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ada8000 DC/gain modification for silent way
MUFF WIGGLER Forum Index -> Expert Sleepers  
Author ada8000 DC/gain modification for silent way
smrl
Well, I managed to figure out the modifications necessary for DC-coupling the Behringer ADA8000, and getting the voltage at the output from the 3.528v measured one one channel up to 10.88v.



I looked at the schematics that had been redrawn by Marcelo Johann, but to my chagrin Behringer has changed the design in the meantime - it now uses a single ADC/DAC chip per 2 channels, the CS4270. In some ways it has made it easier to modify, as the output of this chip is single-ended rather than differential. In the end, I was able to modify the output schematic somewhat elegantly, but it involves desoldering the op amps and swapping in a few resistors. It also requires a small circuit to produce a voltage reference to bias the signal back to 0v.

Before:



After:


Notes on my very quick schematics:

The op-amps were TL072, I subbed them for TL082 for better output offset performance. You could re-use the 072's. MCP6002 was used because it runs off of a single supply. I powered it & the voltage divider in front of it with the 5v supply for the ADC chip -- IC3 according to Marcelo's notes. Trim until the output measures 0v. I desoldered the IC's and bent up the appropriate pins (5&10 I believe) then bridged them. I made 2 voltage sources, one connected to the first 4 channels, the other connected to the other. Probably not necessary but I had an extra op-amp available. If you really wanted to get fancy you could probably make voltage sources for each one to trim them each to 0v. I haven't measured the difference between channels yet.
lukas412
wow nice work man!
os
Cool! I was about to post the link to Johann's schematics, but I see you found them.

I imagine Behringer had to chang the design because the Wavefront DACs they used to use went obsolete.
bafonso
Hi guys,

Has anyone looked at the possibility of doing this to the ADA8200 ? I have it and would like to convert its outputs and inputs to DC coupled.
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