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Spastic VU Meter

T

TinCanAlley

Duck, you sucker!
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If you have two VU meters and one moves slowly and accurately, but the other one only moves smoothly at lower levels and then gets jumpy at higher levels.....is this the meter or the control circuit? It's like watching the needle of a SPL meter in slow response and then in fast response. If I put a steady tone into the inputs the needles are equal, though. It also pegs in the red when it starts to over react even though the signal doesn't go over 0db.

Thanks!

Oh, this in for an Akai 4000DS MkII R2R.
 
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Let's think about this. I guess you are in record mode? I think that many of the circuits just "monitor" the signal level. For example, I have a few Sansui 9090DB receivers. One of them had a VU meter that did not move, however the signal was equal. I looked over the schematic and saw a meter adjustment pot on one of the boards. The service manual gives instructions about how to adjust the meter pots. When I tried to adj the pot, it immediately started working. However, exactly where it was in sync with the other channel, it dropped to the peg again. Dead spot on the carbon trace of the pot.

I guess what I am beating around the bush about is that I don't think that they are very sophisticated. Maybe nothing more than an AC voltmeter connected to the signal path. I don't know this particular machine but I suspect that it has multiple switch contacts in the signal path and maybe there is some "fly in the ointment" there.

BTW, I forgot to ask. Is there any problem with the audio? Does it distort/break up? Is it playback, or during record or whatever?

Do you know of reel to reel forum? They may very well be more up on that machine. Don't hesitate to PM to me and I will give you a link to their site. Not a whole lot goes on there but never any sniping among members, they just help each other. I wish I could help more. (Sorry to throw so many questions at you!
 
kvflyer said:
Let's think about this. I guess you are in record mode? I think that many of the circuits just "monitor" the signal level. For example, I have a few Sansui 9090DB receivers. One of them had a VU meter that did not move, however the signal was equal. I looked over the schematic and saw a meter adjustment pot on one of the boards. The service manual gives instructions about how to adjust the meter pots. When I tried to adj the pot, it immediately started working. However, exactly where it was in sync with the other channel, it dropped to the peg again. Dead spot on the carbon trace of the pot.

I guess what I am beating around the bush about is that I don't think that they are very sophisticated. Maybe nothing more than an AC voltmeter connected to the signal path. I don't know this particular machine but I suspect that it has multiple switch contacts in the signal path and maybe there is some "fly in the ointment" there.

BTW, I forgot to ask. Is there any problem with the audio? Does it distort/break up? Is it playback, or during record or whatever?

Do you know of reel to reel forum? They may very well be more up on that machine. Don't hesitate to PM to me and I will give you a link to their site. Not a whole lot goes on there but never any sniping among members, they just help each other. I wish I could help more. (Sorry to throw so many questions at you!
Click to expand...

The audio is fine (no distortion, etc.). The needle acts the same in either record or playback. If the recording level is below -3db, it move smoothly like the other one. Once the signal goes up to 0db and above, it starts to move more quickly and pegs in the red as if all resistance is gone. It's not moving into the red because that's the signal level. It's moving into the red because it's out of control. The other meter is still moving slowly and in control.

Thanks for the reply. I'll check out the R2R forum. :thmbsp:
 
TinCanAlley said:
Thanks for the reply. I'll check out the R2R forum. :thmbsp:
Click to expand...

You are welcome. Is it possible to swap leads from one meter to the other? That would certainly tell you if it is circuitry or the meter. I don't know if that is possible. If the meter was sluggish, that would make sense but to go wildly higher, that doesn't make sense but I certainly believe you.

Do you want that reel-to-reel site link? I don't want to step on any toes here by posting it. But I will certainly give it to you...
 
kvflyer said:
You are welcome. Is it possible to swap leads from one meter to the other? That would certainly tell you if it is circuitry or the meter. I don't know if that is possible. If the meter was sluggish, that would make sense but to go wildly higher, that doesn't make sense but I certainly believe you.

Do you want that reel-to-reel site link? I don't want to step on any toes here by posting it. But I will certainly give it to you...
Click to expand...

I would have un-solder the leads to test that and that's why I'm saving that test as a last resort. My guess would be a bad meter as it loses control at higher signal levels, but it could also be a capacitor in the control circuit.

I don't think there are any rules against posting a link to other forums of interest. If I'm wrong I'm sure someone will kindly point it out, so go ahead and post the link.

Thanks
 
Hi,

Name of the site is Obsolete Media. Not a lot of traffic there but just like this forum, doesn't cost.

Here is the URL: http://www.obsoletemedia.com/geeklog/index.php

Hope that helps, we gotta keep those reel-to-reel machines going. I use one weekly, not as convenient as MP3 or Compact Disc but neat none the less. Also use Sony Elcaset...
 
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