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






TTSH - ARP 2600 clone - build notes - Electronic Switch (DIY)

Part no.18 of my TTSH (Two thousand six hundred) build which is a clone of the ARP 2600 synthesizer.

The Electronic Switch

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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Ok, we are almost there.
The switch next.

 The unpopulated switch section.

2n4392

The electronic switch is pulsed by the VC clock.
The clock provides the voltage that switches it between the two sockets (A & B).
Looks like the 2N4392 JFETs does the job of switching.

Missing the 150k resistor.


Song of the Daleks - Korg MS20 Mini & Doepfer Dark Time & Energy

The Korg MS 20 uses a different scaling method to most synths.
It's Hertz/Volt not the more common 1v/oct.

The Dark time sequencer is v/oct.
Still they aren't too shabbly together.
Sorry about the audio quality.




It's a small tribute to Dr Who.
Watching John Pertwee & Tom Baker take on the Daleks as a child is etched on my memory forever.



Thursday, 21 August 2014

TTSH (ARP 2600 clone) build notes - Sample & Hold (DIY)

Part no.17 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synthesizer. 

SAMPLE & HOLD

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 ARP 2600 synth used a 4015 sub-module for the sample & hold.


rESISTORS, CAPS, TRANNIES IN

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The sample & hold section on a ARP 2600

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.