Noise caused by chain but not any individual component

[dapolk]

Hey how's it going. I'm having a very interesting noise problem that I cannot isolate in the following chain:

Focusrite Saffire Pro 40 output (using a hardware insert in Logic during mixing)
into API 312 (I built and have used for years no problem)
printing to Otari MX5050 mkiii (recent acquisition)

back into a Focusrite Input

an image of the noise is attached. sounds like white-ish noise w/ a bit of crackle

I know I'm sending a line level signal into the API pre, it's attenuated about -20 before leaving the output so it's not distorting the pre or anything.

So here's the interesting part -

If I just send the signal to the API and back in, there's no noise at all, great S/N ratio - have done this a ton

Same if I just send the signal only thru the tape and back, on every channel of the tape deck,

If i take a mic, or an ipod or anything, and send it into the API, to the tape, there's also no noise...every channel...pristine

Back to the problem chain - if I'm monitoring the tape output in Sync/Input mode, there's no noise...only in Repro...

The noise is getting recorded to the tape. I printed it and listened back off of Sync head. While monitoring off a Mackie which is paralleled off the tape outs


All 8 outputs of the Focusrite introduce approx. the same level of noise when used. Outs 1&2 are somewhat quieter, I guess b/c they split out to some Mon outputs on the interface and that's somehow affecting it? But it's still unacceptably loud using those outs as well.

I have an LA2A I built as well, and am sending out a different track to that, to tape, no problems at all

Interface, LA2 and API are all plugged into same power strip, tape is on a different one but doesn't sound like a grounding problem...

All pieces are connected via patchbay, its not the cables either

So what about the interaction of these 3 pieces would cause such a noise...I'm pretty mystified  ...anyone have any ideas?

Thanks!

 

[Pip]

If what I am hearing is you only have it when listening to recorded signal from playback in Repro. Its the tape itself. It has hiss. When was the last time you aligned your machine with an MRL tape and is your bias right for the tape you are using?

 

[dapolk]

I haven't aligned it yet, but this cant be the issue b/c the noise isn't present on any channel of the tape deck when recording to it with any other permutation of the chain. I.e. using a mic thru the API to tape, or sending a track out of the interface, but skipping the API to tape. It sounds great in those situations

 

[radardoug]

Sounds like when you record it, you are listening to input (sync will go to input) and then playing back listening to repro.

 

[dapolk]

This is not the case unfortunately...the intended point of the chain has been to use the tape as part of a mixing print...so i've always been monitoring off of repro while rolling tape to listen to what i'm actually getting.

In this mix I've been sending 7 tracks from the computer to the tape, and the only 2 that come back with the noise go through the API's before the Otari. However, using an insert with only the API's, I don't get the noise at all, even with gain cranked. And skipping the API's and going straight to tape, I don't get this noise on any channel, in repro. The first thing I ruled out was that it's not any of the tape deck channels. I also tested a mic, as well as an ipod thru the API's, into the tape, in repro, with no problems...

It seems to be an interaction of all 3 pieces which I haven't encountered before.
I'm also sending lines out to an LA2 and a Scully 280 channel, both to tape, no problems there either.

 

[radardoug]

Are you running the API's with gain?

 

[dapolk]

No, just adjusting the send level from the hardware insert, API gain's at minimum

 

[radardoug]

And what is that minimum gain? I cant quickly find any info, but I suspect it would be 20 dB.

 

[radardoug]

Hmm, no further reply! Did you figure out the stupid thing you were doing?

 

[dapolk]

Haha I wish...been on vacation, will get back to it in a couple days.

Not sure about the minimum gain.