Tascam LA-40 Info Needed

sweetbeats

Reel deep thoughts...
Hey all...do any of you have a schematic for the original (mk I) Tascam LA-40 converter box (balance/unbalance -10dBV to +4dBu)? Or if no schematic, if you have an original LA-40 in your arsenal would you be willing to open it up and take some pics of the guts for me?
 

sweetbeats

Reel deep thoughts...
And FWIW this is research to solve a mystery with my prototype Tascam console...so this isn’t just some random inquiry for information...yes...your help could solve a mystery!

:D
 
I spent 30 min trying different search phrases with no luck at all. Seems others have been asking for this same info since 2013 in other communities. You may have to BTB and contact Tascam and purchase one. I hope someone can come to your aid.
 

sweetbeats

Reel deep thoughts...
Thank you. I appreciate the effort! I don’t mind paying for a document, but I’m having trouble getting a Teac to call back. :\
 

sweetbeats

Reel deep thoughts...
Thanks, Mack Caster.

I was dialing that part dept number but it wasn’t going through. Probably something on my end. At any rate I got through to a live person and a reprint of the LA-40 Service Manual is on its way to me...$22 shipped. Not pennies but worth it to me to have a 1st generation authorized reprint. I’ve got burning questions about my prototype console that might be answered by the LA-40 tech docs.
 

yoshi420

New member
Hey Sweetbeats, do you think you could post the LA-40 manual? I've looked everywhere and can only find the manual for the mkii and mkiii. Thanks!
 
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sweetbeats

Reel deep thoughts...
Hey Sweetbeats, do you think you could post the LA-40 manual? I've looked everywhere and can only find the manual for the mkii and mkiii. Thanks!

Sorry, I’m not going to do that for a couple of different reasons. And regardless I’m guessing you want the owner’s or operations manual, yes? I don’t have that. As stated above, what I bought is the Service Manual.

I am, however, happy to share specific info from the Service Manual in the course of assisting a forum member with an issue, at least as much as I’m able to within the limits of my expertise and availability.

So, do you have an issue with a first generation LA-40 with which I might be able to help?
 

yoshi420

New member
I was wondering how to initiate -20dbm on the LA-40. The System Enhancement Series brochure says it’s “switchable” but I don’t see a switch. ... ???
 
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sweetbeats

Reel deep thoughts...
This sounds like a question somebody who has the Owner’s Manual. Again, I have the Service Manual.
 

yoshi420

New member
I ended up just ordering the owner’s manual last night. i’ll be sure to post pics when it comes in.
 
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TalismanRich

Well-known member
The owner manuals and technical documentation for the LA40 MKii and MKIII units are on the website under Discontinued Products. They also have the LA80 and LA81 manuals.
 

sweetbeats

Reel deep thoughts...
The owner manuals and technical documentation for the LA40 MKii and MKIII units are on the website under Discontinued Products. They also have the LA80 and LA81 manuals.

This thread and the information being asked recently is regarding the MkI LA-40.
 
Any unbalanced to Balanced converter has the same thing in it. Power supply, RCA connectors, Op amps and then XLR connectors. The -20dBm to -10dBm is probably just a two pin jumper which adds 10dB of gain in the first stage. This is not so secretive of a device as many different companies made the same thing.
I was installing a Henry Engineering box for a radio station and I saw a schematic in the box so I grabbed it and have it here somewhere. The Tascam is going to be a variation on that. What did you need pictures of one for as the look of the parts does not tell you much. I think there were a lot of companies that made an item like this even Wheatstone even though they do not call it a converter it can be used just the same.
 

yoshi420

New member
The la-40 has the option to convert +4dbm to -20dbm or -10dbv, -20dbm to -10dbv or +4dbm, and -10dbv to -20dbm or +4dbm, using three potentional inputs/outputs (xlr,1/4in,rca). Newer models have switches on each in/out that can adjust from +4dbm to -20dbm, but there aren’t any switches on the la-40 mki.

that’s why I had to order the owners manual.
 

sweetbeats

Reel deep thoughts...
[MENTION=204989]yoshi420[/MENTION] I was finally able to locate my LA-40 Service Manual and found some info in it that may be helpful...maybe more than what is in the Owner’s Manual...or maybe not...they may have included this info in the Owner’s Manual. But the short of it is the switches are on the main PCB inside, accessible after you remove the chassis cover. I’m attaching a couple pics to this post.

[MENTION=130918]skywaveTDR[/MENTION] the thing about the original LA-40 though is it is one of the most versatile converter boxes I’ve seen, with different jack type options, the switchable level, and the high level output amp is not garden variety straight opamp-based...it is actually a semi-discrete opamp/BJT line amp. An opamp drives a complimentary pair of output transistors running with gain and higher than garden variety power rails for greater headroom (i.e. +/-20V vs the more typical, for this echelon of gear, +/-15V). This amp circuit is derived from, and I believe developed for my prototype “Tascam M-__” console. The LA-40 circuit is nearly identical to the same balance amp circuit found in the Tascam 58-OB 1/2” 8-track tape machine. In both cases it is a tamed version of what’s in the prototype console (which is a mildly more complex circuit powered by +/-35V rails). The M-50 12x8 mixing console 2-channel “BALANCE AMP” is the only other place I’ve found the exact same line driver circuit as the prototype console, and so far the LA-40, 58-OB and 122B cassette deck are the only period devices I’m aware of that use the concept. I suspect it’s use was pretty limited...suspect it was dropped due to cost considerations. But I will say the outputs on my prototype console that use the full monty +/-35V circuit sound great. So...my point is I think the LA-40 has a bit more going on than the many other offerings one can get...more Swiss Army I/O options, and higher headroom. I can verify the later iterations from Teac do not offer the same (i.e. LA-40mkII & mkIII, LA-81, LA-81, etc.) and again I don’t think that’s because it wasn’t a good amp design, but it was cheaper to default to a more garden variety full opamp design.

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