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

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Postby greg on Tue Jul 27, 2004 5:28 pm

7/27/4
Problem-
Sovtek Mig 50 input #2 not working.

Solution-
1Meg Ohm Log pot "Volume II" malfunctioned. It might have been bumped. I don't know. It's broken now. This was found by sending a signal to the input and following it (with my scope) past the preamp tube to its demise at the pot. I then measured the pot in circuit (power off) with a ohm meter and saw that the wiper pin did not change its resistance to the other pins over the rotation of the pot.
New Sensor is sending a replacement set for all the pots.

8/3/4- We got the pot, I replaced it, all good now.
Problem-
Royer 122 mic (the phantom powered one) S/N 1112 has "fuffling" noise after being used for a few hours. Sound quality of the mic seem good aside the noise. I'm thinking it has something to do with the head amp.

Solution-
Off to Royer.


Problem-
Coles 4038 has a blown ribbon.

Solution-
That makes three, so off to the labs with those.
I wait until we have 3 down to save on shipping to England.

10/4/04-They are back now.
Last edited by greg on Tue Oct 05, 2004 5:07 am, edited 2 times in total.
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Postby wow&butter on Tue Jul 27, 2004 7:54 pm

any reason why you don't send them to Wes at AEA?

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Postby greg on Tue Aug 03, 2004 5:49 pm

It's nothing personal to Wes.
Steve likes to send it to the company who made them. As long as they're in buisness. . .
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Postby greg on Thu Aug 05, 2004 9:28 pm

8/4-5/4
M-S matrix box circuit board layout.

Problem-
Studer A820 MCH (Czech one)
Occasionally the machine will not go into play. After fast-forwarding or rewinding the machine wont go into play. The capstan will spin but the tape wont move (pinch roller has ok pressure). If you help either reel in the right direction, it will play properly.


Solution-
Unfortunately this problem was not there yesterday (4th), but I went ahead on checking/calibrating the tension sensors (dancer arms on either side of the head block). When Steve showed me the problem the reels felt chunky in their movement in edit mode. This seems like a constant tension servo problem. More to be checked.


The sensors were off a bit. I am going to order a metal jig made so I can do this ajustment without making my own jig out of a ruler and a razor. What jig? you ask. I'll tell you more later.
Last edited by greg on Mon Aug 09, 2004 9:07 pm, edited 1 time in total.
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Postby greg on Thu Aug 05, 2004 9:28 pm

Last Week at home.
Problem-
My MCI JH-24 track
In "sync" mode, no tracks armed, an input signal on track 2 can be heard faintly on the outputs of tracks 1 and 3.


Solution-
Long story short. The problem followed the Record/Cue audio card.
The FET switch (Q3) that when turned off allows channel 2's input signal to go (out of phase) to the neighboring tracks for the crosstalk compensation wouldn't turn on.
This crosstalk signal cancels out the bleed magnetic field picked up by the other two tracks on the sync head. The signal in the manual is called "CFO." It should work only when in record mode. I found out that the Gate of this FET should be at roughly 24 volts when the crosstalk compensation shouldn't be on. On this channel I was measuring less than 1 volt. After checking for shorts and bad resistors. I found that at the Gate there was a relatively low resistance to ground (compared to a working channel). The culprit was a .01uF/50 volt ceramic cap (C47). This cap was bypassing the Gate input signal (filtering noise off of the DC signal). It was leaking DC to ground. This is the second ceramic cap that has failed on me in my brief experience. The other was on an audio card for my ATR. Other techs told me that this doesn't happen. Well, it does for me. I replaced it with an NPO rated cap. All works now.
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your job

Postby A vs B on Fri Aug 13, 2004 12:07 am

your job looks like it must be so much fun. Not like Screaming with your arms in the air like a rollercoaster fun, but fun as in you get to do things that interest you, use your creative, and work with your brain a lot for solutions. Do you love your job?
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Postby greg on Tue Aug 17, 2004 5:18 pm

I do love my job. A lot of work to be done and little time to do it.
8/12/4
Studer 820 MCH-
Recapped/Cleaned 2 NRS control cards
Recapped/Cleaned 2 Line Amplifier cards (one needed a 10 wire ribbon jumper replacement.
+
More PCB layout for the m-s box.
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Postby greg on Thu Aug 19, 2004 6:14 pm

6/19/04
MS circuit board layout- finished the power supply
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Postby greg on Wed Aug 25, 2004 8:03 pm

Last week or so.
Problem-
Eventide H-3000 w/ sampler board (studio A) has noise on the output of the right channel. THis would go away when in bypass (which would make sense because the relay shunts the input straight to the output). The noise would also go away when the input was disconnected. The noise sounded like someone saying "cat-cat-cat-cat-cat" really fast.

Solution-
I replaced it with the one from studio B (no one in there right now) and brought the f-ed one to the shop. It wouldn't make the same noise exactly but that channel would be generally noisier than the left one. Since the noise seemed to appear when the input was terminated I looked at the op-amps near the input. When I noticed a noise I would probe around the outputs of the TL072s looking for something wrong. Sometimes my probing would cause the noise to disappear. After a while sitting there on the bench. A noise resembling the sound of rain on a plastic tarp appeared. I swapped some op amps to see if the noise would follow and it disappeared. Today I noticed a special type of distortion on the output. With a 400Hz tone on the input, and the input level digitally set below "0" the sinewave was horribly disfigured. It looked like a jagged version of itself (little saw-teeth floating on the fundamental wave). The input tone far below clipping level. Listening to the output while in this state the distortion harmonics would change when I would raise or lower the "input level" (changing the "output level" had no unanticipated effect). Since that level is digitally controlled there is a possibility that the converter is f-ed. Right now it is working again. I'll let you know.

Problem-
Ibinez EQ pedal noisy

Solution-
Sprayed tuner cleaner into the faders and pots then exercised them to silence.

I forget what else.
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Postby greg on Fri Sep 03, 2004 11:22 pm

9/3/4
Problem-
The band's Fet 47 mic was not working.


Solution-
The male XLR connector that fit within the collar of the mic's ass was loose. Its one retaining screw was not causing enough friction to hold the Switchcraft made connector in place. Consequently an RF suppressing cap broke when the connector was pushed back into something else. The cap was a 100pF cap between pin 1 (ground) and Pin 2. There was a clone of it between pin 1 and 3. Fortunately I had a bunch of good quality 100pF caps leftover from my MS-16 mod days so I matched a pair and replaced the old ones.
I should charge them $800 you say?
Maybe I will. Maybe I will. . . . . .. . .. . . . . .
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Postby greg on Thu Sep 09, 2004 6:51 pm

9/9/4
Sent off the MS decoder board artwork to the manufacturer. I've been finalizing work on that the last few days. It's going to be great to get the fancy new boards. I'm going to have to make the power supply on a separate board because the license on my layout program only allows for 300 through-holes. Totally lame. It just means it will take a little more time to build.
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Postby greg on Thu Sep 09, 2004 7:16 pm

8/31/4
Problem-
Studer A820 16-track headblock.
When calibrating the record head's high frequency playback the machine would fail to reach zero on some channels. Most of the other tracks had to be cranked to obtain a 0dB level at 10kHz.

Solution-
I checked the tension, swapped audio cards and checked tape height. All that was good. I then noticed that the record head had been worn down pretty well. Time for a relap.
I forget that those heads aren't the normal 318 style super heads which last forever. They are made of the softer material. We've been using them pretty much all the time too. For reference- the record head is a A80/A800 head and the repro head is a custom Flux Magnetics low freq extension head (was operating fine). I sent it off to JRF for relapping (they originally assembled the headblock). It's back now and all is great with the world. The high freq repro gain for the record head was about 1/3 the gain pre relap.
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Postby greg on Mon Sep 13, 2004 5:45 pm

9/13/4
Problem-
Neotek Elite talkback button intermittent.

Solution-
Replaced button


Problem-
Capps mic busted.

Solution-
Found broken wire between the grid of the 5703 tube and the capsule. I made a new wire bundle between the capsule and the head amp. This mic is a home made looking mic with a 5703 used as a cathode follower (transformer out).
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Postby greg on Fri Sep 17, 2004 5:53 pm

9/17/4
Studer A820 machines:
There is a special jig that Studer made to electrically calibrate the tension sensor positions on the A820 and A827 machines. I would build a temporary one out of a razor blade, ruler and tape when I needed it. I thought it might be good to have a solid fixed item like the one Studer used to sell, so I ordered one.
I made a simple drawing of the jig we need and fax-ed it off to a machinist. We will see how it goes.

Problem-
Film Industries Type M.8 Microphone:
Needs odd style 3 pin connector

Solution-
Possibly found a connector on the south side. I'm going there before work on Monday to see.


POS Garnet B.T.O. Special that Steve got-
Russ is almost done tearing the guts out of this shitty amp. He is going to rebuild it next. We got this thing a year ago when it had as much usefulness as a used condom (on a metal box). Dave "The Diamond" Duval made a beautiful Walnut cabinet replacing the rotted shit-box that was there.
Russ has all new parts and a new attitude towards the project.
Go Get-em pally!
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Postby greg on Mon Sep 20, 2004 8:30 pm

9/20/4
Problem-
Traynor Voice Master II buzzing.

Solution-
I removed:
-power cable and installed IEC power connector (grounding Earth securely to the chassis),
-AC female connector,
-ground polarity switch (where the problem might have been for real),
-old in line fuse holder, and installed panel mount holder

Tested out fine on the first few inputs, noisy on the 4th.

We got the M-S matrix circuit boards in today. One big problem. The artwork was inverted or mirrored. They noticed this problem too but sent it to me for inspection. I double checked and the files I sent them were correctly orientated. We are in the process of finding out who's to blame.
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Postby greg on Wed Sep 22, 2004 1:53 am

9/21/4
Problem-
Traynor Bass Master MKII (new from ebay) buzzing like the last one.


Solution-
Same as the last Traynor (yesterday) but without the new fuse holder, and there was more metal cutting involved this time. I checked the large axial filter caps and they are good. There is a home made power resistor (made out of 8 other resistors to approximate a 470 Ohm 10 Watt resistor). That I should replace, but the amp is quiet and works.


Struck-out a couple of jerks in wiffleball.

Fixed a couple of busted wires on an 8 channel snake.

Built a fake T-4 for one of our Skibb'tronics fake LA-2 compressor. This is the kind that can be found here.
http://recording.org/users/kev/T4B.htm
Haven't tested it yet.
The T-4 is the electro-luminescent heart of the LA-2 circuit. Our original one malfunctioned. I had the parts for this test, so I decided to try it out.
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Postby toomanyhelicopters on Wed Sep 22, 2004 3:13 am

greg wrote:9/21/4
Problem-
Traynor Bass Master MKII (new from ebay) buzzing like the last one.


are you that clown that stomped on my max bid at the end to get it for $233? if so, thanks a lot, clown. now i have no spare. hand-wired, eyelet-style, four screws and you got the lid off... is that the ultimate tweak amp to get a boner over or what? is yours fixed bias? you got 6CA7's or EL34's in there? did it have the weird both-way-diode things in the output section? what the fuck is that all about anyways? you gonna do the 1-ohm resistor from tube socket to chassis thing, so you can bias it all easy-like?

greg wrote:Struck-out a couple of jerks in wiffleball.


maybe you got me looking. *maybe*. but at least i got the berrs/pizza/cub game combo going on afterward. so, y'know, HA! TAKE THAT, Workey McWorker!

hey, is it normal for the owner of that joint to offer to buy you and andyk drinks, and then later when you're talking to him and thanking him for the offer but explaining how you have to go home and work, so you can't get hammered, he's all talky and smiley and he rubs your shoulder a little? if that's normal, then man am i releived! cause so far i just been slightly weirded out.
LVP wrote:If, say, 10% of lions tried to kill gazelles, compared with 10% of savannah animals in general, I think that gazelle would be a lousy racist jerk.
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Postby cgarges on Wed Sep 22, 2004 8:07 pm

greg wrote:Built a fake T-4 for one of our Skibb'tronics fake LA-2 compressor. This is the kind that can be found here.
http://recording.org/users/kev/T4B.htm
Haven't tested it yet.


Hey Greg, keep us posted on this!
Thanks!

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Postby greg on Thu Sep 23, 2004 2:26 pm

9/22/4
Problem-
noisy Traynor YBA-3 (big bass amp)

Solution-
Pulled the same routine on that as I did the last 2 with the IEC connector, cap testing, ground switch neutralizing, and such. No weird resistor arrays this time.


The T4 clone I built was really slow and didn't attenuate more than 10-15dB. Its speed was similar to the Altec 436 compressor. This was with two 200k resistors on either end of the led. I'm going to move to 150k and see what we get.

As far as the amp ebay thing. I don't know when steve got this, and I've never got a boner over a Canadian amp.
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Postby Redline on Sat Sep 25, 2004 3:17 pm

Man, I would. Neil Young is Canadian, and he has allot of cool amps I would get a boner over! Bassmans, plexi Marshalls, Tweed Twins, etc...Oh, a Canadian amp, not a Canadian's amp.
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