A800 Noise Floor Testing

[Sisu MT]

With the help of several of the good people in this community, I've managed to bring a somewhat long in the tooth A800 MKIII back into operation and have been doing some test recordings recently. Most caps have been replaced throughout, the heads have been aligned and all meters and cards have been calibrated. What I've noticed in the recordings is that some of the channels have an almost undetectable noise floor, others have a bit more noise, but still low and a couple have, well, an unacceptable noise level.

My current questions to the good folks here:

• What is the scientific way to measure the noise level on the recorded tape? I've found several approaches in the internet, but not clear on this.
• Iis there a published maximum target noise level by Studer? If not, what level do folks shoot for? Been unable to find this...
• What are the key factors the generate too much noise? ie., out of spec components? improper calibration? other? For the couple channels that are pretty noisy, they've been given new caps like the quieter channels as well as the cards being calibrated in the same way. I've completely disassembled and reassembled the machine including refitting/reseating all connectors, so I doubt it's a wiring issue, but who knows....there some many connections in here and all have a chance to glitch.

Many thanks in advance for your thoughtful replies.

Pat Maki

 

[gyraf]

have thoroughly defluxed the heads?

 

[ruffrecords]

There are three sources of noise you need to consider and preferably measure.

1. The noise of the replay amp itself. You can usually measure this in playback mode with the tape paused. THis noise level is usually a good 10dB below virgin tape noise.
2. Tape noise. Measure this by playing some virgin tape. This noise level is usually significantly higher than replay amp noise.
3. Bias oscillator noise. Measure this by recording no signal to a blank tape. This noise level is usually a couple of dB above virgin tape noise but it in a well designed recorder it can actually be lower than virgin tape noise. However, in a poorly designed or faulty recorder it can be much higher and my suspicion is that this is the source of your problem.

Cheers

Ian

 

[Sisu MT]

have thoroughly defluxed the heads?

Actually it's been a few sessions since I've demagnetized. Will do so before continuing. Thanks for the reminder!

 

[Sisu MT]

There are three sources of noise you need to consider and preferably measure.

1. The noise of the replay amp itself. You can usually measure this in playback mode with the tape paused. THis noise level is usually a good 10dB below virgin tape noise.
2. Tape noise. Measure this by playing some virgin tape. This noise level is usually significantly higher than replay amp noise.
3. Bias oscillator noise. Measure this by recording no signal to a blank tape. This noise level is usually a couple of dB above virgin tape noise but it in a well designed recorder it can actually be lower than virgin tape noise. However, in a poorly designed or faulty recorder it can be much higher and my suspicion is that this is the source of your problem.

Cheers

Ian

Thank-you Ian! This is exactly what I was hoping for. A couple clarification questions:

1. Suggestions on most accurate way to read dB's? Ie., checking output voltage and converting it? using VU plugin? etc...I have a scope and some plugins like REW and NAK T-100.
2. Replay amp - Don't have a pause function on this one, so wondering if simply having the channels in Repro mode and the machine on will suffice? If not, possibly running in Play mode without tape loaded?

Br,
Pat

 

[RuudNL]

Running in play without tape will usually work.
I think you only have to 'fool' the light sensitive cell by covering it...
(And maybe simulate tape tension.)