LinnDrum LM-2 clone in progress

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Retrotech
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LinnDrum LM-2 clone in progress

Post by Retrotech » Sun Oct 18, 2020 11:41 am

Well well, seems that nobody has built a (real) LinnDrum (aka the LM-2) clone before ;) . So I picked up the schematics and started transferring them to KiCad. The CPU PCB layout is almost complete now. Once done, I will start with the drum board (sooo many EPROMS ! :yay: ). Since there is no way for me to check the exact dimensions of the device, it is not going to be a perfect copy (unless, of course, someone who knows a bit more wants to contribute). But I will try my best to make it as authentic as possible. I'm also thinking about making this open-source, but most likely I will first build a prototype and verify it works. So yeah, feel free to comment or maybe even join the forces.

PS. As a first-year physics student, my knowledge and experience are somewhat limited - so don't blame me too much. A clone built by an amateur is still better than nothing I guess.

Cheers,
Ergo
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tobb
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Re: LinnDrum LM-2 clone in progress

Post by tobb » Sun Oct 18, 2020 3:00 pm

Well,well,..that's is cool,...but its the LM-1 you should have chosen.

An LM-1 clone you will be able to exploit it to the max and sell much easier (also to collectors!) VS the 'less desirable' LM-2.

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sduck
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Re: LinnDrum LM-2 clone in progress

Post by sduck » Sun Oct 18, 2020 8:40 pm

Very cool! I hope it works out. BTW I find the Linndrum (LM-2) to be the much preferred version.
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Re: LinnDrum LM-2 clone in progress

Post by Flounderguts » Sun Oct 18, 2020 9:48 pm

Yeah, I like the LM-2 better as well. Great effort!
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devinw1
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Re: LinnDrum LM-2 clone in progress

Post by devinw1 » Sun Oct 18, 2020 10:27 pm

Oh shit. Very cool.

Always dug the LM-2.

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Re: LinnDrum LM-2 clone in progress

Post by J3RK » Mon Oct 19, 2020 12:58 pm

tobb wrote:
Sun Oct 18, 2020 3:00 pm
Well,well,..that's is cool,...but its the LM-1 you should have chosen.

An LM-1 clone you will be able to exploit it to the max and sell much easier (also to collectors!) VS the 'less desirable' LM-2.
I know someone working on an LM-1 semi-clone actually. (exact clone the way the sounds are generated, but not exact form-factor etc.) No more info for the time being though. Anyway, not to derail this thread. This looks very cool too!
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ryan-Phayder
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Re: LinnDrum LM-2 clone in progress

Post by ryan-Phayder » Mon Oct 19, 2020 1:02 pm

Cool project. Have you sourced the DACs? IIRC they are a little on the difficult side to find.

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MikeDB
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Re: LinnDrum LM-2 clone in progress

Post by MikeDB » Tue Oct 20, 2020 5:23 am

It might be better to combine the 4 SRAMs into one larger 64k (or larger) SRAM and the 2 32k EPROMS into one 64k (or larger) EPROM simply because the smaller sizes are so rare nowadays. Isn't going to affect the authenticity of the sound in any way.
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Retrotech
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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Sun Oct 25, 2020 7:08 pm

Hello again!

Thanks for your comments - makes it all worthwhile ;) Just a quick update. Fixed some errors and finished the initial CPU PCB track routing - took a long time because a)I was looking for an alternative for the MAN4710A 7-digit display that had a similar footprint, b)had to mess with crazy derivatives and integrals, c)the computer did not want to co-operate. Now the connections are there but they are messy, so I will take some time to clean them up.
As many of you know, the original square push buttons are no longer available (I mean, they are, but waaaay too rare and expensive). So I'm also working on a simple, yet as authentic as reasonably possible, 3D model (either for 3D printing or making a mold for molten plastic casting). The DIY option should work because the switches are basically just two pieces of wire (one of them curled like a spring) that come into contact when the 18mm square plastic cap is pressed down.
When it comes to the parts used on the CPU board, almost all of them are still available (in one form or another). Due to a lack of advanced electrical knowledge, I try not to edit the original design. In addition, I think that replacing the 2732 (on CPU board) with a bigger one is close to pointless, because every single sound on the drum PCB is on a 2732 EPROM - and there are still some cheaper ones available - so you still need many of them if you want to make the machine work.
So yeah, when I'm done with the CPU board, I will start with the sound board, continue with the power supply, and I'm also thinking about making a 2D model of the metal case for laser cutting - so basically a complete copy. Okay, running out of free time, gotta go now!

Cheers,
Ergo
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Retrotech
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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Mon Oct 26, 2020 4:40 pm

Changed the regular track width from 0.25mm to 0.4mm and fixed some design issues. I think the CPU board is now finished (maybe a few things here and there). Finally, I can move on with the other parts. Stay tuned! ;)
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Re: LinnDrum LM-2 clone in progress

Post by loki » Mon Oct 26, 2020 4:47 pm

Hate to be pedantic but: there is the LM-1, the LinnDrum and the Linn 9000. Roger Linn himself points out that there isn't any such thing as an LM-2.
Retrotech wrote:
Sun Oct 25, 2020 7:08 pm
When it comes to the parts used on the CPU board, almost all of them are still available (in one form or another). Due to a lack of advanced electrical knowledge, I try not to edit the original design. In addition, I think that replacing the 2732 (on CPU board) with a bigger one is close to pointless, because every single sound on the drum PCB is on a 2732 EPROM - and there are still some cheaper ones available - so you still need many of them if you want to make the machine work.
Looking at the schematic it is clear that on the processor board you can/should replace the two 2732s of program memory with a 2764 and the four 6116s with a 6264. This saves board area and makes your routing easier for the board layout. When it comes to the EPROMs for the drum sounds he used all 2732s, probably for the price advantage of volume purchase of one part, but many of the sounds occupy more than one EPROM. The crash and the ride cymbal each occupy 8 2732s, use a 27C256 instead. The hihat reduces from four 2732s to a 27C128 and there are several others that reduce from two 2732s to one 2764.

This big reduction in parts count saves board area, cost, and layout difficulty. Tip, don't use any 2732s as they are in a 24 pin package while the larger parts (64, 128, 256, 512) are in a 28 pin package with pinouts that are upwardly compatible.

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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Mon Oct 26, 2020 5:23 pm

loki wrote:
Mon Oct 26, 2020 4:47 pm
This big reduction in parts count saves board area, cost, and layout difficulty. Tip, don't use any 2732s as they are in a 24 pin package while the larger parts (64, 128, 256, 512) are in a 28 pin package with pinouts that are upwardly compatible.
I appreciate the advice but I will happily stick with the original design - this way I will be able to finish it faster (less inventing, more copy-pasting). I'm sure that by using more modern components, one could fit the whole machine inside a matchbox. But you can edit the files yourself when I make them available. I'm trying to build an accurate clone, even if it is not reasonable by today's standards ;)

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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Tue Oct 27, 2020 5:14 am

Hey there! Anyone knows if there are alternatives for the AM6070DC 8-bit DIP-18 companding D-to-A converter? It is still available but expensive.

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Re: LinnDrum LM-2 clone in progress

Post by loki » Tue Oct 27, 2020 12:58 pm

PMI made an equivalent part, the DAC88. Good luck finding any.

Retrotech
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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Tue Oct 27, 2020 1:42 pm


Retrotech
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Re: LinnDrum LM-2 clone in progress

Post by Retrotech » Tue Oct 27, 2020 1:53 pm

What do you think, is this AM6070DC fake? https://www.ebay.com/itm/AMD-AM6070DC-D ... SwEppUPQJa

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Re: LinnDrum LM-2 clone in progress

Post by loki » Tue Oct 27, 2020 6:08 pm



That is labeled right but it looks different than the ones I have. I know mine are authentic, I bought them from an authorized distributor back when they were current parts. Since those are coming from the far east they may or may not be legitimate. You could build a test fixture with an EPROM and test them to see if they produce the proper sound.

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Re: LinnDrum LM-2 clone in progress

Post by loki » Tue Oct 27, 2020 6:34 pm

Retrotech wrote:
Tue Oct 27, 2020 1:53 pm
What do you think, is this AM6070DC fake? https://www.ebay.com/itm/AMD-AM6070DC-D ... SwEppUPQJa
The ceramic package is appropriate for the time period of the date code: 16th week of 1984. I think you might buy the DAC88 and test them since they are cheaper. I looked and they are pin compatible.

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Re: LinnDrum LM-2 clone in progress

Post by Philthy » Tue Oct 27, 2020 7:56 pm

Watching this with interest

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Re: LinnDrum LM-2 clone in progress

Post by 3hands » Tue Oct 27, 2020 7:59 pm

Watching this as well. This will be very cool.
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