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Moving-Magnet Head Amp - without RIAA
Moving-Magnet Head Amp - without RIAA
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Old 3rd March 2019, 01:30 AM   #111
rsdio is offline rsdio  United States
diyAudio Member
Join Date: Feb 2008
Location: Seattle
Here is the main board for the preamp. The LED hasn't been soldered on yet (still waiting for a different color).

The dimensions of the boards are constrained by the 32mm x 64mm x 104mm case that I found which has a turntable grounding screw on the outside. I didn't want to DIY the case, too.
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Old 3rd March 2019, 02:38 PM   #112
Hans Polak is offline Hans Polak  Netherlands
diyAudio Member
Join Date: Mar 2005
Location: Blaricum
Originally Posted by rsdio View Post
I have a 1 MΩ resistor now, and have reduced the gain of the first stage to 20.1x (+26 dB) to create a virtual 47.4 kΩ load.

I didn't understand what you were suggesting the first time, but I could disconnect the 1 MΩ and solder a 47 kΩ with 1 lead on the PCB and the other lead grounded. I might try that to see if there is any difference, but I doubt I could measure it.
With the lower gain, noise improvement is now 3.0dB just a little bit less.
What I suggested was to use not one but two resistors in series.
In this new case 47K + 950K instead of 1 Meg.
All you have to do to notice any difference is to gnd the connection between 47k and 950k,

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