Author Topic: beta lead preamp problem...  (Read 3898 times)

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Offline foxfire

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beta lead preamp problem...
« on: September 04, 2010, 02:16:52 pm »
i picked up my first beta today, when i got it home and started to play i noticed that it was oscillating and squealing pretty good so i opened it up started to wiggle the wires around the input jacks. that seemed to have an affect on the oscillation so pulled the preamp bound out to get a better look at it. with the board out and my guitar plugged in i started to tap on and wiggle things to try to pinpoint things and them the sound cutout completely and i noticed that the channel led wasn't lit. now i don't get any signal on either (or both) channels.

any suggestions will be greatly appreciated...

Offline foxfire

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Re: beta lead preamp problem...
« Reply #1 on: September 04, 2010, 04:54:39 pm »
when i first opened it up i noticed that where i should have -15vdc going into the preamp i have something like 0.8Vdc. then i went back out to the amp to double check somethings and i was getting -14 to -15vdc but my +15vdc had gone down to under a volt. so i shut the amp down and turned it back on and now my +15vdc is back where it should be and my -15vdc is back down to 0.8vdc.

also Q1, R3, and IC1 get pretty hot thought the voltages don't seem to be too far off...

Offline foxfire

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Re: beta lead preamp problem...
« Reply #2 on: September 05, 2010, 05:11:49 am »
i swear i had continuity through F3 yesterday but sure enough it was blown. my -15 (-16 actually) came back and the amp passes signal again. however it sounds horribly misbiased. if you don't pick hard enough you won't get any sound and then when you do the sound dies pretty quickly. any suggestions on where to start looking?

Offline foxfire

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Re: beta lead preamp problem...
« Reply #3 on: September 05, 2010, 08:02:30 am »
ok so i think my preamp is fine. i just ran from the beta's master out in to my coliseum's in and it sounded good. so my problem must be somewhere on the power amp board...i'll keep looking. 

Offline foxfire

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Re: beta lead preamp problem...
« Reply #4 on: September 06, 2010, 01:01:31 pm »
well i think i fixed it. i swapped Q7 (2N3440) out for a work alike and it seems to be working as it should. i only had the thing for maybe 15-20 minutes before it crapped out so i can't can't say it sounds like it used to but it does sound good so i'll take it. the reverb isn't working so i'll have to have a go at that next...