Hi, I'm new here... Got some questions regarding the GSSL and the modding that's been done. I'm from the Netherlands, so please forgive me if I use strange words. I don't mean to offend anyone
Don't know if this is the right topic to post to, but I am in need of a little help and the subject is a SSL-clone..
I recently built a weird looking GSSL.
(yeah the GR-metering on the pic is inverted, it's corrected now) The little red thingy at the right is a simple OTA-based
guitar compressor. That, along with servicing guitar-related equipment is what I'm normally into.
I had 85% of the GSSL parts (including the enormous VU-meter) lying around and as a live sound-engineer, I often lacked a nice compressor to insert to the subgroubs I routed my drumchannels to. Anyway, I love almost everything it does live and in the studio, so it's time for an
upgrade
This one was build cheap and small, with the onboard 5VA transformer, simple single THAT2180 replacement for the
202's and all. For inputcaps I even used 3u3 mks/wima's, with no lack of bass in my application. All to get to know the
circuit a bit. It was a lot more quiet than I thought and turned out very useful.
Now, I've been lurking around this forum a while, because I needed some info on possible upgrades.
The input/output section on the gyraf board is overcrowded indeed, (as Jacob admits) so I decided to redraw the board. I'm
halfway by now.
I'd love to implement some of Keiths ultimate mods. Here are some questions regarding the mods.
1. Audiopath: I plan on running the audio path balanced, but only through 4 2180 VCA's (2 left, 2 right)
What I imagine is a simple 22k Zin inverting buffer in front (NE5534) followed by 22uF, driving the sidechain VCA (though
47k) and the main VCA (through 27k).
I do this for both the hot/in phase and the cold/inverted signal. I guess I should only connect the 47k going to the SC to
the hot path. Am I right? Should I tweak the (47k) value?
2. After the 2180, I use the inverting current to voltage converter as in the Gyraf schematic/THAT datasheet, (NE5534 w 15k feedback R) and send to corresponding output pin on xlr via 100r/100u+100n and 47k to GND.
Do you see any problems in this approach?
3. Sidechain: Let's leave out the HPF and other mods for now. But use what you guys seem to call the 'turbo-mod'.
This is what I imagine to work, and what I learned from Keiths ultimate GSSL notes.
Let's say left channel. You take the hot/in phase signal and send it via 47k to SC IN L.
I have to copy the entire part between the SC IN and point C. (including ratio Sw)
I recombine the rectified signals at point C by connecting the diodes cathodes together. (okay?)
From there through attack and release. At point 'D' I get a bit confused. As I first drew one sidechain, the last part (pin 8,9,10) of the TL074 ended up in parallel. So I kept 1 3M3 resistor to GND and send point D to both + inputs
simultaniously. Is this a problem or just overengineering?
4. I plan to use only one TL072 for both the main- and SC-VCA's Control voltages... So I mixed both TL074 outputs into the - inputs of the 072. Each output via 127k for the main VCA part and 100k for the SC VCA part. Something tells me this will
give twice the gain from the 072, something else tells me it's a simple inverting mixer stage, so twice the same input
gives me only once the output times gain. AAArgh what to listnen to?
I send only one output via trim to meter.
This is quite a bit longer than I first intended, hope it doesn't bother you to much and that you might help me out.
Thanks for reading!
Grtz,
Matthijs
