TTSH, miscellaneous mods
I started putting together a build post about the electronics side of my TTSH, but there really isn’t actually much to write about that. It’s a kit, and they just work straight-out-the-box when you learn even the details before starting and keep soldering sessions at reasonable lengths (don’t rush the build!).
That said, building mine was probably the first time ever in the ~20 years of electronics hobbies, that I managed to install a resistor of wrong value, in this case to VCO2 triangle-to-sine wave shaper circuit.. Live and learn; had some D’OH moments doing a part-by-part trace of the entire circuit :)
Anyway I thought I’d bundle some of the simple mods under this post. All these three were suggested by user Nordcore in the various TTSH build threads the Muffwiggler forum.
AR envelope generator mod
In stock configuration the Attack portion of the AR envelope generator has a rise-time of around 7ms at its fastest setting. This mod makes it faster, and the original attack time can be still dialed in by slightly raising the Attack slider. Not much to this mod, here’s Nordcore’s schematic:
Additionally user LED-Man suggests that value of C69 could be raised slightly without affecting the shorter attack time, but to have the Release portion last a bit longer. I’m yet to test this, but certainly will if I ever start feeling like the Release should be longer.
VCF decoupling mod
Yet another workaround to “features” of the original Arp 2600, this one is for the VCF input. As-is the three VCOs connect to the VCF input as DC-coupled; the saw and square waveforms of all VCOs have a 5V offset to them and thus by design this offset will add a definitive *SNAP* to the audio as the VCA opens. Depending on the case this either is or isn’t usable, and if it’s to be removed then everything going in to the VCF needs to be routed via a capacitor. What’s nice is that the main board comes with the option to have this either way, so there are component spots for the capacitors and the cutting locations of board traces have been marked.
I wanted to have both options available and to effortlessly select between the two, I decided to add the capacitors and also a switch to short-circuit them. Now it’s always not recommended to short out capacitors since there’s a chance to break them by doing so.. But AFAIK this mostly applies only to high-capacity caps as the momentary peak current on time of short-circuit can then burn stuff. As in, low capacity caps like the ones going to the VCF input should be way less risky to short out. I figured that I’m anyway going to use the switch primarily when the TTSH is powered off, and can wait a while for the charge in the caps to drain before switching. So it sounds like a reasonably safe bet huh? ;)
Noise generator mod
Nordcore did this thorough in-circuit analysis of the noise generator output with a whole bunch of different transistors. I added his BC337 + resistor mod on my TTSH but forgot to take photos of it, so perhaps just check out Nordcore’s post here:
Maybe I’ll try and remember take photos the next time I have the TTSH on the operating table..
Slider LED mod
The stock orange LEDs that the Bourns sliders shipped with didn’t really match the color of my case, so I went on to replace them. At first I tried both blue and white LEDs which both were excessively painful to look at even, so I went with purple ones instead. They go neat together with the purple tolex and more importantly, didn’t require modding the LED resistor in any way. Minimum setting on the stock brightness trimmer was enough, so that’s that.
I tried taking a photo of blue, orange and white LEDs side by side, but the brightness was just too difficult for my camera. Anyway you probably get the idea of the amount of eye-bleeding bright. With stock resistor both were so bright you couldn’t even read the panel texts :)
Yeah really, this means something so damn right I count it as a mod too! :)
No build would be complete without accurate panel markings and to bring my project up to speed, I designed and laser-printed a few paper stickers for mine. The panel font is Helvetica and for the printer I used, 8pt size with a bit of negative kerning seemed to match the front panel. I didn’t bother bugging Humancomparator.net about what the original color is, so I just grabbed the Colorometer for IOS and made a few test prints with the hex values suggested by the app. Close enough.
And woah, I think that about covers every detail that went into my TTSH build. Project all done! :)