<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">I've heard of the MM5871, M252, and M253, but never the SN7450.<div class=""><br class=""></div><div class=""><a href="https://www.elektormagazine.com/magazine/elektor-197604/57604" class="">https://www.elektormagazine.com/magazine/elektor-197604/57604</a></div><div class=""><a href="https://datasheet4u.com/datasheets/National-Semiconductor/MM5871/606055" class="">https://datasheet4u.com/datasheets/National-Semiconductor/MM5871/606055</a></div><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">It's a mysterious IC!</div><div class=""><br class=""></div><div class="">Tom</div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 25 Nov 2025, at 03:48, Loscha via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_quote gmail_quote_container"><br class=""><div dir="ltr" class=""><div class="">The "7450" is a specialised rhythm generator chip</div><div class="">Not a 74xx logic chip </div><div class=""><br class=""></div><div class="">It sends pulse out information to the switches and so on.</div><div class=""><br class=""></div><div class="">
I don't have any photos of the insides of mine, and the videos I have on youtube were shot with a potato
<br class=""></div><div class=""><br class=""></div><div class="">The schematic I had is really quite incomplete</div><div class="">But, for modifying the voices, it should help.</div><div class=""><br class=""></div><div class=""><br class=""></div></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, 25 Nov 2025 at 13:59, brianw <<a href="mailto:brianw@audiobanshee.com" target="_blank" class="">brianw@audiobanshee.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">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.<br class="">
<br class="">
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.<br class="">
<br class="">
Brian<br class="">
<br class="">
<br class="">
On Nov 24, 2025, at 6:36 PM, Adam wrote:<br class="">
> Pure gold.<br class="">
> <br class="">
> So... it actually only ever plays at ONE tempo, but you get divisions of that tempo?<br class="">
> <br class="">
> A<br class="">
> <br class="">
> <grab 2025-11-25 at 12.34.27.png><br class="">
> <br class="">
> <br class="">
> On 25 Nov 2025, at 11:51, Loscha wrote:<br class="">
>> Hi David and group<br class="">
>> <br class="">
>> I got one of these machines about 12 years ago<br class="">
>> And it came with the following documentation.<br class="">
>> <br class="">
>> I have a unit somewhere in my garage here in Australia.<br class="">
>> It's missing the to half of the lid I think, but has all the circuitry<br class="">
>> If it'd help you out, I can try and find it over the weekend and we can arrange postage<br class="">
>> <br class="">
>> Pretty sure this schematic will help!<br class="">
>> <br class="">
>> //Edward <br class="">
>> <br class="">
>> On Mon, 24 Nov 2025 at 21:56, David Huss via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" target="_blank" class="">synth-diy@synth-diy.org</a>> wrote:<br class="">
>>> Hi,<br class="">
>>> <br class="">
>>> I have a AK Drummer (CRM-260) Rhythm Machine and I am looking for a schematic. <br class="">
>>> <br class="">
>>> 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). <br class="">
>>> <br class="">
>>> 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. <br class="">
>>> <br class="">
>>> Does anyone know a thing?<br class="">
>>> <br class="">
>>> All the best,<br class="">
>>> <br class="">
>>> David/atoav<br class="">
> <br class="">
<br class="">
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