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GReg/Electrical Tech Journal

All your geeky questions about electronics, microphones, tape machines, etc.

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Re: GReg/Electrical Tech Journal

Postby greg on Mon Jul 24, 2017 3:57 pm

Neve switch cleaning...

Digidesign 192 (different from above) + Unbalancing output amplifier box for studio A

Channel 1 output severe DC spikes, no audio on the output.

Dead channel 1 on my buffer box, and dead output 1 on the 192. Replaced amplifier on the buffer box. Replaced sic DD 192Hd DA card.

Channel 9, no output.

Replaced the DA converter board for channels 9-16.

Calibrated all A and B outputs to our standard.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Aug 04, 2017 3:23 pm

Neve B002 Mixer

Cleaned all the gain switches (alcohol then stabilant), replaced shattered "C" retaining clips, tested.
Let's hope I never open this thing again!
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Aug 10, 2017 2:49 pm

Sovtek Mig 50-

Dead power tube.

We didn't have any original 5881s so I stuffed it with a pair of 6L6GCs to see what that sounded like. It was louder and more broken up than the other Mig 50, so I'm going to keep it as it was with some older tubes.


Manley El-op compressor

VU meters out of calibration, including the mechanical resting point.
Did a full calibration, and test



Neotek Elite -

Cleaned some dirty switches.



-Elsewhere-

Cleaned and tested several Tac Scorpion channels and master section. Man that console is simple.

Corrected mistakes made by people who built the patchbay. I'm told they were high when doing it. Most of the cable looms were cut too short, which made this a little more of a job than necessary. At least they were meticulously labeled correctly.

Mechanically, and electrically aligned Tascam ATR 60 transport and audio. Reel turntable was too high, head assembly tape guide height adjusted. One channel had intermittent connections...
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Aug 14, 2017 11:18 am

Neumann U67

Tremendous noise, the best noise.

Busted wire in the cable connector.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Aug 16, 2017 1:06 pm

Studer A820MCH blacksides

Channel 4 had loud DC pulses when calibrating the repro low frequency, in Auto Rec Align mode.

Swapped Record and HF Driver board with spares at the time. The problem went away.
Tested the boards in another machine under the same conditions, and couldn't repeat the problem. Finally tested in the source machine, and found no noises. Curious.

Ampex MX-35 #2

Irregular output levels, and distortion on all channels.

V7 (12AU7, output driver for both A and B) was bust. After I replaced it, the distortion went away.

I took the opportunity to look at the A/B buss assignment, and input selector switches, which have always been iffy. Depending on how you wiggled them, output levels would jump around, even in oddball circumstances.
An example- Signal on mic input 1 assigned to output A, level would change depending on tapping on buss assignment switch for mic inputs 2, 3, or 4 while they were assigned to output B. The buss assignment switches ground the unused buss (through resistance), somewhat loading the signal on the buss. Whenever the connection to ground lifts, that load changes, and the level changes. The original switches are so beaten up and stressed that we can't trust using them anymore.
I've ordered some guitar pickup switches used in older fenders, which will work in the circuit, are the same size and form factor. We'll give them a shot.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Aug 18, 2017 6:03 pm

Received new switches for the MX-35. Prepping and installing them today.
The treaded mounting holes on the switch frame needed to be drilled out to be able to mount to the 6-32 studs on the MX-35.
Later...
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Aug 24, 2017 4:14 pm

Sovtek Mig 50 (both)

Retubed one with 6L6GCs

Rebiased both amps. One has the original 5881s and the other GT6L6Ss. When there's an open day, I'll see what they sound like now (since all I could do is bench stuff).

Had to fix the multimeter again. The banana post keeps breaking loose, making a flawed connection. Might be time to retire this guy and upgrade.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Aug 25, 2017 4:19 pm

Designing a 2-channel Valley People 800 series rack box.
Incidentally, if someone has a dead or working Valley People PR-2 rack unit they want to get rid of for cheap, let me know.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Aug 31, 2017 4:33 pm

Headphones, shopping, and other/
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Sep 04, 2017 2:44 pm

Bassman Blond-

Pots noisy.

Cleaned.


Neotek SII-

Cue 1-2 occasionally cutting out.

Discovered bad crimp on buss ribbon connector on master side of the console.


Echo Plate Studio B-

Finished wiring with new differential line input amp.
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Re: GReg/Electrical Tech Journal

Postby greg on Tue Sep 05, 2017 4:08 pm

Updated the MXR Noise Gate/Line Driver with a standard 9v wall wart connector. Oh yeah.

MX35 output buffer amp designin'.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Sep 07, 2017 11:37 am

Digidesign 192HD converter Studio A-

Large spikes on inputs 9-12 when audio is present on the input. No noise when there's no audio signal. It's a similar problem to the one we had in studio B, described earlier except in that situation the noise changed depending on whether or not the 24 track was connected to it.

Did the usual resets, connector exercising, etc. Ended up replacing the AD board for that batch of 8 inputs. All is quiet now.

It would be good for Avid to finally release a full technical manual for these obsolete units. Even a block diagram would be good. I could at least shotgun some section then...
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Sep 13, 2017 3:40 pm

Anyone have an Xedit Model 20P wow and flutter meter manual?
Feel free to email my name @electricalaudio.com please...

Shipping things.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Sep 20, 2017 2:53 pm

RCA 74
No output

Wire connecting the bottom end of the ribbon to the transformer was being pinched and shorted by the mu-metal transformer shield.

Replaced the old jumper wire, taking care that it was out of the way of any pinching possibilities.
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Re: GReg/Electrical Tech Journal

Postby steve on Thu Sep 21, 2017 10:39 am

Donchu mean pinche possibilities, esé?
steve albini
Electrical Audio
sa at electricalaudio dot com
Quicumque quattuor feles possidet insanus est.
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Re: GReg/Electrical Tech Journal

Postby greg on Tue Sep 26, 2017 1:22 pm

Neotek Elite

Input level on line 1 in channel 4 -6bB low.

Bad punch on the patchbay punchblock. Re-punched.



-Elsewhere-

Studer A820MCH pulled out of storage-
Meterbridge wont wake up, is in darkness with the display reading "audio test mode" or something similar. Some of the soft keys show limited function. LED test, and BUSS test functioned normally.
No other error messages displayed.


Usually this could mean a glitch with the software, or communications. I had my 820's boards for swapping to see, but no joy there.

Two problems found, related to the serial communication from the transport section to the meterbridge.

1. On the Communications Controller board, resistors R2 and R3 were burned out. Those were the two input/output resistors to the serial bus on the secondary of the transformer. Not sure why they would have burned since they only connect to low current things. My only clue is the wiring to the meterbridge was removed internally, and someone might have tried to reconnect things the wrong way. The meterbridge (and audio remote) simply get 0v, 50vdc (unreg), and the low voltage, balanced serial communication sent to it, four wires total. If the 50vdc was accidentally connected to the serial buss, this could happen. Incidentally, the 50vdc quick connect terminal on the power supply was broken off and stuck in the cable connector, which suggests the meterbridge cable was yanked hard.
An audio remote might be damaged if it were connected as well, but there wasn't one present to see.

2. 8-pin neutrik socket for the meterbridge cable damaged (pins flattened out, not contacting its male counterpart correctly). I found this out simply by tracing the serial buss from the Communications Controller to the MPU motherboard in the meterbridge. Only one of the balanced pair was making it. When I plugged the meterbridge cable into the parallel socket below (used for the audio remote), there was full continuity.

All is good now, except they need to replace the busted neutrik connector.
It reminded me that this machine could be controlled from basically anywhere. You could have a machine in, say, in Fairbanks, and the remote here, connected through phone lines.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Oct 05, 2017 4:06 pm

Fake Marshal JTM45 amp-

Giant noise spikes when nudged, or knocked, with both volume pots completely down.

Opened it up, and tapped around. Found one broken solder splice between two cut legs of a film capacitor.
Found another chunk of unmelted solder hanging off pin 7 (grid) of the phase inverter, causing a short with pin 6 (plate) whenever there was a tiny bit of vibration.
All quiet now with abuse.



Westlake BBSM-10s -
Left speaker woofers stopped working.

Exercised the gain pot on the power amp for the low end of the bi-amped speakers, and it came back on.
Re-calibrated the amps afterward.



RNC compressor -
Distorted output, no compression, meter fully on with or without signal.

Might go off to FMR Audio if they don't want to give us a schematic.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Oct 06, 2017 1:03 pm

GLM 100-

No Output

Broken wire between the cable and XLR PCB


Sennheiser 441

No Output

Brilliance switch was buried inside the housing, presumably forced in by the mic clip or something.
Several wires normally wired to the switch were sheered. Resoldered.



Retrofitted a GLM-100 without a capsule with a Panasonic WM61 electret capsule. The output is higher. We'll see if we like it...
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Oct 23, 2017 3:25 pm

Traynor TS50B -

Two different amps having the same problem in one week (used in different sessions). Loud hum on the output, no matter what the gain settings are, or if anything is plugged into them.

Blown 2n6556 transistors in both amps (power amp section).
Curious coincidence.
Replaced the blown transistors. Recapped (electrolytics) the one amp that had original caps. Removed the power cable and installed an IEC power connector on the same...
Working.



Fender Bassman 6G6B (blonde)-

Sputtering output signal, like a distortion pedal with a dead battery.

One of the 470 ohm screen/grid resistors blew in half on the power tube socket.
later...
A few of the power tube socket pins were barely making contact with the tube's pins.
I replaced both sockets, which were oxidized and tensionless. This involved punching a couple slightly larger holes.
Replacing the 6L6 pair with new ones since one of the tubes was damaged by the whole ordeal. Control grid and screen grid shorted together on one (grounding 430v through the 470Ω resistor).
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Oct 26, 2017 10:26 pm

More aaaamps!

Hiwatt DR 103 "custom 100" crackling a bunch with all the volume pots down.

Replaced V3 and V4 in the preamp section. Some sputtering continued, so I went to another set, and left it on for a while and it died down. Don't like that. Then, discovered-

Crackling with the Bright and Normal gains up.

Replaced V1.


Traynor updates...
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