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<span style="font-family: helvetica; font-size: 14pt;">Thanks for the feedback Mike.</span>
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<span style="font-family: helvetica; font-size: 14pt;">Jay S</span>
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On 03/22/2026 8:48 PM PDT Mike Beauchamp <<a href="mailto:list@mikebeauchamp.com">list@mikebeauchamp.com</a>> wrote:
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Just a 3-month-later follow up to this... info below..
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On 2025-12-13 19:59, Jay Schwichtenberg via Synth-diy wrote:
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Looking at the EDN schematic again I think there is an error. Think C1
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should go from Q1's emitter and ground, not emitter and +12. I built
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mine with C1 going to ground.
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Jay S.
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I just received a pcba that I had fabbed with a few different transistor
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noise circuits, including the one from the EDN article as published and
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with your suggested modification.
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Both outputs look exactly the same on the scope and on the scope's
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spectrum analyzer, with flat noise from 0 to 20kHz. Granted, the FFT on
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the DS1054 isn't great, but enough to see.
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So not sure what C1 is doing, why it's different on several different
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schematics, or why it seems to work in both positions just fine.
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With the latest batch of transistors I have, where the noise is
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super-quiet.. this circuit outputs a very nice 1Vpp noise with no
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asymmetry or clipping that I can see. It is also resilient to mechanical
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noise, unlike 1 transistor circuits using several stages of high-gain
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opamps, where I think the AC coupling caps become microphonic and
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problematic when the PCB is being shared with mechanical switches and jacks.
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Hope this helps,
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Mike
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