Showing posts with label DIY. Show all posts
Showing posts with label DIY. Show all posts

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


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.

Wednesday, 8 October 2014

A visit to Non Linear Circuits - Perth, Western Australia

While on a recent trip to Perth I dropped by to visit my friend Andrew F of  Nonlinear Circuits.


I got to meet Pinky :-)


This is "Synth Porn"

And even more famous than Pinky are Randy & Bill
Randy is on the left. Bill who is only 4 months old is on the right.



Back to the synths:
This is all Eurorack format, consisting of :
2 tri-core VCOs 
2 LFOs 
2 LPGs 
3 VCAs 
VC spring reverb 
diff-rectifier 
jerkoff chaos 
2x  Buchla inspired 281 EGs 
Sauce of Unce (SOU). Based on the Buchla 265


A new NLC Serge format Panel.

This comprises:
Two VCOs
diff-rectifier 
Vibes (a collection of fixed filters) 
VCA
Mixer



This is part of an electronic analog computer which Andrew rescued many years ago.  It's programmed using patchcords that connect op-amps, capacitors, resistors, etc. to carry out calculations.



                                A adder circuit. It's a lovely illustration of how the Op amp's
                                    negative feedback can be used to do computations.


 This circuit adds the 3 inputs.
Vout = -R4[V1/R1+V2/R2+V3/R3]


                                                                     The integrator.
This op-amp circuit performs the mathematical operation of Integration



 The output voltage is proportional to the integral of the input voltage. (ie: the size of the output is controlled by the length of time a voltage is present at its input). This is determined by the negative feedback capacitor which charges/discharges.


I'm not sure of the age of this computer. Maybe 1950s /  1960's ????
It's beautiful though. 



 Pieter Brugel-the-elder, "The Triumph of Death"

  c. 1562. The original can be found in the Museo del Prado, Madrid 

Skeletons hauling a wagon full of skulls.
Death is indiscriminate. We will all have to face it one day.



An early valve synth



All pics are reproduced with the kind permission of NLCs.

Thursday, 2 October 2014

Building the TTSH - A 14 minute Video Diary

Building the TTSH was lots of fun. While building, I collected lots of photos & videos so decided
to put them all together into two videos.

It's not a "How to Build the TTSH". There are plenty of those up on the net already.
It's just a collection of my experiences. Maybe watching it will encourage you to build one too.




Saturday, 27 September 2014

TTSH - Arp clone - first impressions (video)

Not totally finished but I think still worth
recording a video.

The TTSH has been lots of fun to build and a great learning experiemce to boot.


A link to my build notes can be seen here.

And you can download better quality audio here.


Thursday, 4 September 2014

TTSH - ARP 2600 - Build notes - Index

I've really enjoyed building the TTSH.
It's given me a unique perspective of one of the greatest synthesizers of all time - The ARP 2600.
As my build notes are all over this blog I thought it would be good to put them into some sort of order
Thus this index:

1. Preconstruction Pics
2. 2047-1 VCO submodule
3. PSU - We have the Power !!!
4. VCO 1
5. VCO 2
6. VCO 3
7. 4012 Filter (DIY)
8.  The 4020 ADSR
9a. Transistor Matching.
9b. VCA  (4010 & 4019)
10. Ring Modulator (4014)
11. Pre Amp 
12. Envelope Follower 
13. Mixer & Reverb  
14. Noise 
15. Voltage Processors 
16. Internal Clock 
17. Sample & Hold 
18. Electronic Switch 
19. The Amplifiers 
20. Final bits 
21. First Impressions (Video)
22. Building the TTSH in 14 mins (Two Videos)

This order of building the TTSH can be changed of course.
I've basically followed Zthee's notes and found them to be very useful.
It's taken me about 3 months to put together, but I estimate that it can be done in about 20hrs
if you put your mind to it (giving up eating & any toilet breaks).
But if you take the long road this is a very rewarding experience. Studying the circuit diagrams and trying to
understand how the ARP engineers put this together nearly 50 years ago is so cool.
We have a window into the mind of Alan Richard Pearlman.

Thanks Zthee. :-)

Tuesday, 26 August 2014

TTSH - ARP 2600 clone - build notes - Final bits (DIY)

Part no.20 of my TTSH (Two thousand six hundred) build which is a clone of the ARP 2600 synthesizer.
Finishing off some last bits.

You can see my full build thread HERE
There are two awesome TTSH threads in Muffs.
2600 clone - Two Thousand Six Hundred (TTSH)
and
Two Thousand Six Hundred (TTSH) Project General Build Thread
The DSL-Man site has a very good TTSH thread
And of course the official build thread is here
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Adding odd resistors & trimmers for the LEDs.

The power transistors --- orientation ?

Power Transistors (BD236 and BD237). Does the writing face up or down?


Power transistor BD 237


Power transistor BD 236

 There are 5 Switchcraft DPDT slide switches to instal.
This is a bit tricky as they need to be installed quite high.


I inserted them into their holes first then screwed the faceplate on.
When you turn the synth onto its face the switches should fall
into their correct places. Then solder.

Instal the jacks next. There are a lot of them!

It's starting to look good :-)


Linear 100K sliders first.

Testing that the faceplate still fits with the first set of sliders.
Looks Good. ! Onto the audio sliders.

 The standoffs should be 11mm. I'm using 10mm ones with some 1/8' washers.



Just the last 1M slider to install.

 Carrying out some initial tests.
All the modules seen to work fine (apart from the leds not lighting in two cases: The VCA and Noise).
The VCA & Noise do however work. Noise is a bit loud..... might try some other transistors 

Still, I'm really happy. What a awesome project. Thanks Zthee. (THC).

Monday, 25 August 2014

TTSH - ARP 2600 clone - build notes - Amplifiers (DIY)


Part no.19 of my TTSH (Two thousand six hundred) build which is a clone of the ARP 2600 synthesizer.

The Amplifer

You can see my full build thread HERE
There are two awesome TTSH threads in Muffs.
2600 clone - Two Thousand Six Hundred (TTSH)
and
Two Thousand Six Hundred (TTSH) Project General Build Thread
The DSL-Man site has a very good TTSH thread
And of course the official build thread is here
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There are left & right sections to this.

Left amp (from the rear view).

Right amp