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

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Postby greg on Wed Sep 29, 2004 4:48 pm

9/29/4
Problem-
Sony C-17 mic is squealing and oscillating at a high frequency. Plugged in to the GML preamp.

Solution-
Trying to make it fail in the shop. Will reproduce the scenario with the preamp when it is free.


M-S decoder circuit boards are in. I'm going to order some parts and stuff the thing soon.
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Postby MilitaryMan on Thu Sep 30, 2004 5:34 am

Greg,

Problem - I have a TK-421 and it doesn't seem to respond. Any ideas or common problems you know of that might help me out?

-Steve-o
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Postby greg on Fri Oct 01, 2004 5:34 pm

9/30/4
Problem-
Neuman/Geffel 582 has a sputtering noise.

Solution-
Tube was falling out of it's socket. I cleaned the socket and tube pins and reinserted tube. After a day checking every few hours (noise and movement ) all was quiet.

Problem - I have a TK-421 and it doesn't seem to respond. Any ideas or common problems you know of that might help me out?

Solution-
"Rrrarrr"

Sound Effect: wrench whacking a tension wire
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Postby MilitaryMan on Sat Oct 02, 2004 1:09 am

:lol: :lol: :lol: :lol: :lol: :lol: :lol:
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Postby greg on Tue Oct 05, 2004 5:05 am

10/4/4
Problem-
ATR 102 2-tk had a noisy bearing in the timer wheel. It made a low rumble sound as it spun.

Solution-
I pulled it out to have the bearings replaced locally, but I noticed that the top bearing was flush with the top of the drum (is supposed to be recessed). There might have been a burr or something in the way that made whoever last put the last bearing in stop at flush (not an ATR Service-d drum). I sent it off to ATR Service for replacement and possible repair. No repair needed. He replaced the bearings and all is good now.
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Postby greg on Tue Oct 05, 2004 4:39 pm

10/5/4
Sontec MEP-250B equalizer-
Ripped out old power supply parts. Preparing it to be used with an external power supply.
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Postby greg on Mon Oct 11, 2004 5:49 pm

10/11/4
Problem-
Lomo 19-18 making f-f-f-ting and scratchy noises.

Solution-
Kind of weird. I found that I could cause noises by moving the cable around or by wiggling the cable connector. If I alligator clipped the mic body to the back piece of the cable connector (which had a loose connection with the threaded member) the noise would go away completely. That back part had the cable shield soldered to it. That would then make contact (friction only) with the mic body through the threaded collar. Once the connector was on as far as it could go there would be some slack on that friction connection.
Not a good contact.
The problem was that the shield was being grounded to the chassis of the power supply (via the mic connector on the P.S.), while the cicuit ground (separate wire) was going directly to the power supply ground. Both grounds go to the safety ground pin as part of the star ground. The chassis ground is not as direct however (path takes you through some paint, welds, and cold contacts). So we had two ground paths for the microphone which were shorting together intermittently at the mic end of the cable. This is what was making noise.
I lifted the shield from the connector at the mic end of the cable (ground still coming through the other wire). Then joined the shield and the ground at the p.s. side of the cable. This way the ground and the shield are terminated to the same ground.
No noise so far.
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Postby greg on Tue Oct 12, 2004 6:13 pm

10/12/4
Problem-
Studio A Control room Mic Line #3 and #4 not working correctly. These are the extra mic lines on a panel in the control room, and not the main lines to the studio rooms.


Solution-
#3's pin 1 (ground) was not making its way to the patch bay. I re-punched the line at the punch-block. Fixed.
#4 had a short between pin 1 and pin 2. Lifting the cables on both sides (off the XLR conn and of the bunch-block) I found the short was on the cable itself. I can only imagine that it was pinched at some time and the positive wire's insulation split. Either way, stripping back the pair to find the short on either end didn't yield any results. I ended up swapping the bad pair for an unused pair. Fixed.
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Postby greg on Thu Oct 14, 2004 12:11 pm

10/13/4
Stuffed first MS decoder board. When studio A's session is done I'm going to replace the board in that MS decoder so we can test for bugs.

Problem-
Quantec QRS XL
It has a cyclical scratching noise on the right output every 2 seconds or so. The noise will go away when you switch presets around, and it does not appear on the dry signal. There was another problem that was the initial reason to look at this unit and that was a high output level showing on the meters with no input signal. When I saw this, I plugged the o/p into the console to see what it sounded like. As soon as I did that the levels went to zero.

Solution-
It is another intermittent problem that can not be forced into fault. I am seeking assistance.


Problem-
Sony C-17 mic into GML 8400 preamp
An oscillation appears on the output of the GML at higher gain settings. This wont happen with any other preamp.

Solution-
I'm going to see if the o/p impedance of the mic is unusual. It is in use now.
Last edited by greg on Thu Oct 14, 2004 5:28 pm, edited 1 time in total.
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Postby greg on Thu Oct 14, 2004 5:26 pm

10/14/4
Schoeps 221 stereo power supply.
Changed the filament voltage from 6V DC to 5V DC so to be gentler on the AC 701 tubes inside.

Me 9/22/4:
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.

I changed the resistors to 130K and it is still a bit too slow. More later.
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Postby greg on Tue Oct 19, 2004 6:02 pm

10/18/4
Put the new MS decoder board in the old MS decoder box, and wired it up partly.
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Postby greg on Wed Oct 27, 2004 5:02 pm

10/27/4
Problem-
Neotek Series II talkback switch (left side) not working.

Solution-
Replaced the switch.
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Postby bigmuffya on Sat Nov 13, 2004 11:31 pm

"Problem-
Eventide Omnipressor - hum on the output

Solution-
Strapped the audio ground to the chassis ground at a good star-point near the power inlet."

what exactly does that mean? and what did u strap the things with?
thanks i hate hum and buzz and if you dont mind, if there are anygood ways to get rid of it for anything please let me know.
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Postby greg on Wed Nov 17, 2004 6:49 pm

"Problem-
Eventide Omnipressor - hum on the output

Solution-
Strapped the audio ground to the chassis ground at a good star-point near the power inlet."

what exactly does that mean? and what did u strap the things with?
thanks i hate hum and buzz and if you dont mind, if there are anygood ways to get rid of it for anything please let me know.


There was a wire going from the ac ground (117 Volt wall outlet) to the chassis and nowhere else. The audio ground reference was derived by the power supply. There was no direct connection to the ground pin. That audio ground was used for the Pin 1 audio connection (audio and shield ground for outputs and inputs). So the shields on the audio cables weren't being grounded as well as they could have. Soldering a wire from the ac ground to the audio ground (strapping) improves this problem. A star ground is just having one point of ground reference, preferably near the point entry for all things that need grounding to strap to.
Hope that helps.
Getting rid of buzzes and hums in general is a large subject. I couldn't possibly cover it all. Some good reading material can be found on the web.
Books that have helped me include-
"Handbook for Sound Engineers," and
Yamaha's "Sound Reinforcement Handbook."
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Postby toomanyhelicopters on Tue Dec 07, 2004 5:50 am

somebody been a little busy with their new tape machine? ;) you're still doing the tech work, just not keeping a journal, right?

i'll fill in for you for a moment...

Problem : Tascam TSR-8 channels 3 and 4 don't do jack
Solution : Good question

Problem : Shoes are too tight
Solution : Remove third, fourth, and fifth pairs of socks

Problem : Unable to do nearly as good a job in this thread as Greg does
Solution : Canadian Whiskey!
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Postby goosman on Thu Dec 09, 2004 10:15 pm

greg wrote:11/6/03

Problem-
Eventide Omnipressor - hum on the output




I always think of the following when I see the above:

greg wrote:Solution-
Taught the Omnipressor the words.



It's probably only funny to me.
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Postby MTAR on Wed Dec 15, 2004 3:45 pm

toomanyhelicopters wrote:Problem : Shoes are too tight
Solution : Remove third, fourth, and fifth pairs of socks


hmmm... I think you'd actually have to remove the fifth pair, then the fourth pair,and then the third pair.

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Postby greg on Tue Feb 08, 2005 7:25 pm

2/8/5
Sounds of settling back in the chair. Finding that ass groove.
"This place is a mess."
Sounds of finding an intern, slapping, then sweeping.
"Ahhh"


Problem-
Older Josephson E-22 prototype not working.

Solution-
Screen dome on the back was whacked by a drum stick and bent in far enough in to short to the capsule solder point. That point is covered with something on the new ones for probably that reason. I popped off the screen to re-dome it. It works fine now.

Problem-
M-S Decoder prototype,
I destroyed a regulator while testing it a long time ago.

Solution-
Replaced it. It now works fine.

I spent the rest of the time finding the best way for the output trim to work. I decided to go with a line trim that gives you 6 dB of gain on the top end and a little more than 20 dB attenuation on the bottom. This is much like line trim pots on consoles.
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Postby 6-4-3 on Thu Feb 10, 2005 1:46 pm

Hey, I was just the 11,000th view of this thread!!!!
Now that's cool.
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Postby greg on Fri Feb 25, 2005 5:13 pm

2/24/5
More M/S Decoder building in the last few days.
Problem-
Neotek Elite Channel 4 mic preamp distorts and has irregular gain. This was originally noticed when a Josephson e22s mic was "farting-out" on a tom.

Solution-
I checked the phantom power at the mic panel with that mic plugged in. Sometimes a weak connection between the desk and xlr connector will give you a suspicious voltage. That looked fine. I then started testing the pad switch and pot. The pot was bad. When I mic'ed a boom box I discovered that the pot didn't give anymore gain after the 30 degree mark. Under some pressure the pot will track correctly. It will be replaced.
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