Tuesday, June 2, 2015

Reducing Monotribe Clicks and Pops

I was playing the Monotribe with a MIDI keyboard, which is a lot of fun, but the nasty clicks and pops during the note on and off are total dealbreakers when the 'tribe is plugged into a big bass amplifier, or your speakers are cranked up.  It's not so much an issue in most sequences, but when you play it like a keyboard instrument, it's a pretty glaring awful sound.

So I watched THIS YOUTUBE VIDEO and figured out what to do.  Basically I soldered a 4.7 uF capacitor from the base (pin 1) of Q24 to a ground pad (negative cap leg to ground).  He suggests you can use a 1 uF all the way up to 10 uF depending on your preference.

The trade off is it does seem to soften the envelope a bit.  It sounds a bit less snappy, so I might go back in and put this mod on a switch.  The volume envelope sounds a little bit compressed now, which tames the acid edge perhaps a bit much.  Of course you can still get the filter screaming or whatever.  But I recommend a switch.

The mod really does work well, the clicks are almost completely eliminated, which makes the monotribe now a joy to play as a monophonic keyboard instrument (see: MIDI mod in an earlier post).

If you haven't cranked this thing up through a guitar or bass amp, you've got to hear it.

Here's the transistor pinout for Q24:

And here's the best picture I could get of my cap soldered in place.  I would recommend cutting the leads to the right length, and tinning them with solder, before installing the cap.  Do the transistor connection last, and as quickly as possible to avoid damaging the part.  Tinning the capacitor's legs helps here because you only need that tiny bit of solder to make that tiny connection, and it frees up a hand to help position the parts.  It really wasn't that bad of a task.  It came together quite easily with the right technique.

Monday, June 1, 2015

'Lil Speaker Thang, a portable DIY boom box, Logitech X-230

Ok reusing some parts.  I had this old Logitech X-230 subwoofer/amplifier sitting around for a long time without the correct remote I/O and volume unit to have it working.  I googled it and some folks had wiring pinouts and such posted, this was a popular model.  

I took a 9-pin DSUB computer monitor cable, cut off the female end, secured it to my recycled enclosure, and soldered the various wires to: The audio in to RCA jacks, and the amplifier outs to speaker terminals.  A10K stereo volume potentiometer is used to trim the input levels.  Amplifier ground, audio ground, are connected inside my enclosure.  And a little SPDT toggle is used to connect the two wires that give it power.  Maybe you could call these connections "5V" and "Power On/In".  The correct DSUB pinout for the subwoofer is in the image below.

I didn't bother with the status LED wire since the sub never truly turns off.  The power is just sort of a "standby" switch and you can obviously tell when it's turned on--you hear it hissing or passing audio.

The enclosure is a trashy speaker selector that I got from eBay China, that didn't work reliably, so it's being recycled.  You could use any small project box for this.  Its speaker terminals were re-usable and it's a nice solid box at least, even if it used to be an unreliable speaker switcher.  It's nice to get use out of things instead of having to throw them away.  The speaker wire is recycled too, some nasty old skinny cable that was lying around a bit tarnished, but for this application I'm not too bothered with fidelity, since the whole system is pretty lo-fi.  I soldered the speaker cables to the little cube speakers.  Since I'm using standard speaker terminals, I can connect just about any type of standard passive speaker to this amp.  I wonder how well it would drive some of my bigger speakers?

After some mild troubleshooting, it worked wonderfully.  The cube speakers are some leftover bottom shelf ones from my brother's old computer.  In this context they really don't sound so bad.  When paired with a bluetooth audio receiver, this is a fun little system to setup in whatever room and stream phone tunes.  I might use it as monitors for mobile recording (along with headphones).  Or bring it to the beach.  Or as a remote monitoring system for recording around the house, or the electronic drums.  Sort of a tiny grot box PA.

What a somewhat complicated yet satisfying project!  It's not worth anything or the time I spent on it in dollars, but it's a great little thing to have.  I've always wanted a little rig like this, since the last album I recorded for Green.  We were using little computer speakers in a big warehouse to check takes on.  Tiny speakers in an enourmous room.  Mainly due to portability.  So now I've got one.  And it looks cool... of course you can't beat the all black finish either. :-D

This was the correct wiring scheme:

Here is a picture to use to help wiring the 10K stereo volume potentiometer.  I do not trust the power switch section of this diagram, I used the scheme described above.  This is just sort of to show you how the volume pots are connected to the input jack, and then out to the DSUB.  I found this and several other pictures on google image search, some of them seem reliable, others seem to have various errors.  The L and R audio inputs should go to the third leg of the pots, the middle leg is the output to the DSUB, and the 1st legs should be grounded.  Make sure that all of your grounds are connected or you might not get any sound.  I used RCA jacks for my audio inputs rather than a stereo 1/8" plug, but you can use whatever you want.