Ok, deep tech thread about tape calibration

[jbeckva]

So ok. I finally found a suitable idler for the Akai, so we now have reels a spinnin'. Now it is time to dial this guy in...

This is where it gets fuzzy in my mind. The service manual calls for this here... a cal tape that puts out 315hz @ -6db. I have one from Alex (A.N.T.) that puts out 200 nWb/M @ 400hz. With me so far, right?

Now the SM says to adjust for -5.5 dBm. So here's my riddle - with the reference tape I have, how much should I be adjusting for, in volts P-P because I am going to have to use a scope to do this with (no "true RMS voltmeter".. sorry).

What the hey IS dBm, anyway?

So now I'm looking up dBm, right? 0 dBm is supposedly .775 volts RMS because that is the amount of voltage it takes to dissipate 1 mW across a 600 ohm load. So far, so good. Got that part figured out, maybe?

Now back to the cal tape I have... 200 nWb/M. Is that 0db NAB or DIN? Supposedly it's 0db DIN, but in reference to the Akai, what would that really come out to be?

So once I figure out the "actual" db the cal tape I have @ 200 nWb/M is referenced at, given that the manual wants a tape that puts out -6db to be calibrated to that -6db, then whatever the "actual" db the tape I have SHOULD be what I would adjust it to... right???!!!

Sooo... how many volts RMS should I adjust for, eh? (I can figure the rest... "x" volts RMS x 2.82 equals volts P-P).

AND...

Does that mean I should put a 600 ohm load across the output???

I aint got a straight answer for this yet heheheh... I challenge you tape "guru"'s out there to make me understand, LOL.

 

[stuwee]

Just trust your ears dude, they're waaaay better than any tape shit, do you want me to come up threre an straightin your ass out??

Did you read my thread on the dynanics of that Kraftwerk tape??

A deck that allows ya to dial in the level and bias is a good thing indeed, I'm F'up and still nekkid, so don't listen to me

 

[Pure_Brew]

I would post the question also on diyaudio. A lot of audio techs/engineers seem to hang there.

 

[BlazeES]

I aint got a straight answer for this yet heheheh... I challenge you tape "guru"'s out there to make me understand, LOL.

One thing I know for sure about Alex, he's smart. Not determined just from discussion threads either - I met him in person. You haven't asked him about this on TH yet? (or emailed him directly?).

Alex walks & talks in his sleep about this stuff.
Alex bleeds in analog while the rest of world is counting digits.
Contact him.

 

[jbeckva]

Alex would be ideal, but ehhh... can't see myself posting on TH's for the immediate future.

 

[Web Police]

Alex would be ideal, but ehhh... can't see myself posting on TH's for the immediate future.

Maybe Stuwee could post on your behalf.

 

[BlazeES]

Alex would be ideal, but ehhh... can't see myself posting on TH's for the immediate future.

Oh sorry, didn't realize you were in the same boat as me.

He's on Karma.

You could try this too!

http://www.ant-audio.co.uk/index.php?ca ... ry=contact" onclick="window.open(this.href);return false;

Invite him to join here too;he'd make a fine addition.

 

[stuwee]

Alex would be ideal, but ehhh... can't see myself posting on TH's for the immediate future.

Maybe Stuwee could post on your behalf. [/quote

Pfffft!

 

[nakdoc]

I make some assumptions. If you agree with me, I suggest writing down each change you make, both the original reading and the value you adjust it to, so the alignment process may be reversed IF (when) you get in trouble. Very few technicians have the specified alignment tapes (shock). For example, my 1/4" alignment tape is the Ampex professional tape. Ampex operating level is about +4dB on most Japanese consumer decks, and often is higher. The first assumption I make is that my tape is not what Akai wants me to use. I play the reference level, which can be any frequency between 315 and 1kHz, and turn output levels either to maximum, or to detent. I note both the readings on a external AC voltmeter (don't use a Fluke. I have a nice tenma needle meter I'll sell for $35) and on the decks meters. My next step is to decide which channel is likely to be correct, and which meter level is likely to be correct. This judgement is a bit of an art, so I am sorry I cannot translate it into works, but the idea is once you assume the correct levels, you adjust the other level to match. The levels do not have to be 0Vu or 0dB.
Let's say the reference tape plays back at +2 on the VU meter and 0.776 volts on my external voltmeter. What I now do is reference everything else to these levels, rather than translate. I could subtract 2 dB, or convert AC volts to dBm, but it really doesn't help much.
The other adjustments follow in place, but I warn you, on decks with monitor level adjust and record AND play meter level calibrations, you are going to wish you sent the deck to a pro.

 

[jbeckva]

LOL.. which is why I haven't cracked open the LX5 ... yet...

 

[speakerman1]

LOL.. which is why I haven't cracked open the LX5 ... yet...

Why would you. Remember Tom went through and set those levels.

Larry

 

[jbeckva]

Lil weak on the right channel, but more prevalent with metal tapes.

 

[speakerman1]

Is that on play back? Were they recorded on the 5? If I remember Naks have a different set of parameters to make adjustments.

Larry

 

[jbeckva]

Yeah, recorded and played. I aint got the "guts" tho to attempt it...

 

[speakerman1]

Well if it is the record head.It would do it on both. You can check the voltage on the recording head. Also just look at it. I'll email you in the morning.

Larry

 

[nakdoc]

Weak right channel is always dirt hidden under the edge of the pad lifter. If it is just a record level calibrate for metal tapes, you may tweak that inside. The board is labeled "Rec Level ZX R". I can look up the VR number for you if you need it.
I think it is useful for every collector to have a playback reference level tape. With it you can answer questions like 'Is is my play level, my VU meter, my other deck's meters, or the record calibration that is causing the diference? " The other use is to match dolby levels between different machines.

 

[speakerman1]

Weak right channel is always dirt hidden under the edge of the pad lifter. If it is just a record level calibrate for metal tapes, you may tweak that inside. The board is labeled "Rec Level ZX R". I can look up the VR number for you if you need it.
I think it is useful for every collector to have a playback reference level tape. With it you can answer questions like 'Is is my play level, my VU meter, my other deck's meters, or the record calibration that is causing the diference? " The other use is to match dolby levels between different machines.

Tom you did this one. I'm sure you remember.LOL Yea right.

Larry

 

[jbeckva]

Weak right channel is always dirt hidden under the edge of the pad lifter. If it is just a record level calibrate for metal tapes, you may tweak that inside. The board is labeled "Rec Level ZX R". I can look up the VR number for you if you need it.
I think it is useful for every collector to have a playback reference level tape. With it you can answer questions like 'Is is my play level, my VU meter, my other deck's meters, or the record calibration that is causing the diference? " The other use is to match dolby levels between different machines.

Dirt under the edge? Hmmmm... got a pic and and arrow to show me? I might be thinking the lifter is something else, hence a bit of confusion.

I got the '5 back up and going tonight. I also have a dbx 224x in between it and the pre. Honestly... even with these cheap ole TDK mass production "D"'s (they came 50 to a box, no individual cases), this combination is kicking the crap out of all I've heard so far. So if my bias or eq is a lil off in the ZX/Metal position, I'm in no hurry to "fix it" right now.

 

[nakdoc]

I guess I should offer a better idea of where the dirt is and why. Q tips are round. When we try to clean a Nak play head, the pad lifter limits where the Q tip will reach, often leaving a bit of dirt at the head's edge, just enough to drop the right channel a bit. Use a good light and magnifier, and you will probably see the spot.

 

[jbeckva]

I guess I should offer a better idea of where the dirt is and why. Q tips are round. When we try to clean a Nak play head, the pad lifter limits where the Q tip will reach, often leaving a bit of dirt at the head's edge, just enough to drop the right channel a bit. Use a good light and magnifier, and you will probably see the spot.

Ahh good point Doc! But would it be more prevalent with metal than normal and high tapes? Just wondering if I don't have two things going on?