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Old 19th January 2013, 04:43 PM   #32971
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The Ampex ATR1x0 machines were very special. It used a servo-controlled, direct-drive-capstan tape transport, which allowed the tape speed and tension to be continuously monitored by a servo relay, without capstan and counter-capstan. The capstan was replaced by a free turning weel, in contact with the tape, measuring the speed. The purpose was to reduce wow and flutter.
Working very well, while boring to set the tape: needed adhesive to stick the beginning of the tape, and more free turns of the tape on the receiving weel than habit.
The fast rewind process was incredible fast, affraying, while perfectly monitored; the tape was slowed down in a very controlled and smooth way to the chosen locator's point. A science fiction transport.

They too used magnetic heads made of ferrite, to avoid wear.
This was a VERY bad idea, as the ferrite crumbled in the gap, and, if the head was not wearing with tape friction,some heads were often destroyed very fast and in an non predictable way.
When you had the luck to get good heads, you had what was probably the best analog recording machine ever made.
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Last edited by Esperado; 19th January 2013 at 04:47 PM.
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Old 19th January 2013, 04:56 PM   #32972
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Originally Posted by Esperado View Post
When you had the luck to get good heads, you had what was probably the best analog recording machine ever made.
Until you bought your PC with a good sound card :-)
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Old 19th January 2013, 05:13 PM   #32973
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Originally Posted by SY View Post
You haven't shown any results whatever, much less a method. Nothing. Nada. Zip. Bupkis. Rien. Nichts.
Did JC ever admitted wrong? No, so I would think harrasing him is nothing but a waste of time. Minus, of course, the entertaining value of ruffling the feathers of a well known audio designer.
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Old 19th January 2013, 05:25 PM   #32974
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I don't want to be wrong, but I will stand corrected WHEN you give me something to correct.
As far as the ATR100 is concerned, I preferred Studer transports, and my own electronics. That is what I did for Mobile Fidelity and Wilson Audio.
Some of the systems concepts are very good in the ATR100. I used the record system concept, first shown by Allister Heaslett, the major designer of the ATR100, to get optimum phase response.

Last edited by john curl; 19th January 2013 at 05:53 PM.
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Old 19th January 2013, 05:26 PM   #32975
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Originally Posted by SY View Post
OK, then let's do the math without the need for a codex. If I have a bare bones supply (cheap 10,000uF/25V cap, no fancy choke or extra RC) and a whole pile of circuitry (let's say 100mA of draw), raw supply ripple is 120mV. At your chosen 3kHz, harmonics are -40dB wrt 120mV. A 7815 will knock that down another 55dB (and a 317 with cap bypass will be about a hundred times better, but let's stick with a 7815). 797 knocks that down another 95dB. So there's our line stage. The power amp is likely to have 26dB of gain. Overall, then, we deliver a signal -164dB down from 120mV at the speaker terminals (something less than a nanovolt). I haven't taken the math further, but I bet that's pushing the thermal noise of the voice coil.
SY,

CV=q or C dv/dt + Vdc/dt =i dc/dt is close enough to zero we normally neglect the term so dv = i dt / C or .1 x 1/120 x 1/.1 = 83 mV ripple. (100 mV in the UK.)

So at 3kHz we would expect 833 uV. At 3000 Hz. you don't get 55 dB of reduction you are lucky to get 30 so we are now at 26 uV. Use the AD797 at -90 (Negative rail) and you get your less than a nanovolt or .82nV. Now add the preamp gain of 60 db to see 822 nV even if you run your power amp at 0 db that would put the noise at -131 dBW at 3 kHz.

Now lets run those noise figures for each octave, weight them and add up the results!

Freq.....Harmonic Level...Sensitivity...Regulator...Noise
60...........-6....................-55.............55......1.32069E-07
120...........0....................-30.............55......4.68599E-06
240..........-6....................-15.............52......1.86553E-05
480.........-12......................0.............49......7.42 679E-05
960.........-18......................0.............46......5.25 777E-05
1920........-24.....................6.............43......7.426 79E-05
3840........-30.....................6.............40......5.257 77E-05
7680........-36....................-5.............37......1.04906E-05
15360......-42....................-6.............34......6.61914E-06
30720......-48....................-6.............31......4.68599E-06
61440......-54....................-7.............28......2.95666E-06
122880....-60.....................-8.............25......1.86553E-06

.................................................. ..............0.000303782 Volts


Probably why most folks don't use the 7915!



Now the other issue is the actual regulator noise will increase that a bit. Or in practice don't oversize you filter capacitor because at some point it is not the ripple and harmonics it is the self noise. Also a calculable number.

Last edited by simon7000; 19th January 2013 at 05:33 PM.
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Old 19th January 2013, 05:37 PM   #32976
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Originally Posted by simon7000 View Post
SY,

CV=q or C dv/dt + Vdc/dt =i dc/dt is close enough to zero we normally neglect the term so dv = i dt / C or .1 x 1/120 x 1/.1 = 83 mV ripple. (100 mV in the UK.)

So at 3kHz we would expect 833 uV. At 3000 Hz. you don't get 55 dB of reduction you are lucky to get 30 so we are now at 26 uV. Use the AD797 at -90 (Negative rail) and you get your less than a nanovolt or .82nV. Now add the preamp gain of 60 db to see 822 nV even if you run your power amp at 0 db that would put the noise at -131 dBW at 3 kHz.

Now lets run those noise figures for each octave, weight them and add up the results!

Freq.....Harmonic Level...Sensitivity...Regulator...Noise
60...........-6....................-55.............55......1.32069E-07
120...........0....................-30.............55......4.68599E-06
240..........-6....................-15.............52......1.86553E-05
480.........-12......................0.............49......7.42 679E-05
960.........-18......................0.............46......5.25 777E-05
1920........-24.....................6.............43......7.426 79E-05
3840........-30.....................6.............40......5.257 77E-05
7680........-36....................-5.............37......1.04906E-05
15360......-42....................-6.............34......6.61914E-06
30720......-48....................-6.............31......4.68599E-06
61440......-54....................-7.............28......2.95666E-06
122880....-60.....................-8.............25......1.86553E-06

.................................................. ..............0.000303782 Volts


Probably why most folks don't use the 7915!



Now the other issue is the actual regulator noise will decrease that a bit. Or in practice don't oversize you filter capacitor because at some point it is not the ripple and harmonics it is the self noise. Also a calculable number.
a) I don't know what you are talking about within the first paragraph.

b) Fig. 31 shows 75dB of rejection @3KHz, far lower than the 30dB you mentioned.

c) 60dB gain for a line preamp doesn't make any sense.

d) I have no idea what the last paragraph table means and how you used it to prove your point.
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Old 19th January 2013, 05:38 PM   #32977
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Frequency response comparison between Ampex ATR100 and JC modified Studer for Mobile fidelity both at 30ips.
Attached Images
File Type: jpg 30ips Ampex.jpg (818.1 KB, 129 views)
File Type: jpg 30 ips supermaster.jpg (792.3 KB, 126 views)
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Old 19th January 2013, 05:41 PM   #32978
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Originally Posted by Waly View Post
a) I don't know what you are talking about within the first paragraph.

b) Fig. 31 shows 75dB of rejection @3KHz, far lower than the 30dB you mentioned.

c) 60dB gain for a line preamp doesn't make any sense.

d) I have no idea what the last paragraph table means and how you used it to prove your point.
Figure 31 is a 7805 at 1/2A. Let me know what you measure on a 7915!
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Old 19th January 2013, 05:57 PM   #32979
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Quote:
Originally Posted by Waly View Post
Minus, of course, the entertaining value of ruffling the feathers of a well known audio designer.
You are jealous because you don't found the path to the game's registration.
Quote:
Originally Posted by john curl View Post
As far as the ATR100 is concerned, I preferred Studer transports, and my own electronics.
I won 10 points !
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Old 19th January 2013, 05:58 PM   #32980
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Originally Posted by simon7000 View Post
Figure 31 is a 7805 at 1/2A. Let me know what you measure on a 7915!
Oh, sorry, so you shifted the discussion from the 7815 here to a 7915, known as having a much worse frequency response. Good to know.

Still, the rest doesn't make much sense. But the 7915 has it's own noise of 175uV in 100KHz BW, much larger than those 26uV coming from that so-called "ripple" @3KHz. Plus that we have something called "decoupling".

You would pull anything out of thin air to make a point, isn't it?
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