I am looking for some help with creating a strip board layout for the SN Voice module. I got one of the SN76477chips a few years ago at an estate sale in an evaluation kit and it’s been quietly waiting for a real use. I thought about building that into a module, but it doesn’t seem very useful as-is. The SN-Voice PCB goes for $45 with tax and shipping and I just cannot justify that.
I’ve done a first pass on a layout. It’s spread over two boards of different shapes/sizes. That just made sense to me, maybe it’s not such a great idea. I could probably redo the input control board in the same size board as the voice board to make things a bit more uniform. I haven’t added any of the decoupling or power filter caps to the layout. Instead of the LM394 I am going to attempt to use two 2N3904s that I match and thermally bond with the resistor.
Sorry if it’s a bit hard to read some of the text, I like doing layouts on paper. I will try to eventually do a proper layout in software.
It would be really helpful if I could get another couple of eyes on it to make sure I didn’t miss something or make any mistakes. Or let me know if I am crazy and should just buy the PCB!
Thomas Henry Schematics Page
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Well, I did it. I redid the input board to make it the same size as the other one. I’m not super happy with how cramped it is.
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Hope it works for you. I did order the PCB many years ago and it has been lying around, fully populated and I got the last potentiometers in place in a cool panel that I also made a few years ago.
I plan to use the SN Voice as a stand-alone machine or as an addon to my modular.
The problem with the SN76477s is that the later productions came in an odd packade odd 0.06” between pins 
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Thanks! That is quite weird. Mine has a date code of 7827. It’s an old boy in the fat package.
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I got a bunch of the chips on a diet and made me an adapter pcb.
Else it’s fantastic that a chip to make explosions and bird chirps suddenly can be used tonthe full.
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Oops, made some mistakes on the voice board layout. So I just completely redrew it.
I also decided to include the Envelope/Gate mode switch with timing adjustment pot before the 4.7uF cap.
I have all of the parts (I think, I am willing to bet I forgot to order something) besides the 2k tempco resistors, which are on their way across the pond from Thonk. I have done some transistor matching with one of those cheap component testers/identifiers. I don’t think it’s the best way of doing it, but I also don’t have a high precision multi-meter. I’m just checking multiple times to make sure I always get the same reading from the transistor pairs. And yeah…I realized Thonk sells matched transistor pairs well after I made the order for the tempco resistors.
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1 mV is good enough, but if your meter doesn’t do mV, it doesn’t…
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Oh, thanks! That seems a lot easier than some of the ways I found. The one way I kept seeing mentioned says you needed a really closely matched pair of 100k resistors. Comparing against a single transistor like that makes a lot of sense, just looking for a difference.
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Okay, yeah. That worked really well. One of the pairs I matched with the component tester got me 0mV with the transistor matching set-up. That is definitely going to be the exponential converter pair.
I also realized I made a mistake on the Voice board layout. The top trimmer should be 10k, not 50k.
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Made some major progress. Not really looking forward to wiring everything together!
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I got it all wired up…and then nothing from it, did some tinkering. It was making a signal but it wasn’t coming through the op amp, the tuning knob wasn’t working either. Then I realized I had the +/- voltages on the op amps backwards! Real rookie mistake there. I managed to kill two LF444s and TL074. I luckily bought a spare 444 and an 074 is good enough for the output amplification. I also killed another -12V voltage module…I really need to replace that powersupply.
Rats nest, something like 40 wires.
All together. I left the wire long so I can fold the boards up to get access to the underside.
The victims of my stupidity.
Next up, tuning! I might also have to swap a couple of the switch wires. Those aren’t documented very well anywhere.
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Okay, so there is definitely a reason why the instructions for the PCB uses 4 way switches. The LFO is on the signal all the time, it is nice to be able to turn that off…I guess I am going to have to drill an extra hole and wire in an LFO off switch. Again, probably me not doing enough research before diving into building this. But the tuning worked great (after I de-soldered the line to the LFO range switch).
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Hey, I finished it, and it works! And I feel dumb because I thought I also cooked the SN chip and panic ordered a second one off eBay but it’s fine!
Demo coming later.
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Here it is, the demo, there is a lot to learn with how this thing works. I think the LFO off switch might have been a mistake, but it doesn’t hurt, at the very least.
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Here they are, the final layouts!
I didn’t connect everything because there would be quite a mess!
Overall, it’s not really a difficult built, just has some less common resistor values and a LOT of front panel connections. And you can get the SN chips for a relatively decent price from China. I really like it. It’s a pretty cool all on one sort of solution.
If I build another one, I would probably do it more as a stand alone synth with a second envelope generator, a VCA for the Triangle wave, a mixer, and an MS-20 filter. I feel the MS-20 works well with this because it’s got more of a “robotic” sound to my ear, which seems to pair really well with this.
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Adding the corrected layouts here, too.
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