Premier Rock Forum

Did some PCB and box design for a guitar splitter.

Neumann U67 sn2534-

No output, swapped power supply and cable.

Tube was dead, replaced.

Tested, labeled and badged, more DI Boxes.

Ampex ATR #4 stuff...

Ampex ATR #1 partial PSU Rebuild-
Replaced the giant electrolytic capacitors, stud diodes, and refreshed some heated joints. This was on the first ATR Mike Spitz did for us in 1996/7. There was a 120hz ripple on the ± 20v rails which led to this. You could hear it in the audio, which clued us initially.

Studer A820MCH MDA repairs-
Repaired the two damaged MDAs from the bottom of this post.. Need to test them in one of the spare machines.

EA Direct box finishing

Calibrated the tensions on all the active Ampex ATRs using ATR Magnetics 1/2" tape to 7oz.

Some basic testing of Ampex ATR #1, confirming all's good with some of the transport before waking this thing out of hibernation.

Brought the AP in to studio B for some tests, including seeing what a cleaner did to one of our pan pots in the Series II. Thankfully, there's not much of a difference in distortion with an untouched pot. I wanted to make sure months after treatment so I don't sabotage the studio with a half baked plan. I was told carbon pots were chosen on these for lower distortion. Unfortunately, they grow noisy through their rotation, even though they're supposed to be "self cleaning".
Anywho, I might hit the rest of the pots soon.

Gefell M94 capsule has a loose part rattling inside.

The capsule staff was loose and rotating which broke the 10MΩ resistor off one of its posts. I tightened it up and re-soldered the resistor.

Lexicon Primetime-

Distortion with a modest signal level found on Delay A in the mid two positions of the big delay multiplier switch...

Calibrated the output low pass filter null as described in the service manual, section 2.1. The "filter 2" null at 22.5kHz was off. No more distortion.

-Elsewhere-

Various boring patchbay fixes with a new installation-

Outboard compressors showing compression without input signal.

New patchbay set to fully normalled on the related I/Os causing feedback when the gain was high enough.
Removed the normals

Studer J37 1" 4-tracks (yes)

Miscellaneous work on two.
#1 machine- Reel motor torque unusably low at the head of the reel making impossible to rewind without help. Could be a brake issue...
#2 machine- Showed more immediate promise of functionality, so it was fully calibrated to 355nWb/m CCIR/IEC EQ with SM900 tape.
This is a tedious process for a number of reasons.

• The channel amplifiers are stacked on top of each other, two by two, with no easy access to the bottom row. You need to remove the top two channels to access them. This is a tube-based machine, so things need to be nice and warm before tweaking things. Being patient is fine. Power cycling a 60 year-old machine so much is unnerving.

• You need to tilt the deck up to its service position to access any of the amplifier's pots. Sure, no prob, except that the pinch roller has no back tension, so it just falls against the tape when in stop. When it does this, it pushes the tape into the spinning capstan shaft, burnishing the tape. Not cool with a new $500 MRL test tape. So you have to be ready to hold the roller back when you stop or rewind to the top of the tones.

• The studio's MRL test tape is the short form version, with only 15 seconds of 1kHz and 10kHz then sweep. For those of you unfamiliar with calibrating problematic multitracks, 15 seconds is not enough. Buy the minute + versions...

Corrected a brake solenoid issue which was causing drag on the supply motor through cleaning, re-lubing, repositioning (likely this one), and replaced the flyback diode.

Repaired busted wiring in the "monitor" output amplifier section (transformer winding broke free of the "monitor" switch array, and a couple bad solder joints, done sometime since it left the factory.

Beyerdynamic M160s

Our pile of distressed ribbon M160s got up to four. Time for ribbon assembly replacements, and off to Consolidated Sound for the work.
I've replaced a few of these before, and it's labor intensive. With such a big pile, and no free time on my hands, I'm happy to have them do it. I like how there's no guesswork with doing them. You just get a complete assembly done at the factory, and replace the old one with it.

Finding space in our racks to reintroduce the Lexicon Primetime delays back to both control rooms. It's been a while. Thanks to Brian for finding some NOS faders. It was the Achilles heel in these.

Studer A820MCH sn 125X?

The meterbridge froze, then the reel motors went limp on Taylor in session. I ran down from my session to see if it was something dumb and simple. It wasn't, so we moved one of the other 820s in its place temporarily. It's handy having a few around.

After my session ended, I thought I'd give it a better look, and hopefully set Brian up with something fun to do in the morning.
found-
The ±15v power supplies were dead as seen and measured on the fuse / supply fail detector display. Still seeing the +24v power supply led on, however. The ±15v stabilizer includes one 24 volt rail. With the fuse supplying the power to it blown, I'd assume the 24v status would change. I see there's a second 24v rail provided on the other stabilizer. That must be driving the status display.
Measuring around for a short in either the + or - 15 rail path, I found none. I swapped the switching stabilizer with a spare, and nothing changed. That's the point where I discovered fuse F2's status LED was off, suggesting it blew. Replacing the fuse, and switching the machine on, it appeared to blow again. This seemed weird since I didn't find any shorts, and it was a new stabilizer. Inspecting F2, I saw it didn't actually blow, and neither did the one I replaced (the high current ones have that shroud which sometimes hides the burn mark). Looking around back where the main raw DC power supply is hooked up, I saw that a pin on the power connector was completely charred, with the plastic housing deformed around it. The pin of note, was the unregulated 40-50vDC send to the ±15, 24v stabilizer, from F2.
We have pins and housings from when I replaced this connector in another machine, thankfully. [link to that post, lost in the great forum fire of 2020 would have been be here].
The next day Brian pulled the 60lb power supply and dug into it. I had him replace the panel connector, repining the internal wires, and replacing one wire completely, since it was toasted. He also re-pinned the harness that goes to the rest of the machine. Fired it up for a couple days, and she's back in action.
I should exercise/clean these connections regularly, I guess.

Ampex ATR producing static noise on the right channel.

Pulled the heads for core re-grounding, and noticed a bit of a flat zone on the record head in particular. Off to JRF...