crazytooguy
Well-known member
- Joined
- Dec 9, 2005
- Messages
- 57
Looking at THAT Corp’s datasheets, they seem to have designed a set of ICs specifically suited for construction of mixing consoles. I’ve been toying with an idea to design and build a 16 channel line level mixing console with a fully balanced summing buss (since I have several mic preamps I like to use, including my hot-rodded G9), similar to the Speck Lilo or the Neve 5088 (but without all those $$$ transformers… Yikes!). I want to use it primarily for mixing down the outputs of my DAW, but I want some flexible routing options as well.
So, here’s the main question: Is the advantage gained by using a fully balanced summing buss (if any – this is a topic of much debate) offset by the extra silicon the signal has to pass through to achieve it?
Using the THAT chips would require the following extra chips when using a balanced summing buss: a balanced line driver (THAT 1646) to convert the panned and level-controlled signal to balanced to feed the buss, and a balanced line receiver (THAT 1200) to convert the buss signal to unbalanced for master level control (since stereo balanced level control is so expensive). This signal, of course, has to be converted again to balanced for output, but it would in a normal console anyway.
Here’s the signal path: Input goes to a full differential buffer using four NE5524s. From there, it goes to Insert Send/Return (or is hard bypassed by a relay). Next is the THAT 1200 line receiver, which debalances the signal. The channel fader is next, then on to another NE5524 for a 16 dB gain boost prior to the Pan pot. Output of the Pan circuit then goes to a unity gain buffer built on an OP4132 (used here as an impedance converter, since the 1646 requires a low source impedance) and then into the THAT 1646 balanced line driver. The 1646 feeds the balanced summing buss through 10k resistors.
The Summing buss feeds the input of a THAT 1512 gain module, which adds the necessary 20dB of makeup gain, and converts the balanced buss signal to an unbalanced signal for level control. The unbalanced summed signal then goes to a relay for selecting a buss insert (which uses the THAT 1646 line driver and 1200 line receiver for balancing/unbalancing the balanced insert connections) or bypassing the insert. The signal level for the summed buss is set with a fader, then goes to an OP4132 unity gain buffer for impedance conversion prior to a THAT 1646 for conversion back to a balanced signal for a subgroup output. The unbalanced signal after the OP4132 buffer also connects through a 10k resistor to a Master Summing buss, which uses once again the 1512 to provide makeup gain. Then on to a fader for Master level setting, then, finally through another impedance buffer (OP4132) prior to final conversion to a balanced signal for the master output. Whew!
I was thinking of breadboarding a channel and seeing if there was a noticeable sound quality difference in the two summing approaches, but it occurred to me that I would need all sixteen channels to really assess how well it works. This is no cheapie weekend project – just the faceplates from Front Panel Express are $1600! And those THAT chips run about $5 a piece. But, quality line mixing consoles are not cheap either. The Speck Lilo is around $9k and the Neve is (gulp!) around $30k. So, flexibility AND quality exacts a steep price.
So, here’s the main question: Is the advantage gained by using a fully balanced summing buss (if any – this is a topic of much debate) offset by the extra silicon the signal has to pass through to achieve it?
Using the THAT chips would require the following extra chips when using a balanced summing buss: a balanced line driver (THAT 1646) to convert the panned and level-controlled signal to balanced to feed the buss, and a balanced line receiver (THAT 1200) to convert the buss signal to unbalanced for master level control (since stereo balanced level control is so expensive). This signal, of course, has to be converted again to balanced for output, but it would in a normal console anyway.
Here’s the signal path: Input goes to a full differential buffer using four NE5524s. From there, it goes to Insert Send/Return (or is hard bypassed by a relay). Next is the THAT 1200 line receiver, which debalances the signal. The channel fader is next, then on to another NE5524 for a 16 dB gain boost prior to the Pan pot. Output of the Pan circuit then goes to a unity gain buffer built on an OP4132 (used here as an impedance converter, since the 1646 requires a low source impedance) and then into the THAT 1646 balanced line driver. The 1646 feeds the balanced summing buss through 10k resistors.
The Summing buss feeds the input of a THAT 1512 gain module, which adds the necessary 20dB of makeup gain, and converts the balanced buss signal to an unbalanced signal for level control. The unbalanced summed signal then goes to a relay for selecting a buss insert (which uses the THAT 1646 line driver and 1200 line receiver for balancing/unbalancing the balanced insert connections) or bypassing the insert. The signal level for the summed buss is set with a fader, then goes to an OP4132 unity gain buffer for impedance conversion prior to a THAT 1646 for conversion back to a balanced signal for a subgroup output. The unbalanced signal after the OP4132 buffer also connects through a 10k resistor to a Master Summing buss, which uses once again the 1512 to provide makeup gain. Then on to a fader for Master level setting, then, finally through another impedance buffer (OP4132) prior to final conversion to a balanced signal for the master output. Whew!
I was thinking of breadboarding a channel and seeing if there was a noticeable sound quality difference in the two summing approaches, but it occurred to me that I would need all sixteen channels to really assess how well it works. This is no cheapie weekend project – just the faceplates from Front Panel Express are $1600! And those THAT chips run about $5 a piece. But, quality line mixing consoles are not cheap either. The Speck Lilo is around $9k and the Neve is (gulp!) around $30k. So, flexibility AND quality exacts a steep price.