Phase compensation; STUDER A810

yjwu

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Jun 28, 2011
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Taipei, Taiwan, Republic of China
My first R2R was a ReVox B77 Mk-II, bought in July, 1990. I was told that it was equalized in CCIR, not the usual NAB equilization in north America.
I did a frequency response test on that B77 and found the recorded square wave was not as beautiful as it supposed to be. I wrote a letter to ReVox and got a reply from its technical director Mr. Korowski. Detail reason for the square wave response was given and "phase compensation" was clearly mentioned in second paragraph. Then I ordered a new service manual from ReVox's authorized dealer in Nashiville, TN to study what was going on.
20 years later, I started to collect my first professional R2R, a STUDER A807 Mk-I; two months later an A810 , then an A807 Mk-II, HS, all in 2011; followed by an A820 in 2014.
The audio section followed from A810, A820, A812, all the way to A816; thus "phase compensation" was all embedded within. Later version of record amp and HF driver included HX-Pro and skimming, found only in A812 Mk-II, A820 Mk-II and A816.
STUDER A807 Mk-I/II and ReVox C270 were two models developed outside this rim.

I wonder how much the "STUDER" sound was reflected by this feature?

http://www.recordist.com/studer/Phase_compensation.pdf

AP=All pass; BP=Band pass (@20kHz?)

http://lab2104.tu-plovdiv.bg/index.php/2016/01/25/ph_compensation/

Additional bonus of googling was the reel-to-reel project@LAB2104, dated around March 2016. It seems to me that the scope of the new R2R project was quite vibrant, much advance than Ballfinger's M063?! There was no update information ever since.

http://lab2104.tu-plovdiv.bg/index.php/2016/03/03/r2r/
 

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yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
Someone performed a square wave response (1kHz, 3kHz) of a Tascam 32. It is similar to the 2.5kHz square wave frequency "via tape" of conventional solution; 2.5kHz/15ips.
STUDER A807 also has built-in phase compensation before record treble ADC. I haven't checked record amp design of ReVox C270 yet. All the professional R2R lineup after A810, including A820, A812, A807, A816, have this feature, which was attributed to engineer J. Marco Egli.
 

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yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
RC4559 v.s. NE5532?

In later A807 design, the twice time derivative (BP+BP; BP=Band Pass) was accomplished by RC4559 OP amp; while the AP (All Pass) branch was still constructed by NE5532 OP amp. In A810/A820/A812/A816 record amp both AP and BP were done by NE5532's.
Any reason why some of the OP amp were switched from NE5532 to RC4559?

Replacing all OP amp by other manufacture/model was discussed long time ago. The mixed OP amp approach of A807 was quite interesting. Any previous STUDER engineer could rewind this history for us? I wish the answer was not pure economical concern.
 

yjwu

Well-Known Member
Jun 28, 2011
78
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Taipei, Taiwan, Republic of China
The record/reproduce circuitry for STUDER analoge tape recorders developed after 1982, e.g. A810, A820, A812, A816, seemed to stay almost unchanged. The audio plug-in cards were all under 1.820.xxx.xx naming scheme:

HF DRIVER 1.820.713.00
RECORD AMPLIFIER 1.820.712.xx
REPRODUCE AMPLIFIER 1.820.710.xx
LINE AMPLIFIER 1.820.714.xx; 1.820.715.xx
MS SWITCH+TEST GEN 1.820.724.00

(Even A810's MPU, MP-UNIT A810, originally labeled as 1.810.752, was updated through 1.810.780.xx till 1.820.780.xx.)

The major upgrade occurred in the inclusion of HX-PRO capability: HF DRIVER 1.820.713.00 -> 1.820.813.81; RECORD AMPLIFIER 1.820.712.xx -> 1.810.811.xx. (There was no 1.820.812.xx; although 1.820.812 was clearly marked on frame cage of A820 Mk-I?)

HX-PRO came too late so A810 was left behind. Anyone tried a DIY modification on A810 before? Of course a pair of HF DRIVER cards 1.820.813.81 and a pair of RECORD AMPLIFIER HX-PRO 1.820.811.xx were needed. Firmware inadequacy? How about a hard wired HX-PRO, not software selectable?
 
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yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
In this photo there were 6 people in audio team, all except one standing on Dr. STUDER's left side. J. Marco Egli was the one wearing white shirt on the far right side of the photo, next to two persons responsible for A810 documentation (partially blocked in this photo).
There were 4 people in software team, lead by Dr. Alian Junod. The rest in the photo were tape transport team.

A810's work laid down the foundation for STUDER's analoge tape recorders, all the way till its final stage.
 
The record/reproduce circuitry for STUDER analoge tape recorders developed after 1982, e.g. A810, A820, A812, A816, seemed to stay almost unchanged. The audio plug-in cards were all under 1.820.xxx.xx naming scheme:

HF DRIVER 1.820.713.00
RECORD AMPLIFIER 1.820.712.xx
REPRODUCE AMPLIFIER 1.820.710.xx
LINE AMPLIFIER 1.820.714.xx; 1.820.715.xx
MS SWITCH+TEST GEN 1.820.724.00

(Even A810's MPU, MP-UNIT A810, originally labeled as 1.810.752, was updated through 1.810.780.xx till 1.820.780.xx.)

The major upgrade occurred in the inclusion of HX-PRO capability: HF DRIVER 1.820.713.00 -> 1.820.813.81; RECORD AMPLIFIER 1.820.712.xx -> 1.810.811.xx. (There was no 1.820.812.xx; although 1.820.812 was clearly marked on frame cage of A820 Mk-I?)

HX-PRO came too late so A810 was left behind. Anyone tried a DIY modification on A810 before? Of course a pair of HF DRIVER cards 1.820.813.81 and a pair of RECORD AMPLIFIER HX-PRO 1.820.811.xx were needed. Firmware inadequacy? How about a hard wired HX-PRO, not software selectable?

Yes, you are right. The same happened when Guido Besimo designed the audio circuit for the A 77. It was later applied to the B 77 and PR 99 machines with minor revisions! Unfortunately, most of the revisions made were for reducing cost. It happened when they joint together both audio channel circuits in one board on the B 77, when the plastic rotary buttons were used on the PR 99 MK iii instead of the aluminum ones and other parts that they replaced due to lower cost.
 

andromedaaudio

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Sorry to interupt here, but in what is the audiocircuit of the A 820 different from the A 80 B 62 .which use same cards.
And is the J 37 the only tubed one compared to the C 37?
 
In this photo there were 6 people in audio team, all except one standing on Dr. STUDER's left side. J. Marco Egli was the one wearing white shirt on the far right side of the photo, next to two persons responsible for A810 documentation (partially blocked in this photo).
There were 4 people in software team, lead by Dr. Alian Junod. The rest in the photo were tape transport team.

A810's work laid down the foundation for STUDER's analoge tape recorders, all the way till its final stage.

Yes. That information is on the photo footer. Also you can see the mechanics geniuses of Romagna and Fiala. Both next to Willi, left and right, and by that time both with many years working on Studer Revox. These 2 gentlemen were the designers of the A 77 mechanism as well.
 
Sorry to interupt here, but in what is the audiocircuit of the A 820 different from the A 80 B 62 .which use same cards.
And is the J 37 the only tubed one compared to the C 37?

Well, that's precisely what Wu is saying: no change whatsoever. On many occasions, some specific parts has to be changed due to new vendors, parts no longer available, abrupt price increases, etc. A 37, B 37 and B 30 were all tubed designs and the T 26, of course. That was the first one.
 

c1ferrari

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