Adjusting the Erase Head on a Reel to Reel

A

Astralography

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I have a two track (half track) Sony TC 756 2 deck that I mix down onto from my Tascam MSR16.

Tonight I was mixing down a song and noticed that as I was re recording over the tape on the Sony deck that it was not completely erasing the prior mixes. I assume the first head that the tape comes in contact with would be the erase head typically? The second woudl be the record head and the third the play head?

The record head does a great job when recording over fresh tape. Can't hear a difference from what I just mixed from. The playback head sounds great.

So I assume the erase head is out of alignment?

I even tried recording over the tracks with disconnected inputs (L and R) just trying to clean the old sound off the tracks but it would only get about 80% of it... guessing.

Any thoughts on getting the erase heads to do their job?
 
This may be a mechanical alignment issue, but it can also be electronics calibration, particularly if you're using high output tape and the erase output hasn't been boosted to match.
Without magnetic developer or something there's no easy way to tell which problem it is.

On my A807 the erase head was full-track anyway so it was clearly electronic. What I did was I recorded a tape of test tone and then erased it with a blank input signal, listening to the playback head on headphones while it did so. I adjusted the erase output trimmer until the sinewave was no longer audible.

You could do something similar while altering the head position, but it might be worth exploring the electronics side first, especially if it's running a higher output tape than it was originally designed for (The TC756 seems to predate 456).
 
I put my money on an electronics adjustment issue.

Do you have a service manual? If so there should be something in there about adjusting the erasure spec. Also, what kind of tape are you using and what operating level are you using?
 
Been using Scotch 175. I have a lot of new old stock boxes. The mixes I have done on them sound beautiful.

How can I determine which is the erase head?
 
It's the first one in the headblock. You were correct earlier in your assumption the order goes erase, record, play.
 
Most erase heads have a much wider track width then the record and play heads. so it would have to wayyyyyyyyyyyyyyy out of physical alignment to not be erasing properly. So as others have said here, its a calibration level issue.

Cheers! :)
 
I did find a manual online for $5. So, yes, as logic would suggest, the first head in the tape path is the erase head. No real instructions on adjusting or aligning the other heads. It does suggest dropping it by the local Sony dealer downtown!

Anyone know the basics of doing the calibration? I assume the specs are in the tech part of the manual.

I do have a good Fluke meter.
 
Took the head cover off and took a good look. There was some tape shed on the erase head... so of course that solved most all of the problem once I took that off. There was still a little bit of the old recording still coming through, so after looking at the head, I could visually see it was not centered across the tape path as I thought it should be.
I fiddled with the screws that were around and behind the head, and found two of them that seemed to be delicate adjustments. I was able to get the tape centered and that pretty much took care of any bleed coming through. The second pass through and I got clean tape. Oddly enough, there was no sign of tape shed this time. So she should be back in order.
 
Nice to hear you got it fixed! If it was way out of alignment that may have been causing some of the shed.
 
Obviously the problem was mechanical alignment in this case and the OP's meticulous adjustment procedure fixed it!

I would say however that the erase head is generally the last head you should ever touch, rarely do they move or wear as most are ferrite. As has been said, tape levels have improved since most of these machines were designed and a bit of remnant signal might be expected from a heavily modulated tape.

In any case there will be a specification for this in the manual such as "XdB below an erased 1kHz tone recorded at 0vu" or similar. Little point in getting the Stilsons out if the machine is in spec! This is why pro studios generally had a bulk eraser!.....At one point in my impecunious tape recording past I tried to make a BE!

And sort of moot...http://www.zeitnitz.de/Christian/scope_en
Only had it a day but seems quite handy. If anyone knows of similar software that can emulate a double beam hardware scope please tell. This gives a two channel trace but green and red superimposed, not independently "shiftable".
Dave.
 
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