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Building How-to » Triwave Picogenerator » output attenuated a lot
output attenuated a lot [message #2484] Tue, 30 March 2010 21:56 Go to next message
smrl is currently offline smrl
Messages: 11
Registered: February 2010
Junior Member
Hi, trying to figure this out. My triwave has always had really low output. I'm using the stereo mod.

How I've got it wired: Mix from each channel goes to high side of their respective volume pot. Low side to ground, and wiper thru 2 100k resistors to high & low side of pan pot. Center of pan pot is connected to GND, and the high & low side connect to 2 additional 100K resistors to each jack.

I get 1-2V P-P at the 1uF coupling cap. At my jack it's more like .4v. And there's a ton of HF noise. Any ideas?
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Re: output attenuated a lot [message #2485] Tue, 30 March 2010 22:08 Go to previous messageGo to next message
smrl is currently offline smrl
Messages: 11
Registered: February 2010
Junior Member
Wouldn't all that resistance between the cap & the jack produce a really high output impedance? I'm still not really sure how to calculate the impedance, for example, after the 2n3904; though I'm interested to know how it's done.

is all that noise I see inducted?
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Re: output attenuated a lot [message #2507] Mon, 24 May 2010 14:05 Go to previous message
dann is currently offline dann
Messages: 772
Registered: December 2002
Location: Austin TX
Senior Member
Yes, the triwave historically has low output volume.

The newer triwaves I actually add an output stage to boost the level since it gets cut so much by the mix/pan section. The boost stage is the same circuit as the Aux Buffer (clean blend) stage.

the HF noise shouldn't be there, maybe a 100pF cap to ground somewhere where you see the noise will clean it up. It could be inducted from some flying wire, it could be a noisy power supply. Often I'll put an extra 100uF cap on the power supply before and after the regulator and that cleans up weird RF or HF noise...
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