GHR Audio

For GR indication, I ran a cable on underside of board from sidechain CV1 out to onboard J13 (CV1 VU meter driver input). Stuffed R93 and R94 with resistors equivalent to VU meter resistance. Looking good for now. Value of R93 and R94 will depend on what meters are used but probably resistor equali...

In the schematic they are just blank resistors so I was looking for confirmation that I have these shown correctly. Those values look good to me. If your timing cap is 1uF your attack is approximately variable between 1 ms and 50 ms and release between 50ms and 550ms + attack time. What vu meter sp...

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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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More accurate resistor values for the gain switches.

140
170
190
240
280
350
440
560
730
1k
1.4k

The values on the schematic have a tolerance of approximately +/- 0.1dB. Values listed here should be closer to +/- 0.02 dB

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Here is the libre office spreadsheet I used to create the curves

http://ghr.fi/proaudio/diodecomp/diodi.ods

I'll need to check if I still have the ideal values somewhere. The E standard values should be pretty close to 1 dB per step.

You don't necessarily have to measure anything when adjusting RV1. Just set it where the LEDs are starting to light up. The more accurate way to set it is to feed the channel input 1kHz signal and adjust threshold to make sure there is NOT any gain reduction happening. Monitor the output and adjust ...

Just as long D73 and D74 are the same type of silicon diode the exact type shouldn't matter too much. If RV3 and RV4 are 1k instead of 500 ohm it will change the threshold range. Exact type of diode shouldn't matter in the diode string and any silicon diode should work. Again just as long as they ar...

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 - * INA2137 Internal resistors are ratio matche...