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Adding a 3rd Tape Head to (mono) Reel-to-Reel.

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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby ef37a » Sat Aug 24, 2019 2:35 pm

James Perrett wrote:
ef37a wrote:The actual replay electronics is the really easy bit. NE5534/LM4562. I am sure Google will find you a circuit for the EQ.

One of the first pieces of electronics I ever built was a three transistor tape playback circuit for a Brennel tape recorder. The circuit diagram came from the 1972 Henrys Radio catalogue but I think they had taken it from one of the Mullard data books.

I am sure somewhere in my loft James I have a nomograph by Miniflux giving very detailed design data for head amplifiers and several circuits. Must brave the spiders and have a look for it before I get too creaky to get in there!

Dave.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Elephone » Sat Aug 24, 2019 9:24 pm

ef37a wrote:I agree with Hugh et al, not a practical proposition.

"Replay head output on long wires" ! Doomed to failure, you will pickup all the hum and RF in creation plus, if you want replay whist recording, some form of bias trap will be needed.

The actual replay electronics is the really easy bit. NE5534/LM4562. I am sure Google will find you a circuit for the EQ.

Dave.

Thanks. I have done this with a Walkman cassette player head (extended on wires) to rub along strips of tape stuck to card, a few years back.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby ef37a » Sat Aug 24, 2019 9:35 pm

Elephone wrote:
ef37a wrote:I agree with Hugh et al, not a practical proposition.

"Replay head output on long wires" ! Doomed to failure, you will pickup all the hum and RF in creation plus, if you want replay whist recording, some form of bias trap will be needed.

The actual replay electronics is the really easy bit. NE5534/LM4562. I am sure Google will find you a circuit for the EQ.

Dave.

Thanks. I have done this with a Walkman cassette player head (extended on wires) to rub along strips of tape stuck to card, a few years back.

Ok but, low impedance head for transistors and no stonking great mains traff about!

Dave.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Elephone » Thu Aug 29, 2019 6:18 pm

ef37a wrote: Ok but, low impedance head for transistors and no stonking great mains traff about! Dave.

Thanks! That's why I presumed it'd be easier than it most likely is. I'll probably try the 2 machine method.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby cyrano.mac » Sat Aug 31, 2019 4:34 pm

Ditch the EL3542...

Get something like a UHER if you want to experiment with tape. These have a removable tape carrier. And the heads are available too. New. Not cheap, but hey...

You can pick up a mono UHER for next to nothing. Replace belts. Again, available new. Not even expensive. Clean and lubricate. The chassis and capstan flywheel are built like a tank. And they're all exactly the same. Except for the electronics, but even these are interchangeable.

I'm amazed even the NOS tape carriers show up on evilbay quite often.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Elephone » Sun Sep 01, 2019 6:04 pm

cyrano.mac wrote:Ditch the EL3542...

Get something like a UHER if you want to experiment with tape. These have a removable tape carrier. And the heads are available too. New. Not cheap, but hey...

You can pick up a mono UHER for next to nothing. Replace belts. Again, available new. Not even expensive. Clean and lubricate. The chassis and capstan flywheel are built like a tank. And they're all exactly the same. Except for the electronics, but even these are interchangeable.

I'm amazed even the NOS tape carriers show up on evilbay quite often.

Why do they have a dedicated play head that you can use for realtime bouncing and delay?
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby ef37a » Sun Sep 01, 2019 8:05 pm

Elephone wrote:
cyrano.mac wrote:Ditch the EL3542...

Get something like a UHER if you want to experiment with tape. These have a removable tape carrier. And the heads are available too. New. Not cheap, but hey...

You can pick up a mono UHER for next to nothing. Replace belts. Again, available new. Not even expensive. Clean and lubricate. The chassis and capstan flywheel are built like a tank. And they're all exactly the same. Except for the electronics, but even these are interchangeable.

I'm amazed even the NOS tape carriers show up on evilbay quite often.

Why do they have a dedicated play head that you can use for realtime bouncing and delay?

Are you asking why some tape machines had a third replay head?

If so it was becuse the head construction and winding impedance is not the same for optimum record and replay duties. Replay heads typically had finer gaps and a higher impedance, more turns, giving greater output.
That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

Dave.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Folderol » Sun Sep 01, 2019 8:37 pm

ef37a wrote:Are you asking why some tape machines had a third replay head?

If so it was becuse the head construction and winding impedance is not the same for optimum record and replay duties. Replay heads typically had finer gaps and a higher impedance, more turns, giving greater output.
That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

Dave.

Brenell used to do this too.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby ef37a » Sun Sep 01, 2019 9:19 pm

Folderol wrote:
ef37a wrote:Are you asking why some tape machines had a third replay head?

If so it was becuse the head construction and winding impedance is not the same for optimum record and replay duties. Replay heads typically had finer gaps and a higher impedance, more turns, giving greater output.
That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

Dave.

Brenell used to do this too.

Ooo! Brenel, not heard that name in a looong time young Skywalker. Built on the same BSH principles as the Ferrographs and IIRC were two speed but had a capstan sleeve so you could get the other two?

Dave.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Folderol » Sun Sep 01, 2019 9:57 pm

ef37a wrote:
Folderol wrote:
ef37a wrote:Are you asking why some tape machines had a third replay head?

If so it was becuse the head construction and winding impedance is not the same for optimum record and replay duties. Replay heads typically had finer gaps and a higher impedance, more turns, giving greater output.
That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

Dave.

Brenell used to do this too.

Ooo! Brenel, not heard that name in a looong time young Skywalker. Built on the same BSH principles as the Ferrographs and IIRC were two speed but had a capstan sleeve so you could get the other two?

Dave.
Yep! I was gifted with a Mk6 stereo (in dire condition) mid '70s. Did a lot of work restoring it, then like an idiot, sold it for peanuts to a friend - no idea what happened to it :(

P.S. Those two delightfully large VU meters? The were seized solid, but a watchmaker pal, not only cleaned them up thoroughly but also mechanically matched the spring tensions so they tracked perfectly!
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby James Perrett » Sun Sep 01, 2019 10:25 pm

ef37a wrote:That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

I seem to remember that some manufacturers said that at high speed the requirements were very similar - narrow head gaps on replay aren't so critical at high speeds as the wavelengths involved are longer. Apparently some engineers only used the replay head on a multitrack for calibration - all recording and mixing used the record head.

Having said that, the Otari MTR90 used a dual winding on the record head with the two windings connected in parallel for recording but in series when used for playback. The performance is also claimed to be slightly better from the playback head (although playback through the record head sounds pretty good to me).
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Tim Gillett » Mon Sep 02, 2019 4:31 am

ef37a wrote:
Elephone wrote:
cyrano.mac wrote:Ditch the EL3542...

Get something like a UHER if you want to experiment with tape. These have a removable tape carrier. And the heads are available too. New. Not cheap, but hey...

You can pick up a mono UHER for next to nothing. Replace belts. Again, available new. Not even expensive. Clean and lubricate. The chassis and capstan flywheel are built like a tank. And they're all exactly the same. Except for the electronics, but even these are interchangeable.

I'm amazed even the NOS tape carriers show up on evilbay quite often.

Why do they have a dedicated play head that you can use for realtime bouncing and delay?

Are you asking why some tape machines had a third replay head?

If so it was becuse the head construction and winding impedance is not the same for optimum record and replay duties. Replay heads typically had finer gaps and a higher impedance, more turns, giving greater output.
That said, I only recently found out that at least one major tape machine maker (Teac?) used the same head in both positions.

Dave.

Spot on Dave. A repro head's gap length sets the upper frequency limit, or more correctly the upper wavelength limit, whereas from memory the recorded signal isn't so dependent, tending to appear at the trailing edge of the gap. The record head's coil tends to be lower impedance partly to allow practical record amplifiers which don't need ridiculously high voltage rails to avoid clipping. Whereas a repro head needs the somewhat higher impedance to allow a useably high enough signal to feed a practical preamplifier.

Also repro heads usually needed better magnetic shielding than record heads, even to the point of the front face of the head being shielded. A hinged flap often swung over the head's face when record or play was selected.

The third head also enabled "confidence" monitoring of the just recorded signal to confirm by ear that the recording was up to standard.

The third head also made aligning/calibrating of the tape machine to the tape so much faster than the equivalent 2 head machine, especially when aligning a multitrack machine with its many parameters to adjust.

Tape machines still need to be maintained but more of their use these days is playback of old recordings rather than recording new ones, so it's repro (playback) heads that are the more sought after. I haven't bought a record head for many years.

Yes at higher tape speeds, the same head type can be used for record and playback. One reason is that for audio at say 15ips the standard small gap length play head (say 1 micron) can resolve to well above the audible limit, say to 90 kHz, which for audio is of little benefit. So a wider gap, closer to the ideal record head gap, can be used. Very small gap length comes into its own where very short wavelengths need to be resolved such as slow tape speed formats (cassettes), or anywhere where the highest frequency must be recorded and resolved. I think video tape heads could have a gap length of 0.3 microns. Incredibly small.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 9:24 am

Tim Gillett wrote:...from memory the recorded signal isn't so dependent, tending to appear at the trailing edge of the gap.

Technically, the recorded signal emanates from the trailing edge of the magnetic field created by the record head, which extends beyond the gap itself.

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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Tim Gillett » Mon Sep 02, 2019 9:42 am

Spot on Hugh!
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Folderol » Mon Sep 02, 2019 9:57 am

Hugh Robjohns wrote:
Tim Gillett wrote:...from memory the recorded signal isn't so dependent, tending to appear at the trailing edge of the gap.

Technically, the recorded signal emanates from the trailing edge of the magnetic field created by the record head, which extends beyond the gap itself.

H
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