by the Swedish Airforce. The clip blow was shot by Ronny Karlsson when it arrived at Kjula airport (ESSU) together with another Saab Safir 91B (LN-BII) from Norway.

SSM2040

Sat, 04 Apr 2009 12:03:00 GMT

Last week the SSM2040's that I purchased from a guy in Japan finally arrived. I've just tested each one of the them in my Prophet-5 rev 2 and all seem to work as expected. I really like the sound of the SSM2040 so I'm currently feeling very tempted to use one or two SSM2040 to build me a stereophonic filter module to use with my modular synthesizers ... Although, it would have been nice to use vintage SSM's for the filter module I think the best thing to do is to keep the SSM's as spare parts for synthesizers as the E-mu modular, Prophet-5, Octave the CAT, PMS Syntar, RFS Kobol ...

Cost of maintaining old Prophet's

Sun, 01 Mar 2009 17:45:00 GMT

One of my favorite synthesizers is the Sequential Circuit Prophet-5 which was one of the first fully programmable analog polyphonic synthesizers introduced in the 70's. The Prophet-5 was manufactured in tree major revisions between 1978 and 1984. The first and second revision of the Prophet-5 used SSM chips, while the later rev 3's used CEM chips. Sonically there are many people insisting that the SSM-based Prophet's are better sounding than the rev 3's but I think its purely a matter of taste.

The Prophet-5 owned by NEriks Audio is a rev 2 that have undergone extensive updates to the power supply and digital board in order to make it more reliable. Generally, rev 2 Prophet's seem to have a rather bad reputation when it comes to reliability. My experience is however that most issues concerning reliability may be rather easy to fix just by updating the power supply and replacing all the tantalum capacitors in it. From a serviceable point of view it may be wise to continuously maintain an old Prophet since a failure may be very expensive to repair.

One of the most expensive parts in a Prophet-5 rev 1 or rev 2 nowadays is the SSM chips which are getting more and more difficult to source. As an example, the SSM2040 voltage controlled filter chip seems to be getting more and more expensive every time I see one for sale. A few years ago I was asked by a client to restore a Prophet-5 rev 2 which partially had been cannibalized in order to repair another Propet-5 rev 2. When I opened the unit I discovered that all SSM2040 was missing. Getting five new SSM2040 resulted in a total cost of approximately $250 ($50 each).

A few days ago I was contacted by a guy in Japan who I previously have done some business with. He asked me if I was interested in buying his stock of SSM2040 at a price of $120 each. Initially, I turned his offer down due to the high price but after some thinking I finally decided to accept his offer. I'm aware that I probably have paid an overprice for the SSM's but on the other hand I'm one step closer to secure the future of our Prophet-5 rev 2 ...

Vintage Buchla Modules (part III)

Sun, 22 Feb 2009 15:13:00 GMT

Yesterday I finally delivered the Buchla-system that I have been working on for the last few weeks. There have been numerous issues related to the work with it so it was a great feeling to finally hand it over to Mattias Petersson at the Royal College of Music in Stockholm.

Above: Mattias Peterson, Royal College of Music in Stockholm, will use the Buchla for teaching students about sound synthesis.

For a few more hi-res pictures, please click on the links below:

Ready for test
Close-up of the 296 module
View from the right-side
Module 285 in focus ...

Vintage Buchla modules (part II)

Wed, 18 Feb 2009 12:28:00 GMT

As mentioned earlier in this post, I'm currently working on bringing a vintage Buchla 200 system back to life. A few weeks ago I started to design the cabinet and after a few twists and turns the cabinet was finally finished last week.

During the last couple of days I've been working quite hard to mount the modules in the cabinet and test them. The biggest issue I've had so far is the original Buchla power-supply, which was connected through an old step-down transformer. As a precaution I briefly measured the voltage between the power-supply chassis and ground before connecting any of the Buchla modules to it. To my surprise I discovered that the voltage between the power-supply chassis and ground was approximately 230V! Disassembling the step-down transformer revealed that it was and old autotransformer. An autotransformer is an electrical transformer with only one winding. Since the input of the transformer isn't electrically isolated from the output its output may result in 230V between neutral and ground if the power plug happens to be plugged into the outlet the wrong way around.

I'm VERY keen on electrical safety issues so I will replace the old autotransformer with an isolated step-down transformer and rewire it according to modern standards. Hopefully I'll get the Buchla-system up and running in a day or two so I finally can test it!

New EPROM programmer!

Sat, 07 Feb 2009 13:35:00 GMT

Yesterday finally took the plunge and bought a new EPROM programmer for my lab. My old EPROM programmer suddenly decided to give up when I really needed it the most so there wasn't really much to do other than to start looking for a new one. Since I work a lot with old Prophet-5 synthesizers I needed an programmer capable of programming old 2708 and 2716 EPROM's. In contrast to the old 2708 and 2716 EPROM's I also wanted a programmer capable of programming the latest 32-bit microprocessors from Microchip (PIC32). After some serious considerations I finally decided to buy an ELNEC BeeProg+ although it turned out to be more than twice the price of what I initially was prepared to pay for a new programmer.

So, back to work with the Prophet's ... During the last couple of years I done some reverse engineering of the firmware regarding the firmware of the Prophet-5 rev-2. One thing I've been able to fix in the firmware is to prevent it from hanging during auto-tune if one of the voices is malfunctioning. In the latest version I've been able to add support for enabling and disabling individual voices through the program selection buttons.

NOTE: Please, don't send me inquires about selling EPROM's with the updated firmware for the Prophet-5. I have no clue about the copyright issues of the firmware. Fiddling with the firmware of the Prophet-5 is solely for my own personal interest. For general inquires about EPROM programming, please refer to our vintage synthesizer repair page.