So I have a new module I have been working on.
Overall goal is to achieve the complete and lovely sound of a vintage API console channel without the cost of the rest of the console.
A little something different for the 500/51x format. It has grown a little since my original concept but only for the better. Overall, it is a 2 stage console channel with the vintage circuitry of my API board. The first stage is a balanced, transformerless receiver. Everything is true to the original circuit with the exception of feedback R and C. I have only tweaked the R to have unity gain thru the first stage. This entire first stage can be bypassed with shunt jumpers or simply left of the build if one desires.
Next in the block diagram comes the fader. Due to space constraints and a request from my friend Dan D., I have chosen to use a 24 position Elma with a 1K overall value. Original faders in my board were 600 ohm. The fader has 12dB of gain in hand to keep with the vintage API norm. Since the majority of the upper range gain steps are in 2dB increments, I have used a stepped Grayhill for a fader trim that is in .5dB increments.
Next in line is a 6 position stepped LP filter. This filter was not in my board. I have however implemented the same passive philosophy that they used for the HP filter that was in my board. Since it was easy, I added a switch to select 6dB or 12dB per octave for the filters.
I follow this filter stage with a 3 transistor discrete voltage follower using 5087/5088s. This buffer circuit is very reminiscence of the buffer amp found in use, 4 times in the 550a. Very handy indeed.
Next is the switchable HP filter. Again, the overall philosophy is the very same that was used in my board. I actually designed these filters around the same value shunt resistors.
Last stage is the post fader booster amp. Again, the same circuit as found in the vintage console. I have an unbalanced output signal that shows up on pin #3. This can be used to feed a future pan, aux and bus module. This output on pin #3 is VPR compliant BTW. I stuck my little Plug-In Relay PCB for a simple mute between the second DOA and the output tranny. This is also on a mute bus using the linkable DC pins #6 in a VPR rack.
The proto build is done and basically works a treat. The white PCB will go as I really do not like it. Had to try it once. All the switches are NCNR special order and all have been ordered.
Cheers, Jeff
Overall goal is to achieve the complete and lovely sound of a vintage API console channel without the cost of the rest of the console.
A little something different for the 500/51x format. It has grown a little since my original concept but only for the better. Overall, it is a 2 stage console channel with the vintage circuitry of my API board. The first stage is a balanced, transformerless receiver. Everything is true to the original circuit with the exception of feedback R and C. I have only tweaked the R to have unity gain thru the first stage. This entire first stage can be bypassed with shunt jumpers or simply left of the build if one desires.
Next in the block diagram comes the fader. Due to space constraints and a request from my friend Dan D., I have chosen to use a 24 position Elma with a 1K overall value. Original faders in my board were 600 ohm. The fader has 12dB of gain in hand to keep with the vintage API norm. Since the majority of the upper range gain steps are in 2dB increments, I have used a stepped Grayhill for a fader trim that is in .5dB increments.
Next in line is a 6 position stepped LP filter. This filter was not in my board. I have however implemented the same passive philosophy that they used for the HP filter that was in my board. Since it was easy, I added a switch to select 6dB or 12dB per octave for the filters.
I follow this filter stage with a 3 transistor discrete voltage follower using 5087/5088s. This buffer circuit is very reminiscence of the buffer amp found in use, 4 times in the 550a. Very handy indeed.
Next is the switchable HP filter. Again, the overall philosophy is the very same that was used in my board. I actually designed these filters around the same value shunt resistors.
Last stage is the post fader booster amp. Again, the same circuit as found in the vintage console. I have an unbalanced output signal that shows up on pin #3. This can be used to feed a future pan, aux and bus module. This output on pin #3 is VPR compliant BTW. I stuck my little Plug-In Relay PCB for a simple mute between the second DOA and the output tranny. This is also on a mute bus using the linkable DC pins #6 in a VPR rack.
The proto build is done and basically works a treat. The white PCB will go as I really do not like it. Had to try it once. All the switches are NCNR special order and all have been ordered.
Cheers, Jeff
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