Soundcraft 1600/800B

[kaltavilla]

The original starter of this thread hasn't logged into the forum since November 17th last year.
I'm wondering who exactly we're trying to educate in the matter of Soundcraft desk up cycling these last coupla days?
Haha

I didn't start the thread, but I do have a 1624 that I'm fixing up, and I do appreciate the education. Thanks !

 

[Winston OBoogie]

I didn't start the thread, but I do have a 1624 that I'm fixing up, and I do appreciate the education. Thanks !

OK cool Sorry for my part in derailing things.

Other than what's been discussed as far as bus amplifiers etc., my recollection of the 1600's is that the input stage could be improved. We have better hybrid schemes now as far as distortion and noise go.

For mixing line inputs from a DAW that are already at the appropriate level, there's probably quite a bit that can be removed from the existing signal path for that duty.

I think they're pretty good candidates for hot-rodding if an analogue desk is your bag. Not too cramped in there either so POOGE-ing in little updates and daughter-board pcb's wouldn't be a complete nightmare in real estate management.

"Small Signal Design" - D. Self.

 

[FIX]

Just curious, how are you calculating that? I would not think the output resistors on the bus drivers are parallel. They each connect to a separate output stage and the bus.

First, Science is good. Thats why we have a vaccine. Using science to say that one tone is better is not quite there yet....

The calculated bus impedance is the sum of the bus resistors, provided they are connected between an output driver and/or a switch that grounds them. The source of a bus would be either an opamp (virtual ground) or a send pot or pan pot, which should be 1/10 the value of the bus resistor. After that, it's simple math. All opamps have a point where the 1/n noise increase in gain from the bus value ( the op-amp gain is the sum, each channel gain is only it's resistor) starts to go up more than the 1/n noise calculation, meaning that say with a 2520, if you go below 1200 ohms, the noise will increase more than just the gain calculation, where a 990 is around 600 ohms, so it will appear slightly quieter on the same bus if it's below 1200 ohms, but will sound different.

On the larger APIs I designed, I actually lifted the bus resistor from the summing amp (with some trickery) so the bus amp was always the sum of only the channels connected. That kept the noise down a lot. In the new FIX designs, I sum locally in the 8 channel bucket, then sum each bucket balanced into the master section, so the noise gain is never more than the equivalent of 16 channels, even in a 64 input console, plus I am hitting the bus amps at +4dBu instead of -10.

 

[abbey road d enfer]

First, Science is good. Thats why we have a vaccine. Using science to say that one tone is better is not quite there yet....

Indeed.

All opamps have a point where the 1/n noise increase in gain from the bus value ( the op-amp gain is the sum, each channel gain is only it's resistor) starts to go up more than the 1/n noise calculation, meaning that say with a 2520, if you go below 1200 ohms, the noise will increase more than just the gain calculation, where a 990 is around 600 ohms, so it will appear slightly quieter on the same bus if it's below 1200 ohms, but will sound different.

Could you rephrase that in a way that makes sense to other members?

, plus I am hitting the bus amps at +4dBu instead of -10.

Apart from Tascam, Fostex et al, I don't believe any serious designer uses -10 for driving the bus resistors.

 

[Matt Syson]

If I remember correctly the Neve 'suitcase' mixers did. Now it is mentioned the 8128 might too.
Certainly the Audix mixers did, perhaps a result of the 'rent a bike' scheme in that part of the Essex/Cambridge borderlands.

 

[abbey road d enfer]

If I remember correctly the Neve 'suitcase' mixers did. Now it is mentioned the 8128 might too.
Certainly the Audix mixers did, perhaps a result of the 'rent a bike' scheme in that part of the Essex/Cambridge borderlands.

I can understand that choice for a small mixer, something like 10 or 12 channels and/or the desire to publish superior headroom figures. That is certainly what I would not have done for a large recording or live mixer.

 

[JohnRoberts]

Indeed.

Could you rephrase that in a way that makes sense to other members?

yup

Apart from Tascam, Fostex et al, I don't believe any serious designer uses -10 for driving the bus resistors.

The old -10dB mixers were -10dBV so roughly 0VU=0.31 VAC.... +4 dBu is something like 0VU=1.2V so 4x or +12dB hotter. The old -10dB gear could be respectable for modest numbers of channels.

Back in the old days I ran single ended signals inside big consoles at something like -2 dBu so single ended paths would clip similarly to the +6dB hotter balanced outputs. But that was mostly a personal preference.

JR

 

[abbey road d enfer]

Back in the old days I ran single ended signals inside big consoles at something like -2 dBu so single ended paths would clip similarly to the +6dB hotter balanced outputs. But that was mostly a personal preference.

That's the gain structure used by many british mixers, Soundcraft, Amek, DDA...It just makes sense.

 

[JohnRoberts]

The ancients are stealing my ideas again....

JR

 

[godzofguitar]

Old thread response: My rule of thumb is if you are planning on using the console forget about testing the caps in a vintage console just figure in the price to totally recap the console and power supply if you can’t do that there is no point in doing it at all even if you tested some and found them within tolerance they arnt long for this world so out they come…

 

[Matt Syson]

Even reading the 'shelf life' figures for caps tells you that at more than 20 years old it will bepretty much 'stuffed'. Yes electrolytics SHOULD reform if polarised correctly and consistently which is usually the case for many of them BUT they will not perform thev same as they did when fresh.
Back to the earlier mentioned Soundcraft desks there is a 'serious' error in the analog ground trace as it winds it's way acros the module so you have crosstalk and distortion Prefade/postfade signals on top of any discussion about the quality or othrerwise of the simple mic input circuit. Swapping op amps or transistors in the vain hope of 'great sounds' is a mistake until you analyse each circuit block individually THEN look at it as a channel strip as a whole THEN consider it as a complete mixer system. I pulled 200 feet of tHICK 'grounding wire out of one mixer that someone had 'hotrodded' thinking that star grounding would be better, but going back to the way it had been built restored it's original Hum immunity that the star grounds had trashed.

 

[JohnRoberts]

Even reading the 'shelf life' figures for caps tells you that at more than 20 years old it will bepretty much 'stuffed'. Yes electrolytics SHOULD reform if polarised correctly and consistently which is usually the case for many of them BUT they will not perform thev same as they did when fresh.
Back to the earlier mentioned Soundcraft desks there is a 'serious' error in the analog ground trace as it winds it's way acros the module so you have crosstalk and distortion Prefade/postfade signals on top of any discussion about the quality or othrerwise of the simple mic input circuit. Swapping op amps or transistors in the vain hope of 'great sounds' is a mistake until you analyse each circuit block individually THEN look at it as a channel strip as a whole THEN consider it as a complete mixer system. I pulled 200 feet of tHICK 'grounding wire out of one mixer that someone had 'hotrodded' thinking that star grounding would be better, but going back to the way it had been built restored it's original Hum immunity that the star grounds had trashed.

I didn't personally pay attention to it, but as I recall the dodgy internal grounding and solutions for it were pretty widely discussed around the internets years ago.

JR

 

[abbey road d enfer]

I pulled 200 feet of tHICK 'grounding wire out of one mixer that someone had 'hotrodded' thinking that star grounding would be better, but going back to the way it had been built restored it's original Hum immunity that the star grounds had trashed.

Read my sig...