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Old 4th May 2012, 10:28 AM   #1371
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Quote:
Originally Posted by a.wayne View Post
Is there a preference for the V3 and why .....?
Two things jump out. First, it is capable of more power, if needed. Second, the cascoded front end, provides a very stable little nest for the jfets to operate in. Maybe this is important, maybe not. You have to decide.
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Old 4th May 2012, 10:34 AM   #1372
a.wayne is offline a.wayne  United States
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Ok,

More power ...... Chk !
Cascoded front end ..... Chk !

Is this now simplified as to just pick your F5T Kit ......?
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Old 4th May 2012, 10:48 AM   #1373
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Ok,

More power ...... Chk !
Cascoded front end ..... Chk !

Is this now simplified as to just pick your F5T Kit ......?
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Old 4th May 2012, 11:05 AM   #1374
a.wayne is offline a.wayne  United States
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Ahh , not so fast , outputs are a different GB, as is the diodes , so the kit is main Board and PSU, yes ..?
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Old 4th May 2012, 10:40 PM   #1375
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Default The build continues

Got more done today (hope the boss isn't reading this).
Put all the transistors and diodes on the board and heatsink.
Didn't want to use a terminal block for the speaker output so I had to drill the hole out to except 14 gage wire (5/64" drill), then had to scrape the black paint off so there was something to solder to, front and back, as the drill cut all the tinned copper away.
Second thing, the input ground, again not using a terminal block and I had previously soldered the jumper wire, no place to solder the input ground. I did solder it to the jumper on top, not great, but will do. If I was smart, (and we know I am not) I would have used a longer stripped piece of ground wire and run the end up through the second hole and then soldered it.
Andy I would recommend a third hole for the ground; one hole for the input ground wire and two holes for the jumper, even if you use a terminal block, this is easier than stuffing 2 wires in one hole.

More to come later,

Rush
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Old 4th May 2012, 10:55 PM   #1376
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I'm happy .. Progress ...
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Old 5th May 2012, 02:43 AM   #1377
Rush is offline Rush  United States
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Default Thinking Again

I am getting close to hooking up the power supply and warming this baby up.
I have followed the schematic with all resistor values, except as noted with the cascode resistors. R17-24 are all 1 ohm and I will initially bias them to .3 volt as Mr. Pass noted in the Turbo manual. So when I read .3 volts, with two 1 ohm resistors in parallel (.5 ohm) at each MOSFET, they will only be passing .6 amp each at 32 volt rails, 19 watts. This doesn't seem like anywhere near the sweet spot in the original F5, 22 volts at 1.3 amps, 28 watts. The Turbo doesn't look much like a 50 watt class A amp with such low current.
Am I missing something? Like the current passing in the diode at .3 volts? If so how much is it? I may just be a fraidy-cat, not wanting to smoke these rare Fairchild devises.

Rush
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Old 5th May 2012, 06:14 AM   #1378
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I have had mine at .5 with no problems. Just have to watch the diode temperature. Hotter they get, the faster/earlier they conduct. This was the point of my question about seperating them from the heat. Their response is temperature dependent. Should still be ok, just have to find the point of stability. The Rs are there not only for degeneration and linearization, but also to control the mosfet and temper its response in terms of current consumption.
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Old 5th May 2012, 07:42 AM   #1379
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Quote:
Originally Posted by Rush View Post
I am getting close to hooking up the power supply and warming this baby up.
I have followed the schematic with all resistor values, except as noted with the cascode resistors. R17-24 are all 1 ohm and I will initially bias them to .3 volt as Mr. Pass noted in the Turbo manual. So when I read .3 volts, with two 1 ohm resistors in parallel (.5 ohm) at each MOSFET, they will only be passing .6 amp each at 32 volt rails, 19 watts. This doesn't seem like anywhere near the sweet spot in the original F5, 22 volts at 1.3 amps, 28 watts. The Turbo doesn't look much like a 50 watt class A amp with such low current.
Am I missing something? Like the current passing in the diode at .3 volts? If so how much is it? I may just be a fraidy-cat, not wanting to smoke these rare Fairchild devises.

Rush
My tought exactley
what if you reduce the source resistor values? that will let you go up with the bias yes?
I am happy running over 40W on the TO220 FQP19N20s and to me they sound better at hi bias
Just for quick try solder an extra resistor on top of existing one that will give you 0.33 homs and report back

Last edited by Bksabath; 5th May 2012 at 07:55 AM.
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Old 5th May 2012, 07:55 AM   #1380
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Quote:
Originally Posted by buzzforb View Post
I have had mine at .5 with no problems. Just have to watch the diode temperature. Hotter they get, the faster/earlier they conduct. This was the point of my question about seperating them from the heat. Their response is temperature dependent. Should still be ok, just have to find the point of stability. The Rs are there not only for degeneration and linearization, but also to control the mosfet and temper its response in terms of current consumption.
It is all a game of compromises

If you put them on separate heat sink they will warm up and change curves as you get in the mood to play laud

If you put them on the main heat sink the temperature will be more constant yes they conduct earlier but that can be taken care with changing the value of source resistors
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