Uher 4000 Report-L recording level problem - diyAudio
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Old 22nd December 2012, 06:25 AM   #1
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Default Uher 4000 Report-L recording level problem

There seem to be some Uher afficianados here, so perhaps someone can help me with this problem: my Uher seems to be fine mechanically, but when I try to record (using a Shure SM-58 and a proper XLR to DIN adapter cable, and FWIW, I the Uher AC power supply, not batteries), although the VU meter registers a strong signal and there is plenty of monitor volume in the speaker, the recorded level on playback is very weak. A test with an old recorded tape produces much better playback volume, although there is also some hum; the problem seems to be in getting a signal recorded to tape.
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Old 22nd December 2012, 03:34 PM   #2
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No bias? Does the machine erase previously recorded tapes? - if not the problem is probably the bias / erase oscillator.
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Old 23rd December 2012, 03:33 AM   #3
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This may be at least as old as my Sony TC250 reel to reel recorder (1967), that I put away in 2005 because it needed random members of a population of about 8 dozen electrolytic capacitors. I had already done the big power supply ones about 2000, when various functions developed imbalances, frequency filters, and other weird symptoms. the rubber parts were long gone, but i was using it as a LP/CD/FM preamp/10 W power amp until the sound got too weird. Do yourself a favor and change all the electrolytic caps, before you get into scope and schematic debug. Since it sort of works, check after every two to see if you made it better or worse. Amateurs like you and me make a lot of bad solder joints. Also, the parts you bought may have incompatibilities. Checking after two parts focuses your eyes on what you just did wrong when the sound deteriorates. I like caps rated at >3000 hours service life, these have the possibility of outliving you due to the superior sealant, and these tend to not have cost cutting features in other specifications also. At least the caps from premium vendors like farnell and mouser. Cleaning of brass/tin connections, while you are in there, addresses another common problem of transistor consumer electronics where the gold required for low energy signal connector reliability was left out.
When I get done upgrading the organs I have thought of addressing the rubber and cap problems of the TC250 recorder and the TC366 deck I own, but even though I have a desire to record masters with quality mikes, there is no agency able to do anything with a 1/4" quarter track master tape anymore. At least not around here. The shop in Louisville can convert VHS tapes to DVD, but VHS recorders have those vile Automatic Gain Control record circuits which are suitable only for low grade television shows.
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Last edited by indianajo; 23rd December 2012 at 03:40 AM.
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Old 23rd December 2012, 02:07 PM   #4
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Couid you post the schematic for the Uher?
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Old 26th December 2012, 06:32 PM   #5
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Thanks for the suggestions! I just got home from Christmas travels and will do more testing. Here is a schematic that I think is applicable.

<attachment removed>
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Old 26th December 2012, 06:36 PM   #6
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Old 27th December 2012, 03:44 PM   #7
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Pano: After 45 years you still have to worry about that? Totally outdated info, interesting only for historical purpose and rebuilding of antique equipment! The info is available on many sites, but I am just to lazy to sign-up for yet another audio site

Jack A: I was interested in where in the circuit they take of the meters and if the record heads and pb heads are seperate units. E
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Old 27th December 2012, 05:13 PM   #8
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Quote:
Originally Posted by mickeymoose View Post
Jack A: I was interested in where in the circuit they take of the meters and if the record heads and pb heads are seperate units. E
The 4000L has a single record / playback head which presumably is O.K. since playback works. Hence my question about bias / erase. It`s more than 40 years since I last worked on a Uher so I`m a little rusty.
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Old 2nd January 2013, 12:17 AM   #9
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The answer on erasing/recording over prior recordings is yes, prior material is inaudible on playback; new material is there, but very low volume, even though the meter is hitting the red (record volume knob is at 12:00 o'clock).
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Old 2nd January 2013, 08:02 AM   #10
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So the bias / erase oscillator is working, the problem is either in the bias feed to the head or the output stage to the head after the meter feed. Being unable to remember the circuit after all this time I can`t really go much further.
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