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PAiA 9308 FatMan Rackmount Midi Analog Synth
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PAiA FatMan Custom 1u Rackmount!!


PAiA FatMan Synth Electronic Project

Always wanted to build a synth in electronic project kit. I was too young in the days of the old Maplins Synths or the Transcendent 2000 etc. The PAiA FatMan is probably one of the few electronic kits that is still "new" in the '90s (and still around!) !
I actually saw they sell ready built FatMan's in Tokyo, but you have to pay and wait a week for them to build it. So i thought, i'll order the kit one day and build it myself. However, i never had the time in the 90's and actually not until the past few months, i've finally decided to order a few kits from PAiA, which includes the 9700 midi2cv8 and the 9308 FatMan.


I don't want the desktop module version, and I actually ordered the kit and the rackmount front panel.
Supposedly it should look something like this when built:

However, i realized there's gonna be some problems...
bulletAs usual, as with the midi2cv8, PAiA uses a "hanging" wall-wart power adaptor
bulletMidi IN/Thru are on the front
bulletOutput is on the front
bulletThe panel don't come with any case, it's just the panel, so there's a need to find a 2u rack case and mount things etc.
bulletThere're many many mods available and there's no way to fit even a few additional Pots & Switches  onto the panel.

So i decided to actually forget about the original 2u panel and do everything in a 1u rackmount. The front panel is very cramp and i have to use other Pots because the FatMan kit comes with big chunky pots.

The FatMan 1u Rackmount

To make life easier, the 1u rackmount case i've used is actually an ABS Plastic 19" rackmount case. Good thing is it is easier to drill and handle, since there are a vast amount of holes needed for the pots. Have to use Omeg type square plastic pots - cheaper alternative to small ALPS pots - can fit 2 in 1u height if turned sideways.

The 1st thing to do was to solder some 40 jump wires(!) - i thought what the heck - a PCB that needs 40 more jumper wires ?!
They say it takes roughly 4 hours to build if you're fast - well - it took me 4 hours but that's just to solder all the components onto the PCB. Mounting and wiring the pots takes another 4 hours!

Wiring did take up most of the time.... The Midi LED and Gate LED are routed to the front. Added a simple small 12V AC adaptor and a mains Power switch...


The Audio Out, Midi In/Thru, CV/Gate/Velocity are now all routed to the rear panel.

And of course, no flying lead of adaptor. IEC Mains Socket is standard for me!
To make the IEC Mains Inlet hole, I use a screwing hand tool, which is an M10 Radius Hand Hole Cutter, 28x21mm (
RS Cat.#543-614 or or 541-501), with matching 10A Snap In PCB Mount IEC 320 Plug Socket (311-8031 or 488-191).

I've looked at many of the mods available for the FatMan. There are a few that I'd like to do and I preplanned the pots and space needed. Initially i was to add a sub-osc and also preamp for the audio input to filter. However i ran into a little trouble and after sorting that out and got the FatMan running i decided not to add the sub-osc. The way i am adding the Audio In is hot enough for line level, so i skipped the preamp/mixer mod.
The 1st thing i did was the recommended Lee Diode mod - the trouble is, i replaced the resistors but forgot the additional capacitors - and it turned out the tuning and octaves were all out of place. After some more check and adding the required caps, i finally got it running and tuned.
Also, changing the 555 IC's to 7555's is a must - it improves stability a lot!

Mods I added are:
- VCO Pitch Extend (Switch) Simple SPDT switch that bypass the resistor
- VCO Fine Tune Additional Pot in series with the Pitch Offset
- New Hard Sync (Switch) VCO1 (Pin4) reset by VCO2 (Pin3) - I cut the PCB trace at VCO1 Pin4 to add the switch.
- VCF LP/BP Select (Switch) Extra wire out of the Filter IC to a switch
- Extended VCF Freq (Switch) Switch to short resistor
- Max Resonance (Switch) Switch to short resistor
- Total Internal Level Pot Instead of isolating the 2 VCOs, i kept the 1/2 Mix pot, but added a pot to control the total volume of the 2 VCOs
- External Audio In Level Pot External Audio In socket routed to a pot

They're very easy to do, and most of these are from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site.

-> See also the FatMan MODs page.

It's very cramp...
On the left:
- Mains Power Switch, Midi LED, Main Volume
- VCO Pitch, Glide, Extend Switch, Fine Tune, Offset and 1/2 Mix
- A(S)R, A(S)R/AR Switch, Attack, Decay
- Hard Sync Switch, VCF LP/BP Switch
- Internal Level Pot, External Audio In Level Pot

To make the square-ish hole for these illuminating Power Switch, another one of these Hand Hole Cutter is needed. This one is the M10 rectangular hole cutter,22x19.6mm, RS Code: 600-161.
The Power Switch is one of those DPST green (or red) illuminated rocker switch, 10A/4A.
RS Codes are Green: 318-070, Red: 318-064

On the right:
- VCF Velocity, Pitch, Freq, Freq Extend Switch, Resonance Max Switch and Resonance Pot
- VCA ADSR, Velocity, Gate LED, Punch Switch and the A/D/S/R Pots.

Could've done the last A/D/S/R pots in 2 rows, but i didn't have a right valued pot - so i kept the original 4 pots...



Some Comments...

bulletThe FatMan is a nifty little synth.. It has that raw sounding feel and the way the 2 VCOs sync together, it can some interesting sounds.
bulletThe Filter is all right, maybe a little thin as compared to other synths, but maybe that's what gives its own character!
bulletThe PAiA way of constructing is not too bad, but not too much to my personal taste.  Again there were so many wiring points everywhere on the PCB...  (+ the 40 odd jumper wires on the PCB...)

Well, but i suppose one cannot complain too much for a full midi analogue synth at this kit price. 
Or maybe it's the plastic case i use which gives it that cheap feel ? I dunno.

bulletJust wish that the midi could do a little more
- Midi Key Range is only C1-C5 (Midi Note #36 - Note #84)
- Pitch Bend is only +/-1  (+/- a semitone) which anyone would wish it can do at least +/-2...
- there're no midi cc controllers to control anything else.



Some PAiA FatMan 1u Rack Soundz

I feel kinda funny. My FatMan's (both of them) sounded weird at 1st. I felt that the VCOs were dodgy and not stable. Not until recently (Aug 2004) I have finally managed to fix this. Apparently I was running them under-powered!
The clips below.... The 1st 2 were done with the FatMan 1u Rack#1 (at its underpowered stage).
The 3rd was both FatMan #1 and #2 at proper power....
bullet FatMan1 Basic Oct Seq
Playing typical octave bassline riff...
bullet FatMan1 VCF + AR
Tweaking the Filter CutOff with Resonance set relatively high.
Then added some release in the AR.
bullet FatMan 1+2 Oct Seq Tweaks
Both FatMan's playing octave bassline.
1st in AR mode, filter cutoff = 0, then turning up the resonance, and then tweaking the filter.
Towards the last round the AR mode is switched to A(S)R.
-> Play ALL



Other Links on the PAiA 9308 FatMan Analog Synth

bullet PAiA site of course and the official MOD page
bulletScott R. Gravenhorst's excellent Synthaholic's Fatman Site has many mods & info
bulletWayne Scott Jones's FatMan Site with has Fatter Fatman & Audio Samples
bulletJohn Sepulveda's Multimode VCF Mod
bulletGoogle search on PAiA FatMan



C Y 's files on the PAiA 9308 FatMan

bulletThe 9308 FatMan Schematics with little colour coding for easier read


bulletNote: Somehow, the gif (strangely) might not open in Internet Explorer (dunno why), but it is downloadable (ie, do a "Save as...")


bulletThe Pots wiring diagrams, but with added Pots name and values.
Since I'm not working with the original front panel, it's a little confusing looking at the back of the pots in the diagrams and constantly referring back to which pot is which. These 3 wiring diagrams with labels sure helped a lot.



bulletFatMan 1u Front Panel Designer .fpd file - i use the front panel designer to test if i can fit all the pots on the panel and print out a rough drilling guideline.
bulletNote: use Schaeffer Front panel Designer to view/edit!

bulletThis is the full scanned construction/assembly/user guide Acrobat PDF manual
Note: 5.31 Mb zip file

Cubase Device Panel

bulletMy Cubase SX Midi Device Panel (''Dummy'' Panel) for the FatMan - works like a virtual patch sheet for storing patch snapshots!


PAiA 9308 FatMan Rackmount #2

Well, after finishing this FatMan, I came across a 2nd FatMan (fully assembled but not working properly).
I got this and now it's turned into FatMan Rack #2...


PAiA 9308 FatMan Rackmount #3

Can't stop!! Yet another Fatty... #3 !! 






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