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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 25, 2013, 01:47:24 AM »
Done.
Input on the tape lift "issue" most welcome!
Input on the tape lift "issue" most welcome!
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 23, 2013, 02:06:45 AM »
Exactly, it's obviously important to make sure I look a little stupid for asking, but then it changed to "pretty sure".
It is what it is, I will leave it as it is and it seems like it shouldn't be in contact as you say :)
One more thing, the tape lift lever is a little wobbley during rw/fw which makes me a little nervous that it's in contact with the play head, resulting in extra wear. I guess it's due to vibrations, but for now I hold it down a little to keep it steadier.
I don't know if it's possible to do anything about this? When I look at the mechanics it seems that I can't "tighten" it without possibly interfering with the pinch roller arm movement.
It is what it is, I will leave it as it is and it seems like it shouldn't be in contact as you say :)
One more thing, the tape lift lever is a little wobbley during rw/fw which makes me a little nervous that it's in contact with the play head, resulting in extra wear. I guess it's due to vibrations, but for now I hold it down a little to keep it steadier.
I don't know if it's possible to do anything about this? When I look at the mechanics it seems that I can't "tighten" it without possibly interfering with the pinch roller arm movement.
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 18, 2013, 11:02:41 PM »
Thank you Tim. Well, I don't see any instric value in tape contact, just want to make sure there's nothing wrong with my deck.
Besides, in other forums I have been told it should, hence the confusion.
I tilted the entire post a little to the "right"( looking at the front as in the picture below) as I think it wasn't entirely straight but still no contact with the tape so I don't think it's even possible on my machine. If Imove it any more to the right it will bump into the capstan axis. Of course one problem that I'm fearing, if you say that it should be possible to get contact, is that the capstan axis might be slightly bend "downwards". I sure hope not..
Before-picture attached.
Besides, in other forums I have been told it should, hence the confusion.
I tilted the entire post a little to the "right"( looking at the front as in the picture below) as I think it wasn't entirely straight but still no contact with the tape so I don't think it's even possible on my machine. If Imove it any more to the right it will bump into the capstan axis. Of course one problem that I'm fearing, if you say that it should be possible to get contact, is that the capstan axis might be slightly bend "downwards". I sure hope not..
Before-picture attached.
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 18, 2013, 01:33:29 AM »
Recapped now. I also noticed some tangent on the rec head to fixed that and even re-aligned the head height because it was a bit off.
I know experts say you shouldn't touch it but I was carefully observing the signal and found a sweet spot that worked good both sound wise, and I could visually see that the head was much better in line with the taoe and not scewed in any way. Then re-aligned and recalibrated and she sounds really good now. BUT, then I noticed another problem :( I don't know if this can be fixed or if I should just sell it again:
Tape is not in contact with the bronze guide between play head and pinch roller. Laquer on the nut is intact, so I don't think THAT have been touched, I think it's the vertical alignment that's off, a little tilt to the left (looking at the machine standing) which I guess should be OK to mess with (screw that holds guide piece to the block? Though, I miss around 2-3 mm to get tape contact and I can't imagine getting it by just tilting it? But then again, neither head or pinch can be horizontally moved right, so it can't be anything else?
I know experts say you shouldn't touch it but I was carefully observing the signal and found a sweet spot that worked good both sound wise, and I could visually see that the head was much better in line with the taoe and not scewed in any way. Then re-aligned and recalibrated and she sounds really good now. BUT, then I noticed another problem :( I don't know if this can be fixed or if I should just sell it again:
Tape is not in contact with the bronze guide between play head and pinch roller. Laquer on the nut is intact, so I don't think THAT have been touched, I think it's the vertical alignment that's off, a little tilt to the left (looking at the machine standing) which I guess should be OK to mess with (screw that holds guide piece to the block? Though, I miss around 2-3 mm to get tape contact and I can't imagine getting it by just tilting it? But then again, neither head or pinch can be horizontally moved right, so it can't be anything else?
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 12, 2013, 02:40:11 AM »
Trimmers have been replaced and setting are much more stable now.
Azimuth adjustment and frequent head cleanings also gave me a much flatter frequency response. I'm gonna recap also but so far things are sounding much better!
Another thing I noticed yesterday though, when recording I get a little bleed through fr?n the direct input even when monitoring the repro. When recording a snare track for examble you can hear the hit in the background before the tape signal.
It's barely audible but still, is this a problem or as designed?
It's like the signal is bleeding through from the preamps or rec head or something and it happens the first time I record onto that tape so I guess it can't be print through either.
Azimuth adjustment and frequent head cleanings also gave me a much flatter frequency response. I'm gonna recap also but so far things are sounding much better!
Another thing I noticed yesterday though, when recording I get a little bleed through fr?n the direct input even when monitoring the repro. When recording a snare track for examble you can hear the hit in the background before the tape signal.
It's barely audible but still, is this a problem or as designed?
It's like the signal is bleeding through from the preamps or rec head or something and it happens the first time I record onto that tape so I guess it can't be print through either.
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 12, 2013, 12:56:19 AM »
Thank you
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 11, 2013, 02:04:10 AM »
Tim, English is not my native tounge so "sorry" for the misunderstandnings.
Technical terms in combination with translation is gonna cause that.
I had already ordered a new drum when this thread was created so I didn't "ignore" your advice, even thoug that video seemed to suggest noise disappeared with counter still engaged, but must have seen wrong.
I'm not 100% sure which part you mean with "pulley bearing".
Btw, mine is missing the small toothed band. Are there versions without it or has is simply been "lost"?
Technical terms in combination with translation is gonna cause that.
I had already ordered a new drum when this thread was created so I didn't "ignore" your advice, even thoug that video seemed to suggest noise disappeared with counter still engaged, but must have seen wrong.
I'm not 100% sure which part you mean with "pulley bearing".
Btw, mine is missing the small toothed band. Are there versions without it or has is simply been "lost"?
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 10, 2013, 11:22:39 PM »
You are absolutely right Tim, it was the counter.
Counter belt isn't touching the hub or the brake band, sounds like it's coming from the actual counter (gears) rather that friction from the belt.
I removed the belt for now, any tips on how to fix that?
By the way, removing the height washer solved the winding issue, someone previous to me had even put two washers on the left side.
Counter belt isn't touching the hub or the brake band, sounds like it's coming from the actual counter (gears) rather that friction from the belt.
I removed the belt for now, any tips on how to fix that?
By the way, removing the height washer solved the winding issue, someone previous to me had even put two washers on the left side.
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 10, 2013, 12:12:40 AM »Nice video! (Even though I don't speak a word of French)
Now, I wonder if that brake lining tape can still be found?
If so, it sure would be a lot cheaper than replacing the drums.
I think it is, especially in the US but I managed to find a drum in a refurbished state for a reasonable cost so went with it.
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 10, 2013, 12:08:57 AM »One of the bad engineering practices commonly recommended when pretending to calibrate these decks is to use bias trimming to get the frequency response closer, and I see that's just what you're trying to do.I know that, and I don't WANT to do that, it's just what I HAD to do to get somewhat descent results. But I also know it shouldn't be necessary, that's the reason I made this thread!
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And on another note: Tim generally gives very good advice on this forum, so I'd recommend not dismissing his suggestions out of hand. Whenever we are using measurement instruments our first job is to check the measurement setup and make sure it is really measuring what we think it's measuring. It's trickier than we think--at least until we have fooled ourselves a few times, then we gain a respect for this requirement.
This was not my intention, it was I who asked for help, right?
I'm just a little tired of the perfuctory bashing of digital measuring methods, without the technical explaination!
Just give me the techincal reason for not doing this digitally and it's fine, for some reason you rarely get that though.
The whole "Don't buy ANYTHING analog, and most of all DO NOT try to do anything yourself unless you have spent thousands of dollars on a whole setup of analog measuring gear". You get that in EVERY forum, 9 of 10 members and just discouraging. Then 1 in 10 will come along and ask "Tell me what you know and what gear you are using and then we'll see if it will cover what you are trying to do". Basically just not assuming you're an idiot. Most of the time it turns out that it will work just fine.
Thank you for a lot of good input!
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Tape Tech / Re: Revox A77 - calibration problems.
« on: September 09, 2013, 06:35:28 AM »It's not possible that bass response (20 to 1K) changes radically with typical bias levels as you claim it does. That means your measurement methods and measurement equipment (computer-based) is likely flawed. Only use an analog sine-tone generator and analog AC millivolt/DB meter for setting bias, EQ and levels.
http://www.ebay.com/itm/TEST-EQUIPMENT-LEADER-LMV-181A-AC-Millivoltmeter-Wide-Bandwidth-Audio-Volt-/151115625692?pt=LH_DefaultDomain_0&hash=item232f3174dc
http://www.newark.com/tenma/72-505/audio-signal-generator-frequency/dp/66F3575?in_merch=true&MER=ALT_N_L5_ElectricalAndElectronicTest_None
I don't really see the problem using DAW, a good sound card and good software for calibration.
The frequency response is enough and even if the AD FR isn't 100.00% flat a DA/AD loop and good measuring software will tell you how to compensate. Not that that's the case with my setup.
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An addition problem (other than your inaccurate measurements) could be the condition of the heads. They could be damaged from long-term oxide deposits (tape residue left on heads for years can cause corrosion). They could still be dirty. They could have been misaligned by someone and they could be worn-out.
5-6 db overbias with SM911 tape @ 7.5 ips @10K should give you a flat HF (1 and 10K the same level) after adjusting record EQ. It should also give you a good (< 3% ) distortion level at peak record level (+6 VU). Be aware that turning the bias pots CW does not always mean you are increasing bias to the record head. On some decks increase is CCW (I can't recall right now how the A77 is oriented).
Yes, turned out rec head was badly misaligned. This has been corrected but I haven't been able to recalibrate everything yet so I've yet to see whether this caused the weird low end bump or not. Thanks for the help.
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 09, 2013, 05:54:41 AM »Grinding noise during fast wind is likely not a problem with brake drum lining. In fast-wind mode, the brake bands do not (should not) contact the drums.
-check left tape guide ball-bearing or counter as sources for noise during fast-wind .
-If you have noise only when stopping from fast wind, then you could have defective (sticky) brake drum linings. That sometimes can be repaired by cleaning the brake bands and baking the drums. Baking can remove the stickiness of the drum lining cloth.
To answer your original question, concave side should face screw. Both orientations will work, however. It's not critical.
I get the same noise as in this video, only from the right side:
http://www.youtube.com/watch?v=8h8421oWOOQ
There the noise disappears as soon as the break band is removed, so to me it looks like a worn felt.
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 09, 2013, 05:51:22 AM »
Thanks a lot!
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Tape Tech / Re: Revox A77 - Brake drum belleville washer
« on: September 06, 2013, 03:18:27 PM »
Thanks, I'll check that out!
By the way, tape is wound really close to the inside of the take up reel and I've been looking into the alternative to remove the height adjustment washer (part 16)
Is that safe to do without inducing more ware to the brake parts or emergency precaution only?
By the way, tape is wound really close to the inside of the take up reel and I've been looking into the alternative to remove the height adjustment washer (part 16)
Is that safe to do without inducing more ware to the brake parts or emergency precaution only?
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Tape Tech / Revox A77 - Brake drum belleville washer
« on: September 06, 2013, 02:10:08 AM »
So, I've been having problems with grinding noise at FW. It is probably caused by worn felt on drum so I'm gonna replace the brake drum.
Took it apart yesterday to see if previous owners has done any changes and I just need to double check something with you.
The belleville washer highlighted in my attachment, which way it it supposed to be mounted.
Convex side facing screw or vice versa?
Took it apart yesterday to see if previous owners has done any changes and I just need to double check something with you.
The belleville washer highlighted in my attachment, which way it it supposed to be mounted.
Convex side facing screw or vice versa?
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