If you bought the kit from DIYAudio, the the JFET's have bias resistors which match the JFET'S CCS at around 8mA. You would want to replace them with the same type you have in circuit. Do you know what the value of the bias resistors are for that filters CCS?
I have dozens of the JFET's from Nelson with the bias resistors as supplied by the DIYAudio store. I'd be happy to mail you replacements if needed.
I have dozens of the JFET's from Nelson with the bias resistors as supplied by the DIYAudio store. I'd be happy to mail you replacements if needed.
Actually I've just realised that this is an old problem which was never resolved! A couple of years ago when the problem surfaced I replaced all the transistors in the faulty section; this didn't fix it, so, in my time honoured head-in-the-sand approach I put the board aside and built up the other board I happened to have lying around. Job done. However, I now want to run two crossovers for a three way system.
I'm not sure that it is the transistors, as they were all replaced. Unless of course I have two independently faulty transistors?? The fault sounds a bit like what you get if the DC offset is wrong on your amp - a buildup of charge, a discharge, rinse and repeat.
Anyway, the bias resistors are 68ohms. I guess I'll try replacing them again - if someone has some available that match that value that'd be grand.
Many thanks!
I'm not sure that it is the transistors, as they were all replaced. Unless of course I have two independently faulty transistors?? The fault sounds a bit like what you get if the DC offset is wrong on your amp - a buildup of charge, a discharge, rinse and repeat.
Anyway, the bias resistors are 68ohms. I guess I'll try replacing them again - if someone has some available that match that value that'd be grand.
Many thanks!
I too had this question, but decided not to ask. I'll stick with the convenience (for now) of the 50k trim pots.
Are you asking because you are concerned about noise? For what it's worth, the resistors are low noise (max. 1.5 μV/V for R > 1 MΩ) as per data sheet. I suspect if keeping the pots, most noise would be generated there?
Yes, maybe to give some benefit to thermal noice but mainly because I have built other xovers with those values so I have alot of comps to match from. Those were opamp based so my question was more about if this circuit would be affected in terms of current/drive issues related to those values. My plan is to breadboard with fixed values and compare.