Hello, everyone,
I'm slowly circling back to this idea and am about to start doing some rough sketches for board layout. Where I've landed on design is that each board will be essentially eight channels of BA283 with the input transformer on board. The output transformer is omitted as that will be after the summing amp of the end user's choice. There will be a switch point for mono and stereo per each pair. If the end user desires to add faders, pan, insert, etc, then that will have performed by integrating their scheme for such things with the schematic for this circuit. The input will be connected via a separate small board that will be a DB25 connector and header of some sort to simplify wiring to the input channels and allow for more flexibility in case and panel layout. All of the channels will feed a buss resistor network that would then feed a summing amp of the builder's choosing. There will also be solder points for cascading other summing PCBs together. The thing yet to be determined is where to boost signal to each channel. If using the VTB9045 transformer, the highest gain with the input of 1k2 ohms achieved is +6, but since this circuit takes one side of the secondary winding to ground, I think this puts the total gain going into the circuit back to unity, which I could be wrong. If I am correct about what actual signal levels are getting to the input of each channel circuit, then the next place would be to boost the gain at the preamp stage and reduce the gain after the output circuit before the buss resistors. Or maybe this reduction could take place with the selection of the value of the buss resistors. I would like have the signal be at unity before it hits the summing amp. I also want to make sure there is a boost in this circuit so as to not require the various converters to need to be driven harder at their outputs to achieve the main goal of this design.
I do have some questions I'd like to get some input from others who have worked with this style of circuit before:
How necessary is it to have perfectly curved solder traces on the board? I have seen some discussions mentioning this is important but to save some space I might not be able to maintain the wide, flowing curves found on original cards.
Will the MJE3055T work well as a replacement for the 2n3055? The latter is getting harder to find and more expensive. Also, to save space the MJE3055 would be ideal.
Which buss resistors values are preferred for this style of summing circuit? I have read and have used in the past 15k with success, but have noticed a decent amount of cross talk with this amount of resistance.
I'll do some more digging on my own. If anyone has some helpful insight or links to info that would be beneficial to this design I would appreciate having it sent my way.
Thanks!
Paul