WTPA2 0-5V CV mod advice

Hi all,

In the first rev (REV A) of the assembly manual, there's a mistake in the 0-5v CV mod section.
The instructions call out a 47k resistor being added between one side of R55 and ground.

However, in the kit I built and photographed in the manual, I soldered down a 470 ohm resistor.  Dumb.
The clock rate is extremely slow when this happens.

This was the picture in the Rev A assembly manual.  Extra dumb.
If you actually use a 47k where it says to, then the mod works fine.

Please refer to the new assembly manual for a correct (if not beautiful) photo:

Also, since I was A/Bing 5v modded and non-5v modded kits, I noticed that adding the 5v mod makes the "FINE" control fairly insensitive.  So if you're only manually using the WTPA2, you might be happier not installing the 0-5v mod.
(CVs from like 0-2.5v will still work fine).

Best,
Todd

Comments

  • By insensitive, do you mean more "big jumps between values/harder to dial in a particular sweet-spot", or more like "doesn't have much discernible effect on the sound at all"?
  • Insensitive like I think the adjustment range is too small -- too "fine".  I'm running through the preassembled units today and I've made some mods there.  I'll pass on what I've learned here.
     
  • Cool, thanks!

    Shall keep an eye on this thread.
  • When adding the 0-5v CV mod, per the manual, I recommend the following:

    Replacing R56 and R57 (currently 51k) with 22k resistors (or thereabouts, 25.5k is fine too) will result in a greater range of "fine" adjustment.
    You can further reduce R56 and R57 (with say 10k if you want) and the "fine" pot will have an increasingly greater range.

    I put 22ks in my units and am so far pretty happy with them.

    Best,
    TB

  • cool! Thanks, Todd!
  • thanks todd!

    i used 18k and the range is quite good.
  • Great. 22k is still very fine, maybe a half note at most settings. 18k might be better.
  • Cool, I'm trying 15k for starters
  • Probably going to put mine together tomorrow. Would a 50k fine pot + 15-25kish resistors make sense for this?
    As an aside, I've had a sort out of my bits boxes and have way more resistors than I thought - would making all of the ones in the WTPA2 1% do anything terrible/interesting?
  • I think it's just the R2R ladder that needs somewhat close values but they're 1% already.
  • @Fwestivus--
    @rosch is right.  There are some critical values in the VCO too, but probably not 1% critical.  Everything in the audio path (except the doo doo pots) is 1% already too.

    Re: 50k for the fine pot -- sure, give it a shot.  Fine would be less fine, which might be good.

    I wonder if instead of "coarse" and "fine" the controls might have been better as "frequency" and "range" where the "range" control sets the bottom frequency of interest.  So you can just make your entire range controllable with one pot, with whatever sensitivity you want.
    Actually, maybe you could just do this with a resistor.  Some people want to sample down at 100Hz, I guess.  If other people really only want to go, say, 5kHz to 20kHz, then they can have a more fine control.

    Honestly right now I don't touch "fine" very often.  Do you guys?

    A big knob on the VCO adjust helps too.

    TB
  • @ToddBoiley
    Thanks both of you! Everything will be going in tomorrow. As it turns out, what I remembered as 50k pots turn out to be 500k with really short shafts, so that plan's out the window anyway! I'll stick to trying some lower value resistors.
  • "Honestly right now I don't touch "fine" very often.  Do you guys?"

    Not really. It's sitting there all big and beautiful, would be nice if it had a more interesting and useful function.
  • I thought it would be useful for setting musical intervals and precise tuning.  I think most people make fart noises though.  Live and learn.
    I really should try to compose a song with this thing.  I think it would help the next unit.
  • As things turned out today, I only had 22k resistors for the fine mod. As far as I'm concerned it's fine as it is - if you go from the middle to all the way right or all the way left, it's more than the smallest adjustment you can easily make to the course knob, so that works great for me.
    I've not had much of a proper play, but it's working. And the green case looks lovely.
    Next step is to have a crack at doing something vaguely musical with it.
  • Looks great! Nice job. And thanks for the feedback on the controls.
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