Modding Soundcraft 600 (Master Channel first)

[actuel47]

I think this thread is great but as far as the Jim William’s mods go, I believe his intention was to do two things-
1. improve the compromise of this particular design that combes both mic and line inputs in one amp; the line input is padded before being amplified by the mic pre circuitry. Apparently this is a problem when mixing because of the amount of gain required to bring the signal back up after the pads causes distortion. I know from experience the line inputs sound funny compared to mixings with the tape monitor inputs.
2. remove as many signal path coupling caps as possible. This really help with transparency.

Opamp substitution is probably more fashionable than practical but Jim was able to remove more coupling caps by doing so and I’m sure he tested the distortion when comparing substitutions because I know he has an analyzer. Also, when he did the substitutions the non-smd versions of the opamps he recommended were still in production.

That said, I still prefer the monitor inputs. I would much rather send the tape returns to the channels after these line inputs. Also, why did my Soundcraft come with a version of the schematics that never went into production? I can’t find one of the input module that doesn’t have IC6. There’s no ic6 on my boards.

 

[abbey road d enfer]

I think this thread is great but as far as the Jim William’s mods go, I believe his intention was to do two things-

JW's primary intention is to relieve his clients of their money. He's in business.

1. improve the compromise of this particular design that combes both mic and line inputs in one amp; the line input is padded before being amplified by the mic pre circuitry. Apparently this is a problem when mixing because of the amount of gain required to bring the signal back up after the pads causes distortion. I know from experience the line inputs sound funny compared to mixings with the tape monitor inputs.


Also, why did my Soundcraft come with a version of the schematics that never went into production? I can’t find one of the input module that doesn’t have IC6. There’s no ic6 on my boards.

It appears you have the first version, that was identical/similar to the 500. The mic preamp is different. Actually IC6 was a later mod. This preamp, without the additional IC somewhat lacks in performance. Even at moderate gain (in Line mode, it should run with about 20dB gain) its distortion is not stellar.
Perhaps you may find second-hand channels with said IC6, for the sake of comparison.

2. remove as many signal path coupling caps as possible. This really help with transparency.

The problem with removing coupling capacitors is that it opens up risks of scratchy pots and clicking switches. Removing caps implies structural consideratins at the design stage.
I'd rather replace the caps (anyway, they probably need being replaced), and take advantage of the dramatic improvements in electrolytic caps technology. You can pobably double the nominal value (halves LF distortion) and increase the temperature rating (105°C is quite common now).