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Old 28th November 2008, 05:03 PM   #2081
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I'm not sure I understand all of that. R10 measuring 7.5K showed you your jfets were toast, but if your new ones are OK you still have a problem with bias and offset. If both channels are biased the same then the temp will be the same, there is no magic involved.
Bill
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Old 28th November 2008, 10:14 PM   #2082
thermos is offline thermos  Australia
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Quote:
Originally posted by Bill Fuss
I'm not sure I understand all of that. R10 measuring 7.5K showed you your jfets were toast, but if your new ones are OK you still have a problem with bias and offset. If both channels are biased the same then the temp will be the same, there is no magic involved.
Bill
Not sure, I set the bias on both amps and the temps seem the same now.

I guess my question is, would it be better that the jfets matched as a set of quads (for both amps) rather than just a single amp?

In my case one pair on one amp is 7.0ma and the other pair on the other amp is 8.2ma. Does this really matter?

Thanks
Thermos
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Old 28th November 2008, 10:35 PM   #2083
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Glad things are working out.
I dont think matching jfets in this amp is very important, but it cant hurt. If you can hear the difference I would really like to hear about it. I just used what I had in BLs and it sounds stellar.
Best, Bill
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Old 29th November 2008, 12:43 AM   #2084
thermos is offline thermos  Australia
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Quote:
Originally posted by Bill Fuss
Glad things are working out.
I dont think matching jfets in this amp is very important, but it cant hurt. If you can hear the difference I would really like to hear about it. I just used what I had in BLs and it sounds stellar.
Best, Bill
Thanks for all your posts Bill, they have been really helpful.
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Old 29th November 2008, 07:56 AM   #2085
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Default finished H/S for F5

Well they are almost finished. The sides need straightening up where they will butt up against the front plate/slab.

They measure 270mm High x 380mm Deep x 25mm thick, if you look at this pic.
The front plate is 430mm Wide x 270mm High x 60mm Thick

I'm actually worried that the heat will peel the varnish off the wood.
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Old 29th November 2008, 08:10 AM   #2086
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Default tarnish the varnish!

Just add a spacer of insulating material (fibreglass, etc) 'tween h/sink and front block mounting bracket/screws to allow cool air gap - no problem.
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Old 29th November 2008, 10:46 AM   #2087
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Happy to help when I can, Thermos.
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Old 29th November 2008, 03:57 PM   #2088
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i am planning on building this amp using 2x AMB regulated PS´s (one dedicated per channel) in a separated enclosure for the 2 ps modules and then using 2 power cords to power the amp modules on their own enclosure. but i dont know how the grounding should be arranged....any recommendation?
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Old 29th November 2008, 04:18 PM   #2089
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mekanoplastik,

From your link:

"Onboard heatsinks can be used which would allow the σ22 to supply up to 1A continuous (with much higher peak currents). More sustained currents are possible by using larger, offboard heatsinks."

They are too small. They don't have the current capacity needed.
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Old 29th November 2008, 04:58 PM   #2090
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Quote:
Originally posted by Ed LaFontaine
mekanoplastik,

From your link:

"Onboard heatsinks can be used which would allow the Ã22 to supply up to 1A continuous (with much higher peak currents). More sustained currents are possible by using larger, offboard heatsinks."

They are too small. They don't have the current capacity needed.
Hi Ed...

from same link "The high-current MOSFETs are not normally the limit of how much current the σ22 PSU could supply, as long as they are adequately heatsinked. "

and i plan on using an overkill heatsink ....and one PS per channel.....

do you think it would be possible?
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