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 Forum index » DIY Hardware and Software
White Noise and the TR-808
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elmegil



Joined: Mar 20, 2012
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PostPosted: Tue Oct 02, 2012 6:38 pm    Post subject: White Noise and the TR-808
Subject description: preferences?
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Looking in the service manual while building one of the various Snare Clones, I realized that there are actually two versions of the white noise generator, with an arrow going from one to the other, and that one marked "6 lot ~". I built the two and it seems to me that the second one has a slightly deeper, less hissy sound to it. I don't think I have the equipment to measure how 'white' the noise is, but I think I prefer that one.

I'm curious of anyone who's used the 808 or built one of the myriad clones, whether you've noticed a difference in the quality of the noise among the ones you've worked with? If so, which do you prefer, which would you think is more authentic (seems to me that the first circuit was likely only in the first 6 sets built)?
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Sebo



Joined: Apr 27, 2007
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PostPosted: Wed Oct 03, 2012 3:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think that the difference you hear are due to the transistor itself (the sound of the noise varies a lot from transistor to transistor).
The changes in the 808 noise circuit is to avoid DC offset that causes some bad behaviour in the clap, but it should sound the same.

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elmegil



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PostPosted: Sat Oct 13, 2012 10:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built this onto protoboard and the noise is not nearly white enough now. I know I'm not using the transistors I did before so I will have to mess around and try a few to find a good one.
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-minus-



Joined: Oct 26, 2008
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PostPosted: Sat Oct 13, 2012 10:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

I used a PN100 transistor in my snare. It seemed to sound better than the other ones I tried... I can't remember which others I did try though... might have been 2N3904 or 6 or something Confused . If I recall correctly, I think I noticed some transistors of the same type were noisier than others.
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elmegil



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PostPosted: Sun Oct 14, 2012 8:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I found that I didn't ground the base Embarassed

And then I ran through all the various types of NPN transistors I have (didn't have a PN100 though), and settled on a BC547.

Now my problem is that if I turn up snappy, I get noise continuously, not just when I'm triggered. I suspect I may have messed up one or more of the transistors in the lower center section where the noise and triggers come together, so we'll see....thankfully I socketed all my transistors.
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elmegil



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PostPosted: Sun Oct 14, 2012 11:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Not the transistors Sad

Going to have to go over it more finely, that will have to wait.
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elmegil



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PostPosted: Sun Oct 14, 2012 10:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I know why I'm getting noise bleed. As I adjust the snappy pot, I'm getting a proportional DC offset. So my pulse isn't starting at ground, and that baseline is what's letting the bleed through.

Even if I take out the transistor that's gating the noise (T3 in Eric's schematic) I see this offset, so it looks like something in the input is providing an additional constant current. I guess I haven't ruled out the oscillator section 100%, but if I don't have the accent input hooked up at all, I don't see the offset. So it's not just a direct bleed back from the oscillators.

Visual inspection has found nothing unusual so far...

I have some additional ideas for what to test (including swapping out the accent transistor), but if anyone has seen anything like this I'd be interested to hear about it....
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elmegil



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PostPosted: Mon Oct 15, 2012 5:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sure enough, the offset is coming from the arduino side of things. Why this worked with the kick drum is a mystery. At least I'm not crazy Smile
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elmegil



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PostPosted: Mon Oct 15, 2012 10:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Made the same mistake twice on the circuit that does the accent + trigger combination. Didn't connect transistor bases when I thought I had.

Kick drum sounds much better now Smile

Snare is....weird still. If I hook them up per the diagram, it triggers every accent step, regardless of the gate. But if I reverse the inputs, it acts like I'd expect it to. I'll have to look at the circuit further to see if I messed up or what.

I am not getting the constant noise bleed, but it is still a bit crackly. I suspect that's a matter of not having found the best transistor for the noise circuit.

Here's a two bar sample of the two voices together.


kick-and-snare.mp3
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