revox b77mkII

[billy]

Hi guys,

I know the revox is not really a pro machine, rather consumer semi-pro...
But I have this strange problem which to me seems like something that can be fixed.

There is an issue with noise... it's simple white noise kinda, the important thing is that it's not present when the tape itself is played, it's present as soon as the recording starts.

So as far as my brain can understand all this :-), the playback head etc, are all functioning fine.
This would be on the recording part, maybe noisy amps, recording head ? I have no idea where to start. Also this machine hasn't got a lot of places to tweak anything, as far as I can see, there's no bias control, etc...

Any help would be of course, greatly appreciated, I tried on other general forums but without a lot of luck, this seems like the forum of the "connoiseurs" lol :-)

Kindest regards,

Billy

[ironbut]

Hi Billy, welcome to the forum. Please don't think that everyone here has one or several Studer 820's, Nagra T's, or ATR100's. In fact, the majority of members here have prosumer machines and there is a wealth of knowledge on most every machine that could be included in that category.

Regarding you problem, I think it would be useful if you could go into a little more detail on the symptoms. For instance;

When you say it's only present when recording is engaged. Does this mean that you only hear it when you're monitoring while recording and you don't hear it when playing back the same recording later on?
What are you recording? Some details on your signal chain might be useful.
What level is this white noise compared to the recording you've made (comparison to the quietest instrument might be good)? Maybe comparing it to the tape hiss level?
Is the noise equal in both channels and does it increase with recording level and/or output level?
Is the noise consistent in level and frequency and are there other low level noises inside of it (pops or buzzes,..listen closely for this)?
Is the noise on both your outputs and headphone jack?

I'm not the B77 expert around here but I think if you could answer these questions, it'll give the ones who are a better shot at diagnosing the problem.

[billy]

Hi, here's already some more information:

The recording is straight from the computer through motu interface to the tapemachine.
You don't hear the noise when monitoring, so that probably means, the line amps are not the issue...
the noise is exactly the same on both channels and there's no pops or buzzes.
the noise is more clear when silent parts of a song are recorded and it stays there but you pay less attention to it on the harder parts. It's like the noise is added as soon as a recording is started, and it's always at the same volume, it's a basic noise that comes on the tape as soon as I start recording. I'm going to do a test and record the noise itself, also a basic drumloop maybe, so you can hear the kind of noise.

[Tim]

You stated you don't hear the noise when monitoring.   In record mode, you have two monitor modes:  source monitor and tape monitor.   Are you saying you don't hear the noise in both of these modes?

BTW, play mode and record tape monitor modes are identical....If you hear a noise in play mode, you will hear it in record tape monitor mode.

Is what you are hearing simply tape hiss?  Or excessive tape hiss?  Also, if it sound like tape hiss with a lot of low-frequency content, then it's a magnetized play head.  I have seen this problem many times (and only) on Revox A77 and B77 decks.  Demagnetizing fixes it. 

[studiochap]

If you demagnetize, it helps to have  a bit better demagger than the entry-level black ones with the red tips...

Anyway, you need to start with the demagger a metre ( or yard..) back from the head or guide you're going to demag.

Switch it on and bring it slowly into the target, move it gently up and down the head ot guide several times, and then slowly withdraw it back to where you started before either switching it off , or moving in to demag the next head or guide. Do NOT wave the demagger from side to side in front of the headblock assembly...this would not be good...:-)

I note that what  you're hearing is not  tape hiss as you dont hear it when the tape is played, only when you enter record.

The other thing that can cause (additional..)  hiss is problems with the bias signal which is fed to the record head. Bias setting is a compromise between noise and HF response, and you could have a misaligned bias setting, or a noisy bias oscillator maybe. Or even an incorrect HF eq setting or noisy record amp. I have very little experience with Revox, and that not for years  ( although 34 years experience with pro studio tape machines..) and  can't remember offhand about where the alignment stuff is.


The other thing is a possible level mismatch between the MOTU and the recorder. From memory the B77 isn't a +4dB line level machine (  although I could be remembering incorrectly..)  Maybe your MOTU is putting out +4? You don't say which  MOTU you have.

Best regards,

Gwyn