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Modular synth madness

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Davesax1965 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: May 26 2019 at 02:43
I wish it was, I spend so long in here !! ;-)

It's a Lexicon audio interface. The audio outputs go into this and from there into the PC and Reaper or Cubase. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: May 27 2019 at 10:35
Back in a few months.... ;-)



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: June 01 2019 at 04:11
PS I'm afraid I had an idea and the synth has got somewhat bigger and more complicated since the last post. 

I think I actually DO need a new hobby. ;-)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: June 02 2019 at 04:17
A very basic first test of the system. Some oscillator scaling (tuning over an octave) issues. Two of eight sequencers being used in the sequencer cabinet (via six oscillators). Two oscillators (out of eight) being used in the main cabinet. 

The oscillators and filters and amps all have to be calibrated - so this is a very basic test. You'll hear some hideous tuning issues in it. This is "barely ticking over", by the way. No added effects, the output goes through a vintage Alesis Quadraverb which is now on top of the synth, making it even taller. ;-)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: June 02 2019 at 04:19
By taller, I mean.....



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Quinino Quote  Post ReplyReply Direct Link To This Post Posted: June 02 2019 at 07:02
Originally posted by Davesax1965 Davesax1965 wrote:


I think I actually DO need a new hobby. ;-)


I told you ... ! LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: June 02 2019 at 10:32
Naaaah, changed my mind. ;-)

Calibration test. Only two oscillators in the main cabinet calibrated, and they're a bit out. More to do. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: June 09 2019 at 04:36
Calibration time. This is where it gets a little complicated. 

For 8 of the 10 oscillators in the main cabinet, there's quite a lengthy and technical procedure to make them play properly. There are six trim pots here by the red voltage probe. The oscillator cores produce a triangle wave. Using an oscilloscope, you adjust the trimpot to get a good looking triangle wave. You then use another trimpot to set up the square wave duty cycle.

(That's just one oscillator in the photo - the other modules are a filter, amplifier, envelope generators and a low frequency oscillator all commoned onto one panel. All you can see is about 4% of the total electronics in the synth.)

Next step is to adjust the output voltage of the internal temperature control to 0.63v, which I'm doing here. Oscillators drift due to temperature - they have to have temperature control to keep them in pitch. Talking of pitch, another trim pot sets the initial pitch and the remaining two are used to set up the octave scaling and "high end trim", which is the time consuming part. Due to some internal tolerances, I've got to desolder the scaling trim pots and replace them with higher value ones to get enough range to do the adjustments. At the moment, it's not scaling enough and notes go flat as you switch octaves.

So that'll be the oscillators done shortly. The next step is to adjust trim on various filters and amplifiers, envelope generators and a few other modules to get the right kind of response. This varies according to taste, sort of, but lots of fun with an oscilloscope, screwdriver and volt meter ahead. 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 05 2019 at 06:18
Right, it's "finished" - as finished as these things get. Perhaps "finished for now" is better. 

I'm building a valve preamp stage with quad inputs which runs into a mixer and then goes to an Alesis Quadraverb from there. There are two (valve) powered oscilloscopes used to visualise waveforms as well. 

Believe it or not, after a long rest, the next project will be to turn two 10U flightcases into another modular, this time using full size DotCom modules. "Collect the set". 

I'm probably going to add a reel to reel tape recorder of some sort as well. As you do. 





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 05 2019 at 06:23
PS Yes, it sounds astonishing. ;-)

The shame is that it won't ever be played live, due to the complexity of it, and also, I'm very unlikely to release any more commercial music. It's really just a fantastic studio instrument for my own amusement. Oh yes, there's going to be a liquid light show in the studio in the form of an oil wheel projector or two. Freak out, baby. ;-)

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Quinino Quote  Post ReplyReply Direct Link To This Post Posted: August 05 2019 at 08:11
Originally posted by Davesax1965 Davesax1965 wrote:



I'm probably going to add a reel to reel tape recorder of some sort as well. As you do. 



Class touch ! Cool
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 08 2019 at 06:10
Thanks, mate. Well, I feel I must. ;-)

For my next trick, I've got some Chinese two column VU meters. LED jobs, really simple circuit. Now, I can pay 60 a pop to someone in Switzerland who sells these mounted into a panel with a few jacks, or I can get out a pillar drill, coping saw and get a handful of jacks and a connector out and make these into modules myself, therefore saving a small fortune and spending a day swearing in the garage in a cloud of tobacco smoke. 

I choose the latter. ;-)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 08 2019 at 06:21
This being the end result. 

This is the thing about Eurorack, or any modular synth format. It's actually very easy to convert designs (from guitar pedals, digital oscilloscopes etc etc) or use old designs where the patent has expired, if you have a basic grounding (no pun intended) in electronics. People do it and then charge a fortune for a handful of cheap electronics. On the top row, there's a voltage controlled amplifier, the VU meter and an output module to convert a 10v signal to line level, with a bit of filtering. It's all simple op amp stuff. 1970's electronics, anyone with some basic skills and a bit of kit can do it. Hardly rocket science. 

One of my projects is to produce a valve preamp / distortion module using a 12AU7 / ECC82 tube running off 9v. Few resistors and capacitors, a few jacks, valve base, tube.... just as with guitar pedals, you can either pay a fortune for someone to build you one or do it yourself for very little, just a bit of effort. And that's why I built this synth, I'd be bankrupted if I'd bought it all from manufacturers. 

Besides, it's fun. ;-)



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 14 2019 at 06:12
Latest idea.

Build standalone mixer using Bourns PTL series light up slide potentiometers, TL072 op amps and a homemade 12v power supply. All fairly easy stuff, I can find a nice Hammond enclosure, the sloped type with sides. 16 channels, so that's four TL072's - the difficult bit is cutting slots in metal for the slide pots. I can incorporate some two channel VU meters and a line level output module or two. 

Actually, I could even build a valve preamp stage into it as well. Although that's quite power hungry and the voltage regulators I'd be using in the power supply would need big heatsinks, at least. But. All do-able. 

Or I could buy a mixer, but that's hardly the point. ;-)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Davesax1965 Quote  Post ReplyReply Direct Link To This Post Posted: August 14 2019 at 06:17
These being the pots in question. Trouble is, I've got some Eagle component libraries for 30 and 45mm travel, so I have to make a new template for the 60mm variants. Some of these are very difficult to find in certain values - unless you're buying 20,000 at a time, at which juncture, the suppliers get a bit more lenient with you. 

It's the same with a lot of synth DIY, there are famines for 9mm Alpha pots and vactrols at times. Also rare chips (usually re-manufactured) appear and disappear like mayflies. Get 'em while they're hot. 

https://www.digikey.co.uk/product-detail/en/PTL60-15O1-104B2/PTL60-15O1-104B2-ND/3781326/?itemSeq=300818890


Edited by Davesax1965 - August 14 2019 at 06:21

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