Tascam 388 Story...

Okey-doke...

Let me do a little more research but I'm pretty sure your culprit is the same as mine...a bad switching IC.
 
sweetbeats said:
Rikard,
Look at post #128 in this thread. Sound like your problem??
Click to expand...

If it is, note that Sweetbeats seems to have got the IC wrong, apparently it was U104 he swapped out, not U102. U104 is apparently an MC14049B, which I take to be a 6-input logic inverter.
 
Yup-yup!

Thanks, jpmorris.

You are absolutely correct...U104 on the BUSS B PCB is the suspected culprit.
 
Wow, I'm impressed, and yeah I just read back and that is definitly it. Great that it's narrowed down, bumber that it's way above my hack skills to fix. But there is a good shop in Fremont (Seattle) Condor Electronics, that I communicated with right before I bought this bad boy that said they work on the 388's, in fact they have them in often and are Tascam certified. So it will help allot when I do eventually bring it in (when my fiance is no longer mad at me for buying yet another piece of equipment, she has no idea what she's getting into :) ). I really appreciate the help, so amazed at the wealth of knoewledge. If there are any suggestions on fixing it myself I'll take em, I'm good with taking things apart and putting them back, and changing belts and cleaning things (I run large format printers for a living, so I have to do allot of that) but when it comes to electronics, and understanding circuit boards, chips, and all that stuff, I'm a big dummy
 
Sweet!

I got mine third hand Christmas 1995.

Previously, I had been recording decently on a cheapo plastic 4- track cassette...

My old drummer was friends with the original owner... a carman for the railroad in LaPort, Texas. In 1993, he was killed on the job, and the drummer came into possession of it. Noting the strides I was making in my 4 track efforts, and due to his impatience... and not wanting to aquire the discipline to run the 388, it was a gift to me to further our bands' efforts.

Anyways, it was very nice reading your post... I would certainly like to resolve whatever is wrong with my beloved 388 and start using her again!

Happy recording!


Wes
Hockley, Texas
 
I have a buyer for the 388 so I'm finally going through and doing all the transport and electronics setup and calibration.

Brakes are all set, as well as the pinch roller pressure.

Set all the tensions last night as well as the REW/FFWD speed. It was an interesting process but I was able to nail pretty much everything. The intersting part was dealing with some interdependency on some of the settings (i.e. you make some changes which effect other settings so you cycle through the process a few times to hone everything in). It remains a little low on the PLAY holdback tension. Nothing concerning as it is just slightly low and there is still good/positive head contact and this may actually extend the life of the tape path.

What I want fellow 388 owners to know is that there is a typo in the manual in the tape tension settings regarding the REW/FFWD tensions...the manual on page 1-9 in section 1-3-7 sub-sections A & B states that trimmer R105 on the reel servo PCB is used to adjust the tape tension in FFWD, and that R206 is used in REW. THAT IS BACKWARDS. R105 is used for REW mode, and R206 is used for FFWD.

I'm just stepping through the manual so next up is checking the mixer out and setting the meters, but after than I'll get into the tape transport electronics and we'll finally have the answer to the nominal bias amp voltage to use when using LPR35.
 
Coming along well.

I've fully tested the mixer section, all is well.

The reproduce electronics are all setup and they lined up really nice...very consistent from track to track and the response curve is nice.

I've started on the bias section now...the coils have been tuned and next I'll adjust the traps.
 
Spent quite some time last night messing with the bias. IIRC Tascam told me that "LPR35 needs twice the bias". The bias amps only go up to about 200mV output max and I messed with the tuning and the traps (non-ideal) to see if I could tweak that at all but I can tell you it isn't worth doing that...keep the tuning and traps as spec-ed in the manual (minimize the DC and AC voltage respectively). I was doing what was suggested by tascam which was to scope the output of a recorded 10k tone and adjust the bias amp output for minimum distortion, but this is difficult with the narrow format as there is more "noise" in the recorded signal anyway and its hard to decipher the noise and the distortion on the scope.

I decided to try using the LF modulation technique instead to try and find the optimum bias point. This is the "listening for 'rocks'" technique. I know this also isn't as effective with the narrow format, but I decided to try it anyway. I dialed up a 7Hz tone on my oscillator setup and tracked that to 4 tracks with a track in between each (i.e. tracks 2, 4, 6 and 8) and to try to avoid any tape saturation confusion I tracked it at about -3VU. I set the bias amps for those tracks 5mV apart so that I could listen back to the result across a 20mV spread. I started with the lowest output at 70mV (so track 2 at 70mV, track 4 at 75mV and so on). I repeated the process until I could play back a minute or so of the 7Hz tone on a track without hearing any "rocks" and then noted what the bias amp output was set to on that track...its difficult because there is a lot of HF modulation noise...you don't actually hear the 7Hz tone of course but you REALLY hear the modulation noise puff-puff-puff-puff-puff-puff with the "rocks" (kind of a pop-pop-pop-pop-pop to varying degrees) and once the rocks go away then you start to hear more HF noise...the distortion actually seems to start becoming more hissy...excuse the verbage here but the best way to describe it is piss-piss-piss-piss-piss instead of "puff"...I thought that was the "noise" factor I was looking for to balance the distortion (rocks) and noise (hiss) to find the optimum bias point (in between those too) but things were getting more piss-piss-piss (I'm starting to sound like I have tourette's disorder) and I was STILL hearing some rocks. Then I realized the "noise" I was listening for wasn't in rythym with the 7Hz tone, the puff-puff-puff but rather is a more constant hahhhhhhhhh. When I realized that was the upper limit I was looking for, and the disapperance of the rocks was the lower limit, that's when I found what I think to be the optimum point. That was at about 120mV bias amp output. This is totally contrary to what Tascam told me, but I know what I'm hearing. I setup all tracks to 120mV, recorded 2 minutes of 7Hz tone and listened back to all the tracks...no rocks, and little "hahhhhhh". To test I dialed one track up to 150mV bias amp output and while the modulation distortion continues to get more "pissy" (pisss-pisss-pisss) the "hahhhhhhh" also gets louder. So I'm pretty comfortable with the 120mV figure for LPR35.

The only caviat here is that I'm not done with the reproduce frequency response. I can't even HEAR the 16k tone reproduce which is supposed to be within +/-3dB of 0dB at 500Hz. My HF response strarts dropping by 4k. I haven't messed with the record eq yet. I was worried about how it was going to sound because of all the noise artifacts I'm hearing with the tone ladder I'm recording to check the record eq and I was thinking "MAN! If I dial up the record eq to get the response in spec there's going to be too much noise!" because it sounded like there was too much already. I decided to do a test of program material...a selection of snippets of pre-recorded stereo consumer material of varying styles bussed in pairs to all 8 tracks, now with the dbx on of course.

It sounds great. Man I love tape. It is very quiet in terms of noise with the dbx on and everything just sounds really sweet and the 388 really does an amazing job with the low-end thanks in part to the 7.5ips transport speed IMO...puts a little head bump at around 60Hz for those of you that haven't noticed and the bump is often something to contend with in the 100Hz range at 15ips...but even though my HF response is off at this point the highs sounded really good when reproducing the material...smooth and present. I'll tweak the record eq tonight and that may mean tweaking the bias a bit which will mean redoing the record level...and there may be a reproduce eq tweak to do as well. I had to guess at where to start rolling the HF reproduce response because I'm using a 15ips cal tape that only goes up to 20k (so 10k at 7.5ips) so I started rolling at 8k...that may be too late? In which case the HF response may still be too high at 16k to balance with the bias and record eq. So I'll mess with it a bit more and see.

I will tell you though that doing all this testing and tweaking makes me REALLY appreciate a 3-head machine. Once this is set it'll be set and good. Under normal circumstances its not such a big deal but with all the bias experimentation I'm getting REALLY familiar with the RTZ button. :)

The 388 sounds really nice, fellas. Oh, and the transport is operating flawlessly...tensions are enabling nice crisp tape handling and nice fast-wind performance.
 
MAN I love analog tape!!

Its done. Buyer picks it up tomorrow and this 388 is ready to do what it was made to do.

Did some more tweaks to the bias and experimented with the record eq...went back and rechecked a number of things in the process. The record and reproduce frequency responses are now in spec...even the edge tracks are solid. The levels are really stable across the spectrum.

Sweetbeat's final word on the bias amp level for LPR35: 110mV

After all the tweaking that is the best balance AFAIC between minimizing distortion and maximizing response.

And how does it sound? Well that's why I made my opening statement...I just love what tape does to audio, and even this machine, what many would call an inferior format, makes digital program material wider, more natural and more exciting to listen to...easier on the ears and fiery for the soul!

It sounds awesome.
 
Its gone folks!

And I have no regrets...not that the 388 isn't a super cool machine and not that mine wasn't a total winner, but I'm happy because I've got too much stuff and when you've got too much stuff and limited time there's no way to enjoy anything, so I'm making steps to enjoy the stuff I'm keeping.

I'm happy with the young man who bought it.

  1. He'd done his research
  2. Knew what he wanted
  3. Clearly appreciates the genre and respects the equipment
  4. Traveled a long, long way to transport the machine in-person
  5. Will be putting the 388 to good use
Kudos!

So another "Story" closes but it will be living on in another part of the USA, and this thread will continue as a resource for other 388 owners/enthusiasts and for those that need help.

There is absolutely nothing else like a Tascam 388!
 
OH!

And BTW, I'm going to be tearing down the 388 parts machine and selling that off in a hurry so if you need something for your 388 you better let me know quick.
 
So how did you like doing the bias adjust by the LF hearing method? For some reason, I at least thought I had a better sense of the adjustment by listening rather than just using instrumentation. I re-adjusted my 38 using this method.
 
fstrat...I liked it a lot better. Part of that is just because I'm often unreasonjably particular, but the reality is that the "overbias" technique is once-removed from a true feedback adjustment of how the bias tone is effecting distortion, and the method in the 388 manual (of setting the output of the bias amp to a particular level) will never take into account variances in bias requirements between tape brands /types or even different batches of same tape. Maybe its splitting hairs but being able to actually listen to something that you can audibly and cognitively assess as "distortion" and then make adjustments to minimize, and then hearing the noise come up...its a good education and opens the meaningful door to questions like "what happens if I purposely over or underbias for a particular effect?" Its a whole new facet to the art of tape and operation level selection as well as eq tweaks. Its fantastic. There is a whole world of possibilities from the humble tape deck. Yes there are best practices and I think it is essential to get that under your skin but from there? Go for it. Try different things once there is understanding. It can be really powerful as a tape deck operator.

I will say that it IS cumbersome using the LF modulation noise technique on a two-head machine but if you've got the gumption it may be worthwhile particularly if you are using a tape type significantly different than what was specified at the time of manufacture.

Bottom line: I'll be using that method again and I suspect I'll like it even better on a machine with 3 heads and a wider frequency response...I think My BR-20T is up next.
 
I found I like the LF way better also, but I've also read online somewhere that certain tapes cannot be biased this way.
 
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