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 Forum index » DIY Hardware and Software » Developers' Corner
Help with my hihat circuit
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mrand



Joined: Mar 30, 2014
Posts: 27
Location: Ottawa

PostPosted: Thu Apr 17, 2014 5:25 pm    Post subject: Help with my hihat circuit
Subject description: buffers reintroducing low frequencies that had been filtered away before buffer
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Hi there,

I'm looking for some help diagnosing a problem.

I've built up a hihat circuit, just by pasting together various bits of information I've gleaned from the web, then fiddling around on the breadboard.

I'm satisfied with the sound, which I'd like to maintain. Trouble is, whenever I route the signal through a buffer and/or mixer, much of the low frequency noise I filtered away somehow seems to become present again. I'm totally stumped on this one.

I've tested the buffers/mixers with other signal sources, and I can't hear anything funny happening frequency-wise, but with my hihat circuit, the difference is apparent. I've also tried swapping out different op-amps in my buffer, but all have the same effect. I am therefore thinking that the problem must be in my (dodgy?) circuit design. Attached is diagram for most of it. I've left out the noise source, but if someone thinks I should include that, lmk.

Any suggestions would be greatly appreciated.

This is a youtube demo of the sound, pre buffer: http://youtu.be/CxmcWlCfQGc


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elmegil



Joined: Mar 20, 2012
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PostPosted: Thu Apr 17, 2014 10:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is it because the buffer is forcing a virtual ground?

Maybe try a 1K resistor between your circuit and the buffer?
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Blue Hell
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PostPosted: Fri Apr 18, 2014 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

When it does sound good, with what do you load the circuit, or what do you use to listen to it?
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mrand



Joined: Mar 30, 2014
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PostPosted: Fri Apr 18, 2014 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I have it plugged directly into some some dinkey, powered computer speakers.
I'm very curious to try adding the 1k.
Thanks for looking at this!
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Blue Hell
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PostPosted: Fri Apr 18, 2014 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah ok, those are maybe not able to do the low frequencies or maybe have a bit of a low input impedance ...

You could try to put in a lower value for the output capacitor and / or lower the resistor marked '?'.

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mrand



Joined: Mar 30, 2014
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PostPosted: Fri Apr 18, 2014 8:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm, I'm a little confused. Changing the output cap is going to change the sound, and I've got that where I like it. Shouldn't there be some way I can buffer the output of this circuit without changing how it sounds?

Not that I've got the sweetest hihat here or anything... Just viewing this as a learning exercise.

Changing the "?" resistor shouldn't change the sound though, right?, I think it's at 1m right now.
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Blue Hell
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PostPosted: Fri Apr 18, 2014 9:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Actually you do want to change the sound :p

You are getting too much bass when connecting it to a buffer, so make the cap smaller or the R smaller to get rid of that bass, then buffer it, and then it won't matter anymore with what you load it.

It may still not sound as you like on those speakers though, but then you can blame the speakers.

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mrand



Joined: Mar 30, 2014
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PostPosted: Fri Apr 18, 2014 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Omg, you're so right...
Gonna get to my studio later this aft to try these things out.
Thanks!
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mrand



Joined: Mar 30, 2014
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PostPosted: Fri Apr 18, 2014 6:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, I did a bunch of additional filtering before the buffer and managed to get the sound pretty close! I think I used a 1k at the output, then a .1uf, then a 2k2 to gnd at the buffer's input.
Thanks for the suggestions Smile
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Blue Hell
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PostPosted: Sat Apr 19, 2014 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

great Exclamation
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mrand



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PostPosted: Tue Apr 22, 2014 8:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

I figured I may as well post the final circuit, in case some other noob wants to try an easy hihat.

Adapted from:
MFOS white noise
Zavner AR
Can't remember where the VCA is from... but I think it is a standard issue type.

I'm sure this could be improved, sound-wise, and made more efficient, circuit-wise.

Here is a demo of it, I think the ipod recording made it sound a wee bit better... room acoustics, hipassing mic, I dunno.
http://youtu.be/EQzDZiaDe1M


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