summing with 2520 balanced transformerless amp as makeup?

what would you think about using NYdave's 16 ch. balanced passive summing schem - into this 2520 balanced amp - lowering the input impedance of the amp to 600R? or better to get higher output impedance from the summing resistors?

This is a virtual ground active summer already.

sorry, i didnt mention that i am refering to fig. 4 on the 2520 page....not fig. 3....

bump

fantomas,

i've made a pcb for this on a 100 x 160 mm board with 6 channels of LCR pan switches ,and 10 channels wired directly to bus (5xL ,5xR) and the 2 opamps and its sorounding components.

it seemed easier to do then breadboarding all this.....so i'll etch it soon and tell you how/if it works...

great, i hope it turns out ok

Advancing ....






signal is passing - now have to wire up the patch for 16 channels for testing....

its a box of cables now,but i did a mix with it today - works nice!

Hi

What version of the 2520 did you use? Any oscillation? What are those out transformers?
Great job :thumb:

Seems to be Melcor 1731.
Did you add a cap to prevent oscillation?
Very inspiring by the way. :thumb:

yes, those are the melcors, and i ended up using 10pf as feedback cap .

the output trafos are 2503 clones made by a local guy...

almost there......one more thingy...the clicks & pops when changing the gain setting- how do i soften that?

i have only 4 gain steps ,and sometimes the click will slam the needle to the top of the scale and it will stay there...(oscillation) and sometimes it wont........


here is the last pic to conclude this journey .......

[quote author="mich"]almost there......one more thingy...the clicks & pops when changing the gain setting- how do i soften that?

i have only 4 gain steps ,and sometimes the click will slam the needle to the top of the scale and it will stay there...(oscillation) and sometimes it wont........


here is the last pic to conclude this journey .......

[/quote]

Are you using shorting or non-shorting switches (I'm guessing non)

im using the shorting type if i understand this correctly.

the switch is shorting inbetween positions.

i forgot to mention that if someone is intrested in the pcb design for home etching - just ask - i have it in proteus format,but can convert to pdf .