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RE: My New DIY Passive Preamplifier

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In Reply to: RE: My New DIY Passive Preamplifier posted by Tre' on February 09, 2023 at 07:32:22

The resistor trick here is having 1/2W 100K Takman REY metal film resistors between the input and the wiper contact, and the wiper contact and ground. I believe this was first discovered by the late Bob Crump. The TKD pot becomes a parallel variable resistor with the fixed resistors. The actual input value is only lowered slightly. I have not measured the capacitance of the interconnects, but they are very low, and 0.5 meter or less in length. The input of my amplifier has a very low value capacitor in series, and with 120 K Ohm input impedance to form a 1st order high pass at 94 Hz.

Follow Ups:

RE: My New DIY Passive Preamplifier - Tre' 15:01:53 02/09/23 (2)
The 10k pot will have an output impedance of 2500 ohms at -6db attenuation.
The 100k resistors will lower that a little.
1st order low pass at 94kHz will shift phase all the way down to 9.4kHz
If you want 20kHz undisturbed then all your low pass filters need to be at 200kHz min.
I'm sure it sound just fine.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 02/09/23
- RE: My New DIY Passive Preamplifier - fastcat 18:30:52 02/09/23 (1)
  Oops! I meant high pass filter at 94 Hz. The unit sounds quite good, and has good dynamics with my cables and equipment.
  - RE: My New DIY Passive Preamplifier - Tre' 19:25:05 02/09/23 (0)
    I'm sorry. I totally misread your post.
    
    I understand now that you have a high pass filter installed, keeping the bass out of the main outputs, with a -3db point of 94 hz.
    
    I was interested and worried about the low pass filter that is created by the output impedance of your pots and the total shunt capacitance (cable plus Miller capacitance of the amp being used) that that impedance is having to drive.
    
    With short cables you probably don't have a problem.
    
    Again, sorry for my confusion.
    
    Tre'
    
    Have Fun and Enjoy the Music
    "Still Working the Problem"

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