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Postby greg on Thu Apr 29, 2004 10:45 pm

4/29/4
Yamaha 1010 Delay-
I replaced the power transformer (240V) with a new toroid transformer (120V) so we can use it now.

Problem-
Neumann 563 has a week and trebly output.


Solution-
Broken solder joint in the cable connector. This was for one of the output legs. I should have done a continuity test on the cable first, but did a lengthy test on the mic to make sure it was working instead.


Problem-
Ampex ATR 2-track #3: Input signal bleeds through when output is set to repro.


Solution-
I swapped the I/Os to see if the problem followed them and the problem went away altogether. I put the I/Os in their original position and still no problem. I left it for observation over time. 2 days now and there and all is good. Must have been something with the connection.
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Postby greg on Mon May 10, 2004 7:35 pm

5/10/4
Fixed cables.
Worked on M-S Matrix mods and faceplate.
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Postby cgarges on Mon May 10, 2004 9:57 pm

greg wrote:Worked on M-S Matrix mods and faceplate.


Oh, do tell.

Chris Garges
Charlotte, NC
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Postby greg on Tue May 11, 2004 9:48 pm

I'm creating the trims for the left and right outputs. They will range from -12dB to +12dB. I'm also seeing if I can use a burlier output op amp. The Burr Brown OP176 is a likely candidate.
I'm going to have a nice new faceplate made engraved with the legends. I placed the order today.
I can't wait.
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Postby greg on Tue Jun 01, 2004 6:29 pm

6/1/4
Problem-
Studer A820 Studio A (#2 machine) Channel 14 output not making it to the patchbay.

Solution-
Edac pin loose on the output connector on tape machine snake.
snooze
Created new mic pads for studio A's patchbay.
Repaired to bad mults on that patchbay.
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Postby greg on Tue Jun 08, 2004 3:35 pm

6/2/4
Problem-
C-12 s/n-38 PSU s/n-19477 has no output.

Solution-
There was a bad regulator tube (150B2). Replaced, everything is well.

Problem-
Neuman SM-2 PSU has no output on the top capsule.

Solution-
It was just a broken solder joint on the output XLR connector.
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6/14/4

Postby greg on Mon Jun 14, 2004 9:03 pm

6/14/4
Problem-
Sontec has noisy op amps.

Solution-
This is actually an old problem that I'm trying to find a new solution for. The op amps of concern are the input and output amps. They are home made discrete amps. I made a daughter board that will host a normal monolithic DIP op-amp (to replace the old ones). The board regulates the incoming bipolar power supply rails +-28 volts down to +- 22 volts. This is so I can try out other amps.

My food is here.
More later.

12/9/5
My plan now is to replace the input section with a Jensen input transformer JT-6110k feeding a 990 (or like amp), and a 990 (or like amp) to replace the output amp.
The power will be coming from a GML PS (puts out a rock stable +-18VDC and +-28VDC). The 28v rails will be regulated down to 24v in the Sontec box with 7824 and 7924 regulators (replacing the TO-3 transistors on the back panel). This will undoubtedly change the "sound" of the unit, but I'm not too concerned with that as it will be more predictable with different sources. More important, it will not be a thunderstorm sound effect generator. I will let you all know how it comes.
Last edited by greg on Fri Dec 09, 2005 3:47 pm, edited 4 times in total.
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Postby greg on Mon Jun 21, 2004 7:08 pm

6/21/4
Problem-
GML limiter Left channel not passing audio, unless in bypass mode. This happens only once in a while.

Solution-
I pulled it out of the rack and set it up on the bench. Now I am waiting for it to fail so I can find the problem. Jeff at GML has given me the info on what to look for. If it isn't one of the three main amps I'm sending it back. That thing is beautiful and insanely complex inside.

Later- Found that when I kick the input signal up in level the channel freaks out. The effect as seen on the oscilloscope is the sinewave (input signal) gets half its wave clipped as if one half of a push-pull circuit shut down. The output of the channel looks like a half wave rectified version of the input (not DC though, but centered around ground). I probed around and thankfully found the problem right off the input op amp. I got a new one from Manley (in cahoots with GML) and installed it (7/1/4). After a bit of testing no problems so far.


Problem-
Old Josephson e22s mic not responding S/N 4311.

Solution-
Tried remounting the ground screw to get a better contact with the shell, (this was a problem with the earlier prototypes) but the problem was not that. I'll probably send it back for them to look at.

Problem-
Studer A-820 MCH in studio B (blacksides) in "edit" mode has a stuttered/ chunky motion when manually rocking/scrubbing. In "edit" mode the transport is in a constant tension (servo) state. This means you can move the tape with a light hand on either reel and have constant tension across the heads (so you can hear your edit point). It is a complex feature which allows you to smoothly scrub with one hand, and mark your edit point with the other
.
Solution-
I built a special test jig as per the manual's description and calibrated the two tension sensors. This involved removing all the rollers, head block and top plate off the machine. While everything was removed I cleaned all the parts (just cause I was there) and the deck top. After everything was put together I re readjusted the tensions and the edit mode worked smoothly.
Last edited by greg on Fri Sep 23, 2005 7:59 pm, edited 4 times in total.
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Postby greg on Thu Jun 24, 2004 1:49 pm

6/23/4
-Tested out the replacement op amp for our Sontec eq. So far so good.
For now I am just replacing the input op amp with a 5534 because of its high supply voltage and low noise capabilities. I will do more research on finding the best op amp for that voltage range (+-22v). I need it to be quiet, fast, and low on distortion.
Problem-
(Studio B) B&K Precision oscilloscope CRT gone craaaazy. Looks cool though. Some sort of Tron visual going on.

Solution-
To be sent back to B&K for repair and calibration.
Last edited by greg on Fri Jun 25, 2004 6:00 pm, edited 1 time in total.
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Postby greg on Fri Jun 25, 2004 5:54 pm

6/25/4
Problem-
Altec 175 has no output.

Solution-
Cleaned and reseated the tube (5840). Works now.
I narrowed the problem down by swapping parts with a working 175 system.
PSU to
Mic body (includes tube and permanently attached cable) to
capsule
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Postby greg on Mon Jun 28, 2004 6:13 pm

6/28/4
Problem-
Mann amp from ebay has a loose multi-section cap and missing tubes.

Solution-
Re-bent the mounting brackets and hot glued the case of the cap (so it wouldn't rattle). I re-wired the power with a safety ground and IEC connector, and replaced a few tubes. The amp works.
Last edited by greg on Thu Jul 01, 2004 3:50 pm, edited 1 time in total.
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Postby greg on Thu Jul 01, 2004 3:34 pm

6/29/4
Assembled the new version of our M-S matrix box with the output trims and installed it in studio A.

7/1/4
Got GML op amp and put it in the limiter. See 6/21/4 for more details.
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Postby danmaksym on Thu Jul 01, 2004 7:06 pm

Greg,

Can we see an updated schematic and/or have some details about how the output trimmers were added to the MS Matrix?

Thanks

Dan
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Postby cgarges on Mon Jul 05, 2004 5:05 pm

Hey Greg, the MS Matrix looks great. I love the lighted Electrical logo.

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Postby greg on Tue Jul 06, 2004 2:04 pm

Thanks. Were going to try to get a better photo soon and some new knobs.

Can we see an updated schematic and/or have some details about how the output trimmers were added to the MS Matrix?


I've still got some things I want to try out before committing to a design.
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Postby greg on Wed Jul 07, 2004 5:10 pm

7/6-8/4
Problem-
Neve 3115 chan 1 has distortion and low frequency roll off.

Solution-
Bass frequency pot dirty, and caused off and on roll off. It's been cleaned and works now.

Problem-
Neve 3115 chan 2 is limited to 45 dB gain (should get to 80 dB).

Solution-
Cold solder joint on the input sensitivity switch. Re-soldered now works like new.

Problem-
AKG 414 S/N ? noisy in a short session.

Solution-
Worked fine on the bench and in the studio when I looked at it. Must assume there was a bad connection somewhere when problem was noticed.
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Postby greg on Fri Jul 09, 2004 7:16 pm

Problem-
John Hardy M-2 channel 3 no output.

Solution-
Pin 2's wire broke off on our output connector. The preamp was working fine.


Problem-
Neotek Series II- Echo 2 solo push button shaft broken.

Solution-
Replaced the button.


More Sontec work.

Who's snoring!
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Postby greg on Mon Jul 12, 2004 7:12 pm

7.12.4
More Sontec op amp work. I got the 990 amp working as the output driver and a standard 5534 chip as the input amp just for testing. I noticed a bit of a buzz noise on the right channel (unrelated to what I was doing). This is from the power supply being an inch away from the audio electronics. Not a good layout for a fancy eq.
More later.
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Postby greg on Tue Jul 13, 2004 1:31 pm

More on the Sontec
I built a channel with the 990 op amp as the o/p driver (5534 as the i/p amp) and did some listening tests yesterday. After calibrating the offsets and noiseless switching circuit I couldn't notice a change in sound quality. I had a mono signal split to the two inputs. I monitored the o/p as a stereo signal with the eq in bypass (signal goes through the two replacement amps in bypass). There was no deviation from mono. I like listening to things this way to see if there is a difference, then trying find out what the difference is (phase shift, eq, level, and so on). In this crude listening test the two channels sounded almost identical (eq in and out). The noise floor was not improved by the new amps, but it wasn't worse either. My main complaint with the Sontec amps was that they occasionally made low level hissing and crackling noises (even new ones!).
I cut the test short when I discovered a harmonic of the power supply regulator on the right channel (very quiet, but there). This was with the eq filters at max gain. At first I thought the 990 was drawing too much current, but after I swapped the channel's op amps I realized that it was the power supply itself causing the problem. On our Sontec the bridge rectifier, a regulator, and main filter caps are about 1-2 inches from the right channel's amps and bypass circuit. The transformer is also on that side of the box. I brought the eq back to the shop and powered it up with the bench supply. No buzz. So now I am going to power it remotely.
Some other notes:
John Hardy said that his amp will work at 28 Volts but be a bit hot. He wasn't joking. It gets HOT. It's probably a good idea for me to regulate the +-28V down to 24V in the end.
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Postby greg on Fri Jul 16, 2004 9:06 pm

7/16/4
Problem-
Garnet BTO B260D S/N 5350 has a busted "stinger" switch.


Solution-
I replaced it with the deactivated "ground reverse" switch.


Problem-
Same amp has a bunch of 60-120Hz hum in any state when on (plugged in to 4x12 cab. Amp works well otherwise.


Solution-
I'm guessing, but I think it is a filter cap. We'll see Monday.
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