SiriusBlack Posted April 11, 2015 Posted April 11, 2015 I have recently bought a brilliant (USA made) Musicman SUB with a faulty preamp. To remedy that, I went and bought a JEast MMSR 2 Band premap which I installed myself and now the bass is sounds awesome. I still have the old, original faulty preamp, which I would like to repair. Having done few checks, it looks like that the op amp IC is faulty and it needs replacing. OP Amp has the following stamped on top of it: 4250d jrc 2004b I have searched around but could not find much information where to get one. Any idea? Quote
Woodinblack Posted April 11, 2015 Posted April 11, 2015 Is this not just a LM4250 that you can get from quite a few places. Are you sure it is the opamp? they tend to be pretty reliable without power damage. Quote
SiriusBlack Posted April 13, 2015 Author Posted April 13, 2015 (edited) well, i assumed it is the pre as there was sound when plugged in albeit (with the broken original pre) very little and i thought it must be the bit which amplifies the signal. how do i check what might be wrong with it then? cheers thanks for LM2450 info Edited April 13, 2015 by SiriusBlack Quote
Woodinblack Posted April 13, 2015 Posted April 13, 2015 Well, yes it is the bit that amplifies the signal, but the amount of amplification on a circuit depends entirely on the circuit, and the relationship between the input attenuation and the feedback. One of those resistors break and you have a perfectly functional ampifiers that amplifies to a lower signal than comes in. Generally if the opamp broke, you wouldn't have anything at all. Best measure the circuit and check it is all there. If it is the opamp you can get one off ebay or somewhere for only a couple of quid. Quote
SiriusBlack Posted November 5, 2015 Author Posted November 5, 2015 (edited) hi Woodinblack. thanks very much but sorry for a 6 month delay :-D. i guess this just kinda' slipped off my mind but now i want to fix it. how do i find out which resistor is faulty please? what tools do i need and how to apply them. i really want to have this preamp fixed. cheers Edited November 5, 2015 by SiriusBlack Quote
Woodinblack Posted November 5, 2015 Posted November 5, 2015 I would suspect it is mostly the leads, but if you have a multimeter you can check all the connections and the board to see if there is any damage Quote
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