Premier Rock Forum

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.

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.

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

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

Chris Garges
Charlotte, NC

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.

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.

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!

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.

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.

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.