[sdiy] Fwd: Looking for: AK Drummer (CRM-260) schematic

[Tom Wiltshire]

I've heard of the MM5871, M252, and M253, but never the SN7450.

https://www.elektormagazine.com/magazine/elektor-197604/57604 <https://www.elektormagazine.com/magazine/elektor-197604/57604>
https://datasheet4u.com/datasheets/National-Semiconductor/MM5871/606055 <https://datasheet4u.com/datasheets/National-Semiconductor/MM5871/606055>

I can't find *anything* about the SN7450. It makes some sense though - there were other SN-series chips which were for sound generation, like the SN76489 programmable sound generator, used in the BBC microcomputer amongst other places.

It's a mysterious IC!

Tom


> On 25 Nov 2025, at 03:48, Loscha via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> 
> The "7450" is a specialised rhythm generator chip
> Not a 74xx logic chip 
> 
> It sends pulse out information to the switches and so on.
> 
> I don't have any photos of the insides of mine, and the videos I have on youtube were shot with a potato 
> 
> The schematic I had is really quite incomplete
> But, for modifying the voices, it should help.
> 
> 
> 
> On Tue, 25 Nov 2025 at 13:59, brianw <brianw at audiobanshee.com <mailto:brianw at audiobanshee.com>> wrote:
> I can't tell what it does without pin numbers for the SN7450. That's a dual AND-OR-INVERT package, so I'm not really sure what they've set it up to do.
> 
> The 50K control in the schematic, lower left, sets the tempo, but the faceplate shows what appears to be a stepped attenuator rather than a potentiometer.
> 
> Brian
> 
> 
> On Nov 24, 2025, at 6:36 PM, Adam wrote:
> > Pure gold.
> > 
> > So... it actually only ever plays at ONE tempo, but you get divisions of that tempo?
> > 
> > A
> > 
> > <grab 2025-11-25 at 12.34.27.png>
> > 
> > 
> > On 25 Nov 2025, at 11:51, Loscha wrote:
> >> Hi David and group
> >> 
> >>  I got one of these machines about 12 years ago
> >> And it came with the following documentation.
> >> 
> >> I have a unit somewhere in my garage here in Australia.
> >> It's missing the to half of the lid I think, but has all the circuitry
> >> If it'd help you out, I can try and find it over the weekend and we can arrange postage
> >> 
> >> Pretty sure this schematic will help!
> >> 
> >> //Edward 
> >> 
> >> On Mon, 24 Nov 2025 at 21:56, David Huss via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
> >>> Hi,
> >>> 
> >>> I have a AK Drummer (CRM-260) Rhythm Machine and I am looking for a schematic. 
> >>> 
> >>> I searched the web high and low. I figured out that this was also sold under the names Conrad CRM‑260 or CORT CRM-260 in what seems to be identical devices (apart from the different manufacturer logo).  
> >>> 
> >>> I found a 10 year old youtube video where someone has moded the thing, but there is no description and in a comment from 5 years ago  they say the documentation has been lost.  
> >>> 
> >>> Does anyone know a thing?
> >>> 
> >>> All the best,
> >>> 
> >>> David/atoav
> > 
> 
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