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

Monday, 28 July 2014

TTSH Synth - The Human Comparator - VCO 3

Finally the third VCO of the TTSH synthesizer.
This is part 6 of my TTSH (Two thousand six hundred) build.
You can see my full build thread HERE


The VCO3 section before population (well almost)

Resistors & Diodes first. Then caps, headers, etc.

Install trimpots on the front side of PCB


 Almost there. 

This is what the front PCB looks like now.

Now to test for the waveforms.The square first.




And the ramp. Yahoo !!!


Wednesday, 23 July 2014

TTSH - The Human Comparator - ARP 2600 Replica - VCO 2

This is part 5 of my TTSH (Two thousand six hundred) build.
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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VCO 2
The 2nd VCO has four waveforms: sine, pulse, saw, ramp.
It's my favoutite VCO

 Rear panel view

Front panel view for VCO 2

First install resistors, IC sockets, MTAs if you like.


Install trim-pots, caps, etc.

 2N3954 TRANSISTOR
This is a ultrarare transistor.

3.5mm jacks The one on the left is from Thonk.

The PJ301BM jack from Thonk on the left is ideal for the TTSH project.
The one on the right is a standard (modified my me) 3.5mm jack.
It's simpler just to get the ones from Thonk.

The jack needs to be installed on the sine VCO. Then test with your scope for the relevant waveforms.

You will need a 2N3906 & 2N5172
The 2N3906 a common PNP bipolar junction transistor.
The 2N5172 is a NPN. 

Tuesday, 22 July 2014

GenoQ Nemo Sequencer repair (Power supply)

It's sad that GenoQs who manufactured the Nemo & Octopus sequencers are no longer with us.
I have owned a Octopus for a few years now and love it to death.
It's a beautiful instrument to behold and is built like a Mercedes (they both hail from Stuttgart Germany).

So when the chance to buy the more portable Nemo came up I jumped on it.

I was upset when I first tried to power it up. ....Nothing happened. :-)

After checking the PSU (5V DC @ 3A, center +ve) I decided the only thing left to do was open it up and have a look (before I gave up and sent it to my technician).

This is what I found.

The blue metal is the base.The green section is the underside of the faceplate.


The power enters via the green PCB behind the red PCB.

The problem turned out to be a faulty power socket.
 These were the problem.

So if you encounter a similar problem it would probably be worthwhile to check this first before sending it
to a technician. There is no longer any warranty to void as the company is long gone. Plus I think it's always useful to know how things work in order to do simple repairs.



There is a diode installed to prevent accidental polarity reversal though still be careful. 
No soldering required. All you need is a Philips Head Screwdriver. Red is +ve, Black is -ve.

Thursday, 3 July 2014

Vermona DRM - How to install CV triggers

I've owned a Vermona drum for many years. It's a DRM 1 - Mark III.
I love it to bits but purchased it in the days when I was only interested in midi triggering.


Since getting into modulars I started to regret not buying the version with the CV triggers.
I've read that adding the triggers is easy but could never find info on the web relating to this.
Hopefully these pics will help others wanting to do this mod on their own.
Once you see how easy it is you will prob want to get to it right away.
The triggers are placed  into the spot on the left with the 10 caps.

Once you have opened the drum, remove these caps.

These are the trigger modules. You will need two (there are 5 trigger inputs in each).
 The underside of a trigger module.

This is the inside of the DRM.   Beautiful to behold!!

The CV trigger modules have a ribbon cable that simply plugs into the PCB as shown.


That's all that is really needed. No soldering :-)




Many thanks to Matt of "RhythmActive" for supplying the trigger modules.

Sunday, 29 June 2014

TTSH - ARP 2600 Replica - VCO 1

This is the 4th part of my TTSH (Two thousand six hundred) build.
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 unpopulated rear section of VCO 1

Install the IC headers,  resistors & caps first.

This is the front view of VCO 1



These headers connect the VCO submodules to the motherboard.
I'm installing these on the motherboard as high as as I can to 
provide as much room as possible between the two boards.



Connecting VCO1 to the PSU.

I'm soldering the connections directly to the PSU, though you many wish to use MTA connectors.

The red wire to the base of the resistor is temporary only.
+15V needs to be applied there for testing.

If all is working you should see a square wave from this pad and a saw from the pad above.

The VCO uses fairly inexpensive LM301 op amps which can be found in many vintage ARP 2600s:


This is the pinout:

I might in the future try replacing these with more modern 711's, LF351s or 411s. ???
It's probably not a matter of simply swapping the chips. Maybe the 301's are better left in the VCOs and changed in the filter ??? These 301s are everywhere. They can be found in the VCOs, the filter, the EGs and the VCA.

This modification is just a personal idea and I haven't tested it yet.
I don't recommend any modifications unless you are a qualified technician. 


In Mark Vail's book "Vintage Synthesizers" he discusses the SL19986 describing it as "nothing more than a selected LM-301. He goes on to say that" The reason ARP selected them was for their DC performance. But because they aren't of very high input impedence .... they are not as good as an LF-351,411, or other high-performance op-amps."



Anyway, I'm a bit undecided about changing op-amps. New op-amps may clean the path but I kinda like dirt and noise. Maybe ill keep the old 301's in the end. 





Another ARP guru, Phil Cirocco, has some great info on this website:

 To quote him:
"...The 2600 uses microchip technology in all of its gain stages! The first 2600's .......used hi-fi chips (Teledyne 1339 octal op-amps) with a high slew rate. Although these chips sound great, they were very unreliable and prone to latch up. Around 1972, plagued by failures in the field, ARP was forced to change these chips to a much more reliable type (National Semiconductor LM-301 or SL-1998) The problem is that they slew the wave shape producing a muffled sound. The LM-301 is classified as a general purpose amplifier, and is considered inadequate for audio by present standards. Nearly all the standard production gray-face 2600's use the LM301. This is the main reason why the legendary Blue Marvins sound better!

So I wonder what he replaces the 301's with today ??? 

***********************
Many thanks to "unknown" for his comment re the MC1439
"I've seen picture of 2500 modules where the 301s had been
replaced by MC1439. The PCB looked like it could accommodate
either; the 301, according to the older schematic only used
a cap whereas the 1439 looks like it use series RC for
compensation."

 
Yes it looks like the pinouts for the LM301 & the MC1439 are identical. Ins are on pin 2 & 3. Out on pin 6.
I'll give this a try on one of my next builds.