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Cassette Phasing Issues at low Frequencies

mattstech

mattstech

New Member
I had a large (>100 C-60s) tape duplication job to complete, so I decided to align my master deck to the duplication.ca alignment tape to achieve a good treble response, to send the master tape out for duplicating.

Output attached to scope, I turn the head screws until I get the most output I possibly can on the 10KHz tone. It's an autoreverse deck, so I did this for both side A and side B.

I checked my alignment with a known well prerecorded tape (Dire Straits - Brothers in Arms) and it sounds spot on, even summing the deck's output to mono suggests it is matching perfectly in alignment and there is zero phase cancellation in the high frequencies.

The deck is a Sony TC-RX70ES

Since then, every tape I've recorded has perfect phasing and balance in the treble frequencies, however there is some absolutely unexplainable oddness in the bass frequencies that is particularly noticeable switching from source to tape, played back in the same deck.
Upon analysis in Audacity, a 10KHz tone played back in the same deck has perfect phase, while a 60HZ test tone plays back with around a 5-10 degrees visually observable phase shift between the channels.

This issue only started to occur after these minor head azimuth adjustments. I would be hard pressed to think this was a sudden electronic failure that happened so suddenly at the same time of aligning my heads.

Any help is appreciated.
 
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First of all: I’m not an expert.

Your alignment was an electrical response alignment (test tape), which is good. However, doesn’t the head need to be aligned mechanically first? To make certain the position in X, Y and Z direction is precise?

Another thought: being a spinning head (or dual head) do you feel the head position remains the same when a tape is in the transport?
 
Another thought: since other sources respond correctly, is it possible the material has an issue? I guess not as switching between source and tape shows the difference...

Out of ideas now.
 
j!m said:
First of all: I’m not an expert.

Your alignment was an electrical response alignment (test tape), which is good. However, doesn’t the head need to be aligned mechanically first? To make certain the position in X, Y and Z direction is precise?

Another thought: being a spinning head (or dual head) do you feel the head position remains the same when a tape is in the transport?
Click to expand...

The head tilt screws (Which I am assuming are the screws along the top and bottom of the head, and spin with it) Still have the greenish glue from the factory... I do not want to adjust these. Visually from the side, the head tilt and azimuth looks to be at a perfect angle with the tape guides and pinchroller, and I don't see how skewing the heads vertically would somehow help with low frequency phasing.

I really don't reverse the heads much as some say it will throw them out of alignment, but they currently sound absolutely identical regardless if playing forwards or backwards.

Head position remains solidly reliable, and it always has been since owning this deck.
 
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