SSL 4000 summing, question about part on schematics

[Olegarich]

Hello guys, could you help me with identifying correctly what are those parts on SSL 4000 summing board schematics.

1. Input Pin 5 and 8, On the schematics pin 5 is signal, Pin 8 is 0V. In the Manual, one page before, it's written. Pin5-Mix Amp O, Pin8-Mix Amp180.
Does it mean that pin 5 is "hot" and pin 8 is "cold"? or is it signal and screen? Cause before entering the summing I cannot find any palce where signal get's balanced just before getting to summing. It goes threw 15K bus resistor tu bus summing.

2. There are diodes on the schematics and I cannot find any info on what diodes are there. Perhaps you know what it could be?
Thank you for the help guys!

 

[gyraf]

1 - It's not really balanced, the mix-0V is just the reference for the mix bus, it's extended all way out to all channels and acts for cancellation of incoming interference and noise

2 - My 82E26 schematic http://gyraf.dk/gy_pd/ssl/ssl_82e26.gif says "all diodes 1S44"

/Jakob E.

 

[Olegarich]

Thanks Jakob,
If I may ask, if I understand correctly this mix-0V is only for summings and it's not the same as "ground" of the channel strips. Wonder how it done practically. Is it something like, let's say16 channels / 16 cabels. Every cable have hot and screen. Hot goes to the signal pin (Threw 15K resistor) but cable screen is connected only in that mix 0V point and not in other end. All the noises that cable screen will catch, will be canceled. Is it something like this?

 

[ruffrecords]

In each source, the Mix-0V is usually connected to signal ground via a small resistor, typically 10 ohms. The technique is described in Doug Self's excellent book "Small Signal Audio Design". I highly recommend investing in a copy.

Cheers

Ian

Cheers

Ian

 

[Michael Tibes]

If I may ask, if I understand correctly this mix-0V is only for summings and it's not the same as "ground" of the channel strips. Wonder how it done practically.

2 Heavy copper bars, connected only at the center section.

I haven’t really analysed it, but I guess the summing amp is ‚kindof‘ impedance balanced. If I remember correctly, the upgrade from E to G involved adding a lot of resistors on each channel, probably the impedance addon for the gnd end?
So to fully understand the bus, one has to look at the series and have the correct schematics in context with the actual mechanical realisation. For more fun there might also be intentional errors and missing service bulletins with upgrades not yet shown in the schematics ;-)

Michael