4/29/4
Yamaha 1010 Delay-
I replaced the power transformer (240V) with a new toroid transformer (120V) so we can use it now.

Problem-
Neumann 563 has a week and trebly output.

Solution-
Broken solder joint in the cable connector. This was for one of the output legs. I should have done a continuity test on the cable first, but did a lengthy test on the mic to make sure it was working instead.

Problem-
Ampex ATR 2-track #3: Input signal bleeds through when output is set to repro.

Solution-
I swapped the I/Os to see if the problem followed them and the problem went away altogether. I put the I/Os in their original position and still no problem. I left it for observation over time. 2 days now and there and all is good. Must have been something with the connection.

5/10/4
Fixed cables.
Worked on M-S Matrix mods and faceplate.

greg wrote:Worked on M-S Matrix mods and faceplate.

Oh, do tell.

Chris Garges
Charlotte, NC

I'm creating the trims for the left and right outputs. They will range from -12dB to +12dB. I'm also seeing if I can use a burlier output op amp. The Burr Brown OP176 is a likely candidate.
I'm going to have a nice new faceplate made engraved with the legends. I placed the order today.
I can't wait.

6/1/4
Problem-
Studer A820 Studio A (#2 machine) Channel 14 output not making it to the patchbay.
Solution-
Edac pin loose on the output connector on tape machine snake.snooze
Created new mic pads for studio A's patchbay.
Repaired to bad mults on that patchbay.

6/2/4
Problem-
C-12 s/n-38 PSU s/n-19477 has no output.
Solution-
There was a bad regulator tube (150B2). Replaced, everything is well.
Problem-
Neuman SM-2 PSU has no output on the top capsule.
Solution-
It was just a broken solder joint on the output XLR connector.

6/14/4
Problem-
Sontec has noisy op amps.
Solution-
This is actually an old problem that I'm trying to find a new solution for. The op amps of concern are the input and output amps. They are home made discrete amps. I made a daughter board that will host a normal monolithic DIP op-amp (to replace the old ones). The board regulates the incoming bipolar power supply rails +-28 volts down to +- 22 volts. This is so I can try out other amps.
My food is here.
More later.

12/9/5
My plan now is to replace the input section with a Jensen input transformer JT-6110k feeding a 990 (or like amp), and a 990 (or like amp) to replace the output amp.
The power will be coming from a GML PS (puts out a rock stable +-18VDC and +-28VDC). The 28v rails will be regulated down to 24v in the Sontec box with 7824 and 7924 regulators (replacing the TO-3 transistors on the back panel). This will undoubtedly change the "sound" of the unit, but I'm not too concerned with that as it will be more predictable with different sources. More important, it will not be a thunderstorm sound effect generator. I will let you all know how it comes.

6/21/4
Problem-
GML limiter Left channel not passing audio, unless in bypass mode. This happens only once in a while.
Solution-
I pulled it out of the rack and set it up on the bench. Now I am waiting for it to fail so I can find the problem. Jeff at GML has given me the info on what to look for. If it isn't one of the three main amps I'm sending it back. That thing is beautiful and insanely complex inside.

Later- Found that when I kick the input signal up in level the channel freaks out. The effect as seen on the oscilloscope is the sinewave (input signal) gets half its wave clipped as if one half of a push-pull circuit shut down. The output of the channel looks like a half wave rectified version of the input (not DC though, but centered around ground). I probed around and thankfully found the problem right off the input op amp. I got a new one from Manley (in cahoots with GML) and installed it (7/1/4). After a bit of testing no problems so far.

Problem-
Old Josephson e22s mic not responding S/N 4311.
Solution-
Tried remounting the ground screw to get a better contact with the shell, (this was a problem with the earlier prototypes) but the problem was not that. I'll probably send it back for them to look at.
Problem-
Studer A-820 MCH in studio B (blacksides) in "edit" mode has a stuttered/ chunky motion when manually rocking/scrubbing. In "edit" mode the transport is in a constant tension (servo) state. This means you can move the tape with a light hand on either reel and have constant tension across the heads (so you can hear your edit point). It is a complex feature which allows you to smoothly scrub with one hand, and mark your edit point with the other.
Solution-
I built a special test jig as per the manual's description and calibrated the two tension sensors. This involved removing all the rollers, head block and top plate off the machine. While everything was removed I cleaned all the parts (just cause I was there) and the deck top. After everything was put together I re readjusted the tensions and the edit mode worked smoothly.

6/23/4
-Tested out the replacement op amp for our Sontec eq. So far so good.
For now I am just replacing the input op amp with a 5534 because of its high supply voltage and low noise capabilities. I will do more research on finding the best op amp for that voltage range (+-22v). I need it to be quiet, fast, and low on distortion.
Problem-
(Studio B) B&K Precision oscilloscope CRT gone craaaazy. Looks cool though. Some sort of Tron visual going on.
Solution-
To be sent back to B&K for repair and calibration.

6/25/4
Problem-
Altec 175 has no output.
Solution-
Cleaned and reseated the tube (5840). Works now.
I narrowed the problem down by swapping parts with a working 175 system.
PSU to
Mic body (includes tube and permanently attached cable) to
capsule