Transformerless Feedforward Vari-Mu

[Heikki]

Transformerless vari-mu based on the U73 compressor/limiter.

Design files

notU73.zip

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Schematic

73.pdf

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Layout

73layout.pdf

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Fully tried and tested design. I'll post measurements and more pictures later.
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Gerber files here
viewtopic.php?t=75
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Boards for sale
viewtopic.php?t=49
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not73.JPG

[Heikki]

Specifications

Input impedance ≈ 12k ohms, balanced line-to-line *

S/N > 86 dB re +4 dBu, 22 kHz BW, unity gain

Frequency response = 20 - 20 kHz, ±0.5 dB

Gain = 0 dB at limit mode, 6 dB at compress mode

Output impedance = 50 ohms, balanced line-to-line
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* INA2137 Internal resistors are ratio matched but have ±25% absolute value

[scott2000]

I can make out U5 on the DCDC board pic. What model Recom is used?

[Heikki]

Recom R12-150B

Regulators for the DC-DC converters are 12V and regulator for the heaters is 5V.

R1 = 1 ohms

R2 = 2.2 ohms

R3 = 4.7 ohms

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