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Old 26th August 2011, 10:17 PM   #1291
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mravinsky, my calculations are all wrong, I blame a late night and too much coffee.
It appears my build is in fine working order.

Balanced signal ground connection to chassis
I connected signal ground to a ground loop breaker (10Ω 5W resistor in parallel with a 0.1F capacitor) and then to chassis ground.
This shorts everything... all mosfet legs, diodes to chassis ground @ 10Ω continuity. I did not off course power up in this state and Im unsure whether this would work.
Right now signal ground on both boards is left floating, but I need to reference it according to ranes notes, any help would be appreciated.

Thanks for a great project.
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Old 26th August 2011, 10:25 PM   #1292
Salas is online now Salas  Greece
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What do you mean shorts? Is it connected only to the 0V GND line or not? Because if it shorts anything with voltage on it, its bye bye happiness.
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Old 26th August 2011, 11:50 PM   #1293
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Salas,
Yes, connected only from the 0V GND on each board.
Once I make this connection, my mosfet legs, diodes do not become isolated, I read a continuity of 10Ω to chassis ground through the ground loop breaker.

As I say I have not powered up in this state...
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Old 27th August 2011, 12:02 AM   #1294
Salas is online now Salas  Greece
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There are Mosfet legs that should go to ground and others that don't. The output Mosfets drains should. Disconnect the transformers and see with the DVM in Ohm, if only things that show connection to a ground see 10 Ohm to chassis. The diagram is on post #4 in this thread also.
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Old 27th August 2011, 12:36 AM   #1295
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Thanks Salas, that explains the reason, I will confirm with the diagram to be sure.

As for temperature measured under pcb between mosfets on each board I read 34C after 2 hours.
The 3.3R resistors have measured 91C. The spec sheet from Mills states a temperature range from ambient -65C - 125C. (10,000hrs @ 125C).
Still very hot imo...
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Old 28th August 2011, 09:02 AM   #1296
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Hum, on this photo i see 1 Ohm resistors are replaced with wire:

Click the image to open in full size.

.. or, i should leave 1 ohm i soldered already ?

.
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Old 28th August 2011, 09:08 AM   #1297
Salas is online now Salas  Greece
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Leave them.
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Old 28th August 2011, 02:32 PM   #1298
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by johnwmclean View Post
Across 3.3ohm resistors 1.938v & 1.688v

My mills 3,3 R resistors are getting pretty hot!
1.938V and 3r3 is ~1.1W, yes they will run hot.

1.938V & 10r ~376mW, yes a 10r 600mW will run hot. Three 10r give your total CCS current. Fine tune with a 4th resistor.
Or start with 15r 600mW resistors for cooler running.
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Old 29th August 2011, 01:22 AM   #1299
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Thanks Andrew for this info,

Although concerned at first the resistors installed do meet or exceed MIL-PRF-26H spec, the temp recorded after 2 hours is well within operating tolerances.
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Old 5th September 2011, 11:15 AM   #1300
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Quote:
Originally Posted by Salas View Post
You would need dead on matched FETS to near 0mV, but up to 5mV is OK for the F5 which will not multiply it much due to its a low gain amp. The general disclaimer that when mating a DC preamp/buffer to a DC amp without any output DC sensor protection, your speakers are in danger in case of any failures in the future still stands. Nobody cares and most mate an F5, but anyway.
OK, i changed JFETS, and now i have:

on R10-1: 2,037V / 279.8mA
on R10-2: 1.813V / 241.0mA

on Shunt output i have:
+9.85V / 196.4mA
-9.86V / 171.9mA

on LOUT i have: -0.8mV
on ROUT i have: -1.5mV

Also ma matched all LEDS on 1.848V and triplets on 1.850V !

What else i should do, or this is good enough ?
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