[quote author="NewYorkDave"]Here's a block diagram of what I have in mind:
http://electronicdave.myhosting.net/pdf/mxrblockdiag.PDF[/quote]
I would suggest using a good op amp instead of the transformer input, as the load after it will lower your level much more than -10, especially if you switch the pre/post switch. The general rule is a 1/10 ratio on the secondary of the transformer so the reflected load doesn't do anything to the source. That alone is quite a bit of loss to start with.
When you are at line level, using a good IC op amp works fine, as they really hurt the sound when used as a gain stage (mic pre/summing) or driving a low imp load. Having a balanced in amp and then a post fader amp will insure that the mix bus is driven harder, resulting in less of a noise problem and "IC" problem.
Unless you have each prior pot 1/10th the value of the ones after it, you will see large amounts of signal loss. Lets say you use a 10K P&G linear fader for the main fader. If you load it with anything less than 100K, you will see a change in the taper, and as you approach a 10K load, you will see some strange things like the level wandering up and down as the fader is pulled down. Audio taper faders (and pots) are nothing more than a collection of linear sections all in series. That is why you see what looks like a ladder pattern next to the element in a linear fader. Each ladder pulls down on the linear element to give it a log feel. This is pretty smooth if the load is correct, but becomes very sectional as the load is increased. Rotary audio taper pots are generally layers of resist screened on top of others to stack a pile of resist that from the side looks like a stair step.
If you used a 1K fader, the panner would be 20K (2 elements) and the sends would have to be 200K (2 X 200K = 100K). This gives the minimum load effect on the chain. Now the problem is the input transformer has a 1K load on it, and if it is a 1:1 transformer, it will reflect the load to the other side. If the source cannot drive a 1K load, you will loose gain and may get distortion. If the input transformer is any other ratio, the reflected impedance will be the same ratio, so if it was 1K primary and 10K secondary, and the secondary is loaded with 5K, the primary will look like 500 ohms and so on.
Placing a balanced amp before the fader isolates the input and provides a low imp source for the fader. Using a buffer after the fader allows the sends and panner to be isolated also. Then you have a pre and post source and can hang as many pots as needed.
Just some thoughts...
Paul
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