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Nelson Pass F5 Mono's

ejfud said:
Looking great Jeff. I'm getting excited about these things.
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Well let's hope they work!

MB-2 is ready to be fired up... smoke test later Sunday!

mb2-mounted.jpg
 
Been following you inquiry over on DIYaudio forum. Have you tried the last suggestion on less bias for the toshibas? I'm on stand still until this problem is worked out.....:scratch2:

Russellc
 
Russellc said:
Been following you inquiry over on DIYaudio forum. Have you tried the last suggestion on less bias for the toshibas? I'm on stand still until this problem is worked out.....:scratch2:

Russellc
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Thanks Russell. What the poster doesn't understand is that I've barely cracked the dial on the variac, I'm only at an input of about 20 vac when r11 and r12 reach .600vdc. I can't see how a value of 1k for r3 and r4 is going to resolve that.
 
ejfud said:
Could it be a power supply problem Jeff?
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I don't think so, the pos and neg rails measured at +/- 24.5 - 24.8 vdc with no load on them.

I haven't measured the rails at 20vac input, but I doubt they are even 4 or 5 vdc at that point.

But I'll double check where the rails are when I'm at correct bias.
 
You may want to yank out R11 and R12 and make sure the resistance is OK.

I was pulling my hair out on an Aleph Mini build and it turned out that the source resistors fried and one of the zener diodes blew...took forever to figure that one out.
 
Jeff sent me an email that one was playing music last night. I belive the outputs were messed up.
 
ejfud said:
Jeff sent me an email that one was playing music last night. I belive the outputs were messed up.
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yep, I misread the data sheet or something. :( The outputs were in the opposite spots. They don't like it when you do that.

And it was an expensive lesson for me.
 
specialidiot said:
yep, I misread the data sheet or something. :( The outputs were in the opposite spots. They don't like it when you do that.

And it was an expensive lesson for me.
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Ouch!

Glad its figured out,please show in picks as to correct orientation so my dumb ass doesnt do the same exact thing!:D:tresbon:
I have made MANY payments to the "Tuition of life" lord knows...
thanks,

Russellc
 
Russellc said:
Glad its figured out,please show in picks as to correct orientation so my dumb ass doesnt do the same exact thing!
Click to expand...

Well the nomenclature on the device doesn't show on the picture.

The main thing is to get the right device in the right spot. In my case, we ordered alternate output FETs that don't have the same part number as the devices in the schematic.

I guess I was careless in reading the data sheet or something. Just make sure that if the location calls for a P channel device, put a P channel device in there.

The board exhibited behavior like the FET was full on so I was concentrating on the circuit upstream to it, thinking Q1 and Q2 were bad. But with a NPN where a PNP goes, and visa versa, of course they are going to be full on.

And fried.

I ran it for a couple of hours last night. I got it dialed in fairly close at 608/604 on the bias and 7mv offset, then played a bit of music through a crappy test speaker.

Gary you are going to have a couple of room heaters there.
 
Thanks for sharing, Jeff. I bet that was a head scratcher for a while.

Will these mono's be at Cobblefest?
 
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