Emperor-TK
Well-known member
This is a warning to everyone who wants to install a turbo board into a GSSL with deleted resistors in the side chain. About 2.5 years ago when I built my GSSLs, there were discussions on weather or not to delete the 47R between pin 4 and ground, and the 10K between pins 3 and 5 of the SC VCA. Based on the THAT data sheets, it seemed like these resistors might not belong when using the newer 2180/2181 VCA's. At least a few of us proceeded without stuffing these resistors, and my GSSLs seemed to work fine....until I went to add a turbo board today.
My builds use both 2180LB and dbx C1252H2 VCAs without the SC resistors mentioned above. For the sake of symmetry, I also deleted these resistors on the turbo board. I fed the GSSL a 1K sine wave through a mixer and panned L to R. Relative to the center, the left channel rose steadily a few dB when panned. The right channel however, dipped down a dB or two. If I wiggled the pot randomly from center to right, I could get the gain reduction to drop another dB or two from hard right.
I stuffed the missing SC resistors into the Turbo board and tried again. This time, the right channel was good, and the left channel was off. Although this time the gain reduction increased slightly, it still had that same random behavior when I wiggled it (from center to left this time). It also never rose as high as the right channel.
So, like the story of the three bears, the third time is the charm. I stuffed the missing SC resistors onto the main board along with the Turbo board. Panning both left and right now lead to smooth monotonic increases in gain reduction with no random behavior.
The moral of the story: Put the missing side chain resistors back on the main board if you want to go turbo.
-Chris
My builds use both 2180LB and dbx C1252H2 VCAs without the SC resistors mentioned above. For the sake of symmetry, I also deleted these resistors on the turbo board. I fed the GSSL a 1K sine wave through a mixer and panned L to R. Relative to the center, the left channel rose steadily a few dB when panned. The right channel however, dipped down a dB or two. If I wiggled the pot randomly from center to right, I could get the gain reduction to drop another dB or two from hard right.
I stuffed the missing SC resistors into the Turbo board and tried again. This time, the right channel was good, and the left channel was off. Although this time the gain reduction increased slightly, it still had that same random behavior when I wiggled it (from center to left this time). It also never rose as high as the right channel.
So, like the story of the three bears, the third time is the charm. I stuffed the missing SC resistors onto the main board along with the Turbo board. Panning both left and right now lead to smooth monotonic increases in gain reduction with no random behavior.
The moral of the story: Put the missing side chain resistors back on the main board if you want to go turbo.
-Chris