Thursday, 21 August 2014

TTSH (ARP 2600 clone) build notes - Internal Clock (DIY)

Part no.16 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synthesizer.
The Internal clock.

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

The clock section in the ARP 2600  is integral to the Sample & Hold module.

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Most of the clock circuit in the TTSH occupies the bottom half of the PCB.
In this section there is a sample & hold (on the right) and electronic switch (on the left).


I'm building the clock circuit first.
Here is a little on how it works.

THE internal clock is basically a LFO (square wave).
It's  pulse width is determined by the variable resistor R385 (which is a linear 100K trim)..

The circuit uses the combination of Q45 (2N4870) & C115 (1µ5 x 1 Electrolytic cap) to make a relaxation oscillator. This produces a sawtooth wave which is then converted to a square by
A42 (a LM 301 comparator). It's output is pin 6  -- leads to the diode (CR47).

A relaxation oscillator is a non-linear circuit consisting of a feedback loop containing a switching device - in this case a transistor (Q45) that repetitively charges a capacitor (C115) through a resistance until it reaches a threshold level, then discharges it again. Relaxation oscillators are commonly used in car blinker lights to indicate which way you wish to turn.



This closeup shows the relaxation oscillator (including the 1.5uF cap & the 2n4870 trannie). At the base of the 47k resistor (R384 in the 2600 schematic) is your saw wave test point.

The square wave test point in the centre of pic.
It's at the base of the diode.



Elektron Analog Rytm & Analog 4 jam - flying

You gotta love these two machines. Such an awesome combo.

Wednesday, 20 August 2014

TTSH (ARP 2600 clone) build notes - Voltage Processors (DIY)

Part 15 of the TTSH build.
I love this section of the ARP 2600. They are not as sexy as the filter or VCOs but still very useful.

This is the voltage processor section on a ARP 2600




Below are some demos using my vintage 2600.


And the lag processor:



It's a awesome module.
Anyway, this is the next part (no.14) of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synthesizer.
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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The TTSH rear section of the Voltage processor PCB

 Front section.



Tuesday, 19 August 2014

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

Part 14 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synthesizer.
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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 The Noise module pre-population


The ARP 2600 used the 4022 submodule to generate noise.
Here is a link to the schematic care of ArpTech
The transistor Q1 (2N5172) acts like a zener diode. The base-emitter junction of any silicon transistor can function as a noise-generating zener diode if its emitter base junction is reversed biased.
The zener produces random noise. The noise is then fed to an amplifier (LM 301)

The official TTSH build states that "a 2N5172 should be selected for maximum noise. But the 2N5172 may be too noisy!... causing clipping and distortion. Any other transistor will probably do. Try a BC547 ??? (Beware the pinout though, the 2N5172 is BCE and not CBE/EBC as most other transistors)".

DSL man suggest using a bc337 instead and/or soldering a 10K resistor to the 1uf cap.


RESISTORS FIRST

Music from Outer Space have a great page devoted to noise generator circuits and they make special mention of the 2N5172 transistor.

Quote:
"These 2N5172 NPN transistors have been tested and selected for their emitter base reverse bias noise. They give greater than 3V peak to peak noise with a non-inverting gain of 100. While testing I observed a wide range of noise levels with > 3V p-p as what I consider the lowest acceptable level. However several of the tested transistors caused clipping at a gain of 100 because they are very noisy. Due to this fact it is often necessary to reduce the gain in the white noise generation section of many MFOS circuits when using one of these selected 2N5172 noise transistors."

Anyway, I'll stick with the 2n5172 for now. I've cut up some female headers to make a socket for the transistor. The original ARP 2600 schematics use a "selected 2N5172". I may have to try out a few 2N5172s before I find one I like.


IC's and transistors installed.


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The ARP 2600 Noise section - part of the sample/hold & clock section.

Monday, 18 August 2014

TTSH (ARP 2600 clone) build notes - Mixer & Reverb (DIY)

This is part 13 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synth.

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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  The Mixer section before components.



A little on how it works
The mixer circuit looks like it uses a standard Op-amp inverting config.
Signals enter the mixer through sliders R200(100K log) & R201 (100K log).. then through R202(100k) & 203(100K). They enter the first LM301 op-amp via pin 2.(in the schematic it's identified as A25).

The signal leaving A25 goes to the pan slider & reverb.

At the pan slider the signal again splits into left & right channels.
The right channel passes through R256(100k) into pin 2 (inverting input) of A27 (LM301 op-amp).
The left channel passes through R255(100k) into pin 2 of A26 (LM301).
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So basically op-amp A25 inverts the initial input signal.
Then op-amps A26 & A27 re-invert, buffer & amplify it for output to the left & right channels.

TTSH (ARP 2600 clone) build notes - Envelope Follower (DIY)

The ARP 2600 envelope follower is a really cool module.
The pre-amp is internally wired (normaled) to the envelope follower.
It converts amplitude to voltages.The louder the input signal, the greater the output voltage.
It's a great way of introducing external sounds (like drums) into your TTSH to modulate the filter cutoff for example.

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This is part 12 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synth.
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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A bit on how this works.
The Envelope Follower is basically a full wave rectifier.
It generates a +ve DC voltage output directly proportional to its input. (a 2V peak to peak = 5V DC).
The rectifier basically consists of A1 & A2 (both LM301s) and two diodes.
The +ve input leaves pin 6 of A1 & passes through CR2(diode),then enters A2 via pin3(non inverting input)
The -ve input passes through the diode CR1, and enters A2 via pin 2 (inverting input)
The rectified signal leaves A2 via pin 6.
The resistors R12,13,14,15 & caps C7,8,9,10 filter the signal.
Finally A3 amplifies the signal.


Pre soldering of components.

Resistors, Diodes, Caps

The LM 301s are in. 

Test then on to the mixer.


Sunday, 17 August 2014

MUSEO FRIDA KAHLO

The Frida Kahlo Museum (in Spanish it's called the Museo Frida Kahlo) is one of the must sees when you visit Mexico city. It is also known as the Blue House (La Casa Azul) after its cobalt-blue walls. You can find it in the Colonia del Carmen neighborhood of Coyoacán in Mexico City.


 It's a moving tribute to Freda. She was born (1907) & died here.The home is today a museum dedicated her art (& tragic) life. She spent the last 13 years of her life there.

The house is built around a central courtyard with garden space in a French-style.
It gives a good glimpse of how wealthy Mexican bohemian artists and intellectuals lived during the first half of the 20th century.


Freda spent much of her childhood here and this is where she developed her sense of social consciousness. Her connections to the communist party are well documented. During the Mexican Revolution, her mother would open the windows of this house in order to donate supplies to the Zapata army. 

In 1918 she was struck with polio. This left her with one leg shorter than the other. And when she was 18 a tram accident almost killed her. She spent over 2 years in hospital and never totally recovered. This was a very painful period in her life, full of casts and orthopedic devices. It was however a blessing in disguise as in order to pass the time & communicate her anguish & pain she began to paint.




The museum is decorated with lots of Mexican folk art, Kahlo’s own personal art collection, pre-Hispanic art, photographs, postcards and letters.There are also works by José María Velasco, Paul Klee and Diego Rivera (her husband).




This wing was added on by Diego Rivera (volcanic stone and shells).

For more travel postcards click here: