Changing between Studer A820 quarter and half-inch headblocks

Fred Thal

[Industry Expert]
Jul 15, 2016
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The Studer A820 has a built-in headblock identification circuit that immediately detects when you have installed a half-inch (or a quarter-inch) headblock. The tape tensions then automatically change over to the appropriate values. Those values can be the factory furnished defaults, or optionally, custom tension settings programmed in by you.

It's with the A80 transports (and not the A820!) where the changeover from quarter-inch to half-inch format (and back) requires changing a host of hidden internal parts and a tedious, expert tension recalibration.
 

Mike Lavigne

Member Sponsor & WBF Founding Member
Apr 25, 2010
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The Studer A820 has a built-in headblock identification circuit that immediately detects when you have installed a half-inch (or a quarter-inch) headblock. The tape tensions then automatically change over to the appropriate values. Those values can be the factory furnished defaults, or optionally, custom tension settings programmed in by you.

It's with the A80 transports (and not the A820!) where the changeover from quarter-inch to half-inch format (and back) requires changing a host of hidden internal parts and a tedious, expert tension recalibration.

thank you Fred. that is very helpful to know.
 

Ron Resnick

Site Co-Owner, Administrator
Jan 24, 2015
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Beverly Hills, CA
This is very interesting, Fred! Thank you.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
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You are welcome, Mike and Ron.

It's not a huge deal, but many owners aren't aware of it. The A820 owner's manual can appear a bit daunting, I think.

Some people laugh at the idea of a one-week 820 operator training course. They almost always change that perspective after they have attended.

Credit where it is due: Headblock identification for auto-switchover from quarter-inch to half-inch tension values (effected by the reel motor servo control circuit) was first seen in the Ampex ATR-100 introduced in 1976. The ATR-100 was very advanced for its time.
 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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The Studer A820 has a built-in headblock identification circuit that immediately detects when you have installed a half-inch (or a quarter-inch) headblock. The tape tensions then automatically change over to the appropriate values.
Would headblock i.d. be compatible with SHRO headblocks, Fred? :confused:


It's with the A80 transports (and not the A820!) where the changeover from quarter-inch to half-inch format (and back) requires changing a host of hidden internal parts and a tedious, expert tension recalibration.
Thank you for the confirmation.
 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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The A820 owner's manual can appear a bit daunting, I think.
:cool:

Some people laugh at the idea of a one-week 820 operator training course.
Not here! :)

Credit where it is due: Headblock identification for auto-switchover from quarter-inch to half-inch tension values (effected by the reel motor servo control circuit) was first seen in the Ampex ATR-100 introduced in 1976. The ATR-100 was very advanced for its time.
Was entirely unaware of it -- thanks.
 

yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
Even STUDER could make a mistake here. My A820 started recognize its head correctly about a year ago, after nearly thirty years in dark!
Its 1/2" capability was built on a STUDER time code demo piece. The magnetic heads was from a 4 track A807. This configuration was similar to a A820 1/2" MR. (If configured with four sets of custom-built record/reproduce electronics, it has the potential of being a four track machine..... Just daydreaming...)

This 4 track head will never be identified automatically since it was not listed in the table. Only A820 MR's firmware has proper parameters for 2 track 3.75/7.5 ips configuration. There should be no real problem: the missing part is only the factory default values of audio parameters. It will retain factory default tension parameters if 2 track 1/2" head was chosen at properly soldered pads. When alignment procedures were followed through and all audio parameters stored, the head block configuration will be recognized. The only difference is that 2 track 1/2" head's factory default parameters were invoked when rechargeable battery failed.

Right now there was no real advantage of going 1/2"; two out of four tracks operation. I used it once in playing a 30ips 1/2" tape in 14" reel.

Yeun-Jung Wu
 

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Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
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Would headblock i.d. be compatible with SHRO headblocks, Fred? :confused:

Hi Sam,

Yes, ATAE SHRO headblocks for the A820 preserve the headblock identity function. Studer allocated a 4-bit data buss for this, so there were sixteen possible variations, provided that your installed firmware supports that many.
 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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Wow, Yeun-Jung -- I've never seen a 4-channel TC erase head on an A820 -- thanks for sharing! :)
 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
2,162
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Would headblock i.d. be compatible with SHRO headblocks, Fred? :confused:

Hi Sam,

Yes, ATAE SHRO headblocks for the A820 preserve the headblock identity function. Studer allocated a 4-bit data buss for this, so there were sixteen possible variations, provided that your installed firmware supports that many.

Excellent, Fred! :D
 

yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
Wow, Yeun-Jung -- I've never seen a 4-channel TC erase head on an A820 -- thanks for sharing! :)

Hi Sam:

I don't know anything about TC in four track configuration. Wish Fred can tell us the story behind the leading and trailing thin part of erase head. All three heads are for STUDER A807 1/2" four track version. I modified the base shielding of reproduce head to the style fit for A820 and A812's.

Yeun-Jung Wu
 
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yjwu

Well-Known Member
Jun 28, 2011
78
12
913
Taipei, Taiwan, Republic of China
My fault: there is no rechargeable battery in STUDER A820. Backup of CMOS SRAM was done by a 1/2AA, 3.6V lithium battery. There wasn't enough space for installing a battery holder, two metal clippers was there to hold the battery and made electrical contact.

My A820 came without battery holder and any battery on master MPU card two and a half years ago. Actually this card had contact problem which took me half a month to track down. I follow the thinking of A810 and installed a rechargeable lithium battery for it. A person from eBay kindly pointed out my mistake. The learning curve keep going! It is the miracle of web interacting world - an universe of connecting people!

Last minute modification. Now both MP-UNIT MASTER and MP-UNIT TD CONTROL can accept 1/2 AA 3.6V lithium primary battery, as shown in the pictures. The orange solid aluminum electrolytic capacitor has to be moved further back. Battery holders were borrowed from Macintosh LC and Macintosh Classic motherboard. Lithium primary battery was long gone. I installed two pins on the battey holder so that a fully charged lithium rechargeable battery can be used too.

Happy New Year!

Yeun-Jung Wu
 

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Marcata Recording

New Member
Jan 26, 2024
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when you change the lithium battery, do you need to provide DCV while making the change so you do not lose the memory in storage? and if so, can you just install the new battery in parallel with the old battery, and then disconnect the old battery?
 

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