So playing catch up on building some boards…but had to wait for parts. Was expecting a Tayda order today and Mouser order tomorrow…but mouser showed up today and Tayda got delayed.
So these two are both close but can’t be finished until at least tomorrow:
The Steiner is almost done. Just a few caps I didn’t have I had to order, and instead of digging in my bin for the resistors I didn’t have in my sorted collections I went ahead and ordered a few while I was at it.
And I need to match some transistors. Quite a few for the ARP VCF and that’s all it needs to be finished, just the two for the Steiner. So tomorrow night will probably be transistor matching night.
Also ran into one little mistake on the ARP - can anyone spot it?
But looks like I should have two new filters in my case in a few more days. Need to shift gears and make a few more oscillators next I think. Though I also have a couple of 12AX7’s I picked up a few weeks back before I got sucked into my circuit board experiments - only one socket though due to an ordering mistake. So now I keep debating if I just want to make a safety valve or go full bore and do the VCA (my original plan was to do both but with only one socket I now have to prioritize!)
And yeah…I still need to add those trigger outputs to the sequencer and figure out drum mode. But it’s still a pain to get power to the sequencer so I need to spend some quality time with the socket and 5v power supply I picked up and make the hard decision about how to do a case on that whole setup. I’m dying to use it more but the power situation makes it a real pain to setup and use right now.
Yep. Missed one of the holes for the output header. Took care of it just twirling a bit in my fingers.
I also wasn’t able to match the styroflex caps, I’m just hoping they’re within 2% out of the bag. My meter won’t do pF and even if it did I doubt it would be within 2%. I did use nice name brand 1% resistors for all the matched resistors and confirmed that they were all well within 1% (the total deviation between them was about .5k from the lowest to the highest) so those should be ok.
Thanks guys. And yes…just looking at it puts a smile on my face
Though…I’m still frustrated that the main reason I started building it is I wanted a synth with more voices and so far I really only have one usable voice. Kind of two but the avalanche isn’t a great VCO. I’ve been spending too much time on effects and filters and really need to refocus on getting a few more oscillators in there to do what I want.
I’m mostly happy with the drums so far. Or at least with the Kick (though I really want CV control of the pitch on it) and the hi-hat (though the hi-hat is a bit quiet so I’m thinking about doing another and modifying it to have higher output.) I still want a nice tom/snare and a bell to round out the percussion.
I should just spend some time with what I have and try making some actual music with it instead of just playing around. But…as with most of my hobbies the build is as much or fairly often even more fun for me than actually using the finished product!
That’s a big part of what drew me to modular…it’s never “done” and I can just keep on building and building and building…
Quick fix for one voice is a cheap looper or old multitrack (even a puter) with either a trigger mod from a sequencer or a master clock… (you know, it made sense before I finished that sentence)
OR
simply man up and accept you still have many modules to build and racks to fill. I found Teensy a good entry into DIY polyphony.
Wondering if I’m doing something wrong with this transistor matching.
Tried my other DMM to confirm and apparently while it’s a $15 cheapie it does more sensitive mV readings than my Fluke (or I just can’t figure out the manual ranges on the Fluke.) But both meters are showing me 50mv differences between just about every transistor I test. (with the 2n3906’s I’m seeing between 54.5 and 55.7mv) From what I’ve seen on here from @ctorp (My build progress) and what Kassu posted on his blog https://kassu2000.blogspot.com/2015/10/transistor-matching.html ) I was expecting smaller differences.
But…I also tried swapping my reference for one of a set of matched values (i.e. one that tested as 55.0mv) and put in another that measured the same…and I’m still seeing 55mv difference between them even though they both measured 55mv against the reference I used.
I’m suspecting the value I’m seeing is more just a difference in measurement accuracy from my DMM’s than a difference in the transistors. And questioning if I did something wrong. But I used two 100k resistors that both measured the same and have checked the circuit a few times. I’m just using a 1n4148 for the diode…none of the articles I read were specific about what diode to use since it’s just about the voltage drop apparently…
Well, something is wrong then since I don’t get a sign change when swapping the transistors.
But damned if I can tell what’s wrong. Double checked the circuit and it looks right to me…also tried rebuilding it on a newer breadboard and it’s acting the same on there:
Note this is the reversed form of the circuit since I’m now working on the PNP 2N3906’s.
The red wire from my power supply is +12, Brown is GND, and Grey is -12 (I know not the best choice of colors but they were the wires I had on hand when I rigged up a cable to go from my PS to the breadboard.)
I checked continuity to make sure the breadboard connection are valid and all seems good.
I can see the voltage drift when I first put a transistor in and then it slowly settles in after a minute or two as the temp stabilizes.
Oh…wait…now I see my mistake.
Works a lot better if you connect the collector of BOTH transistors. I’m seeing the sign change and getting a more reasonable .5mV on the first pair I shoved in there.
Guess I need to recheck those BC547’s on the Steiner filter now…
Took them a few minutes to settle but once they did it was a match. The next few I tried weren’t 0’s but are still within 2mV so I’m pretty sure it’s actually working.
Thanks for @analogoutput for taking a look at my WIP on the board earlier today and pointing out that I was using 1mm headers instead of 2.54mm (though it was 0.1" not 1mm!) which solved a number of issues.
I still had to add some jumper wires off the headers because I used a generic PNP symbol and footprint which apparently didn’t match 2N3906.
Mostly helped…but everything I matched when the AC was running was 0.1-0.2mv off when the AC shut off. And vice versa. Probably close enough…but I took a bit more time and matched within my initial matches and eveything on the ARP VCF was reading 00.0v or -00.0v (I wasn’t anal enough to care about the difference between 00.0 and -00.0 - heck it’s just a $15 cheapie meter so I doubt it’s accurate to within .5mv anyway!)
But I got enough matched pairs to “finish” this guy up last tonight:
Ok, took Tuesday night off. Just didn’t feel like dealing with wiring and panel components.
Then last night soldered up the other side of my transistor matching board and re-matched my BC547’s for the Steiner. Once again the very first ones I put in were a perfect match, then went through the other 12 I had and found one other pair. I only need one pair for the Steiner so unsoldered the two I had in there and swapped in the initial matched pair I found. (didn’t bother to retest the two that came out - leads are a bit short to fit into my matcher so I’ll just use those somewhere they don’t need to be matched.)
And with the Steiner updated I decided to wire it up:
Then went to bed instead of testing it because While I have two power supplies one is still missing an AC in connector so I had to tear the one in my rack out to power my transistor matcher and didn’t feel like putting it all back together by the time I finished wiring up the panel last night.
But this morning before digging into work for the day I decided to give it a go. Power checked out on the board so I installed the TL074 and patched a signal through.
Got nothing Hmm…Oh…wait…R30, the 82ohm resistor I didn’t have on hand and had to order…never installed that. Ok. Now let’s give it a try.
And…still nothing. Just a tiny bit of sound coming through if I turn the input level all the way up. I can hear a slight change in tone as I adjust the cutoff or change the selector … but something isn’t happy
Bummer. Looks like I have to break out the scope tonight and start tracing signals to figure out what’s going on as nothing obvious is jumping out at me
The one thing I’m not super confident in is the rotary switch. I can’t quite get my head around just how the switch works…and how it’s working in the circuit. I’m also not sure why he called for a 3 pole switch since he only uses 2 of the polls. I wired mine following the diagram on the yusynth site…but if my switch isn’t wired the same internally that could be mixing things up. But shouldn’t stop the signal entirely I’d think.
I’d try just bypassing the switch - but I’m still having a hard time getting my head around the switch in the schematic and which pins are which on the header for it.
Hmm…Oh…wait…R30, the 82ohm resistor I didn’t have on hand and had to order…never installed that. Ok. Now let’s give it a try.