Dolby Calibration Cassette

[4tified]

OK, so alot of us don't use dolby in our recordings....from what I've heard anyway. I've been told alot of cassette decks out there drift out of spec and need to be recalibrated in order to use dolby to it's fullest. Well, I believe every one of my decks is out-of-spec. So this brings me to my first question. WHERE IN THE HECK DO I FIND ONE? I have searched up and down on eBay and cannot find anything. Google searches turn up reel-to-reel resources, but nothing on cassettes. Does anyone here have one or know where I can get one? Also, what about head azimuth adjustment, bias adjustment, etc? Are there any resources for these too? The piece in question is my Sony TC-K670. It seems to be weak on the left channel while recording, but I don't know if it's due to head misalignment or if it needs a pot adjustment somewhere on the board. Any help is greatly appreciated. Thanks!

[4tified]

Ok, so I guess my second question would be, does anyone have any of these cassettes for adjustments? At this point, I will go for anything non-vendor specific even. I can't seem to find anything, except info on how to calibrate.....with the tools I don't have.

[Scorpion8]

Here's one source of calibration tapes, but I don't know if they are Dolby-level referenced or just for Naks. http://peromarta.org/naks/cal_tapes.html

[stuwee]

Ok, so I guess my second question would be, does anyone have any of these cassettes for adjustments? At this point, I will go for anything non-vendor specific even. I can't seem to find anything, except info on how to calibrate.....with the tools I don't have.

There are some that pop up every now and then like this one for a Nakamichi.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150274596824&ssPageName=STRK:MEWA:IT&ih=005

Very pricey though, if you don't have the tools, other than the calibration tape, am I reading that right? You may want to send it to a tech. Maybe someone here??

Sorry 4tified, that's all I got for ya.
Craig

[4tified]

There are some that pop up every now and then like this one for a Nakamichi.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150274596824&ssPageName=STRK:MEWA:IT&ih=005

Very pricey though, if you don't have the tools, other than the calibration tape, am I reading that right? You may want to send it to a tech. Maybe someone here??

Sorry 4tified, that's all I got for ya.
Craig

Thanks for the link Craig, it's a start. I sent the guy an email to see if he could send me in the right direction, but all I see is Nak, Nak, Nak... and yeah, I don't have any tools for these types of adjustments. If anyone here would be willing to do the adjustments for a decent price, or lend me the tapes to perform at least a tune-up, I'd be happy as can be.

[Scorpion8]

For you I'd think the best bet would be dr*audio or EchoWars. I don't know if EW works on tape decks, but I see dr*audio on Naktalk periodically. I know he has the equipment; I don't know if he has the time. I've been pondering gathering the equipment and expertise but my corner of lack-of-civilzation has little need and shipping in and out of the last frontier would be excessive. Still, I may do so just to humor myself and to flip a middle finger to old AKquaintences.....

[JXBJXB]

The piece in question is my Sony TC-K670. It seems to be weak on the left channel while recording, but I don't know if it's due to head misalignment or if it needs a pot adjustment somewhere on the board.

There are a few things you can do, carefully, to check that Sony deck out and fix it yourself without getting into trouble. Before I continue - your mileage may vary, and I'm not responsible for you royally messing anything up or electrocuting yourself.

First, if you suspect head misalignment - get either a quality pre-recorded tape or a tape that you KNOW was recorded on a properly aligned and calibrated deck. Clean your Sony's heads. Play tape back, use headphones. Got a good center image? High frequencies sound good (check Dolby setting to see if tape needs it or not)? Then your head is most likely in alignment.

High frequencies sound good but image (like vocals) is left or right of center? Playback level is suspect. Find pots on circuit board (they are often marked), play tape back, adjust playback level L or R pot CAREFULLY as you play back that known good tape until you get a good center image.

IF you are sure that your head is reasonably aligned AND you can play tapes back with a good center image, then you can CAREFULLY adjust the record level pot for the left channel. Get a test CD that has a mono test tone (the Stereophile CD is excellent for this) and record it (heads cleaned and demagged, right?) using a good tape, no Dolby. Since the Sony is a 3-head, you should hear the deficiency in the left channel (and see it on the meters) as you record. Slowly adjust that left record level pot upwards until you have a defined center image. Assuming your deck's meters are still calibrated, you should also see them registering the same peak level at the same time.

I do NOT recommend messing around with any of the following by ear: internal bias adjustments, internal meter level adjustments, and head alignment (especially on a three-head). That Sony deck is relatively new and unless it has been abused in some way or a tech has messed with it, or there wasn't any loctite on the head alignment screws, it should still be in alignment. But maybe the internal level pots have gotten dirty or drifted over time - in which case my DIY advice applies.

[Scorpion8]

High frequencies sound good but image (like vocals) is left or right of center? Playback level is suspect. Find pots on circuit board (they are often marked), play tape back, adjust playback level L or R pot CAREFULLY as you play back that known good tape until you get a good center image.

The proper way to do this is electrically. That is, use a level reference tape which you can buy or make on a known-good deck by recording either test tones off CD or even FM interstation hiss. Then play it back on the suspect deck and using a DMM examine the voltages present at test points or identical spots in each playback channel, and then adjust those pots to give the same playback level signal voltage.

I do NOT recommend messing around with any of the following by ear: internal bias adjustments, internal meter level adjustments, and head alignment (especially on a three-head). That Sony deck is relatively new and unless it has been abused in some way or a tech has messed with it, or there wasn't any loctite on the head alignment screws, it should still be in alignment. But maybe the internal level pots have gotten dirty or drifted over time - in which case my DIY advice applies.

Agreed, I'd second that.

[4tified]

Thanks guys for all the info, I did forget all about verifying voltages on the rec input pots. Guess ya'll are right about that Dolby and bias levels, they shouldn't need adjustment (I'd be weary to anyway withou the correct tools.)
I'll give the input adjustments a try later on this week.

Now, one more question... I know I should get a service manual, if nothing else, for verifying voltages of those pots on the board (the pots are easily marked with what they go to.) Where is a reputable place for me to obtain a service manual? I know a goolge search may suffice, but that got me in trouble last time.... the service manual webiste (manuals in pdf.com) took two months to send me the manual....not a trustworthy place that states 24 hours or less.

[niklasthedolphin]

I did not examine in details about the request in the OP and the options on the page I link to here (http://home.flash.net/~mrltapes/), but they make calibration tapes.
Maybe there is something there?

"dolph"

[geauxldmember]

The proper way to do this is electrically. That is, use a level reference tape which you can buy or make on a known-good deck by recording either test tones off CD or even FM interstation hiss. Then play it back on the suspect deck and using a DMM examine the voltages present at test points or identical spots in each playback channel, and then adjust those pots to give the same playback level signal voltage.



Agreed, I'd second that.

Hi, since I have some time to "play", I was trying to verify Dolby on a deck I have. The SM states the voltages (DC voltage at no input signal):

OFF - .18V
B - 5.88v
C - 9.28v

If I'm understanding it right those should be voltages I get by testing. If they read that voltage then the deck is operating within specs as set by factory?

So I hooked up the handy multimeter and started measuring by switching Dolby modes on the front panel. The points I tested showed both B and C voltages being higher than stated. B is 6.4v and C is 10.1v The Off reading appeared normal.

Does anyone have experience with this situation and actually fine tuning the dolby level? I don't have a calibration tape but wasn't sure I really needed it since I had the measurements. The dolby circuitry has 2 adjustments TP1 Right TP2 Left. Wondering if those actually control the levels??

Just looking for advice, tips and warnings.

thanks.

[390FE]

When you were making these mesurments did you have a tape in the deck & in say record mode (with no input signal) or play mode with a blank tape to put a "load" on it? You can try that but I don't think it will make a diff in your measurements but it may.

Also you need to follow exactly the procedure in the Service Manual starting from the begining of that section. Otherwise you may not get the proper readings. If there is a Flow Chart follow that as it may help troubleshoot.

Another thing is you need to make sure your meter's negative (black) lead is placed/attached to the proper common/ground point as shown/listed in the Service Manual. Because if it is NOT on the proper ground/common point for each test section/point/procedure you COULD/WILL get the wrong readings.

Also let the deck warm up a little & wait a minute after you switched/changed settings on the deck for the voltage to stablize.

If the measurments are still off/wrong then follow exactly what the Service Manual says & what pots to adjust. It may say something like "Adjust VR105 or R105 so voltage reading is X + or - x". If it tells you that a Calabration Tape is needed for that part of the testing/alignment then DO NOT attempt ANY adjustments.

You can also scan that section of the Service Manual & post it in this thread so someone here can look it over & see/verify if you are doing it correctly.

[Nakdoc]

I am in the midst of QC-ing Dolby level and azimuth test tapes made by Tom Majerus. The level tapes are ready to sell. Tom has asked me to distribute them for the time being. The price is $35 per tape in the US. I will have a real post about these after the Azimuth tests are finished, but if you need one quickly PM me.

[geauxldmember]

When you were making these mesurments did you have a tape in the deck & in say record mode (with no input signal) or play mode with a blank tape to put a "load" on it? You can try that but I don't think it will make a diff in your measurements but it may.

Also you need to follow exactly the procedure in the Service Manual starting from the begining of that section. Otherwise you may not get the proper readings. If there is a Flow Chart follow that as it may help troubleshoot.

Another thing is you need to make sure your meter's negative (black) lead is placed/attached to the proper common/ground point as shown/listed in the Service Manual. Because if it is NOT on the proper ground/common point for each test section/point/procedure you COULD/WILL get the wrong readings.

Also let the deck warm up a little & wait a minute after you switched/changed settings on the deck for the voltage to stablize.

If the measurments are still off/wrong then follow exactly what the Service Manual says & what pots to adjust. It may say something like "Adjust VR105 or R105 so voltage reading is X + or - x". If it tells you that a Calabration Tape is needed for that part of the testing/alignment then DO NOT attempt ANY adjustments.

You can also scan that section of the Service Manual & post it in this thread so someone here can look it over & see/verify if you are doing it correctly.

I tried playing a tape and without. I really need to go back and check what you suggested. Using the exact ground, etc... I'm definitely not tweaking anything until I know that I'm doing that procedure properly. I see now that a level tape is almost ready for sale. So that will be helpful.

thanks for all your suggestions and tips.

[Skywavebe]

Hello 4tified and others;
Having worked on cassette tapes for a good many years I can add some information to what was already said. First a Dolby tape such as A Teac MTT150 was made not only for the purpose of Dolby alignment but for the general setting of output levels. It was made to set decks playback up to a standard of 160nWb/M. I do not think they are available anymore.
While there were Dolby test points that required the 580 mV to be in the right area of adjustment for Dolby to track properly, voltage measurements were usually not the final say on the output or input calibration levels but a well designed dB meter. This is mainly because most all deck ins and outs are
designated as in dB values. The Teac M826A was a test set used at all benches at the Facility and was only replaced by such better equipment such as the Leader MV182A. I still have a 826A on my bench. It is just more work to use than an Audio Precision One Plus. Adjustments that can be relied upon have to be done with good reference tapes. Not those recorded on some machine you think is right. I have seen machines adjusted to abstract standards and a lot of the time it is comical but that only lasts until the job is corrected. I am not trying to be a snob or put down all of these pink noise home remeadies, but there is a reason Teac, Sony and a few other companies set up and ran their own service facilities to establish a standard for repair where the standard would otherwise be all over the place. I have so often looked at service facilities names on incoming equipment- sometimes with fright, to say that not all authorized facilities had a good handle on how to fix this equipment. I continue to get an occasional reel deck from clients that already spend $200 to have nearly nothing done to the machine from a shop that hardly knows what a reel machine is for. This extends to cassette decks to some extent as well.

[Nakdoc]

Sam's post is right on. What I find helpful is to use the dolby tape to establish the signal at line out, and then reference everything to that. Many decks use 0.5 volt, many 0.7 volt, and better Naks 1 volt. Once you know how the reference level translates alignment is easy. The good feature of any Dolby deck are the meter symbols telling you exactly where Dolby level ought to be.