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Old 26th October 2012, 08:28 AM   #21
Salas is offline Salas  Greece
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Those big repro reel2reel heads maybe have different characteristics to cassette heads, but nice info compiled there. I just did a sim run from 5mH to 200mH watching the last octave, plays for a dB or so and the variable input load compensates.

P.S. Gain is ~35dB
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Old 26th October 2012, 09:05 AM   #22
miklos is offline miklos  Canada
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Here's some info on Revox heads:
Show Posts - C_Campbell
Most consumer solid state reel to reel tape recorders would have something like 50 and up to 120mH ,or as you see it 270mH. A tube recorder is much higher , for example I have a 1H Philips head in my collection. The highest I ever encountered.
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Old 26th October 2012, 04:38 PM   #23
Salas is offline Salas  Greece
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That manual was about studio multitrack. It mentions that tube heads are high at 500mH but the modern replace heads for solid state or transformer input are low. For 270mH and 35k load the response is not affected in the JFET examples. For 100k load it picks up high range treble. They can be easily tweaked for 10-20kHz in high load. Do you have any info on measured source resistance also?
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Old 26th October 2012, 10:11 PM   #24
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I'd love to try a discrete circuit in a Nakamichi, but the output is low at 0.18mV and would also need 120 and 70us switchable EQ, so you'd need around 60db gain.
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Old 27th October 2012, 02:19 AM   #25
miklos is offline miklos  Canada
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"Do you have any info on measured source resistance also?"
Sorry Salas, no such info. I just picked up on the 5mH. I don't have any experience with transformer coupled PB heads. The output of such head must be very low.
Regards.
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Old 27th October 2012, 04:41 AM   #26
studeb is offline studeb  United States
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i am not sure if this is what you mean by measrured source reistance, but the Akai GX heads are 210 or 400ish ohms, depending on model. If you trust my LCR meter i can check inductance as well
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Old 27th October 2012, 05:35 AM   #27
Salas is offline Salas  Greece
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That resistive part of the head's coil, yes. Guys, I had inserted 300 Ohm and 250mH in series to a voltage source in the sim with the pot and resistor load combination circa 35K Ohm. It does not lose it in the highs. Studeb, lets see where stands yours for mH too. Those circuits were an older exercise just based on curve data I could see floating on the web. I had used old Ampex papers for NAB. I thought I better post them ccts, this thread rang a bell, so not to remain as dusty files only. In any case I don't have the hardware opportunity to practice them. If anybody will ever be curious enough to try them in a reel 2 reel deck, only then we will know if and what they might need in tweaking. Studio units have enough EQ pots on them, proof its a tweak thing to get it right with each machine anyway.
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Old 27th October 2012, 06:31 AM   #28
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Default magnetoresistive PB-heads in R2R machines

Sorry for being off-topic, but do you know about the use of magnetoresistive PB-heads in reel-to-reel tape recorders? These have a higher output signal than induction heads and do not need IEC/NAB EQ. They were used e.g. in the RS-AZ 6 and 7 cassette tape recorders from Technics. The later has a direct head output.
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Old 27th October 2012, 10:51 AM   #29
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by franzm View Post
Sorry for being off-topic, but do you know about the use of magnetoresistive PB-heads in reel-to-reel tape recorders? These have a higher output signal than induction heads and do not need IEC/NAB EQ. They were used e.g. in the RS-AZ 6 and 7 cassette tape recorders from Technics. The later has a direct head output.
Technics created these myths about MR heads in tape recorders. In reality: 1) The Signal-to-Noise ratio on these heads is not better than that of good conventional heads - amorphous alloy for instance. 2) MR heads need quite complicated EQ to provide a flat PB response in a tape deck. 3) The "direct head output" in the RS-AZ7 is just a marketing gimmick.

Even in cassette decks MR heads don't give any real advantage, as for R2R decks - the tape noise there is so high that the heads output and noise is not a problem whatsoever is any properly designed recorder. On the other hand MR heads won't last as long as conventional heads in a R2R.

Cheers

Alex

Last edited by x-pro; 27th October 2012 at 11:12 AM.
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Old 27th October 2012, 11:11 AM   #30
x-pro is offline x-pro  United Kingdom
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As on the thread topic. There are quite a few good circuits for PB amps. Even my Kora 3T phono stage circuit (MC version) can be easily adapted into an excellent PB EQ amplifier with gain about 70-72dB at 315 Hz which is enough for most PB heads. For R2R decks a resistive load to control the head/load capacitance resonance is usually enough so the design can be fairly simple. For a good cassette deck PB head (ferrite of amorphous alloy) a "virtually cooled" head load can give several dB improvement in the SNR. If there is enough interest I can show how to make a top quality PB EQ amp out of my phono stage. Otherwise a PB EQ amp from, for example, the Techncs RS-B965 is a good circuit to copy - the service manual is available on the Internet.

Cheers

Alex
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