Wednesday, 22 October 2014

Roland M-240 mixer - power supply replacement (Part 1)

I picked up a beautiful old Roland M-240 24 channel line mixer the other day. Sadly the mixer didn't
have a power supply so it's kinda useless. Roland don't appear to know where I can find a PSU and eBay was equally unhelpful.



The 3 pronged input reads DC -/+ 21.5V and 500mA. It's not your standard Wall Wart.

  Rather than throw it away I've decided to attempt building a new power supply.

Some pics of the circuit board:



This is the underside of the power PCB of the mixer.  It contains 4 voltage regulators: AN7812F / AN7815F / AN7912F / AN7915F. They provide voltages of +/- 12V & +/-15V.
These regulators should be able to handle voltages ranging between 35V to 18V. ..... though I'm not totally sure about how it will effect the rest of the mixer...... So do be careful if you are making these sorts of mods.

Anyway, I decided to test the mixer with a variable DC power supply.
At +/- 18V the mixer works with the exception of the UV meter which doesn't light up.

Nice! +/- 21.5 V and the meter is now also working.:-)

Ok, so we do need at least 21.5 V.
As I mentioned earlier, the internal voltage regulators are AN7812F / AN7815F / AN7912F / AN7915F - They can all handle a +/- 35V input, so anything between 21.5V and 35V should be OK ... though I havent tested this.

Possible soltions: 

I'm thinking of building one of Ken Stone's PSUs.
http://www.cgs.synth.net/modules/cgs14_psu.html

Varying the 78XX and 79XX regulators on the CGS14 board will hopefully give me the required voltage
A 7822 & 7922 regulator would be really nice but these are nearly impossible to find.
Maybe the LM317 & LM337 could be used instead.???

The LM317 has three pins: Input, output, and adjustment. The device behaves like an op amp
Vout = Vref (1 + RL/RH)
or
Vout = 1,25v (1 + RL/RH) .... there might be a small error due to some slight current flows from the
                                               adjustment pin.




It will be fun to play around with and experiment with different resistor values. Also these regulators
look like they could be very useful in future projects where unusual voltages are called for.

Finally, a good tech friend of mine has also suggested I build just the rectifier section of the CGS14 board, leaving out the regulators. (The Roland mixer already has the required regulators on board).

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I stumbled upon a very cool site the other day. ModularSynth.ru
There is a useful entry on their blog relating to bipolar power supplies:
http://www.modularsynth.ru/en/2014/07/18/regulated_psu_update/

They use the LM317 & LM337 regulators.

I'll update this page as I go along.:-)
These ideas are so far untested so proceed with caution if you are doing a similar thing.
I take no responsibility if you connect a power supply to the mixer and it burns out!

Part 2 of the PSU replacement is here


Monday, 20 October 2014

Korg MS-20 mini sequenced by Elektron Machine Drum

What's not to love about those Korg filters.
The Ms-20 is still after all these years one of my favorite instruments.



I'm  using the External Signal Processor in this patch.
Like an envelope follower ... its a very useful addition to the MS20 arsenal.

Sunday, 19 October 2014

Cuba - Havana 1

A few pics taken on a recent trip to Cuba.
The beautiful old buildings are undergoing graceful decay.

















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For more Travel Postcards Click Here
For more on Cuba Click Here

Saturday, 18 October 2014

Elektron A4 synth & Rytm drums - Entrancer

Analog Four, Elektron Rtym & a Buchla 200 modular synth,

The track was recorded in a single take. No audio processing.
I'm using a combination of LZX modules & a Korg entrancer to process the video.

Some pics of the setup:






hERE is a link to the audio file for this composition.

And finally, below is the same video pre video manipulation:


Friday, 10 October 2014

Video on a oscilloscope

Exploring vector rescanning.

Found this video (it's not mine) but I'm experimenting
using the LZX modular system to do a similar thing.


Input the video signal into the z-input of your scope and supply the X & Y inputs with
ramps.

 The circuit uses a LM1881 IC - Its a video sync separator.

Here is another video using the same idea:
Creating X and Y sawtooth ramp signals from the vertical and horizontal sync pulses.

Schematic is here:

Using a Tektronix 485 in XY mode
There is a useful muffs post on Vector Rescanning

Op-amp basics

A friend of mine was asking about op-amps the other day.
They are used extensively in the synth world.
I found this great little video and thought I'd share.
It's very basic but a great introduction to this very important
building block of electronic music.
https://www.youtube.com/watch?v=K03Rom3Cs28

Around 7.15 into the video is a integrator circuit.
It's a classic way to convert a square wave to a triangle wave.

Thursday, 9 October 2014

Elektron Analog 4 & Rytm - Feedback 2

The Elektron A4 & Rytm are a great pair. They are made for each other.
Though the video is processed, the audio was done in a single live take.


Below is a free link to some high quality Wav files of this video
If you wanna have a go at remixing this be my guest.

I've had a few requests for a version without the video editing. ...so everyone can see the machines without the video synthesis getting in the way. Here it is: