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.
GReg-Electrical Tech Journal
102Greg,
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
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
GReg-Electrical Tech Journal
1039/30/4
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.
Solution-
"Rrrarrr"
Sound Effect: wrench whacking a tension wire
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
Greg Norman FG
GReg-Electrical Tech Journal
10510/4/4
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.
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.
Greg Norman FG
GReg-Electrical Tech Journal
10610/5/4
Sontec MEP-250B equalizer-
Ripped out old power supply parts. Preparing it to be used with an external power supply.
Sontec MEP-250B equalizer-
Ripped out old power supply parts. Preparing it to be used with an external power supply.
Greg Norman FG
GReg-Electrical Tech Journal
10710/11/4
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.
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.
Greg Norman FG
GReg-Electrical Tech Journal
10810/12/4
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.
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.
Greg Norman FG
GReg-Electrical Tech Journal
10910/13/4
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.
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_Archive on Thu Oct 14, 2004 5:28 pm, edited 1 time in total.
Greg Norman FG
GReg-Electrical Tech Journal
11010/14/4
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:
I changed the resistors to 130K and it is still a bit too slow. More later.
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.
Greg Norman FG