Dead preamp

[Jerome]

Hoping someone can help with this. I just bought an old Sting Ray bass, 1977, from a pawn shop, and the preamp is dead. Since it is covered in black epoxy(?), it's pretty hard to figure the circuit out. Can somebody point me to a schematic for the preamp? When I bought the bass, the preamp had been disconnected, and the pickup was wired to the volume control. I've wired everything back to stock, but the output is very low, so I'm guessing the preamp had been disconnected because it was faulty.
I had one of these basses about thirty years ago, and remembered how fat and punchy it sounded, how great the neck was, and how heavy it was. This one I just got is heavy!
Thanks for any help...

 

[strummer]

Hoping someone can help with this. I just bought an old Sting Ray bass, 1977, from a pawn shop, and the preamp is dead. Since it is covered in black epoxy(?), it's pretty hard to figure the circuit out. Can somebody point me to a schematic for the preamp? When I bought the bass, the preamp had been disconnected, and the pickup was wired to the volume control. I've wired everything back to stock, but the output is very low, so I'm guessing the preamp had been disconnected because it was faulty.
I had one of these basses about thirty years ago, and remembered how fat and punchy it sounded, how great the neck was, and how heavy it was. This one I just got is heavy!
Thanks for any help...

I *think* you can give customer service a call, I seem to remember they have exchange preamps you can buy if you send in the broken one, but I may be wrong there.
Also, you should visit Rod Trussbrokens' site, he's got a lot of info on all kinds of preamps. Home - Musicmanbass.org, Musicman Bass.org, Musicman Bass

 

[bovinehost]

I know you checked the battery, but I'd be remiss if I didn't bring it up.

 

[Jerome]

Thanks, I replaced the battery and the battery connector. I think I could build a preamp on some perfboard, and install it, if I had a schematic...

 

[Spectre]

Call customer service. I'm betting they can hook you up.

 

[Caca de Kick]

That detailed of a schematic doesn't exsist that I know of. You can look at the schematics on Home - Musicmanbass.org, Musicman Bass.org, Musicman Bass but they don't go into that much detail that you could build one from.
It would just be easier to get a replacement preamp from EB. Also while your getting parts from EB, I would recommend getting a replacement output jack that switches off the preamp when you unplug your cable. The original 76-79 jacks didn't do that and would drain batteries...my '78 would drain a 9v in less than a month.

before and after:

 

[Jerome]

I appreciate the suggestions about replacing the preamp, but am now wondering if I could remove the old IC, and install a socket and a new IC. As the board is covered in epoxy, this won't be easy. Of course, the IC may not be the problem, though it seems that's the best guess as they have a tendency to die.
I see in the pics of the white '78 that there is a socket, and that the IC is an LF351 not an LM4250. I suppose there are a number of choices when it comes to replacement IC's, as long as the pin out is the same. The LF351 is the single op amp version of the LF353, which was used in the Music Man amps..Jerry

 

[AnttiK62]

Do I also have a dead preamp?

I appreciate the suggestions about replacing the preamp, but am now wondering if I could remove the old IC, and install a socket and a new IC. As the board is covered in epoxy, this won't be easy. Of course, the IC may not be the problem, though it seems that's the best guess as they have a tendency to die.
I see in the pics of the white '78 that there is a socket, and that the IC is an LF351 not an LM4250. I suppose there are a number of choices when it comes to replacement IC's, as long as the pin out is the same. The LF351 is the single op amp version of the LF353, which was used in the Music Man amps..Jerry

Hello everyone! I am new to the EB forum and this is my first writing "on the wall". Pardon my english and all. Anyways: I have had my -79 StingRay since 1984 or -85 (well, a friend of mine possessed it for two years when times were rough, but that is another story).

I never have had a problem with the preamp and the battery has been able to do it´s job for over a year although the jack is a mono one. Just last Saturday I took my new Ampeg V4BH to the gig. On the sound check I was surprised that there was distortion on the sound and finally there was no sound at all. I picked up my G&L and everything was cool, so I thought battery had gone. After the sound check I replaced the battery and went to the stage to try: very weak response. I had to tweak the pedal to the medal on the V4BH and still weak. So I played the night with the G&L with no problems at all. At home I replaced the battery once more but no luck.

My humble question is: do I have a dead preamp now? Mine is non-epoxied and the chip is LM4250CN. As the bass is seventyniner, there is no protection resistor on. Well, you can be certain that if I get out of this clean there will be one.

Thanks in advance; this forum seems to be great!

 

[kevin]

Hoping someone can help with this. I just bought an old Sting Ray bass, 1977, from a pawn shop, and the preamp is dead. Since it is covered in black epoxy(?), it's pretty hard to figure the circuit out. Can somebody point me to a schematic for the preamp? .

Hey Jerom...PM me your email address and I'll get that wiring diagram out to you.

 

[kevin]

My humble question is: do I have a dead preamp now? Mine is non-epoxied and the chip is LM4250CN. As the bass is seventyniner, there is no protection resistor on. Well, you can be certain that if I get out of this clean there will be one.

Thanks in advance; this forum seems to be great!

it's certainly possible, take it in to a local trusted Luthier and have them take a peek. If they have any detailed questions have them contact Englund Musik

Englund Musik (Robert Huberin)
tie 2, FI-01510
Vantaa
P: +358 9 8254 560
F: +358 9 5254 5609 Yes
http://www.ernieball.com/international-dealers/

 

[AnttiK62]

it's certainly possible, take it in to a local trusted Luthier and have them take a peek. If they have any detailed questions have them contact Englund Musik

Englund Musik (Robert Huberin)
tie 2, FI-01510
Vantaa
P: +358 9 8254 560
F: +358 9 5254 5609 Yes
http://www.ernieball.com/international-dealers/

Thanks Kevin! I will do that!

 

[AnttiK62]

Hi guys! What a relief! My StingRay is alive and kicking again!

I am a little ashamed, but must tell you the solution for my problem:

The black wire from battery had gotten loose. Perhaps I pulled it too hard when changing the battery. Should have seen it the first time I opened the cavity, but ...

Anyways, now I have a 1k "protection resistor" and stereo jack on my StingRay to prevent future chip disaster. The battery life had not been an issue before although the battery was always on!

Special thanks to Gav and all the best to all MusicMan bass players!

"Although L-2000 is a very good bass the StingRay is more!"