B-401 Electronics

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Has anybody got a schematic for the electronics in a B-401?
I'm trying to fix one at the minute and its difficult without the circuit diagram.
Alternatively, if I reverse engineer the schematic from the board would anyone be interested in me posting it here?

Also - I'm new here. Hello everyone.
 

SFIV1967

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Welcome to LTG! Can't remember schematics for the B-40x series, but maybe somebody here has that info. Stay tuned.
Ralf
 

Nuuska

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Hello from Finlad


Welcome to LTG !!!

A quick look via Google reveals, that it has series-parallel switch - that is easy. Check the switch.
Then there is active B+T circuit, which probably is done with OP-amp and fairly straightforward - at least to anybody comfortable with analog electronics.

No - I do not have the circuit diagram - but I would replace the IC - check all caps and check for bad solder joints.

While you do not give more info of what the problem is - I'll stop here and "listen"

Good luck
 

SFIV1967

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Then there is active B+T circuit, which probably is done with OP-amp
Correct, here's a picture of a B-401. The PCB is the same as used in the B-402. The Op-am (I asume it's a Texas Instruments TL062CP http://www.ti.com/lit/gpn/tl064) seems to be in a socket, so replacing would be easy if there is an issue with it.



The only schematics I found for basses using the TL062CP are for the Musicman Stingray bass:
http://static.musicforums.ru/agora/forums/mfor/masterskaya/notes/1218823.musicmanstingraypre01.jpg
http://static.musicforums.ru/agora/forums/mfor/masterskaya/notes/1218824.musicman_stingray_bass_preamp_schematic.jpg

Ralf
 
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Hi - thanks for all your replies.
The TL062 is the op-amp of choice for battery powered applications because its optimised for low power.
In my case, the op-amp is fine. The problem was neither of the tone controls worked and there was no output from the bass with no battery fitted - regadless of the switch position.
I assumed, therefore, that there was something wrong with the active circuitry.
The actual problem was, however, that there was a bad connection on the output jack meaning that the pickup return wire was only connected to the output jack via the battery.
With a battery fitted, it only worked with the switch in the passive position - so neither of the tone controls worked.
The schematic is still a work in progress, and I need to verify it, but the first draft is complete so I'll post it here tomorrow.
 

adorshki

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Hi - thanks for all your replies.
The TL062 is the op-amp of choice for battery powered applications because its optimised for low power.
In my case, the op-amp is fine. The problem was neither of the tone controls worked and there was no output from the bass with no battery fitted - regadless of the switch position.
I assumed, therefore, that there was something wrong with the active circuitry.
The actual problem was, however, that there was a bad connection on the output jack meaning that the pickup return wire was only connected to the output jack via the battery.
With a battery fitted, it only worked with the switch in the passive position - so neither of the tone controls worked.
The schematic is still a work in progress, and I need to verify it, but the first draft is complete so I'll post it here tomorrow.
Wonderful trouble-shooting summary.
I'm not even an "electric guy", but I'm sure I speak for at least several folks here in saying "You, sir are a fine contributing citizen and many thanks!"
And btw, "Welcome Aboard!"
:smile:
 

SFIV1967

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I am really surprised no schematics are available for the B-401 and B-402 yet.

Ralf
 
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OK - here is the first draft of schematic.
This still needs verification and I haven't yet worked out how it all works.
Please feel free to make any comments at all - if anyone wants anything changed or updated, please let me know.
The jpeg shows the component references I have used in the schematic.
I promise that R14 is definitely there - hiding under the green wire.

https://app.box.com/s/w0t7qhy98e8hc2kx1fco228ruijfi3fj

https://app.box.com/s/yy507nd699f8qbcq1rqb7nrij4ecz2wi

Thanks also to everyone for your kind & helpful comments.
 
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adorshki

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OK - here is the first draft of schematic.
This still needs verification and I haven't yet worked out how it all works.
Please feel free to make any comments at all - if anyone wants anything changed or updated, please let me know.
The jpeg shows the component references I have used in the schematic.
I promise that R14 is definitely there - hiding under the green wire.



https://app.box.com/s/yy507nd699f8qbcq1rqb7nrij4ecz2wi

Thanks also to everyone for your kind & helpful comments.
Link works but file type isn't compatible with the image linking function here (or at least, not under my browser), in case you were wondering.

:friendly_wink:
 

Nuuska

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Hello

Link works - image opens - Chrome browser on Mac Mini

Schematic looks basic - only tone controls are in active circuit - first half of TLO62 has band-pass filtering via R4 - C11 - R13 - C5 - and then B&T +/- control - finally the other half of OP as voltage follower and providing low output impedance - for some reason output series resistor R8 is 5,1kOhm - for short circuit protection 100 Ohm should be enough.

Four things to go wrong besides bad pots & switches - OP-amp - resistors - capacitors - solder connections.
 
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Thanks adorshki. Should be fixed now. I've just updated the picture as a link, but you should be able to see it.
I'll review the schematic over the weekend and update those links with any relevant updates.
And, of course, if any of you have any more comments please let me know.
Nuuska - thanks for your comments. With regard to the value of R8 - I worked most of those out in my head so its possible that I've got some values wrong.
 
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fronobulax

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Thanks adorshki. Should be fixed now. I've just updated the picture as a link, but you should be able to see it.
I'll review the schematic over the weekend and update those links with any relevant updates.
And, of course, if any of you have any more comments please let me know.
Nuuska - thanks for your comments. With regard to the value of R8 - I worked most of those out in my head so its possible that I've got some values wrong.
Belated welcome and thanks for doing and sharing this.
 
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