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

[David Huss]

Interestingly enough I can't seem to find such an IC on my unit, PCB picture attached. The IC on the left is the 4017 clock divider. It seems they have replaced the rhythm chip with discrete diode logic in that unit tho. 

On November 25, 2025 1:05:05 PM UTC, Tom Wiltshire <tom at electricdruid.net> wrote:
>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
>> > 
>> 
>> ________________________________________________________
>> This is the Synth-diy mailing list
>> Submit email to: Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> View archive at: https://synth-diy.org/pipermail/synth-diy/ <https://synth-diy.org/pipermail/synth-diy/>
>> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy <https://synth-diy.org/mailman/listinfo/synth-diy>
>> Selling or trading? Use marketplace at synth-diy.org <mailto:marketplace at synth-diy.org>
>> ________________________________________________________
>> This is the Synth-diy mailing list
>> Submit email to: Synth-diy at synth-diy.org
>> View archive at: https://synth-diy.org/pipermail/synth-diy/
>> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace at synth-diy.org
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20251124_143112_s.jpg
Type: image/jpeg
Size: 604291 bytes
Desc: not available
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20251125/3ea41362/attachment.jpg>