This round of Emergency Room features the 6-channel Furman HDS-6 Headphone Distribution System after a mild power surge incapacitated 5 of the 6 channels. This unit is pretty neat, it utilizes Cat 5 cabling to distribute power and channel signals to remote units (HR-6’s) which are used in the studio booth by the recording artist for monitoring the other tracks through a pair of headphones. The HR-6 can be daisy-chained with other HR-6 units, enabling recording artists the ability to locally monitor tracks while recording.
I opened up the chassis and, after some visual inspection, saw one of the capacitors had blown. I replaced the cap and powered the unit back up; no good. Other than that there was an odd white discoloration of the main board around one other capacitor. It didn’t seem to be an issue, but I replaced the cap it was surrounding for good measure. There was no schematic to go by, so I traced out one of the channels and drafted it for reference (shown below). I have a more detailed schematic written out, if needed don’t hesitate on sending me a message.
This revealed two op amps utilized in the signal path. This unit has six identical channels, so the circuit above is duplicated 5 times with only the component names varying, making it easy to troubleshoot the rest of the unit.
I injected an audio signal into each of the channels and probed the signal paths. This revealed that, for almost every channel, the second op amp in the signal path wasn’t functioning. This was confirmed when measuring the DC voltages on each op amp chip. The figure below shows the voltage measurements for the three dual op amp chips U101, U201 and U301:
I had a couple TL082s on-hand, and replacing them fixed the issue. The TL082 has an input noise voltage of 16nV/√Hz, but if available, replacement with something with a lower input noise voltage like an NE5532 is recommended since these particular op amps are in the signal path.
Thanks for visiting! If you have a piece of gear needing repair contact me here and please follow Mimmotronics on Instagram and Facebook. This fix was done for DMS Productions located in Ransomville, NY!