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Voltage Divider at input to Power Amp




Hi, be gentle, I'm trying to make the move from being a consumer buying shiny new gear, to making my own simple designs and mods...

Would be grateful for someone more experienced to audit my work - I'm making a voltage divider at the inputs to a pair of monoblock amps. The goal is to reduce audible hiss from the preamp's mosfet output stage.


The specs are:

Speaker sensitivity ~ 107dB/w/m (front loaded horns)

Desired attenuation = 15dB

Power amp input Z = 41K shunted by 47pf

Preamp output Z = 130R 'corrected' (per manufacturer)

There's a parallel load on the preamp from the monoblocks and a Velodyne SMS-1 bass management processor. I've searched the documentation and web for the input impedance of the SMS-1 but come up empty. So I'm assuming it is 'high', ~100K.

My math is based on these formula:

1) Vd = 1 + (R1 / R2)

2) dB = 20 * Log10 (Vd)

3) Zin = R1 + R2

4) Zout = (R1 * R2) / (R1 + R2)



Following are 5 R1 / R2 combinations for a 15dB voltage divider:

R1 R2 Z(in) Z(out)

4K99 1K06 6050 874

6K8 1K5 8300 1229

10K 2K2 12,200 1803

15K 3K3 18,300 2705

22K 4K7 26,700 3873


If my math is correct, any of the above R1/R2 combinations will work to attenuate the signal by 15dB. My lack of experience is around matching impedances with the pre and power amps. I'm trying to design a voltage divider with adequately high load for the preamp and low impedance for the power amp.

1) Which combination would be 'best' in this application, and why?

Much thanks!




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Topic - Voltage Divider at input to Power Amp - tetsuo 17:13:38 07/27/13 (9)

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