More tape machine woes: crosstalk in sync only

[Brian Roth]

I had to think waaaay back about the audio switching logic...last 2" session I did was probably 20+ years ago. I think Roadrunner and I have the same logic in mind.

Example....vocal overdub. machine "normal" mode..

Track armed, machine stopped. That track is in input mode.

Roll tape, but not recording. Sync mode.

Punch into record. Input mode.

Punch out. Sync mode.

Stop. Back to input mode.

Non armed tracks, sync mode regardless of anything.

Individual tracks had some override switches for "not normal" situations.

At least that's what I recall in my aging brain! lol

Bri

 

[radardoug]

Is the OP still in the house? You need to clarify. Just for the record, you are trying the most difficult test of sync performance, by having one track in sync between two in record. All us oldtimers know, YOU DONT DO THAT! Plan your overdubs so you aren't doing this. On limited width track machines, the results will be worse than pro 2 inch machines. Bri, you are spot on. But we need to know, does the OP have tracks 1 and 3 IN RECORD? If not, then bias leakage is not the problem.

 

[RoadrunnerOZ]

Is the OP still in the house? You need to clarify. Just for the record, you are trying the most difficult test of sync performance, by having one track in sync between two in record. All us oldtimers know, YOU DONT DO THAT! Plan your overdubs so you aren't doing this. On limited width track machines, the results will be worse than pro 2 inch machines. Bri, you are spot on. But we need to know, does the OP have tracks 1 and 3 IN RECORD? If not, then bias leakage is not the problem.

He said the 2 adjacent tracks 1&3 were in sync mode, not armed, track 2 armed with signal on input, at rest, no tape. This occurs anywhere on the machine whether track 2 or track 10 - the adjacent tracks in sync mode light up.
OP may still be asleep now.

 

[radardoug]

If that is accurate then this is not bias bleedthrough, and it is a fault condition.

 

[RoadrunnerOZ]

Correct - that’s why he’s going to pull the connector board and look for any broken print traces - seems like a lifted common ground somewhere on the board

 

[aurt]

Although....maybe Emil figured out a way to "fool" the machine into going into record mode with no tape???? Ie, the spooling motors madly spinning in opposite directions and the pinch roller engaged/capstan turning....

It looks like that's what's happening in the pic in post #8. The reel motor is definitely moving, but there's no tape.

This one is a bit of a brain bender.

 

[EmilFrid]

Is the OP still in the house? You need to clarify. Just for the record, you are trying the most difficult test of sync performance, by having one track in sync between two in record. All us oldtimers know, YOU DONT DO THAT! Plan your overdubs so you aren't doing this. On limited width track machines, the results will be worse than pro 2 inch machines. Bri, you are spot on. But we need to know, does the OP have tracks 1 and 3 IN RECORD? If not, then bias leakage is not the problem.

Sorry I was sleeping. To clarify again: ONE TRACK is in record, the other two IN SYNC PLAYBACK. The issue is the channel in record mode is leaking into the other two adjacent tracks, way more than it should. What we hear from channel two is input monitoring as it is in record in sync mode. The red lights on the pic are PEAK LIGHTS, not record lights.

Edit: extra clarification: the machine is set to RECORD

 

[EmilFrid]

So the level you read in sync playback (channel 1 and 3) has more level than the signal you send on channel 2 ?
really weird!
When you say that you don't even need to have a tape threaded, are you only in rec ready in channel 2 or
do you manage that the multitrack believe there is a tape and you can press record ?

Yes, I'm having the machine "believe" there's tape threaded and press record

 

[RoadrunnerOZ]

Which lends itself to the idea that maybe the ground is broken to the head cable shields.
What happens if you place a piece of mag tape against the head? You could do that without loading up a reel

 

[EmilFrid]

@RoadrunnerOZ Yes, exactly. I feel like this is very plausible.

If I put tape to the head... Say I play a tape with channel two in record, then adjacent channels will play what's on tape, with the content of the leaky channel superimposed on top of this prerecorded material.

 

[RoadrunnerOZ]

Got it. Guess that pesky board needs to come out…..

 

[EmilFrid]

Yes I guess so... Unfortunately. It will be a PITA but has to be done! What I think might be the case is that I've accidentally cracked the board somewhere while plugging a card in. But who knows, could be a thousand different things!

 

[RoadrunnerOZ]

Or at the head cable connector - is there a socket on the board or is the loom wired direct to the board?

 

[EmilFrid]

It is a loom directly soldered to the board, but in the head end of the loom there is sockets for the heads, so I won't have to desolder anything

 

[juanito2008]

Yes, I'm having the machine "believe" there's tape threaded and press record

If your tape machine is well aligned, you can't have a crosstalk with a higher level than the source.
Or it's because you don't use a tape.
I will suspect mostly a wiring problem as suggested by Roadrunner.


N.B: Maybe you know but If you record without a tape, be carefull not to record during a long time.
The recording head energy can't be tranfered to the tape and can damage your head.

 

[RoadrunnerOZ]

Have a look at the common ground sections of print for the cards that run across the board there’s a couple of traces - make sure they link to the incoming connections on power supply loom.
Does the machine play back in repro mode properly?

 

[EmilFrid]

@juanito2008 yes, it is well-aligned. I've been recording to tape for years basically every day so I don't doubt my calibration, which makes me quite confident that this is something independent of alignment. Good idea not to record for too long of s time without tape. Very strange issue I've run into, huh?

@RoadrunnerOZ will have a look at this! Yes, it plays back perfectly in sync, no crosstalk or other issues at all.

 

[juanito2008]

@juanito2008 yes, it is well-aligned. I've been recording to tape for years basically every day so I don't doubt my calibration, which makes me quite confident that this is something independent of alignment. Good idea not to record for too long of s time without tape. Very strange issue I've run into, huh?

@RoadrunnerOZ will have a look at this! Yes, it plays back perfectly in sync, no crosstalk or other issues at all.

Yes. Not a usual issue...

 

[RoadrunnerOZ]

will have a look at this! Yes, it plays back perfectly in sync, no crosstalk or other issues at all.

In play mode, not sync mode - perfect repro with a test tape?

 

[EmilFrid]

Yes, plays back perfectly!