D
Dee_nos
New member
Thanks a lot yoshi420 !
Themotionlessair
New member
I have a LA-40 mki that turns on but no audio signal is passing through. I wonder if you can share with me the service manual in order to track the problem with my unit.
sweetbeats
Reel deep thoughts...
The first thing I would do is remove the top cover and exercise all the level adjust switches the span from left to right across the rear portion of the PCB. And also verify your connections are appropriate. If the problem is global across all 4 channels, it could be user error, or, if not, a problem with the power supply. So:
1. Verify you have things hooked up correctly and maybe even share the setup here (and note the the XLR jacks are pin 3 hot/high, which, depending on your individual setup, can be problematic for signal continuity)
2. Exercise the level adjust switches, and
3. Check the +/-15V supply outputs…like just measure for DC volts from pin 4 to ground and pin 8 to ground of any of the 5532 or 2041 audio opamps.
1. Verify you have things hooked up correctly and maybe even share the setup here (and note the the XLR jacks are pin 3 hot/high, which, depending on your individual setup, can be problematic for signal continuity)
2. Exercise the level adjust switches, and
3. Check the +/-15V supply outputs…like just measure for DC volts from pin 4 to ground and pin 8 to ground of any of the 5532 or 2041 audio opamps.
L
LLooiicc
New member
Hello all,
Hello yoshi420, is it possible to provide me the doc (or shema only). The picture here is not really good quality, I can’t read it clearly
If someone know where I can found the service manual, welcome
Many thanks for answer
Hello yoshi420, is it possible to provide me the doc (or shema only). The picture here is not really good quality, I can’t read it clearly
If someone know where I can found the service manual, welcome
Many thanks for answer
BeatleFred
Member
Bumping up an old discussion.
Is it correct to presume when it comes to the Inputs and Outputs that are numbered 1, 2, 3, and 4, that are in the front & back of the original LA-40,
that the connectors must match in order for any signals to pass thru?
In other words, there are Rca, 1/4" and XLR connectors. I imagine only Rca inputs can pass to Rca outputs and ditto 1/4" In to 1/4" out, and XLR in to XLR out, 1 in to 1 out, 2 in to 2 out, 3 in to 3 out and 4 in to 4 out.
But, can they be mixed together such that, for example, RCA 1, 2, 3, 4, can pass thru 1/4" or XLR 1, 2, 3, 4 ?
I have an LA-40 I acquired a long time ago and never used, but may have a use for it now- I was thinking to use it as an interface to my Teac 2A mixer, which does not have XLR's, and based on how the mixer is placed in my room, its a little hard to get access to the back of the 2A, so I was thinking to connect to the LA-40 first, and then from the LA-40 to the 2A/MB-20, kinda like a patchbay.. Its nice that there are connectors on the Front of the LA-40, but I was not sure if the front connectors would only pass signal to the outputs in front, or if they could pass to either of the outputs in the back as well.... (if the LA-40 is internally wired to allow that)
Is it correct to presume when it comes to the Inputs and Outputs that are numbered 1, 2, 3, and 4, that are in the front & back of the original LA-40,
that the connectors must match in order for any signals to pass thru?
In other words, there are Rca, 1/4" and XLR connectors. I imagine only Rca inputs can pass to Rca outputs and ditto 1/4" In to 1/4" out, and XLR in to XLR out, 1 in to 1 out, 2 in to 2 out, 3 in to 3 out and 4 in to 4 out.
But, can they be mixed together such that, for example, RCA 1, 2, 3, 4, can pass thru 1/4" or XLR 1, 2, 3, 4 ?
I have an LA-40 I acquired a long time ago and never used, but may have a use for it now- I was thinking to use it as an interface to my Teac 2A mixer, which does not have XLR's, and based on how the mixer is placed in my room, its a little hard to get access to the back of the 2A, so I was thinking to connect to the LA-40 first, and then from the LA-40 to the 2A/MB-20, kinda like a patchbay.. Its nice that there are connectors on the Front of the LA-40, but I was not sure if the front connectors would only pass signal to the outputs in front, or if they could pass to either of the outputs in the back as well.... (if the LA-40 is internally wired to allow that)
sweetbeats
Reel deep thoughts...
The LA-40 is not really a patchbay. It’s a leveling amplifier (hence “LA”). It converts balanced +4dBu type signals to unbalanced -10dBv type signals and vice versa. Balanced +4dBu nominal signals connected to the 1/4” or XLR input jacks are unbalanced and level-dropped and output to the correspondingly numbered RCA jacks. Inserting a 1/4” plug into a 1/4” input jack breaks signal from the correspondingly numbered XLR input jack. And conversely unbalanced -10dBv nominal signals connected to the RCA input jacks are balanced and level bumped and output to the correspondingly numbered 1/4” or XLR jacks. Inserting a 1/4” plug into a 1/4” output jack breaks signal to the correspondingly numbered XLR output jack. Here is what I just described in a picture…the Block Diagram:
BeatleFred
Member
Thanks for the info. The Teac 2A/MB-20 only has 1/4" jacks for microphone inputs. Thus, if someone had microphones with either XLR or TRS plugs,
I imagine they could plug the mics into any or all 4 of the (XLR or 1/4 TRS) balanced input jacks of the LA-40, where its converted to an unbalanced signal at the RCA jack outputs, and then to send that signal to the Mic input of the 2A/MB-20, an adapter cable (RCA to 1/4" TS) would be needed, correct? (to connect the rca out of LA-40 to the 1/4" mic in of the 2A/MB-20).
The reason for possibly doing this is if the back of the 2A/MB-20 mixer might be hard to access, depending on how someone happens to have all their equipment setup in a certain amount of space and location in the room. Thus, if an LA-40 happens to be situated closer to where the mic stands are to do some recording and whatnot, then perhaps connecting to the LA-40 first, and then interfacing it to the 2A/MB-20 might be beneficial- thats basically the idea I had in mind. Keep in mind as well- all the cables behind the 2A/MB-20 that connect to an A-3440 recorder for example, and having to turn the 2A/MB-20 around to access the back of it without twisting the wires if space is limited on the table where an 2A/MB-20 rests... so again- the idea being to make life easier to use the LA-40 as sort of a patchbay to extend wires, although of course, the difference is the LA-40 is doing a signal conversion as well.
Another scenario might be connecting a cd player to the LA-40 and passing that signal (left and right channels) to the E & F rca inputs of the 2A/MB-20 (to dub a music cd onto a 3440. (I mention E & F because there are only two available line in's on the 2A after the MB-20 is wired to it and the A-3440, as opposed to a 2A itself without an attached MB-20).
But cd's players mostly have just rca connectors, thus LA-40 wont work unless the cd player has XLR outs and can then connect cd player XLR out to LA-40 XLR in, and then LA-40 rca out to 2A E & F rca in, unless I overlooked anything...
I imagine they could plug the mics into any or all 4 of the (XLR or 1/4 TRS) balanced input jacks of the LA-40, where its converted to an unbalanced signal at the RCA jack outputs, and then to send that signal to the Mic input of the 2A/MB-20, an adapter cable (RCA to 1/4" TS) would be needed, correct? (to connect the rca out of LA-40 to the 1/4" mic in of the 2A/MB-20).
The reason for possibly doing this is if the back of the 2A/MB-20 mixer might be hard to access, depending on how someone happens to have all their equipment setup in a certain amount of space and location in the room. Thus, if an LA-40 happens to be situated closer to where the mic stands are to do some recording and whatnot, then perhaps connecting to the LA-40 first, and then interfacing it to the 2A/MB-20 might be beneficial- thats basically the idea I had in mind. Keep in mind as well- all the cables behind the 2A/MB-20 that connect to an A-3440 recorder for example, and having to turn the 2A/MB-20 around to access the back of it without twisting the wires if space is limited on the table where an 2A/MB-20 rests... so again- the idea being to make life easier to use the LA-40 as sort of a patchbay to extend wires, although of course, the difference is the LA-40 is doing a signal conversion as well.
Another scenario might be connecting a cd player to the LA-40 and passing that signal (left and right channels) to the E & F rca inputs of the 2A/MB-20 (to dub a music cd onto a 3440. (I mention E & F because there are only two available line in's on the 2A after the MB-20 is wired to it and the A-3440, as opposed to a 2A itself without an attached MB-20).
But cd's players mostly have just rca connectors, thus LA-40 wont work unless the cd player has XLR outs and can then connect cd player XLR out to LA-40 XLR in, and then LA-40 rca out to 2A E & F rca in, unless I overlooked anything...
sweetbeats
Reel deep thoughts...
Quick reply regarding plugging mics into the LA-40…the answer is no, full stop. Mics produce mic level nominal signals. This is much, much lower than line level. The LA-40 handles line level signals. The inputs are not microphone preamplifiers. They are line level amplifiers. If you plug a microphone into the LA-40 you’ll barely hear anything at the output. It’ll take the tiny signal, and drop the level even lower (because you’re running the tiny signal through a +4dBu to -10dBv level drop, plus balanced to unbalanced)…think about it…plugging into an LA-40 does nothing for you with a mic except make it too quiet for the mic amp in the Model 2 to boost. Just plug the mic directly into the Model 2. Yes, it won’t take advantage of the balanced circuitry of the mic, but that’s probably not a problem in a single room in your house. Just get a simple XLR to TS adapter, or plug that TRS mic right in. If noise is a problem get an XLR to TS transformer coupled adapter. The LA-40 will only make your mic signal too quiet, and add noise and distortion with all the circuitry that does nothing for you. You don’t *have* to connect a balanced mic to a balanced mic input. Many, many, many home studio mixers and multitrackers from the late 1970s and 1980s, even open reel machines, cassette decks, had 1/4” unbalanced mic inputs, and you can plug a balanced mic right in with a simple adapter and typically have no noise problems with a mic cable up to 20-25’.
I’ll read the rest of your post later and follow up, but I wanted to promptly respond in order to prevent you from rabbit-trailing on a faulty notion.
I’ll read the rest of your post later and follow up, but I wanted to promptly respond in order to prevent you from rabbit-trailing on a faulty notion.
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sweetbeats
Reel deep thoughts...
I read the rest of your post.
Respectfully I offer this: as with some other instances in the past you are passionate about trying to find ways to use what you have, even if the idea is a mis-use of equipment. You cite good reasons for the application of a patchbay. Three words: get a patchbay.
The LA-40 is *not* a patchbay. It is a multichannel leveling amplifier and balance/unbalance converter. A neat one u quiet in the LA-40 series with higher headroom. But what you need is a passive unbalanced patchbay. The LA-40 would come in handy if you had balanced line level equipment placed far away from your Model 2 mixer, and wanted to interface that balanced equipment with your mixer over long cable runs. Again, full stop. That’s what it’s for.
Respectfully I offer this: as with some other instances in the past you are passionate about trying to find ways to use what you have, even if the idea is a mis-use of equipment. You cite good reasons for the application of a patchbay. Three words: get a patchbay.
The LA-40 is *not* a patchbay. It is a multichannel leveling amplifier and balance/unbalance converter. A neat one u quiet in the LA-40 series with higher headroom. But what you need is a passive unbalanced patchbay. The LA-40 would come in handy if you had balanced line level equipment placed far away from your Model 2 mixer, and wanted to interface that balanced equipment with your mixer over long cable runs. Again, full stop. That’s what it’s for.
BeatleFred
Member
I read the rest of your post.
Respectfully I offer this: as with some other instances in the past you are passionate about trying to find ways to use what you have, even if the idea is a mis-use of equipment. You cite good reasons for the application of a patchbay. Three words: get a patchbay.
BeatleFred
Member
As usual, thanks for the info, SB. I acquired the LA-40 quite a few years ago, I cant even recall, it was probably very inexpensive,
and its just been sitting around, so I was wondering if I could find a use for it, thus my questions on its functions, which by now
pretty much has clarified it wont really be benefical with a 2a/MB-20. I suppose my first impressions led my astray when I visualized
XLR's on the LA-40 and none on the 2A, and thinking they could interface with each other, but its ok, atleast its a good thinking exercise for the
brain and learning a little bit more along the way.
and its just been sitting around, so I was wondering if I could find a use for it, thus my questions on its functions, which by now
pretty much has clarified it wont really be benefical with a 2a/MB-20. I suppose my first impressions led my astray when I visualized
XLR's on the LA-40 and none on the 2A, and thinking they could interface with each other, but its ok, atleast its a good thinking exercise for the
brain and learning a little bit more along the way.
sweetbeats
Reel deep thoughts...
No worries…I understand completely your desire to integrate the LA-40. And it would be a great companion to your 2A as far as line level equipment goes. If you have balanced line level equipment you want to interface with the 2A, the LA-40 will halontoy with that. Again, the “mkI” LA-40 is unique from the rest of the series (mkII and mkIII) in that it has unique interfacing and higher headroom.