© 2013 Benden Sound Technology
Made by Serif
Gyraf Audio's clone of the mix bus compressor found in certain vintage analogue mixing
desks is a popular DIY project and many custom parts are now available off-
I was asked by a client to build and test two units, and the results can be seen in the photographs.
Neither of the two units are standard G-
Highpass filtered at one of four different frequencies (to compress bass frequencies less).
Thr*st High and Medium strength (more complex sidechain frequency responses designed to add punch).
A known shortcoming of the G-
To put this right requires a second sidechain to be built which, in the case of the extended sidechain described above, calls for quite a bit of extra circuitry. Nonetheless, this was done for one of the two units; the other has the standard, mono sidechain.
Cases came from Purusha via the Prodigy-
When testing, I found that signal distortion in bypass mode (not a true, hard bypass) was rather high. The solution, found buried in the forums, is to ensure that the bypass switch grounds the 620K makeup gain mix resistor rather than leaving it floating. Otherwise, noise coupling into this high impedance point raises the distortion.
Also, quite a bit of manual trimming was required to achieve the specified compression ratios. I suspect this is caused by opamp offsets in the sidechain circuitry and would investigate further before building further units.
Rear view of G-
Internal view of G-
Extra board containing stereo sidechain with multiple filter options.
Internal view of second G-
Extra board containing mono sidechain with multiple filter options.
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