My Mini Moog Voyager. Click to go to my web site...

Monday, August 3, 2015

PCBs are here

I received my large order of PCBs today. As soon as I can unpack and make sure they're right, I'll update the website www.analoguerealities.com, with the new inventory.

David

Thursday, April 16, 2015


Nyle came by today, which is always a treat. The occasion was there is a documentary being made about him and his life. Part of that life crossed mine and so I got to be a small part, too. When the documentary is finished, I'll post a link if it's allowed. It was a lot of fun. Nyle played his EVI hooked into my Synthasystem. Then, Nyle (and I) played around with it having fun (mostly Nyle tweaking the knobs). The photo on top is just a sort of long shot while the crew was setting up lights. The one at the bottom is Nyle himself in front of my Synthasystem.

Thursday, January 1, 2015

New Web Site and Web Log

My new site is running on about 1 of 8 cylinders, but it is useable. The old web site is officially closed down and the new one Analogue Realities is taking over the duties. It's also a Web Log, so I will be making most updates there, but posting links here so those who follow this blog will get the news.

Thanks and Happy New Year!

Tuesday, December 2, 2014

Audio for 914 comparison

Here is audio comparing my 914 to Yves Usson's design. I compared the inductor version. There are a couple of things to remember:
  1. Yves uses two cascaded filter cells, each one having the same cutoff frequency but different "Q". Mine has two cascaded filter cells as well but also follows the Moog where the first cell's cutoff is a little lower than the second cell's cutoff. The "Q" of the second cell is essentially fixed with a resistor and the trimmer on the input to the first cell is adjusted to change the overall "Q" to get a "Q" of 3.7 (per Yves' research) which seems consistent with the component values on the Moog schematics (although there are a couple of errors on those schematics, no surprise). One glaring is a missing resistor on the second cell which sets the "Q". Somehow, Jurgen missed this. I caught it when I was unable to get a close visual match to the Moog frequency response curves so I did a detailed study of the only photographs I could find of the Moog 914 and worked through the math.
  2. The Moog has a fixed high pass filter with an effective cutoff of about 60Hz (if memory serves me) between the summing node of the filter cells and the input to the output amplifier. The 907 did not have this and I don't think Yves included this on his 914, but I could be wrong. Jurgen included it on his 914. This affects the low pass cell response.
  3. Yves changed the 700Hz cell to a center frequency of 750Hz.
  4. I think the actual cutoff frequencies for the HP and LP cells are a bit different in my 914 as opposed to Yves.

In the audio, my 914 is in the left channel and Yves' is in the right. There is some kind of funky echo or ray gun sound at the beginning of the audio. I have no clue what artifact it is. I recorded the two using a Tascam DP-24. The output of each filter was fed directly into the DP-24 with no additional EQ, or other modification. I'm driving the filters with the same sawtooth from a Steiner Type "A" VCO whose frequency is driven by a sine wave from a Steiner Type "B" VCO. The resulting audio files were mixed down to a stereo track using the DP-24 then uploaded here.

I start with all cells and let you hear the YU 914 alone, then mine. I then take out each cell one at a time HF down. I then compare each cell one at a time. I end by adding all the cells back in and then letting each filter play on its own again, YU first then mine. Saw tooth with frequency swept by a sine wave.

The most exciting 4 minutes of synthesizer sounds you will ever hear! :)

Here is a link to the uncompressed audio. It's 40 MBytes.

AR 914 v. YUSynth 914

Sunday, March 16, 2014

Synthasystem VCF

Ronny just finished a build and here are some photos and excellent modifications he made. Thanks for sharing Ronny.






Ronny wrote:
"- I added a second CV potentiometer.

"- I omitted the switch and added three separate attenuator potentiometers (25k)
  for the three inputs (LP, BP, HP). They sit before the 47k resistors. The 47k resistors
  connect directly to the former "switch outputs" now. This enables to get a kind
  of all-pass characteristic when mixing the same signal to multiple inputs or to get
  a kind of frequency-dependent interpolation with different input signals. I also like
  to add a bit of HP while primarily using the LP. I normailzed the "BP in" and "HP in"
  connectors to "LP in".

"- I used 330nF instead of 1.2uF for C10 at CV in to reduce drifting with steady CV
  and to enable faster modulation. Maybe I reduce it even further.

"- I drilled a hole into the Power PCB to easily adjust the "CV reject" trimmer without
  taking the filter apart. Luckily there was just a ground plane at this position on
  the power PCB that could be drilled without damaging something.

"- I had to omit the nice Steiner wave logo on the frontpanel, but added a little hint
  to you "DI" and me "RV" :-)

"Here are some other build notes that might be of interest for you:

"- feed it with +-12V in a Doepfer Eurorack system, but reduce -12V to -10V with
  your Power PCB, also use the filtering on the Power PCB (V+, V-)

"- used SSM2210 and 2N5172 as specified
 
"- used two 2N2907 with HFE of about 140 instead of the PN5138 (HFE measured
  with a  medium-class multi-meter)
 
"- had to use linear potentiometers for everything, because I did not get logarithmic
  ones of this size, but this still feels fine

"- used a trimmer having 200 Ohm instead of 250 Ohm, works fine

"==> self resonance starts at about 2 o'clock resonance potentiometer position, this is fine
" ==> have no problems with power noise, crosstalk or whatever"

Thanks again Ronny.

Monday, September 2, 2013

Moog 914 Fixed filter Bank progress

914 Clone and studio

914 clone, Eagle v. DipTrace...

I decided mid stream I wanted to migrate from Eagle to something new. A thread on the SDIY list got me thinking again about the offerings and some of the frustrations I have with Eagle. Eagle has been a great capture/layout system, but I've been more and more frustrated with some of its core operation and workings.

One package which came up was DipTrace. I gave it a look and like it. It's got a few oddities, but seems to be well supported, with reasonable pricing even for the full unlimited version, and full featured, more than I'll ever need for the 2 layer synthesizer circuits I do. And, very important, PCB-Pool, who I use for PCBs, accepts DipTrace format directly.

I've already found that editing/creating parts is as easy if not more so than in Eagle. Schematic capture is intuitive, PCB layout is also nice and the auto place is nice for a first go at least. A nice feature is you can hand place components which have to be in certain areas, the the auto place will put the other components around trying to minimize the signal length. Again, for the simple stuff I'm doing maybe not needed, but also works nicely and saves some time. There are some quirks I'm finding, like selecting which labels to display and placement, but I think I can make it work.

In the end, I bought a license and will be migrating my future work into DipTrace. The Steiner stuff is pretty fixed and I don't plan on any modifications. But if needed, I can export the Eagle schematic or PCB and bring it into DipTrace. Not the ideal, but a workable solution should the need arise. I'll also output all the Eagle designs into Gerber files for future proofing. This is something I tested quite a bit before I decided to buy.

That leaves the 914 clone I was doing a bit in limbo. I had already laid out one PCB and had two schematics completed. While I can import the schematic and even the PCB into DipTrace, I found that there is still some work to make the schematic useable. At this point, I think I will probably just start over in DipTrace. The schematics are really pretty simple for this clone and then I'll be able to make use of the enclosed and custom libraries I've got in DipTrace.

My time line for PCB prototypes is now a couple of months out at least. I need to learn DipTrace, double check the schematics, etc. but, I'm excited to get it done. I still intend to build two, one with inductors for everything and one with GIC simulated inductors.

Studio

My new studio is done. I just need to make time to actually re-connect all the instruments and a little organizing. I'll put up some photos after it's all hooked up and neat.

Tuesday, June 25, 2013

New studio and Moog 914 clone

I am moving to a newly finished attic space for my studio. I'm pretty excited about it. This photo shows it with sheetrock and baseboards. The painters finished today and I should be able to move in this weekend. I get the far end, about 12 feet wide, and 15 feet long out of about 30 feet. The rest will be for storage. the two round "lights" are actually skylights. They install a mirrored tube to a clear dome cover and it collects and reflects the light like crazy. I will put some diffusers over the openings to help soften the very bright highlights.


Next, I have a new project. I decided to roll my own Moog 914 fixed filter bank. I have two of Yves Usson's version, and PCBs for Jurgen Haible's version, so why my own? A couple of reasons. First, I want it to easily fit behind a euro rack panel. Second, I want to have PCB mounted pots to minimize flying wires. Third, I found a source for inductors and I want to make it easy to use either inductors or a GIC simulated inductor like Jurgen offered. The result will be 4 PCBs which will fit behind a 28 HP euro panel.

Carsten Toensmann at www.analog-monster.de has his own 914 clone for which he made his own inductors. He has decided to offer a service of winding custom inductor values, in particular those found in the 914. I think he is also offering PCBs. Carsten is very helpful and I encourage you to look at his work. Really amazing.

I purchased two sets of coils from him and will build at least one of these clones with real inductors. The layout I'm making will allow for the size inductor Carsten is making as well as a simulated inductor for the high pass and band pass cells. The low pass will have to use real inductors or an active low pass filter like Yves Usson designed or Jurgen Haible designed.

I decided that I will have the option of using all the original Moog circuitry. Most of the parts are still readily available and the one transistor which is out of production, 2N2926, is still to be had at Nikko Electronics http://www.dalbani.co.uk/index.php. I have always had great service from them and highly recommend them.

Besides using the original Moog circuits, by flipping a couple of DIP switches and moving a jumper or two I'm going add the options of having a more useable output stage as well as an input stage that can handle higher input levels than the Moog original. In my simulations, the circuits I borrowed (from Jurgen Haible's fixed filter bank clone) match the frequency response of the original very closely with the advantage of a higher level output and higher level inputs. I am also adding even and odd cell outputs following Yves Usson's great idea.

I'm almost read to actually start the layout process. I've got the input and output stages designed and simulated. I have the basic bandpass filter cell designed as well as the high pass and low pass sections. I just have to copy and paste all the filter cells and adjust the values. Then, layout the PCBs. I think I might realistically have PCBs in hand by the end of July to middle of August. I'll post some samples when I have it built.