Reverse Engineering Finished
I finally finished the reverse engineering.
There are component differences between the original and the Chinese copy.
Extra components I've designated as 40+.
Components marked SD are for supply decoupling and aren't shown on the schematic.
I still can't see why the op-amps run so warm.
I finally finished the reverse engineering.
There are component differences between the original and the Chinese copy.
Extra components I've designated as 40+.
Components marked SD are for supply decoupling and aren't shown on the schematic.
I still can't see why the op-amps run so warm.
Attachments
Max power is when opamp output is + or - 20V, with a load of 10k is 2mA (assumed node between R7-R8 stays 0V), so power dissipated is 2*20V * 2mA = 800mW.
The picture in #49 does not show the OP27's, but if it's 8-Lead PDIP the temp specs are (θJA=103,) θJC=43 °C/W yielding in 0.8 * 43 = 34.4 above room temperature, so it's 45 - 34.4 = 10.6°C in your shed if it was possible to use them as coolers.
Expecting some 20°C instead, there is 25°C temp raise, and with this 43°C/W results in 580mW dissipation, which results in 580mW / (2*18V) = 1.6mA current from the output, lifting the output voltage up or down towards the rails, say some 1.6m*10k = 16V.
So, what is the actual output voltage of the opamps?
The picture in #49 does not show the OP27's, but if it's 8-Lead PDIP the temp specs are (θJA=103,) θJC=43 °C/W yielding in 0.8 * 43 = 34.4 above room temperature, so it's 45 - 34.4 = 10.6°C in your shed if it was possible to use them as coolers.
Expecting some 20°C instead, there is 25°C temp raise, and with this 43°C/W results in 580mW dissipation, which results in 580mW / (2*18V) = 1.6mA current from the output, lifting the output voltage up or down towards the rails, say some 1.6m*10k = 16V.
So, what is the actual output voltage of the opamps?
I've got some IC heatsinks on order. I'm not quite sure how I'm going to fit them in order to get a decent TJC.
Hopefully they will come with self adhesive pads.
9x9x12mm Heatsink Heat Sink A4988 DRV8825 Ramps Cooling Pi IC | eBay
Hopefully they will come with self adhesive pads.
9x9x12mm Heatsink Heat Sink A4988 DRV8825 Ramps Cooling Pi IC | eBay
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All working now.
Thank you everyone for your help and comments in this thread, the Kevin Gilmore UnBalanced to Balanced Convertor is now working.
Although the wrong op-amps wouldn't have helped the problem they were not the true source of the problem.
I decided to swap out all the LEDs with "Identical" items, ie all from the same batch.
With identical LEDs throughout the circuit it balances out nicely. The op-amps only help to zero the output to an almost perfect 0mV DC offset.
Kind regards
K&D
Thank you everyone for your help and comments in this thread, the Kevin Gilmore UnBalanced to Balanced Convertor is now working.
Although the wrong op-amps wouldn't have helped the problem they were not the true source of the problem.
I decided to swap out all the LEDs with "Identical" items, ie all from the same batch.
With identical LEDs throughout the circuit it balances out nicely. The op-amps only help to zero the output to an almost perfect 0mV DC offset.
Kind regards
K&D
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