Tag Archives: niagara falls audio repair

Emergency Room #12: The Silent ZenDrive

Espoused by guitarists like Robben Ford, Sonny Landreth, and Nalle Colt, the ZenDrive by Hermida Audio continues to live up to overdrive connoisseurs. This particular overdrive is an NE5532 Op Amp based drive, and the one ending up on the bench today suffered from an op amp gone awry.

ZenDrive Gut Shot featuring the NE5532 op amp, the heart of the ZenDrive circuit.

ZenDrive Gut Shot featuring the NE5532 op amp, the heart of the ZenDrive circuit.

The original complaint was that no output could be heard when engaging the effect, but when bypassed all was well. On opening the backplate and removing the circuit board I was surprised that the op amp used in this unit was seated in an IC socket. This made the repair much easier (thanks Hermida Audio!). I removed the op amp, breadboarded it within a simple buffer circuit and, sure enough, the op amp’s I/O terminals were stuck at the rails. Replacement with another NE5532 fixed the issue.


This fix was done for Buffalo-based guitarist Matt Fantini of Space Junk. Check them out at Funk n’ Waffles Rochester on January 10th with special guests SKYwalker!

Emergency Room #11: Furman HDS-6 Headphone Distribution System

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.

Figure 1: Showing the HR-6 Headphone Remote unit connected to the HDS-6 main board for a test-run.

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.

Figure 2: Mock-schematic detailing the HDS-6s signal path.

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:

Figure 3: Showing all three defective op amp values. These should all be biased to 0V!

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.

Figure 4: One of the newly installed op amp ICs.

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!