Switching Obsession to 16 voice mono mode sounds massive!
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Tom Sawyer uses almost- well techically I don’t think it’s “almost”, it is- a ring mod modulation on the filter. I used to get a close sound on the MiniMoog using the third osc. as a mod source but it wasn’t as fat because of the lack of extra voices. I didn’t realize the Xa didn’t have that ability… I guess it explains why TS isn’t the first preset on each one! And the accursed Jump patch 
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Argggggg … I’m so weak 
… but it sounds so good so I took the plunge. Like Fred said the effects alone are fantastic sounding but I turned them off and this synth was very fat and in your pug to be sure without them. Dave_C is right about the dragon slayer mono mode too, I won’t need to trim my brows for a month after trying that out! 
I like it a lot …
Cheers,
Dave
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The cross mod feature on the OB-X sounds like the secret sauce from what has been gathered here IMO.
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Interesting. I’ve just watched 7 videos on “how to make the Tom Sawyer sound” and I son’t think any of them are right. A guy with a Dave Smith OB6 came pretty close. We may have to take it on ourselves to nail this.
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We can kidnap Geddy and keep him handy … 
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I’ll get a bag of popcorn and watch.
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Same here - couldn’t resist… 
For dramatic filter sweeps like Tom Sawyer, I’m struggling with the Obsession’s filter envelope amount. Seems a bit restricted for really wide sweeps, even when at 10.
One thing about the filter is confusing for me: When the envelope amount is turned all the way down, the sound is still filtered quite a bit with the frequency turned all the way up. I need to increase the Envelope amount and have some filter sustain to actually open the filter all the way.
Is this an original OB-Xa ideosyncrasy? The Arturia OB-Xa behaves the same, but the OB-Xd behaves like a “standard” subtractive synth, i.e. turning the cutoff frequency all the way up opens up the filter. Is this the difference between the original S.E.M. filters of the OB-X and the Curtis filters of the Xa?
Cheers,
Torsten
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Argggggg … I’m so weak
… but it sounds so good so I took the plunge.
Same here - couldn’t resist…
Welcome to the club 
For dramatic filter sweeps like Tom Sawyer, I’m struggling with the Obsession’s filter envelope amount. Seems a bit restricted for really wide sweeps, even when at 10.
For me Daves hint to do a finetuning on single channels brought in some improvements as the trimmers are capable of increasing the adjustable range for frequency and especially Q
Regards, Volker
Fiddled with the Obsession a bit, but the filter just seems too “nice” and well-behaved for Tom Sawyer. With OB-Xd, it took me only a couple of minutes to get to a decent approximation - give it a bit of EQ and some effects and it could definitely do it for live…
Sawyer-ish.zip (3.8 KB)
So I guess it doesn’t hurt to have two (or three) different Obie emulations around 
- especially since OB-Xd is free.
Cheers,
Torsten
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Just listened to the original and heard that the filter doesn’t really close all the way, but stays open a bit, so you may want to adjust filter decay and sustain to taste:
And I’d definitely insert a low cut in the mix channel.
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Wasn’t the OB-X filter unique because it had simultaneous high pass, low pass, and band pass outputs, all with a 12 dB/oct slope? I think the OB-X had just a ladder filter.
AFAIK the OB-X only had a 12 dB lo-pass filter; the Xa added the 24 dB mode.
I think the SEM had individual filter outputs. The OB-Xd copied this - the “Multi” knob allows you to morph through low-pass, notch, and high-pass modes, while the “BP” button activates band-pass instead of notch filtering. Nice! Plus, on the Xd the cross-modulation is not simply a switch, but can be dialed in gradually - makes a huge difference in making the Tom Sawyer sound growl…
For the nerdy types I gathered these diagrams which can cause blindness when overused 
OB-X 1979 Skit VCA, VCF & fiter envelope
Closeup of filter
OB-XA 1981 Filter envelope, VCF and Amp Envelope
Closeup of filter area
data sheet for 3320
Major archetecture differences here with the discreet op-amp design in B=OBX vs the LSI chip in OB-XA. It’s an under the hood thing for sure on this part as well …
Cheers,
Dave
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Spent many a year reading schematics. That is why I am blind now…well that, and what my Mom told me not to do. 
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Hair on the back of your hands as I well, you naughty boy?! 
Back OT, fantastic nerdy discussion. 
this is what we want, not more COVID doom and gloom… That TS sound is so distinctive - it sounds so simple, but …
I find Geddy is pretty good at creating distinctive sounds. The other ones I have tried to nail, albeit years ago on Yamaha AN VL and came no where near, are the little synth lines in Xanadu the ones that are quite high pitched and shrill.
Totally OT, I am on a mission in the autumn (this time of year I am outside if it is nice!) to try and nail some of the Tim Blake sounds you hear on Steve Hillage’s Fish Rising. Has anybody ever done those to save me some time! ?
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I hate to be the outlier here, but I always felt the Tom Sawyer sound was just a so-so rip-off of Edgar Winter’s “Frankenstein” effects. I have no idea why it makes you folks drool and act all swoony and all. (Ok, perhaps that was too harsh…) 
Terry
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I saw him perform it live back in the day, but though I was sitting darn close, I didn’t catch the settings! Sorry!
Terry
(He performed it using a Keytar from those days as a controller, btw.) (Wait - wrong about that. It was a keyboard with a strap.) (It is why I hold onto my Korg Poly-800!)
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I met him in the early 2000’s at an Easy Rider show in Memphis. He was using a Keytar then. During break, he sat down with my wife and I, and apparently she was putting out her “do me” vibes, because he was interested in talking to her. He even had her dance on stage with him later. Wasn’t impressed with his Keytar use, nor the sounds he was getting.