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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 four_oclocker_2 on Fri Jan 31, 2020 12:33 am

greg wrote:Ordering a Jasper (Wasp) synth kit.
https://www.jaspersynth.co.uk/buying-jasper/


Let us know how this goes! I've been eyeing one of these kits for a few months now but haven't taken the plunge.
Jazz Titan/Ruthie Cohen


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"I'm not in the Kiss Army. But I am in the reserves, and could be called up at any time." - Warmowski
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Jan 31, 2020 2:14 am

four_oclocker_2 wrote:
greg wrote:Ordering a Jasper (Wasp) synth kit.
https://www.jaspersynth.co.uk/buying-jasper/


Let us know how this goes! I've been eyeing one of these kits for a few months now but haven't taken the plunge.


I saw a couple that worked just as well as the real thing in NY. The case is the wild card. Theres a separate person who makes them, one was great the other didn't seem to come together right. It might have been a prototype though...
It'll probably come together slowly, but I'll report back.
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Feb 03, 2020 6:47 pm

Removed and packed a pair of Lomo 19a9 Capsules for reskinning.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Feb 05, 2020 4:50 pm

Work on the other Altec 438.

Trying to get us new couch cushions...
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Feb 24, 2020 6:53 pm

Electrical Audio Custom Rack blew a fuse.

This is a repurposed Allison rack I built to house a bunch of Urei 509 eqs we fell into. I built it in 2001? Holy shit. I'm getting old. It's API 500-like but with more width for the Urei modules, ±18v, 5v and 48v supply rails. I built one John Hardy/Jensen style preamp for it, and thought I'd build more (why there's a 48v rail for phantom power).
Anyway, the phantom regulator died, and blew the fuse. I replaced it with a modernized design.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Feb 27, 2020 5:15 pm

Reassembled the "parts" Ampex ATR 102 and packed it in ATR Service's custom flight case for shipping. We're going to get it completely rebuilt. This was a machine we purchased with two Studer A820MCHs years ago, all three machines look beaten with a chain. Now the ATR is finally going to get turned into a new machine.

Rock tumbling a bunch of Electrical "e" badges. I forget what the time, and formula was when I did it last time. Oh well. I'll just stop things when they look cool...

JSP just finished stuffing the last 3 EAPreq preamp circuit boards (of this batch anyway).

Getting parts together, and scheduling for the pile of direct boxes we're making.

Man, that rock tumbler is annoyingly loud. I'm moving into the office.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Feb 28, 2020 5:17 pm

Gain Brain II not functioning.

Wiggling the Attack pot causes some kind of action, but for the most part, busted.
Pulled the channel out, and saw the phenolic wafer was broken on two pots. These pots aren't secured at the bushing, rather just supported by the pcb pins, and hole through the faceplate (loose). This might have been whacked by a foot or chair.
Looking for suitable replacements.


While pulling it out, the Valley People 4 channel (TR804) lunchbox worked loose from its home made rack housing (it shares with an RNC compressor). The TR804 was sandwiched between four support bars holding it in place simply with friction and weatherstripping. I replaced the decomposed weatherstripping with rubber pads, and clamped things back together. Temporarily, I recapped and installed a spare Maxi-Q in the Gain Brain's place.
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Mar 02, 2020 7:12 pm

Turned two busted Weller WCC100 soldering irons in to one working one. Took longer than I expected, but done...

Loaded the ATR into the UPS truck. This went quicker than I thought it would.

EAPreq prototype, EA Mid Side Matrix, and Valley People Dynamite returned from France in pieces. Steve brought them with him for the latest Mix with the Masters, and apparently the airline wanted to see how high our flight case could bounce. It looks like none of the main circuit boards were destroyed. Need new parts for the Dynamite, which I can get down the street from micro center.

...all checked out, and are back in the studio, uglier.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Mar 04, 2020 12:10 pm

Valley People Dynamite-

Bent faceplate and frame, loose heatsinks and hardware all around.

Remarkably, the main pcb is in good shape. Most of the stress was put on the rack ears, and where the faceplate mounts to the chassis. The disappearing heatsink hardware would be a riddle if I hadn't seen it before. The two regulators are bonded to the pcb and heatsinks with nylon screws for isolation (negative regulator's body is live). After 30 years of hot-cold cycling, the screws have the strength of a pretzel stick. Any tension or shock causes them to shatter and disappear through the vent holes. This is confusing when you open it up and see two loose heatsinks flopping around with no nuts or bolts or evidence that they ever existed (no metal on metal marks). Anyway, replaced everything, added new heatsink compound, tightened, and straightened the chassis.
Went through the calibration checklist, and all is good.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Mar 05, 2020 11:53 am

AKG C12 -

Hum on the output. Tried swapping preamps, power supplies, and cables

Problem went away when the mic was using a different input (on the mic panel).
I measured >100kΩ between ground and pin 1 on the panel connector (channel 10). I refreshed the punch of the shield for that mic line at the patchbay punchblock. I'll do a complete check of the rest of them when there's no action in the studio...
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Re: GReg/Electrical Tech Journal

Postby greg on Tue Mar 17, 2020 1:39 am

-Elsewhere-
Been recapping and repairing Neve 3114 and 3115 modules. I'll include any nifty details as I remember to.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Mar 18, 2020 6:27 pm

-Home with the sick family-

Making use of my time in self-quarantine by gettin to things I have needed to for a long time at Studio Greg Studios III.

Sony MXP3036-

Replaced main control room monitor pot.
Recapped the monitor signal path while I was at it.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Mar 20, 2020 11:40 pm

-Home-

Lomo 19a13 (not Electrical's)-

Low, noisy output. It was much lower than one of ours, but sounded roughly the same.

I replaced the ancient cathode electrolytic and checked the gain of the amp by injecting a -20dBu signal (via 30pF cap) to the point where the capsule couples. The signal was about 31dB lower on the output of the mic. With a new tube, the overall gain was unity.
Next is rebuilding the power supply. After it's all together and voltages set, I'll do another comparison test.
Update- Rebuilt power supply (replaced intermittent power switch, rectifiers, capacitors, 120vac power transformer, IEC power connector, 5v filament regulator). I was chasing down a persistent hum which ended up being solved by more of a star ground wiring scheme, and heavier gauge wires. I never had to do that before with these old supplies, and might have been unnecessary based on the following.
The mic output would vary intermittently in volume and sound quality, depending on mic orientation. I suspected the tiny, aftermarket connector someone retrofitted to the mic. It ended up being the cable. Measuring between the (+) and (-) audio legs of the cable (nothing connected), I would get anywhere between 2kΩ and 5Ω, depending on how I moved and squeezed it. No part of the cable had any physical damage, so this is confusing. I'd grab somewhere in the middle, twist and curl, and read a different value. Anyway, I replaced the cable with a new, fancy mogami one made for tube mics. Tested for a while against another 19a13. Sounds great, and at the expected output level. I wish I bought one of these when they were available more. It's really a great mic.
N.B. I've seen two capsule styles in this mic, both original looking with a dummy diaphragm in the rear. One with an edge termination (like a Ck-12) and the other has a center tap like a Neuman k67.
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Re: GReg/Electrical Tech Journal

Postby greg on Wed Apr 01, 2020 10:23 pm

-Elsewhere/Home-

Recapped another two Neve 3114 channels (one with the BA6xx amps). One of the gain switches (three section Elma 24 position switch (you know the one)), was super crackly and intermittent.
Upon inspection, it was caked with some sort of thick grease which seemed a bit looser than something like Vaseline. Long story short, it was everywhere. I completely disassembled the switch, degreased the parts you don't want greased. The contacts were the silver plated ones, and were blackened in spots. Alcohol q-tips and elbo grease didn't get far. I soaked q-tips with deoxit, and scrubbed until shiny new, cleared the product with alcohol, then applied some contact lubricant.
I reassembled the switch, being extra careful to make sure the different decks were lined up exactly as they were supposed to be (marked the edges before). After getting it wired and mounted back into the preamp, I tested it. Then I promptly removed the switch and set out to disassemble it again.
I put the decks on the post 180º out of position. Fortunately, I didn't have to disassemble the decks completely just remove them as a module. This is good because the little plastic C-clip holding each section together only has a few cycles left in it's brittle, elderly body.
After everything was back together, the switch worked like new! Honestly, I think I'll clean every one like this. It's a long, painstaking process (I left out a lot of wire and resistor relocating), but I don't know how you can really clean the contacts in a confident way other wise. I hate just spraying and hoping for the best.

Really Nice Compressor-

Loud buzz on the outputs, nothing working.

Power supply electrolytic capacitor dead. Recapped the entire thing. Everything good again. Dead quiet.

Lexicon PCM60-

Level inconsistencies and eventually the Right output died.

Mix pot was really dirty and had been sitting at "wet" for as long as I've had it, at least. Exercised it a bunch, everything came back better.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Apr 16, 2020 2:25 pm

-home-

Sony MXP3036-

Buss 1 has extreme low frequency roll off of signals sent to it, but slate test tone is as solid as a rock.

Dead electrolytic capacitor in the summing amplifier (ACN) section. The slate signal sums with the output of the ACN at the input of the balance output driver amp (why that signal was normal). Replaced C1000 and C1003, and all is good.


Not able to send to bus 2 from channels 9-36.

Reseated bus ribbon jumper between bucket 1-8 and 9-16. Not totally confident, as I could cause it to fail by being aggressive with the cable. I suspect a bad crimp.


Installed original Sony output transformers on the main stereo mix output amplifiers, replaced all electrolytic capacitors related to the 2-mix bus (summing amps, insert send and return amps, output driver amps).

Spare input channel from ebay has no signal from the "upper" part of the channel.

Looks like two current limiting/fuse resistors in series with IC500' power supply blew up at some point, burning the circuit board. A sloppy repair job replacing the resistors ripped a trace that belonged to the output of the "MIC/LINE" switch. I pulled the replacement resistors and scrapped away the carbonized circuit board, which was measuring a resistance of somewhere between 1M-10MΩ with the probes just stabbed into raw material. I cleaned as much of the crust off the board as it would take to not measure any resistance between any nearby trace or pad and the raw board. I reinstalled the resistors, and added a jumper to replace the broken trace. All working now.

Same channel, distorted signal when polarity reverse switch engaged.

Bad inverting op amp- replaced.
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Re: GReg/Electrical Tech Journal

Postby greg on Sat May 02, 2020 2:30 am

Making direct boxes for the studio to sell.

Recapping Neve 3114 modules for another studio.

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Re: GReg/Electrical Tech Journal

Postby greg on Sun May 10, 2020 9:00 am

-Home-

ADR F601-RS-

I bought this off of ebay after using it during the last GYBE session. The guy sent it to me from Europe packed with a skinny layer of padding on the front and back, no padding anywhere else, just a layer of that soft cardboard. It showed up with the faceplate broken off the chassis, and a bunch of knobs and shafts bent or damaged.

I drilled out where the broken studs were on the faceplate, then remounted it to the chassis with some new machine screws. I did a alignment as per the manual (which seemed to skip a couple setup steps). All good now. I might mod it to have a better input and output section later.

Tried & failed to upgrade my Lynx Aurora 16 and 8 LT HD firmware. I bailed after a few hours, because I didn't want to brick it all before doing a project. It's an absurdly unreliable process.
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Re: GReg/Electrical Tech Journal

Postby greg on Mon May 18, 2020 1:58 pm

-Elsewhere-

Neve 3114 Module-

The LF shelf eq noisy in only when the 180Hz band is selected (pink noise sounding noise).

C47 or C53 (can't remember which) measured 50nF instead of 150nF (the other one was correct).
I replaced both with the correct value, and all is normal again.
Going to do a freq sweep and compare with
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