Sorry, the Nortronics head I’m using is a 9207. It has a listed inductance of 200mH at 1Khz.
Hachidori Fukami Tape/Phono Preamplifier
- Thread starter Zeotrope
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He mentioned a 600ohm cable driver, but was a bit evasive about it. It is really not hard to properly load the input if you know the head inductance and cable capacitance. But to make it “idiot proof” for any user will require some ingenuity. At this price, he can tailor the preamp to each customer’s machine. Making a “universal” input might not be optimal.
J
use the standard tank circuit equation f= 1/2pi*Sq root(LC) Resistance will change the Q of the peak.
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You are correct in the sense that if he personally installed every box, that would be the preferred way, but I am not sure this is his business model.
OTOH, selectable loading resistance has been standard way of life in the phono world, but in that case the cartridge manufacturers usually provided their recommendations.
Another aspect to consider with the function of a head-amp is how to deal with “hot” tapes. Some tapes are recorded with a strong magnetic signal. In some cases, the hot tapes can cause the head-amp to clip (distort) because the signal coming off the head is too high. If a head-amp has an adjustment that reduces the strength of the signal before it goes to the head-amp, clipping can be avoided or at least reduced. I only have a few tapes where I need to reduce the strength of the signal coming off the tape head but it definitely improves the fidelity of these tapes when I do reduce the strength of the signal coming from hot tapes.F = R/(6.28*L)
And yes, with 200mH 55K is perfectly fine.
All tape playback amps/stages should have a calibration provision. Tapes can be recorded at many levels & it's not some are "hot", but some are recorded at 396nW/m (like mine) and I've seen some from Europe recorded at 520nW/m. One technically needs to calibrate the output level of the deck to that level so that the meters can actually read the tape level properly. If your deck is calibrated to 250 & you're playing a 396 tape, the needles will be buried in the red & you will think this tape is too hot, and you may get distortion.
Most early tapes were recorded at 250nW/m. Decca recorded their fantastic early SXLs in the late 50's early 60's, at 396nW/m NAB eq.
My sense, & I maybe wrong but I don't think most outboard tape amps include an accurate calibration stage. Maybe just a click onto a few set levels, which should likely suffice.
Ed
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I believe the Hachidori, Doshi and Merrill all allow for level, high frequency and low frequency calibration.
In reality the output level has significance in a pro world, where all such things are standartized, but not in the consumer world where head preamps, phono stages, CD players, etc are connected to line preamps, that always have VOLUME control.
So whether your head preamp produces +4dB at 320nWb, or 0dB is not important, because you still set your listening volume by your ears.
As long as your output is withing some reasonable range, you are OK.
If you bring home ten randomly selected audio sources you will get ten very different levels. Some CD's will output up to 10V, many phono stages much, much less.
That is why some preamps have Relative Volume function, that allows you to equalize the volumes when switching the sources. I have it on mine... although I rarely use it myself
So I would not get stuck on some "standard" level, unless you are building a studio. Every preamp has its own most comfortable volume control range, say, it is between 6 and 10 o'clock, or between 60 and 100 display counts... as long as your head preamp works in that range you are fine.
Some +4dB calibrated sources will force you to set your volume too low, which will damage your sound quality. We had some customers report using super-low settings, and that is not good for sound.
This is specific to playback device for home audio, the recording chain is a totally separate question, and there I wish more producers were using PPM meters, but that is entirely different subject.
Whether doing calibration is going to help you avoid an overload - it shouldn't, if your device is properly designed.
So whether your head preamp produces +4dB at 320nWb, or 0dB is not important, because you still set your listening volume by your ears.
As long as your output is withing some reasonable range, you are OK.
If you bring home ten randomly selected audio sources you will get ten very different levels. Some CD's will output up to 10V, many phono stages much, much less.
That is why some preamps have Relative Volume function, that allows you to equalize the volumes when switching the sources. I have it on mine... although I rarely use it myself
So I would not get stuck on some "standard" level, unless you are building a studio. Every preamp has its own most comfortable volume control range, say, it is between 6 and 10 o'clock, or between 60 and 100 display counts... as long as your head preamp works in that range you are fine.
Some +4dB calibrated sources will force you to set your volume too low, which will damage your sound quality. We had some customers report using super-low settings, and that is not good for sound.
This is specific to playback device for home audio, the recording chain is a totally separate question, and there I wish more producers were using PPM meters, but that is entirely different subject.
Whether doing calibration is going to help you avoid an overload - it shouldn't, if your device is properly designed.
The VU meters on my tape player are bypassed because I don't want the signal to go through them. I have adjustable step-up transformers at the input of my head-amp. I can select gain of 3db, 6db, 9db, 12db and 15db. I like adjusting gain using a transformer rather varying resistance. I use the adjustable gain of the step-up transformers to set the level I want with a particular tape. For example, for tapes recorded at 520nW/m I use 3db of gain. If I use any other setting, the head-amp will distort. With tapes that are recorded at 396nW/m (like Ed's), I use 6db of gain. The majority of tapes I have are recorded at 320nWb, so I use 9db of gain. Occasionally, I have a tape that sounds best at 12db of gain. For each of these gain settings, I use a different resistor to load the tape head.
If I decide to use a different tape head with a different output voltage, the adjustable step-up transformers can help make gain adjustments for the new tape head.
If I decide to use a different tape head with a different output voltage, the adjustable step-up transformers can help make gain adjustments for the new tape head.
As a non techie my knowledge is surface only, but relative output at each frequency is quite critical. Even essential. Overall output is less critical within limits.
Right?
Right?
John, your circuit needs a revision, your overload margin is way, way too narrow, it shouldn't be like this. Using transformers is good way of adjusting the levels, but the system should not require such a tight matching.
BTW, when you say "tapes recorded at X" that is not the full picture. I have seen tapes "recorded at 500" that went to over 1,500nWb on peak meters. The crest factor is super-important, and your VU meters don't show it. So the tape might look OK on them, but sound overloaded. I had seen my share of such tapes. That is why I am saying PPM meters are absolutely essential for good recording.
Even the best producers can be inconsistent. One of their tape might be perfect, and another - overloaded. It is not possible to know whether it is intentional or happened by mistake, but the net result remains, some of the prerecorded tapes are unacceptable.
When you have a tape "recorded at XnW/m" - what does that even mean? I don't know, as there is no standard.
BTW, when you say "tapes recorded at X" that is not the full picture. I have seen tapes "recorded at 500" that went to over 1,500nWb on peak meters. The crest factor is super-important, and your VU meters don't show it. So the tape might look OK on them, but sound overloaded. I had seen my share of such tapes. That is why I am saying PPM meters are absolutely essential for good recording.
Even the best producers can be inconsistent. One of their tape might be perfect, and another - overloaded. It is not possible to know whether it is intentional or happened by mistake, but the net result remains, some of the prerecorded tapes are unacceptable.
When you have a tape "recorded at XnW/m" - what does that even mean? I don't know, as there is no standard.
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The frequency dependent output voltage is done by the EQ filter (NAB etc.) in the head amp. Some times the voltage on the input of the head- amp is too high and can cause distortion. Both are definitely important.
i'm more referring to EQ'ing your heads to tapes with tones for playback. need VU meters for that as i understand it.
You will need two things: the VU meters and willingness to adjust your azimuth for every tape.
Which means - you will never have the perfect azimuth set on your machine, as you will be forever adjusting it to the other, imperfect, tapes.
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