| Author |
Topic: MB Studio Pre, 16 kHz Hum |
Tom Gorr
From:
Three Hills, Alberta
|
Posted 20 Aug 2004 9:18 am |
|
I bought a used Studio Pre off ebay.
Although I don't have much for sensitivy or pitch recognition at such frequencies, I can sense/hear a high freq screech both using main outputs to speaker and recording outputs to board.
Any of the electronic guru's know whats up?
Note that the reverb unit was removed, but the reverb tube is still installed. Would this cause such a problem?
|
|
|
 |
Brad Sarno
From:
St. Louis, MO USA
|
Posted 20 Aug 2004 11:54 am
|
|
If you're hearing a 16kHz tone, the very first place is always to look to see if there's a TV or CRT screen on nearby. Televisions have a scan rate of 15.7kHz or so. Sometimes I can pick up that tone in my audio gear if the TV upstairs is on. Try to keep a good distance from a TV or just plain turn them all off. I'd start there.
Brad Sarno
|
|
|
|
Tom Gorr
From:
Three Hills, Alberta
|
Posted 20 Aug 2004 2:29 pm
|
|
The TV is two rooms away, 40 feet?
I do have a Roland VS-890 mounted about 1 foot above it, but it is off when I play directly through amp. Still get the high freq...I think. Its hard to hear. |
|
|
|
John Daugherty
From:
Rolla, Missouri, USA
|
Posted 21 Aug 2004 4:12 am
|
|
If you know where the reverb output connected to the amp, connect a jumper across the two connections. This will ground the input to the reverb amp.
There could be a microphonic tube in the circuit or a dirty tube socket. Try wiggling the tubes in the sockets and tapping the tubes(or replace tubes if you have them) to see if you can locate a fault.
If this fails, a technician may need to troubleshoot the preamp to localize the fault.............JD |
|
|
|
Tom Gorr
From:
Three Hills, Alberta
|
Posted 21 Aug 2004 9:58 am
|
|
I'll give that a try, John. A
Any precautions to keep from electrocuting myself? Never worked on tube stuff before...[This message was edited by Tom Gorr on 21 August 2004 at 10:59 AM.] |
|
|
|
Bobby Lee
From:
Cloverdale, California, USA
|
Posted 21 Aug 2004 10:13 am
|
|
Sounds like a bad tube to me.
There is no shock hazard when changing tubes. Get a 12ax7 that's known to be good, and swap it with the first tube (closest to the input jack). If you still hear the squeal, swap the one you took from the first socket with the one in the second socket. Repeat the process for all of the 12ax7 tubes.
I think that the last tube might be a 12at7. It doesn't have a lot of gain, so its unlikely that the noise you're hearing comes from it. If it's not one of the 12ax7 tubes, and you've eliminated any video or digital equipment nearby as the cause, it's time for a trip to the repair shop. |
|
|
|
jim milewski
From:
stowe, vermont
|
Posted 24 Aug 2004 3:39 am
|
|
| man you have good ears, are the nieghborhood dogs showing up? |
|
|
|
Tom Gorr
From:
Three Hills, Alberta
|
Posted 27 Aug 2004 8:05 pm
|
|
Thanks for the help. Just in the middle of moving - so I'll try out the suggestions next week.
Jim - I was getting 'fatigue' at relatively low volumes, and higher volumes were making me cringe. THEN the dogs showed  .[This message was edited by Tom Gorr on 27 August 2004 at 09:06 PM.] |
|
|
|
