New PCB for SSL 9K with balanced out
- Thread starter dinesh
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chrissugar
Well-known member
It will work but it will introduce two more opamps in series in the signal path. Also the SSL guys designed this preamp with DC servo to avoid electrolyt capacitors in the signal path, so adding this circuit will contradict this effort.
chrissugar
chrissugar
But think this over: Do you really need balanced?
For low-impedance line-level signals like on the 9KPre, it is very rare to run into problems with unbalanced interfacing.
Jakob E.
For low-impedance line-level signals like on the 9KPre, it is very rare to run into problems with unbalanced interfacing.
Jakob E.
Samuel Groner
Well-known member
I'm not sure if it is very clever to let a NE5534 drive cable capacity directly as shown in the SSL 9k schematic I have at hand--for longer cable runs oscillation is almost certain. I'd add a 49 ohm in series with the output and a 49 ohm to ground for pin 3, giving an impedance balanced output providing good CMRR (if run into a balanced input) and simple implementation without PCB reworking.
Samuel
Samuel
:thumb: I completely agree!!
chrissugar
Well-known member
Jakob and Samuel are right. In most of the cases there is no need for electrical balancing.
Impedance balancing is a very good solution. I use real balanced outs only in the transformer coupled circuits and impedance balancing in most of my solid state projects.
If you want to have low Z driving capability you can use the JLM Hybrid as an output buffer. Add two 50 ohm resistors, one from buffer out to pin 2 and one fron GND to pin 3 of XLR connector. The advantage is that it also has DC servo like the SSL 9K, so you can direct couple to the next stage.
chrissugar
Impedance balancing is a very good solution. I use real balanced outs only in the transformer coupled circuits and impedance balancing in most of my solid state projects.
If you want to have low Z driving capability you can use the JLM Hybrid as an output buffer. Add two 50 ohm resistors, one from buffer out to pin 2 and one fron GND to pin 3 of XLR connector. The advantage is that it also has DC servo like the SSL 9K, so you can direct couple to the next stage.
chrissugar
SSLtech
Well-known member
Also the GSSL output as you show it is VERY intolerant of having one leg tied to ground. It will sink a LOT of current and cause all sort sof crosstalk.
If you don't NEED balanced, don't do balanced. That's why the pre has an unbalanced out. The balancing board is there as a 'bolt-on' option for times when it is NEEDED. -If you don't need it, don't do it.
Keith
If you don't NEED balanced, don't do balanced. That's why the pre has an unbalanced out. The balancing board is there as a 'bolt-on' option for times when it is NEEDED. -If you don't need it, don't do it.
Keith
[quote author="dinesh"]Hi there,
I am rebuilding SSL 9K PCB with balanced outputs.Can we use this as a Balanced out for 9K mic pre?
This is the out put section of SSL mixbus compressor
other inputs are welcome.
Regards
Dinesh[/quote]
Indeed, If you are not sending over longer distances or need +26 dBu outputs to impress customers perhaps you don't need it.
If you still want it, the schematic you posted is probably the least desirable approach. It generates a differential output but doesn't tolerate shorts on either line very well.
For probably more information than you want, there is a thread over on PSW about an old parametric (Porter's design) but about halfway down the thread we get into a discussion on an early approach at active balancing (with output short compensation). The discussion ranges to an AES papaer by the mod and more discussion. More theoretical than practical perhaps.
http://recforums.prosoundweb.com/index.php/t/15104/361/
Several chip vendors sell packaged variants on these safer active balanced approaches. If you roll your own be sure to confirm DC and load stability as they utilize positive feedback that can be tricky if misused.
JR
I am rebuilding SSL 9K PCB with balanced outputs.Can we use this as a Balanced out for 9K mic pre?
This is the out put section of SSL mixbus compressor
other inputs are welcome.
Regards
Dinesh[/quote]
Indeed, If you are not sending over longer distances or need +26 dBu outputs to impress customers perhaps you don't need it.
If you still want it, the schematic you posted is probably the least desirable approach. It generates a differential output but doesn't tolerate shorts on either line very well.
For probably more information than you want, there is a thread over on PSW about an old parametric (Porter's design) but about halfway down the thread we get into a discussion on an early approach at active balancing (with output short compensation). The discussion ranges to an AES papaer by the mod and more discussion. More theoretical than practical perhaps.
http://recforums.prosoundweb.com/index.php/t/15104/361/
Several chip vendors sell packaged variants on these safer active balanced approaches. If you roll your own be sure to confirm DC and load stability as they utilize positive feedback that can be tricky if misused.
JR
chrissugar
Well-known member
Good choice. :thumb:
:grin:
chrissugar
:grin:
chrissugar
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