Do you use ESD control when handling the bare devices? A bare device is much more susceptible to ESD damage than a device on an assembled PCB with power supply bypass, input filtering, etc. in place.
Simple unbalancing and balancing line amp
- Thread starter thomasdf
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Do you use ESD control when handling the bare devices? A bare device is much more susceptible to ESD damage than a device on an assembled PCB with power supply bypass, input filtering, etc. in place.
I don’t, maybe I should ? Never had such a problem before. And it was working fine on the PCB in its socket from day 1 of the prototyping.
But maybe it received a ESD during the mounting of the PCB in the enclosure..
Maybe I should add an input cap to protect the ICs from DC on the line ?
But maybe it received a ESD during the mounting of the PCB in the enclosure..
Maybe I should add an input cap to protect the ICs from DC on the line ?
Check the DC values on all the pins, sometimes that can give you a clue where the fault is (e.g. if one of the input or output pins is stuck at a supply voltage, or if the input pins are not within a couple of mV of each other).
Hello
Thanks for your input. On the IC that's shot I have -12VDC on pin 2, and -6VDC on pin 3 (power is +/- 12VDC).
When I swap channels the problems stays the same on that very IC... So I guess it's dead !
I'll change both and will have a spare one in case.
I've based my schematic on the datasheet exemple so I guess there is no need for an input DC blocking cap, I dont know what I did wrong (ESD, hookup error ... ). I'll be more careful next time
I'll give some news here when the unit will be fully finished and working.
Thanks for your input. On the IC that's shot I have -12VDC on pin 2, and -6VDC on pin 3 (power is +/- 12VDC).
When I swap channels the problems stays the same on that very IC... So I guess it's dead !
I'll change both and will have a spare one in case.
I've based my schematic on the datasheet exemple so I guess there is no need for an input DC blocking cap, I dont know what I did wrong (ESD, hookup error ... ). I'll be more careful next time
I'll give some news here when the unit will be fully finished and working.
It would be interesting to know where thi voltage drop happens. Do you have rail distribution/protection resistors, or is the regulator dropping down?
EDIT: wrongly assumed that the -6V was a supply pin.
After reading correctly, I figured out it's an output, so a "normal" failure.
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This is the exact design I ended up with.
My power rails are fine, +/- 12VDC are spot on everywhere else : IC pins power pins (including the one that's dead), as well as in the DBX118.
This power supply powers the I/O card I've designed, but also replaces the original PSU resulting in much much cleaner and powerful supply.
On the working THAT1250 IC input pins read 0VDC.
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Edit : I'd also like to add a pad before the compressor, so I am considering switching from a THAT1250 to a THAT 1253 (-3dB line receiver) or THAT1256 (-6dB line receiver). They are pin compatible .
My power rails are fine, +/- 12VDC are spot on everywhere else : IC pins power pins (including the one that's dead), as well as in the DBX118.
This power supply powers the I/O card I've designed, but also replaces the original PSU resulting in much much cleaner and powerful supply.
On the working THAT1250 IC input pins read 0VDC.
----
Edit : I'd also like to add a pad before the compressor, so I am considering switching from a THAT1250 to a THAT 1253 (-3dB line receiver) or THAT1256 (-6dB line receiver). They are pin compatible .
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The device is a difference amplifier with internal resistors. Pin 3 is the positive input, so it has a resistor from op-amp input to ref pin (tied to gnd).
If the input protection developed a short to -12V there is a resistor to inv input, resistor from there to output. That could drop to -6V.
Sounds like electrical overstress to pin 3 which killed the ESD device is most likely.
[ Edit: stress to pin 2, not 3. Pin 3 is just getting pulled by the -12V on pin 2]
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After some time I can say the build is finally over ! I have ended up replacing both 1250 with 1253 (-3dB att) and in my setup it's just the right amount of padding to give some room to the DBX118 to perform its magic. Overall I am super impressed with the sound, it's fat and warm, VCA compression with an attitude and I'll keep on using it on the mixbus or crushing things to death and other duties along much more expensive pieces of equipment. It's dead silent and the I/O card provides lots of makeup gain.
Thanks a TON for all the help here, I can't tell you how much I love this community. Some pictures ! I went for a dirty period correct look.
Beside the IO card design and new PSU, I had to trim the wooden sides, cut and bend precisely a 2U steel front panel saved from trash, fit everything in an Amazon aluminium enclosure and then do some drilling and soldering.
Cheers !
Thanks a TON for all the help here, I can't tell you how much I love this community. Some pictures ! I went for a dirty period correct look.
Beside the IO card design and new PSU, I had to trim the wooden sides, cut and bend precisely a 2U steel front panel saved from trash, fit everything in an Amazon aluminium enclosure and then do some drilling and soldering.
Cheers !
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Looks amazing! Congratulations!
Are those switching supplies sat on top of the chassis? I would listen again loud for any induced hum in the noise floor.
Mike
Mike
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