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Messages - Ki Choi

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Reel to Reel Tape Machines / Re: PLL Capstan Light on A810
« on: March 02, 2014, 05:06:11 PM »
Sorry for being late to the post.

There are simple problem areas to look for quick fix fist:

One is to look at the capacitive techo sensor output from the capstan motor. Its functions are described in the section 3.5.9 in the manual.

Second is as Doc B had suggested - there are three electrolytic caps (c12 100uF 16VDC, C16 10uF 16VDC, C18 2.2uF 16V) in the capstan control board need to be replaced.  Even the youngest A810s with serial numbers >6000 are still more than 30 years old.

However, most likely reason for losing PLL signal that I had been experiencing was due to failure of L1 and L2 variable inductors in the capstan control board from machines with serial numbers older (smaller) than ~4000s region.

One of the things that are less than Studer-like was to use these cheap variable inductors with very questionable quality.  These old inductors used some plastic like material to hold the ferrite core in place after being tuned to 5.5Mhz +/- 500Khz.  I found most of the ferrite cores to be out of place due to the holding material that had gone soft from age and no longer holds.

Since I hadn't been able to locate these variable inductors, the only solution was to temporarily position the ferrite core to its proper position and fix it with epoxy glue.  As it dries, I have to double check with a digital scope with counter capability to make sure it holds 5.5Mhz signal.

Hope it helps.


Tape Tech / Re: Firmware versions for Studer A807 ....
« on: February 05, 2014, 12:11:13 AM »
You need the 1.717.651.26 chip.  It is IC14.

Send me an email if you can't locate the BIN file.


Tape Tech / Re: Studer A810 fast forward problems‏‏
« on: December 06, 2013, 11:52:48 AM »
Hi Guglielmo:

Sorry to hear about your problems with A810.

There is a very good instruction in the service manual on setting REW and FF tension to increase torque.  However, if you have not replaced any of the components for the winding section, I would not recommend readjusting tension. 

Instead, I would start the normal process of troubleshooting by measuring supply voltages from the back of the machine with it in winding mode under load.  I would pay attention to the 24VDC section. 

These machines are in general 30+ years old...  more than 50% of the time, I see the bad filter caps in the power section and on basis board as causes of many problems.

Let us know what you find out on supply voltage measurements.

Good luck,

Tape Tech / Re: Firmware versions for Studer A807 ....
« on: November 19, 2013, 01:31:53 PM »
it's an old question... and sorry no one had responded to you yet.

If you don't have any transport issue with your 30/88 firmware, I wouldn't bother updating it.

There are newer versions for Mk I and Mk II:

1.727.351.25 IC14 10/89 27128 8C45 MKI 1.727.350.25
1.727.351.25 IC15 10/89 27128 824B MKI 1.727.350.25
1.727.651.26 IC14 20/92 27256 E79A MKII 1.727.650.26

However, considering the Studer firmware developers did their last significant work in 1988, I would guess the 89 version would include only trivial changes.  Even for Studer A810, most experts consider 01/88 version to be more stable than the later 25/91.


Tape Tech / Re: A810 with 13.83 firmware Eprom error
« on: November 19, 2013, 01:24:34 PM »
Hi Leo:

I just sent you a PM and am thinking I had responded to you already with BIN files for your A810. 

It's been a while since I came by here (where it all started...) and want to make sure you got help just in case.


Reel to Reel Tape Machines / Re: Otari MTR-15 manual wanted
« on: November 19, 2013, 01:09:48 PM »
I had sent out my MTR-15 manual with full schematics to a member in East Coast few years back I believe.  He had scanned the package and returned the originals to me.  I will search my email history and see if I can get a copy of the PDF from him.


Hi Hani

Started to reply to your post and saw the date... realizing we had already got you going with the T-Audio BIN file.  Let me know if you need further help.


Reel to Reel Tape Machines / Re: Finally a Tascam BR-20 for me
« on: August 04, 2013, 11:51:14 AM »
Doc B

Just looking at the funky shaped holes in take up reel, I can't tell the tape being played to save by butt either...

Reel to Reel Tape Machines / Re: Studer A807 Button Labels/Stickers
« on: May 17, 2013, 11:50:32 PM »
Audiohouse in Swiss stocks the labels.


Reel to Reel Tape Machines / Re: Hagerman Bugle
« on: March 04, 2013, 03:39:08 PM »
Excellent thread.

Any discussions that will lead to infecting another unsuspecting tapeheads are good.

I had also contacted Jim earlier and asked about the conversion and have ordered his new phono preamp that I find it very intriguing:

Five days to go... according to the site.

I am pretty sure (although I have not looked at the schematic) the R value are applicable to both models.

Now I had a chance to read your post more carefully, I have few questions:

1) did you change the R17 to 100Kohm or left it alone?
2) would R13 value change to 3.12K ohm for IEC EQ would still be valid?



Reel to Reel Tape Machines / Re: Tape recorder Museum in Hungary
« on: February 26, 2013, 12:52:09 PM »
Not sure whether this has been posted before.

If you are visiting Hungary - a place to visit.  Larry

Hi Larry:

Thanks for posting the link.  I had seen it before and have used it to justify my insanity.  Considering there's no way I can compete, I had been concentrating on hoarding mostly two track master recorders.  I will need to build an extension to my house since I am running out of room. ;)


Tape Tech / Re: Tape Playback Head Cables
« on: August 27, 2012, 03:12:41 PM »

Hope your project will work out well.  Keep us posted with your progress.

I have helped a friend to add a set of RCA female connectors in the back of a Studer A810 to be connected via a set of interconnect cables to his out board tape head preamp, but he experienced some hum.  So we by passed the RCA connectors and went directly from a head wire switch to a set of male RCA connectors using the same cables to the outboard preamp.  No hums.

Good luck.


Tape Tech / Re: Tape Playback Head Cables
« on: August 07, 2012, 11:28:40 PM »
Hi Bob:

Please send me an email.


Tape Tech / Re: A810 faults
« on: June 27, 2012, 09:45:08 AM »

Make sure your 1 mil tape is not sticky and leaving residue and your tape path is clean.  Excess friction from the SSS will stop the machine during FF or REW.

If it's not tape related, you need to adjust tape tensions.  It must start with Play, FF, and REW.  The manual is very good at explaining how to make the adjustments.

Studer Lifter is to keep the tape away from the heads during FF or REW only or when pushed manually.  If your adjustment is off, the tape may make contact with the heads too soon and you will hear the unwanted signal.   You can also configure the machine so that it will mute during FF or REW.


Hi Yoko:

Unfortunately, the Nagra T Audio has "reel holder" mechanism under the cover that makes difficult to adjust the reel spindle height for one set and leave the inner holders alone.

I would suggest you use rubber shims like that are widely used for Otari machines to lift the reel up from the CINE or NAB adapters for your T Audio.

If you need further info on the rubber shims, please let me know.


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