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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: Still no stereoPosted by anthony on: 8/21/2019
Yes, the second DSET is still not biasing properly and I cannot find enough consecutive time to look for the fault.  In the meantime I've got a couple of minor side projects off the electronics bench, and started thinking seriously about preamplifiers.  Part of the thought process is to do with analogue volume controls and to make some decent decisions I need to know the input impedance of the DSET's.  So I measured it...see below.

DSET Input Impedance 2V Pink Noise FFT.png


Romy, the back-of-the-envelope estimation of about 5k Zin is roughly correct.  You can see in the graph above that at 20K Zin gets as low as 3.5k.  Phase is flat until the inductors kick in circa 600Hz, 3.2kHz and 10kHz which causes it to roll off or less linearly with frequency.

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