DIY Alignment and Calibration

That sounds like a bad relay on channel 1.

Thanks for the reminder...I forgot that 38 still has 1 card per channel.

Swap cards 1 and 2 and see if the problem follows the card, but that sounds exactly like a bad relay...and to get the cards out...

That crossbar and the friction of the card connectors are the only things holding them in. Do you see holes through the corners of the cards? You can make a bale out of a piece of coat hanger or something like that. Hook it through and then you've got a handle to pull and gently rock back and forth as you pull. It'll come but they can indeed be tough if they haven't been pulled in a long time. Who knows...reseating the cards may addrfess your channel 1 problem and is sort of SOP with a vintage deck if it hasn't been done...a little contact cleaner and seat and reseat each card.

BTW, nice job.
 
Well, I swapped cards. Channel 3, which is working great, I put that card in channel 1.

Same thing still happens on track 1, input meter 0VU perfect, record 10kHz, little to no reading on the VU on Repro, then up to -7, then down on the meter, etc. All track 1. (track 2 I thought was ok, but I'm not 100% sure).

Now I FF'd closer to the end of tape and tried it. I get better readings here.

I also noticed that cleaning the heads etc afterwards its quite dirty, especially on the capstan and posts. The RMGI S911 tape is less than a year old, could a tape be a problem on just tracks 1 and 2?

Could it be the heads or is there another test or electronic adjustment I can try?
 
fstrat76 said:
Well, I swapped cards. Channel 3, which is working great, I put that card in channel 1.

Same thing still happens on track 1, input meter 0VU perfect, record 10kHz, little to no reading on the VU on Repro, then up to -7, then down on the meter, etc. All track 1. (track 2 I thought was ok, but I'm not 100% sure).

Now I FF'd closer to the end of tape and tried it. I get better readings here.

I also noticed that cleaning the heads etc afterwards its quite dirty, especially on the capstan and posts. The RMGI S911 tape is less than a year old, could a tape be a problem on just tracks 1 and 2?

Could it be the heads or is there another test or electronic adjustment I can try?
Click to expand...

Can you post a few pics? I did have some bad RMG at one time and it did some strange things, but it sounds like their more worries then bad tape.
 
Strat, are you getting any edge flaking on any of the guides or anything?

Where did you buy the tape from?

I had an experience on my 58 when I had where my record level totally dropped out. Turned out to be a *tiny* oxide flake over the head for that track. It takes very little. The tape I had turned out to be from an early batch of RMGI SM911. I'd purchased the tape from an authorized RMGI dealer (US Recording Media); they got me in touch with RMGI and they confirmed that the tape was from one of those batches and they replaced it expediently and free of charge. The replacement reel worked flawlessly.

Is the yuck on the capstan toward the top of the shaft then? That's why I ask if you are getting any flaking on a guide. I was having trouble with SM900 on my BR-20T but it wasn't the tape's fault. Generally you'll find that the AGFA/BASF/EMTEC/RMGI stock is slit slightly wider...12.7mm as opposed to 12.5mm for Ampex/Quantegy stock. If the guides and heads have a wear path worn into them from the latter you'll often have issues with the former flaking on the edges because its getting abused by the 0.2mm more narrow tape path. If the wear path is significant the only expedient solution I know is to rotate the guides and lap the heads or switch to Ampex/Quantegy tape. The lifters can come into play in this too and the lifter posts can't be rotated (easily).

Let's make sure the tape isn't getting beat up and that your tape path is set up right before we continue because you'll be forever struggling with debris in the path.
 
Well, that's interesting. I'm having a similar problem with the new MRL tape I just purchased. After using it just for a half and hour or so at a time, I clean the heads and posts and they are really dirty after use. Especially the guide right past the capstan, on which the back side of the tape makes contact. I have also seen small oxide particles near the erase head and post capstan guide, especially after using the MRL tape, and just a little bit after using the RMGI tape (which I purchased from US Recording last year). I am in contact with MRL and was going to send the tape back to them. And yes, the capstan is dirty especially at the top of it.

I inspected everything in the path, I don't see anything off-hand. I will inspect closer and I will take pics if necessary. When I got the machine, a auth tascam service guy looked at the heads at least and said there wasn't even any wear on them and this looks to be true.
 
OK, I've inspected closely and see an uneven wear on the left guide post at the top. The lifters also have even wear in them, but if that were wear caused by a narrower tape, then I can see how the groove in the lifters could affect a wider tape.

I was able to rotate the guide and get the wear out of the way in case it was the cause of this issue.

After playing the tape some, RW and FF some, it is still leaving some very small particles behind near the left guide.

The guide shaft on the far right between the capstan and the right tension arm, where the back of that tape makes contact, is extremely dirty after cleaning.

Though should there be any at all after 15 minutes of play?
 
New MRL tapes are on RMGI stock.

Its not uncommon for there to be something to clean up after 15 minutes, but it should be scant AFAIC...

So stuff gets all dirty even if you don't FF or REW (i.e. avoiding the lifters)?

And you've setup the tape path according to the manual?
 
sweetbeats said:
And you've setup the tape path according to the manual?
Click to expand...

Well, I've re-checked this, I can't see a problem. Everything seems straight. You are right though, if its 12.7mm, its pretty snug fitting on the tension arms and guide posts, but it still looks correct. I mean it looks fantastic going across the heads and guides.

Hard to describe but one interesting thing is that there is a very very narrow machined groove around the tops and bottoms of the right post and the tension arms. This looks OK but if the tape is wider as you say, I can see if there's too much tension that the tape moves into these grooves, don't know if that makes sense.

sweetbeats said:
So stuff gets all dirty even if you don't FF or REW (i.e. avoiding the lifters)?
Click to expand...

Yes, after about 15 minutes of just play, I clean the heads, they are pretty clean but the guide posts and capstan are dirty. The right post where the back of the tape passes had some small black buildup on it. It had a lot of black buildup before this last cleaning.

I don't remember this as being normal, is this normal?

Even if I try the bias adjust on track 1 using the very end of the tape, while it is much higher in level on the repro, it still jumps all over the place, down -5, -7, back up again.

I am looking at another machine that is local this weekend. I will have to purchase some new tapes also, but frustration is setting in with this machine. So close, but better to know I guess.
 
Can you rotate that right guide (the one just before the capstan shaft)?

Wait a minute...you're threading the tape OVER that right guide (i.e. the back of the tape is coming in contact with that guide)?

Strat, I think the oxide side of the tape is supposed to got through that guide...
 
No, its the guide right after the capstan but before the right tension arm that the backing of the tape makes contact with on its way to the tension arm and to the takeup reel. Its called the guide shaft. Its threaded properly. Otherwise, yeah, that would be a disaster.

I just ran a 0VU 1kHz tone recorded on all tracks and checked repro, and tracks 1, 8. and sometimes 2 have drop outs. Sometimes its perfect. Very weird.

I'm out of options I think. I'll check out another machine and get some new tapes unless you can think of other options.
 
I'm sorry for your frustration...did you contact US Recording Media? It is worth double checking to make sure the reel of tape you have isn't from a bad batch. And I wouldn't rule out bad relays either.
 
Wouldn't the bad relays follow the card though? I've swapped the cards and the trouble is not following the cards, so it's either the record heads or some circuit in between, or a bad tape.

Yes, I contacted US recording and they gave me the number for RMGI. It's still under warranty as is the mrl tape.

I get to do this all over again. Becoming second nature!

Thanks for all the help. Will be back here soon with good news I hope!
 
Yes, a relay problem would follow the card. Relay problems I've encountered however are phantom-esque though...hard to follow/trace/nail down...I'm just saying donzt assume there is only one issue occurring...also don't want to discourage you.

Get a handle on the tape situation...contact RMGI...see if a different reel is different.
 
Hi everybody,

I also have been trying to put together tools to do a calibration on Tascam 38, but I've been hitting snags pretty much every step of the way.

Probably the biggest issue has been finding a good tweaker. I did some searching and simply could not find anything that resembled the right tool. Even did a search for plastic screwdrivers and found nothing at all. Checked both local hardware/electronics shops as well as online. I'm thinking they have a name I'm not familiar with.

I ultimately settled on a set of "permanently demagnetized" electronics screwdrivers. Tried them tonight and they still caused the VU meters to peg. I know this is bad to do to the meters, so I'm hoping somebody has some insight on how to find the right tool for the job.

Next big issue I'm hitting is the comparison between input and output. I set up my Multimeter to read the output of the MRL tape (15 ips, IEC curve). The VU meters were reading at -3dB, and the multimeter read 0.06x V (i.e., in the range of 60 millivolts). I rigged up an input source (an iPhone running a signal gen app) to read about 60 mV on the same voltmeter, and the 38's VU meters (in Input mode) were reading about -18dB across all channels. So methinks something went awry with the previous user (particularly since the manual says that the MRL tape should be read -10dB). Hopefully somebody can give some insight into the matter.

If I missed any pertinent info, I'll be happy to fill you in as best as I can, but any help would be greatly appreciated.
 
Moseph said:
Hi everybody,

I also have been trying to put together tools to do a calibration on Tascam 38, but I've been hitting snags pretty much every step of the way.

Probably the biggest issue has been finding a good tweaker. I did some searching and simply could not find anything that resembled the right tool. Even did a search for plastic screwdrivers and found nothing at all. Checked both local hardware/electronics shops as well as online. I'm thinking they have a name I'm not familiar with.

I ultimately settled on a set of "permanently demagnetized" electronics screwdrivers. Tried them tonight and they still caused the VU meters to peg. I know this is bad to do to the meters, so I'm hoping somebody has some insight on how to find the right tool for the job.

Next big issue I'm hitting is the comparison between input and output. I set up my Multimeter to read the output of the MRL tape (15 ips, IEC curve). The VU meters were reading at -3dB, and the multimeter read 0.06x V (i.e., in the range of 60 millivolts). I rigged up an input source (an iPhone running a signal gen app) to read about 60 mV on the same voltmeter, and the 38's VU meters (in Input mode) were reading about -18dB across all channels. So methinks something went awry with the previous user (particularly since the manual says that the MRL tape should be read -10dB). Hopefully somebody can give some insight into the matter.

If I missed any pertinent info, I'll be happy to fill you in as best as I can, but any help would be greatly appreciated.
Click to expand...

http://www.weisd.com/store2/GC 00-5009-0000.php
has what might work. I'll keep looking.
 
Moseph said:
Next big issue I'm hitting is the comparison between input and output. I set up my Multimeter to read the output of the MRL tape (15 ips, IEC curve). The VU meters were reading at -3dB, and the multimeter read 0.06x V (i.e., in the range of 60 millivolts). I rigged up an input source (an iPhone running a signal gen app) to read about 60 mV on the same voltmeter, and the 38's VU meters (in Input mode) were reading about -18dB across all channels. So methinks something went awry with the previous user (particularly since the manual says that the MRL tape should be read -10dB). Hopefully somebody can give some insight into the matter.
Click to expand...

If I recall, the MRL Tape output on the Repro head calibration should read 0VU on the meters and 3.16V on the multimeter for each channel. You calibrate the Repro and Sync outputs to 3.16V first, then adjust the meter trim to read 0 VU. 0VU = 3.16V = -10db.
 
dodgeaspen said:
http://www.weisd.com/store2/GC 00-5009-0000.php
has what might work. I'll keep looking.
Click to expand...

Awesome, thanks. Has anyone dealt with this supplier before? Do they have any sort of reputation?


fstrat76 said:
If I recall, the MRL Tape output on the Repro head calibration should read 0VU on the meters and 3.16V on the multimeter for each channel. You calibrate the Repro and Sync outputs to 3.16V first, then adjust the meter trim to read 0 VU. 0VU = 3.16V = -10db.
Click to expand...

Okay, having a fresh night of sleep, I think I've got a little bit better thought process about things in view of this:

After a quick calculation*, doesn't this suggest that the reference voltage is about 10V? Granted I'm still pretty new to this but that seems high to be considered a "line level" signal.

The 38 Manual says that 0.3 V should be -10dB. Doing the same calculation, that puts the reference value just under 1 V, which I think is how "line level" is defined? More troubling to me last night, though was that I was reading 60 mV = -3 dB, which is a factor of 5 less than what the manual said and more than triple the VU reading. That's kind of where I'm concerned about how things are set up currently.

Assuming either log situation is correct, does that suggest that my input level and Sync/Repro head levels were just sort of arbitrarily set? There's a big difference in meter readings there, so I'm just wary if I've got things all mixed up compared to the previous owner.


Also, thanks for the quick and helpful advice: really appreciate it!


*20 log (x/y) = z; z is the dB value, y is the ref value, and x is the measured value, log is in base-10
 
Yes,I believe its 0.316V not 3.16V as I stated previously. I don't have the manual in front of me, but it should give the references there.
 
Don't get your signal level confused with the tape reference level.

-10dBv is indeed "line level" as is 0dBv or +4dBu or +8dBu...those are all considered line level, just different flavors.

Your 38 line amps are built around the -10dBv standard which is indeed -0.316VAC RMS.

Do you have a meter that reads RMS voltage? If you don't you really ought to think about it.

SO...

Do like you did and setup your generator to connect to your 38 input, but use a 'Y' cable so you can put your meter probes on the generator output while it is also connected to the 38 input.

Adjust the generator until it reads -0.316VAC RMS.

NOW...move your meter to the corresponding output jack, put the 38 in INPUT monitor mode and adjust the input level trimmer on the amp card until the output level reads as close as you can get to -0.316VAC RMS.

NOW adjust the meter trimmer so that it reads "0VU".

Repeat with the other channels.

You've just calibrated your input levels and meters.

Don't fret if they are off and need adjustment. That's why you're calibrating right???

If you follow the steps above as written your machine's inputs will be calibrated to -10dBv as well as the meters and you'll be ready for the next steps.
 
sweetbeats said:
Don't get your signal level confused with the tape reference level.

-10dBv is indeed "line level" as is 0dBv or +4dBu or +8dBu...those are all considered line level, just different flavors.

Your 38 line amps are built around the -10dBv standard which is indeed -0.316VAC RMS.

Do you have a meter that reads RMS voltage? If you don't you really ought to think about it.
Click to expand...

Yeah, I made certain to get something that was True RMS. I think it's got good specs for the other needs, too (based on this thread and some other random reading):

http://www.triplett.com/product_info.php?products_id=52&osCsid=93e68a3d2e361d0836e9a2f358197d5c


SO...

Do like you did and setup your generator to connect to your 38 input, but use a 'Y' cable so you can put your meter probes on the generator output while it is also connected to the 38 input.
Click to expand...


You know, I should have realized this myself. That makes a lot more sense than what I was doing (of course, I was also working off the wrong voltage level in the first place...).
 
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