I have notice on some Studers, Revox and my Tascam 42B there is a square flip up head shield on the head stock, dose anyone know what this is used for? The owners manual calls it head shield assembly and nothing more also I can’t find anything on the internet.
Studer and others Head shield
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A power transformer in a power amp will emit a rather strong electromagnetic field (EMF) that can travel several feet. If your tape deck is near that amp, the play head in a tape deck can pick up/detect that field which gets amplified by the play amplifiers, producing 60Hz tones (and harmonics of those tones) at the output of your tape deck. Commonly referred to as hum and/or buzz. The head shield blocks most of those electromagnetic fields from getting into the play head.
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Even with the head shield I had to apply MuMetal sheets under the top shelf to eliminate the last of bit of Hum coming thru. I have 2 Audio Research REF 250 that were just too much EMF for the decks.
After experimentation I applied 4 stacked sheets right under the head position then covered them a with matrix of 4 sheets in a single layer over a larger area. Worked out to 5 layers 8X10.5" directly under the heads and 1 layer 21" x 16" covering the whole area above the Amps.
Products:
https://www.partsconnexion.com/CONNEX-76151.html
https://www.nooelec.com/store/mumetal.html
Duct Tape all around!
After experimentation I applied 4 stacked sheets right under the head position then covered them a with matrix of 4 sheets in a single layer over a larger area. Worked out to 5 layers 8X10.5" directly under the heads and 1 layer 21" x 16" covering the whole area above the Amps.
Products:
https://www.partsconnexion.com/CONNEX-76151.html
https://www.nooelec.com/store/mumetal.html
Duct Tape all around!
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Yikes! You were asking for trouble by putting that power amp so close to the tape deck to begin with. I would have moved the power amps, but if your solution works, then good for you. Does your Studer have a front head shield? (a flap that covers the face of the head)
The Studer have a flip cover, the Lyrec also have some shielding on the top cover but not on the head face itself.
I had more hum from the Studer before shielding the shelf. I also have a Nagra IV/S that I rotate on the same spot and the shielding fix that one also.
The Amps are located in the only spot that I had for them, not optimal but It works with the shielding.
Spending $200 on shielding was cheaper that a larger loft!
I would love to see photos of the head shield you made. I need to make one for my Metaxas Papillon, or get one made.
Thanks! So the tape passes between the head and the shield? I guess you want to minimize the gap between the head and the shield?
To best block external hum fields, the shield should cover the face of the head as in actually touch the other shields on the head (top and side shields). Your photo looks like the shield would be 1 inch away from the face which would do almost nothing as far as stopping a field from entering the front of the head. I can see hum shields already on the top and sides of that head, BTW. Here is a phono of a Revox play head with the front shield "engaged" to cover the face of the head. That flap pivots down for tape loading. The tape enters and exits from slots on the sides of the "flap". This way there are shields on all six sides of the play head.
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The bar moves in when you start playback. Tape loading would actually be easy as the shield would move closer when playback is engaged.
What about the top of the head? The head is completely exposed. Not a great design, it seems; but not difficult to fix.
What about the top of the head? The head is completely exposed. Not a great design, it seems; but not difficult to fix.
As I indicated in post 12, I can see that the top and sides of the head in your photo already have hum shields installed. I don't know about the back of the head or under the head.
So is the head now picking up external hum fields like from a nearby power amp transformer? Or is this just to keep the deck quiet no matter where you locate it? (even near an amp). Put on a blank tape and enter Play. Slowly turn up the volume until you hear the the tape hiss (a steady white or pink noise) and then stop turning up the volume. Now stop the tape from turning and see if you hear any noise from your speakers be it hum or hiss. At this point you should not hear any hum or hiss. As in quiet. I'm assuming your deck does not mute the audio amps when in stop or pause mode.
So is the head now picking up external hum fields like from a nearby power amp transformer? Or is this just to keep the deck quiet no matter where you locate it? (even near an amp). Put on a blank tape and enter Play. Slowly turn up the volume until you hear the the tape hiss (a steady white or pink noise) and then stop turning up the volume. Now stop the tape from turning and see if you hear any noise from your speakers be it hum or hiss. At this point you should not hear any hum or hiss. As in quiet. I'm assuming your deck does not mute the audio amps when in stop or pause mode.
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Hi Tim, thank you, great eye to notice that!
What I noticed is that the hum is not initially there when the machine is turned on. After playing a few tracks, it becomes audible, even above the music. When I stop playback, after maybe 15-20 min, the hum goes away!
With the machine powered off, the hum always goes away right away.
Given this, I don’t think it’s from a nearby power amp transformer. Correct, the audio amps are not muted automatically when the deck is stopped/paused.
What I noticed is that the hum is not initially there when the machine is turned on. After playing a few tracks, it becomes audible, even above the music. When I stop playback, after maybe 15-20 min, the hum goes away!
With the machine powered off, the hum always goes away right away.
Given this, I don’t think it’s from a nearby power amp transformer. Correct, the audio amps are not muted automatically when the deck is stopped/paused.
Yes. that does not sound like hum being picked up by the head. More like hum from the deck's power supply or perhaps a defect connector or cable. You're using the tape preamp built into the deck or an external tape preamp?
Thanks again. I am using another tape preamp. I recall the preamp that came with the deck, which is also external, had a hum issue as well; but not as bad. I had the external PSU chassis grounded when I was using the stock preamp; I’ll ground it again today and see if that makes a difference.
It could also be the interconnect from the tape head to the pre, which is now longer. It has an effective capacitance of only 38pF; btw.
It could also be the interconnect from the tape head to the pre, which is now longer. It has an effective capacitance of only 38pF; btw.
yes, with an external preamp and power supply grounding issues can surface and cause hum. The only noise you should be hearing from any tape deck is "tape hiss or tape noise" which is why I told you to play a blank tape and turn up the volume until you hear the hiss from the tape. And at that volume point you shouldn't hear anything else like hum or buzz. If you can't find the problem you could always take the deck, external preamp and all cables to your local friendly technician and have him sort it out.
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Tape hiss / noise is low. On most of my albums I cannot hear any, even at ~85dB average SPL.
I’m working with the designers of both components to figure it out, thanks for your help!
I’m working with the designers of both components to figure it out, thanks for your help!
Yes, tape hiss is perfectly normal and expected and usually at a quite low level. I'm just saying that with any tape deck, the tape hiss is the only noise you should be hearing if you turn the system volume up when playing a blank tape.This is a valid test.. If you also hear hum mixed in with that tape hiss, then something is wrong.
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