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Re: GReg/Electrical Tech Journal

PostPosted: Fri Oct 04, 2019 11:39 am
by greg
Audio Kitchen Little Chopper Amp -

Blows mains fuses whenever turned on.


Pulled all the tubes, which essentially unloaded the power transformer, and it still blew the fuse. Checked the mains voltage switch, then found shorted filament windings.
Steve at Audio Kitchen sent us a nice shiny new power transformer, wired it in, and we're back to loud again.


Some patchbay ground hum hunting, fixing. A couple of poor punches on the block.

Re: GReg/Electrical Tech Journal

PostPosted: Mon Oct 07, 2019 4:31 pm
by greg
Skibtronics LA-2 clone-

Distortion on clean bass.

No distortion around me and my testing.

Pricing new run of Electrical DI Boxes (Jensen ap note with XLR In/Out). Someone is interested in buying a set of 4.

Re: GReg/Electrical Tech Journal

PostPosted: Mon Oct 07, 2019 4:39 pm
by greg
greg wrote:Gefell 563 -

No output.

Busted wire on 5-pin XLR end of the cable.

Seems trivial to mention these things, but maybe it's good to note the frequency.


Not the same parts as a above...

Gefell 563 -

Crackling, intermittent output.

Problems could be stimulated by wiggling the microphone end cable/connector.
Replaced really old, and stressed 5-pin female cable connector. Mic was fine...

Re: GReg/Electrical Tech Journal

PostPosted: Tue Oct 08, 2019 5:16 pm
by greg
Looks like the new Avid HD I/O has cross coupled balanced outputs! We have two which came with some other things we picked up. I wonder if there was enough people like me whining about the old 192s to change things?

Re: GReg/Electrical Tech Journal

PostPosted: Fri Oct 11, 2019 4:58 pm
by greg
Neumann SM-2 SM-23 work...

Orange Amp filament supply...

Re: GReg/Electrical Tech Journal

PostPosted: Wed Oct 23, 2019 5:58 pm
by greg
AKG 414 B-uls

Another busted frame (where the windscreen section meets the main body). Someone pretended it wasn't broken and sheepishly returned it to the mic drawer.

This will be the 3rd or 4th?

Trying some JB Weld on this before ordering a new frame.

1.17.20 Update: The epoxy didn't hold for very long. There's barely anything for it to hold on to. This part of the frame is very thin (why it breaks so often, I guess). Ordered a new frame (same as the current production), and transferred the guts today. The tiny screws holding the switches to the frame seem stripped, and don't grab well. In the service manual, the screws are listed with two threading options, M1,2 and M1,4. I guess I have M1,2 screws and holes are tapped for M1,4? We'll find out when my bag of M1,4 screws shows up.
1.20.20 Update: M1,4 it is.

Re: GReg/Electrical Tech Journal

PostPosted: Thu Nov 07, 2019 9:30 pm
by greg
Related...
Sony C500 webbing frame on the inside of the windscreen was broken in some joints. JB Welding that as well.
I had to remove the capsule to keep it safe. The screws on the clamp were lacquered in place. It took some work to get them out. I would just scrape the threads with a needle tip, back the screw as much as possible, then scrape some more...

Re: GReg/Electrical Tech Journal

PostPosted: Tue Nov 12, 2019 1:09 pm
by greg
-Elsewhere-
Sphere Eclipse C -

Auditioning a modification on a channel in efforts to replace the VCA faders with a regular old audio one.

Found and repaired some bad wiring in and outside the console.

ATR 102 1/2" 2-track (stock) -

Urethane Capstan Surface turned into melted ice cream then solidified again over everything beneath.

This was a mess.
Removed all the parts and panels in the area, and cleaned, and cleaned, and also cleaned. The photo transistor lens for the capstan tach was glued to the encoder glass on the motor. It popped off when I was trying to remove the photo transistor pcb. Glued it back on once everything was clean. Installed the new capstan assembly, with fresh urethane surface. Performed the mechanical and electrical capstan tach alignment. Took apart the takeup tension roller and cleaned everything. The parts were glued together. This would have been a great time to replace the bearings, but we had none, and they moved apparently well.
Machine is back together and singing.

Re: GReg/Electrical Tech Journal

PostPosted: Fri Nov 15, 2019 6:05 pm
by greg
AKG C12 (Siemens 204/23) No38-

Replaced noisy tube.

Sony C500 tested after reassembly (epoxied broken parts).

Re: GReg/Electrical Tech Journal

PostPosted: Tue Nov 19, 2019 4:15 pm
by greg
Beyerdynamic M160c -

Trying to replace the ribbon. I got as far as pulling the old ribbon assembly out, but I need instructions to go the rest of the way. I'm not sure how this thing came together to begin with. It seems like the part that the XLR connector barrel screws into (where the label SN band is) should be something that you can remove, but I looks welded to the main body. I'm not sure I can fish the solid core wires extending from the ribbon motor past the transformer. It looks like that's supposed to be removed first. The transformer is almost small enough to move through the bottleneck at the XLR end. It'd be great if it did. This would be done now. Ha.
Emailing the factory for a step buy step. Hopefully they'll share...
Anyone ever replaced the ribbon on one of these?

Re: GReg/Electrical Tech Journal

PostPosted: Tue Nov 26, 2019 6:26 pm
by greg
Replaced a voltage selector switch on a homebrew mic preamp power supply.

Rearranged the Josephson mic drawer, adding 4 new e22 capsules to the mix.
We had some C606 prototype head amps without capsules (C606 are transformerless amps that will fit the e22 capsule). Now they will be usable again...

Also added are 2 new Josephson C617s and 2 new e22s

We're going to need a bigger drawer.

Re: GReg/Electrical Tech Journal

PostPosted: Mon Dec 09, 2019 12:10 pm
by greg
-Elsewhere-

Neve 5300 40 channel, 16 bus broadcast board (3114 and 3115 input modules) -
Installed, tested and troubleshot. This is the board I did a bunch of patchbay wiring on a month or so ago. Noted wiring and routing changes to do. This was initially built for a 16 track studio and had some elaborate routing for tracking/overdub/mixing modes. Since it will be working with a 24 track, 24 i/o daw standard, a lot has to be reconfigured to make the new workflow sensible. I'll update this post with fixes as I go,

Solo (cue) only appears in full fidelity on left monitor channel.

Busted relay socket terminal for the (-) leg of the cue bus. Socket pin replaced without needing to do the whole socket assembly, by local tech.

Monitor "Tilt" pot removed. This was a knob placed where you'd expect the monitor volume to be that just tilts the balance of the monitor output in favor of left or right. If turned fully CCW, left would be about twice as loud as the right, fully CW, right would be louder. The center point wasn't center, and the owner knew he would hate the thing, so we removed it from the circuit. Functionally, it amounted to two level trims mounted on a dual gang pot.

A handful of other issues with switches, which is to be expected. Generally speaking, the board is in great shape.


Sphere Eclipse C with VCA faders 24 channels x 24 busses x 4 mix busses (quad).

Partial technical manual, and multiple undocumented modifications made for some tough memory exercises.
More later....

Re: GReg/Electrical Tech Journal

PostPosted: Mon Dec 09, 2019 5:20 pm
by greg
Update on our sick Sony C38

Direct box machining quote search...

Re: GReg/Electrical Tech Journal

PostPosted: Thu Dec 12, 2019 7:06 pm
by greg
Checked out, cleaned, calibrated, and lubed a TEAC 3440 4-track for a transfer project. Odd that it's an NAB eq machine. I thought all the Japanese small format guys were IEC.

Re: GReg/Electrical Tech Journal

PostPosted: Fri Dec 13, 2019 5:45 pm
by greg
Studer A820MCH "Blacksides" -

"Remote Shuttle Value Invalid" (or something similar) error message on start up, and occasional transport shuddering when at rest, with tape loaded. The shuddering could be stopped by exercising the shuttle wheel..

Took apart the auto locator, cleaned everything, replaced the electrolytics (some were about 1/2 their stated value), and adjusted the electrical center point of the shuttle wheel, as described in the A820 2-track manual (for some reason this section is referred to in the 820 and 827mch manuals, but the instructions aren't there). I also reseated some key ICs.
Powered up, and things look clear. We'll see after a few weeks.


Channel 12 input level was down 1dB compared to all the other channels only at frequencies above 5kHz (100hz @ 0dB) using an external oscillator.

This was witnessed on the tape machine meter and confirmed on the output with an external meter. With the internal tone generator engaged, all levels at all frequencies were even. This narrowed the problem down quite a bit, to just the input amplifier section (Line Amp Board) that then feeds the NRS Control board (signal name INPDI-xy).
The electrolytic cap C8 was not replaced when I recapped this board, I believe because I hadn't yet sourced or ran out of the special sized ones. The original cap was tall and covered in heat shrink (from the factory). I sourced a shorter one that cleared any contact with other parts on the daughter board above it. Unfortunately this board slipped past me. It measured 8nF when it was supposed to be 47uF. The fact that it was rolling off the high end was odd. I would expect that low frequencies would be attenuated instead. Looking at the schematic, I have ideas, but still learning things...
Going to check all the rest of the channels to see if I forgot any mor
e.

Re: GReg/Electrical Tech Journal

PostPosted: Thu Dec 19, 2019 2:56 pm
by greg

Re: GReg/Electrical Tech Journal

PostPosted: Fri Jan 10, 2020 3:18 pm
by greg
Neumann n52 tube mic power supply (modified to work with our Gefell 582s and 563s) -

Blown fuse.

Since this is a fairly low current power supply, I looked into things a bit further and found a failed Valvo 150 B2 regulator tube. Waiting for replacements.

Re: GReg/Electrical Tech Journal

PostPosted: Thu Jan 16, 2020 10:51 pm
by greg
Organizing and moving Studer parts between machines.

Updates to earlier posts.

Re: GReg/Electrical Tech Journal

PostPosted: Tue Jan 21, 2020 5:41 pm
by greg
Beyerdynamic M169N (C) sn5410

Blown ribbon.

Replaced ribbon assembly (sold as a complete part).
Boy this was a thing to get apart and back together.

Re: GReg/Electrical Tech Journal

PostPosted: Thu Jan 30, 2020 5:00 pm
by greg
Ordering a Jasper (Wasp) synth kit.
https://www.jaspersynth.co.uk/buying-jasper/
and starting to mod our other Altec 436 compressor to an EMI "RS124"
The other one is doing well in studio A. We bought some nicer dual pots for the input gain.