From jneumann@mcs.kent.eduMon May 22 13:09:57 1995 Date: Mon, 22 May 1995 15:26:02 -0400 (EDT) From: John Neumann To: analog heaven list Cc: paia@aol.com, lx@fht.com Subject: Fatman review After several weeks, and a couple of letters expressing interest, I finally have a little time to give my impression of the Paia Fatman. It takes about 16 hours to build, and works better than I expected. Here are my detailed pros and cons: Cons: (1) When the offset between the two oscillators is very small, they tend to sync together, killing gentle phasing effects. I would guess this is due to the oscillators coupling via the power supply, much like two pendulum clocks on opposite sides of the same wall. Since I plan to eventually add a PWM/waveshaping module to get phasing effects, this doesn't affect me too much. (2) The finite discharge time of the capacitor in the VCO's makes pitches a little flat at high frequencies (it uses a 555 as a sawtooth generator). Since I think I will be either putting in frequency-doubling circuits or replacing the existing caps with smaller ones and using octave-dividers to obtain a switch-selectable range, this is only a small problem. (3) The glide control interacts slightly with the pitch control (which is on the output side of an op-amp buffer). (4) The resonance on the filter could go higher. See my mods section. (5) The synth has linear, not exponential response to CV, making things like adding a uniform vibrato difficult w/o an extra VCA. Pros: (1) Really, really, inexpensive. (2) Much more stable than I expected. There are no components to correct for thermal changes, yet I haven't had to tune it since a month ago when I first put it together. It probably helps that I don't have it in an enclosure and there are no warm parts near the VCO's. (3) The MIDI implementation is excellent (if like me, you only need note, pitch bend, and velocity control.) I haven't experienced any glitches at all, and I've connected it to several keyboards and my computer. The software somehow remembers the last 2 or 3 notes, so you can hold down a note with the left hand and play short notes with the right and it will alternate between them ("pedal notes"?). The newest note always takes precedence, for a nice lead feel. (4) Most of the common patch points come out to a knob on the panel anyway, so rerouting and adding new modules shouldn't be too hard. Mods: (1) Improve filter tracking. By shorting R73 (on the VCF freq. knob), the functions of the "Pitch" and "freq" knobs are interchanged, and the VCF can now track the VCOs. Set the Freq. knob to zero (this is now a constant frequency offset knob) and use the pitch control to choose at what multiple of the fundamental frequency you want F_c. This can now go all the way to zero (below the fundamental) if you want. (2) Increasing resonance. I found with some experimentation that the resonance increases with the resistance of the resonance knob. I put a SPST switch in series with it, and with the switch open, it doesn't quite oscillate but I get a very noticable (roughly the same volume as the fundamental) and ear-piercing resonance at the harmonics, enough for my tastes. (3) Two types of gating. I haven't done this one yet, but it might be nice to try smoothing out the gate signal so that the EG's only re-trigger when all keys are released, rather than retriggering at the beginning of each note. This might be a little tricky since part of the envelope control is in firmware. If anyone else has some mods, send them to PAIA@aol.com so John can put them on the fatman mods web page (what's the URL for this?). P.S. According to John Simonton, the Japanese have been ordering large quantities of the Fatman. How do you think they are translating the word "Fatman"? :) From mpulver@netcom.comMon May 22 14:03:10 1995 Date: Mon, 22 May 1995 20:41:20 GMT From: Mark Pulver To: John Neumann , analog heaven list Cc: paia@aol.com, lx@fht.com Subject: Re: Fatman review >Mods: > >(1) Improve filter tracking. cool... > >(2) Increasing resonance. as you say... needed And... if you ever happen to graft an LFO into yours, please lemme know! ---- ---------------------------------------------------------------------------- Mark Pulver/Chicago, IL analog analog analog and umm, analog mpulver@netcom.com Voyetra 8, Xpander, P5, MKS-70, 2600, stuff From mpulver@netcom.comMon May 22 14:41:06 1995 Date: Mon, 22 May 1995 21:31:47 GMT From: Mark Pulver To: Mike Perkowitz , analogue heaven Subject: Re: Fatman review At 02:02 PM 5/22/95 -0700, Mike Perkowitz wrote: > >> And... if you ever happen to graft an LFO into yours, please lemme know! > >no LFO? yow, that's a pretty big lack in my book! :-/ Yeah, I know... I wasn't too happy about that... The kicker is that there's no firmware support for one to magically show up with the intent of being tied to the MOD wheel. So... even if you do graft in the hardware, you're tied to the front panel only for control. On the high side though, John did upload the FatMan firmware source... The box does sound good though Mike... It's getting use in my digs, (but I broke VCO1 somewhere, gotta find that...). ---- ---------------------------------------------------------------------------- Mark Pulver/Chicago, IL analog analog analog and umm, analog mpulver@netcom.com Voyetra 8, Xpander, P5, MKS-70, 2600, stuff From oldcrow@Access.Mountain.NetTue May 23 10:46:54 1995 Date: Mon, 22 May 1995 23:23:20 -0400 (EDT) From: The Old Crow^? To: John Neumann Cc: analog heaven list , paia@aol.com, lx@fht.com Subject: Re: Fatman review On Mon, 22 May 1995, John Neumann wrote: > After several weeks, and a couple of letters expressing interest, I > finally have a little time to give my impression of the Paia Fatman. > > It takes about 16 hours to build, and works better than I expected. > Here are my detailed pros and cons: > > Cons: > (1) When the offset between the two oscillators is very small, they tend > to sync together, killing gentle phasing effects. I would guess this is due to > the oscillators coupling via the power supply, much like two pendulum clocks on > opposite sides of the same wall. > (2) The finite discharge time of the capacitor in the VCOs makes > pitches a little flat at high frequencies. I've been working on this very problem, among others. I suspect that the sawtooth output of one VCO is coupling across to the other VCO through the 1/2 mix pot, causing a slight pull on the frequency. Rotating the offset control demonstrates this. I just got back from traveling over the weekend, but I am going to try a couple of tricks to see what improvements can be made. Specifically, adding a follower at the output of each VCO prior to their respective decoupling cap, as well as a follower at each CV input. (The latter to unload the pitch pot a bit). I added a third VCO (with stacked level and offset knobs), a clone of VCO1. > (3) The glide control interacts slightly with the pitch control (which is on > the output side of an op-amp buffer). I fixed this. They (relatively) low impedance looking into an LM324 stage become significant when the series resistance into the opamp is also high, as in the 1 meg glide pot. Use a fet opamp stage instead. (I used a section of an LF347.) > (3) Two types of gating. > I haven't done this one yet, but it might be nice to try smoothing out > the gate signal so that the EG's only re-trigger when all keys are released, > rather than retriggering at the beginning of each note. This might be a little > tricky since part of the envelope control is in firmware. I've looked at the 8031 source; this shouldn't be very difficult. I would try some software alterations, but I need to find what assembler PAiA uses. -Scott /* http://www.mcs.com/~syzygy/ */ From honcho@paia.comTue May 23 11:17:16 1995 Date: Tue, 23 May 95 13:10:33 CDT From: honcho@paia.com To: analogue@hyperreal.com Subject: not over 'til the FatMan sings... My goodness. I turn my back for a couple of days to tweak the pages for public opening and put the Federal Building to rest and the next you know we're the topic of the week. Ever notice how a week is only about 36 hours long on the 'net? Anyway, thanks to John Neumann for what I take to be a good review. Anytime a customer says they got more than they expected I feel like we've succeeded. I agree that the lack of and LFO is a short-coming in the FatMan normalization. And I also agree that this is not the end of the world. I have a pretty slick mod that adds an LFO function to the AR, but it's not posted anywhere yet because I haven't tried it. Many of my things work the first time out these days, but by no means all. It will show up on the web page the end of the week. Designing real life instruments is more about compromises than any other thing. What to leave in, what to leave out. You can never make compromises that please everyone. I haven't had a chance to really digest the comments completely, but offhand the various mods suggested sound reasonable. I'm sure many of them will wind up posted on the pages too. The locking VCOs are worth note because of what can be learned from them. First, if John's unit is working properly and all components are up to snuff, careful tuning should be able to get flanges with cycle times of a second or so. But, in every integrated synth that I know of the oscillators will finally lock if the interval between them gets small enough. There are a lot of paths that can account for the coupling that causes this locking (including, in the end, free space), but the power supply lines are by far the most common, remember the Grounz is Groundz debate? I have to say that 555s are not the best choice for VCOs because they have the annoying habit of shorting the two power supply lines together *very* briefly when they switch. If I had it to do over I would not use them. The locking tendencies of the FatMan VCOs can be improved by increasing the size of the bypass capacitors associated with them (C28 and C29). They presently are 100 uF and the next logical step up would be 1000uF units. It also would not hurt to add a .01 uF ceramic disk in parallel with the electrolytic. For my part, I kind of like being able to set up tuning so that the VCOs lock at one end of the keyboard and flange at the other which produces some interesting human-ness to different notes in different registers (not saying this very well, sorry). I know that sounds a little like an attempt to turn documented bugs into features - but hey, what do you think I do here, anyway? Best wishes to all, John Simonton