AM8040 Audity/E-mu Systems/Dave Rossum VCF

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SmartBits
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AM8040 Audity/E-mu Systems/Dave Rossum VCF

Post by SmartBits » Thu Dec 17, 2015 5:12 am

Last year I got my hands on a PCB for the AM2040 including an HM2040 Hearn-Morley clone of the rare SSM2040 chip. It took me some time to build this as I wanted to get my feet wet doing other (easier to build) DIY modules first. I haven't seen any pictures of this one in the wild so here is mine:

Image

Image

Image

I replaced the TL071 for an OP177 and the TL072 with an OP2134 as per Rob's suggestion. The rest is according to the specs in the v2.2 project notes. There were some components missing on the BOM, might be useful for others who want to build this one:

Capacitors:
C2 100nF, 5mm.
C14 100nF, 5mm.
C17 10uF electrolytic, 2.5mm.
C18 2n2F, 5mm.
C21 100nF, 2.5mm.
C22 100nF, 2.5mm.
C23 100nF, 2.5mm. 5, C16?

Resistors:
10K: R12, R23, R28

The filter works fine and sounds great, nice and smooth. The only thing I still have to troubleshoot is the switch. When the module is powered up it is in 12 dB/Oct mode, I can then switch it to 24 db/Oct but not back anymore. So the flipflop flips but doesn't flop. Might be that the flipflop chip is defective or I made a mistake with the components around the switch. But it's no biggie as I like the 24 dB/Oct setting better... :hihi:
Last edited by SmartBits on Tue Feb 06, 2018 5:01 am, edited 1 time in total.

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leeski
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Post by leeski » Thu Feb 11, 2016 4:39 pm

Wow looks good any sound samples of this great module :yay: :despair:
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Post by SmartBits » Mon Mar 14, 2016 5:17 am

Thanks! I'll try to make a few samples soon(ish)...

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leeski
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Post by leeski » Tue Mar 15, 2016 3:00 pm

SmartBits wrote:Thanks! I'll try to make a few samples soon(ish)...
That would be very cool :tu:
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SmartBits
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Re: AM8040 Audity/E-mu Systems/Dave Rossum VCF

Post by SmartBits » Sun Jul 24, 2016 11:42 am

SmartBits wrote:So the flipflop flips but doesn't flop. Might be that the flipflop chip is defective or I made a mistake with the components around the switch.
The Flip that didn't Flop... was just me not soldering a capacitor where it should be, I totally forget it and overlooked it when checking for errors (you can even see it on the picture...). I'm an idiot. :doh:
But at least it works great now that I've soldered it! :nana:

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Post by SmartBits » Thu Aug 18, 2016 12:46 am

Here are some audio samples I made a while back. First file of each slope mode is just an envelope into the CV in. Second one is a bit of FM, can't remember exactly but I think it was the sine output of a TH-555 that modulates it. The 3rd sample of the 24 dB mode are a bit longer notes so the sweep can be heard a bit better.

The volume drops a bit sometimes, especially on the 6 dB mode, that happens when there's more resonance. I didn't process the files, this is just as the module sounds.
Attachments
AM8040_12dB_01.wav
(19.62 MiB) Downloaded 13 times
AM8040_12dB_02.wav
(22.5 MiB) Downloaded 15 times
AM8040_24dB_01.wav
(20.7 MiB) Downloaded 16 times
AM8040_24dB_02.wav
(20.91 MiB) Downloaded 16 times
AM8040_24dB_03.wav
(10.02 MiB) Downloaded 44 times

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Post by truman_k » Sat Mar 10, 2018 3:57 am

I wonder if you have the same problem, I have the HM2040 chip installed to the AM8040 that I built from AmSynths' PCB. Everything works just fine. Except that the Resonance will be very squeaky (i.e. high pitch) when turned way up. I have adjusted the V/Oct trimmer to the very end to reduce the squeaky sound.

Maybe there are some resistors that I need to change for the HM2040 chip? Any thoughts on this?

AMSynth's circuit design is very cool. I've loved it very much.

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Post by SmartBits » Mon Mar 12, 2018 3:05 pm

I can't say that mine has that issue, do you have that on both slope modes? I haven't strayed from the BOM, other than the changes mentioned in the first post. Have you used those same values? I haven't calibrated mine so that it would track 1 V/Oct, so that might be a difference as well.

Nice panel, looks good in black!

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Post by truman_k » Mon Mar 12, 2018 8:30 pm

SmartBits wrote:I can't say that mine has that issue, do you have that on both slope modes? I haven't strayed from the BOM, other than the changes mentioned in the first post. Have you used those same values? I haven't calibrated mine so that it would track 1 V/Oct, so that might be a difference as well.

Nice panel, looks good in black!
Thanks for your reply. This only happens in 24db mode. I followed the schematic closely and have not changed anything. Well, this is not a big problem as long as I don't turn the resonance to the far CW.

Since AmSynths don't have the panel anymore, so I have to make my own. :banana:

I do wish AMSynths has more projects for us to build, however it seems that Rob is just too busy. :sadbanana:

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Post by SmartBits » Tue Mar 13, 2018 1:21 am

I checked mine yesterday just to be sure, mine doesn't go into self-oscillation when it's in the 12 dB mode. When in 24 dB mode it does, but only when resonance is at approximately 4 o'clock.

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