BA3 output, using F4 boards. Fried DAC chip when i hooked it up directly because DC fed back through DAC output transformers
you had a (killing) spike probably
you can go back with me , to Dumb Bench - one of xformer's virtues is - it will not pass DC
put here exact sch ( don't be lazy ) and we'll see where was a mistake
you can go back with me , to Dumb Bench - one of xformer's virtues is - it will not pass DC
put here exact sch ( don't be lazy ) and we'll see where was a mistake
Sorry. I know nothing of transformers. I am using the crippled F4 board. I do not have the diodes on the FE as I thought they were there to protect the Jfets, but I relize now, they would have kept DC off of the input. I don't have R1-4, D1-2, Q1-2. Input is jumpered to between the electrolytics.
wrong ; they're here to protect input jfets of too much of input swing
so - now - besides xformers , you forgot that caps also have virtue of decoupling DC ....... when properly implemented , you also will not have any spikes.
what's value of input shunt resistor , or you didn't put that one ?
in other words - you need that R2 , as bleeder resistor for coupling caps ; without it , you have pre-stage zapper , not output amp
I'm curious - which DAC you fried ?
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So i need the shunt resistor if i plan to use output stage with something other than BA FE.
I fried CS4398 ebay dac. Got any suggestons. Nows the time! I know it might not seem like it, but i learn something mew everyday😀
I fried CS4398 ebay dac. Got any suggestons. Nows the time! I know it might not seem like it, but i learn something mew everyday😀
if interconnecting is in case , you always need to have that - for discharge of cap
I have another mystery. On my second BA-3 set of boards, I have everything adjusted and all looks good in terms of DC operating points. When i hook up the left channel to the output stage, the bias across the source resistors in the channel it hooks to drops by 200mV or about .5A. Is this an indication of a problem with the fets in the BA3 Fe? It does not do it when i hook up the right channel from the BA3 FE. It would seem that something is shunting the current away. Checked RCA connections to make sure no short to the case, but that would affect pre-connection readings anyway, so it seems it is happening on the FE board.
what scope on output sez ?
counting that output stage is DC decoupled on input side , it seems that you have some ground loop , or oscillation .
counting that output stage is DC decoupled on input side , it seems that you have some ground loop , or oscillation .
output of FE? ONce again, a new problem i have not experienced, so a chance to learn, but i don't know where to start.
look with scope on output of output stage , when FE is connected ;
is that , presumably faulty , FE channel - causing troubles on any output stage , when connected ?
is that , presumably faulty , FE channel - causing troubles on any output stage , when connected ?
Try both FE channels with both output stage channels, that'll help narrow the problem location down...
Roscoe
Roscoe
The right FE channel works fine on both output channels. The left FE channel causes the bias on output resistors to drop. I assumed some sort of ground loop or short, but couldn't find anything. Fired up my oscilloscope for the first time. I am probably going to destroy something very soon.
be sure that either amp or scope are off safety gnd - in case that you connect gnd probe to live output
first time when that happens to me , I spent entire afternoon searching why fuse blew ......
dumb ZM .......
(off course that best solution is that both amp and scope are on safety gnd , and black probe on output gnd 😉 )
first time when that happens to me , I spent entire afternoon searching why fuse blew ......
dumb ZM .......
(off course that best solution is that both amp and scope are on safety gnd , and black probe on output gnd 😉 )
I only have one probe and have never used an an oscillosope. I managed to calibrate the probe,... I will try not to make the magic smoke. I do not have a signal generator, so this may be excercise in futility. I assume that I connect probe to output fo the amp. what do i do with ground clip?
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