Getting the 2600 Bass sound right in 5U...

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Micronians
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Getting the 2600 Bass sound right in 5U...

Post by Micronians »

Full disclosure, I spent nearly all day on this haha. I had nothing better to do (not true).

So I have a vintage 2600 from 1973 with the 4012 that I love for bass sounds. I'm not trying to achieve every 'classic' 2600 sound on my 5U, just a PWM bass sound I like. It appears the difference I'm looking for really is just in the filter... so i think. There's a looser yet bigger bloom to the bass notes when I use the 4012 that I just love.

Yes the 4012 is a ladder design but compared to all the ladder filters I have at my disposal, it sounds unique. The Grove 294a sounds closest so we'll just stick with that. I'm using the same EG to modulate both filters simultaneously and it sounds like I have two slightly different envelope times when I compare the two. So my question is this: How does the 4012's cv input design contribute to the sound i like?


The signal chain:
When using just the 2600's VCF with my 5U system, I get the sound. I used all Oakley modules: Two VCOs (one for each filter), one VCA (i have the quad version so each filter has its own channel for real time comparison) and just one single ADSR to control each VCF and VCA (using the wonderful STG buffered mult for the routing). I used dummy pins in all the 2600 VCF inputs I wasn't using to isolate it and even sent kbd cv over from the 5U.

When I use the 294a (or the Q150, auto level off), it's always a much punchier/tighter/stiffer sound. The decay is perceived as shorter compared to the 4012. I would also offset the CV from the EG with a Q125 to get the feel & shape closer but it's never quite right. The Q125 was not affecting the 4012, just the 294a.

I don't think the sound i'm looking for is in the gain staging. I think it's how the VCF is modulated by and interacts with an EG and *maybe* how a VCO interacts with the input. I messed with the gain staging all fkn day. It didn't get me there.

Any ideas/theories?
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cornutt
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Re: Getting the 2600 Bass sound right in 5U...

Post by cornutt »

I wonder if it's the difference between the old 741 op amps used throughout the 2600, and modern op amps.
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Micronians
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Re: Getting the 2600 Bass sound right in 5U...

Post by Micronians »

I think you mean LM301. I don't think that's it because I think the opamp is used to amplify the signal after the filtering. But who knows, I'm no engineer. I can repair stuff but I can't design stuff.

* Actual Full disclosure: I want to nail this sound so I can feel fine about selling the 2600 if I need to (need $$ but not dire yet).
I was actually pretty happy with the TTSH but I didn't appreciate how heavy it was. I'd rather have something in 5U anyway.
Maybe I can get Tony from Analog Crafstman to make me a 4012 version of his ac2600 VCF using a Synth Restore 4012 board instead of the Yusynth board.
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Micronians
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Re: Getting the 2600 Bass sound right in 5U...

Post by Micronians »

Another update. We don’t really do TG and I’ve got a bit of the flu or a heavy cold atm.

I’ve been comparing my STG PL-LPF to the 4012 today. In this setup, there’s not much difference between the 4012 and the 4072. I think it’s safe to say that the sound I’m looking for is in the Arp design. They both do that round, rubber-y bass thing but that envelope mod difference is still there. But I discovered something.

I switched the EG to my Q109. I modified my Q109 so I have the time range and output swing on toggle switches on the front panel instead of using the jumpers. If I switch to the -5v to +5v output swing setting, i pretty much get what I’m looking for. Pretty cool!
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