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 Forum index » DIY Hardware and Software
Transistor choice in TR-808 voice clones -- 2N2222 vs BC547
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 16
Location: Grand Rapids MI

PostPosted: Wed Feb 14, 2018 10:45 am    Post subject: Transistor choice in TR-808 voice clones -- 2N2222 vs BC547 Reply with quote  Mark this post and the followings unread

I'm "card-boarding" (like a mix between breadboarding and point-to-point where components and power rails are on the top of the card and all the ground connections get poked through the card) voices for the TR-808, and the first version of the hat sounded *amazing* but it broke because I was inexperienced and my technique has improved, so I built a 2nd one.

It sounded **so much worse** -- very distorted and crackly. As though the 6-oscillator-metallic noise was clipping hard.

Last night when I was troubleshooting the cymbal, experiencing the same issue, it occured to me that maybe it's my transistors. My first three voices I used BC547s for the NPN transistors, and I switched to the 2N2222 simply because that's a really cool name, and also the orientation makes more sense to me in my brain with the flat side to the right in most schematics.

However, the specs aren't identical. The 2N2222 has more current output? In the "swing-type" VCAs in these voices, that's going to make a difference, right? I've tried different op amps (NE5532 vs TL07x) and types of capacitor, and neither of those things made any difference I could hear with my regular ears.

Oh, I *am* running off +/-12V and not +/-15, so I'm voltage-starving these circuits. But remember my first hi-hat sounded great.

Here's a video of a 4-pole high-pass VCF and at the end you can see the circuitboard in case you're wondering about my construction technique.
https://www.youtube.com/watch?v=Qf-mEcOW0nk
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 16
Location: Grand Rapids MI

PostPosted: Thu Feb 15, 2018 5:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I swapped out the transistors in the audio path, which didn't change much. Putting a 1.5M resistor between the noise source and the first filter got the clipping under control. Now my hat sounds perfect! Next it'll be the cymbal.
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