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F5Turbo Illustrated Build Guide
F5Turbo Illustrated Build Guide
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Old 17th April 2019, 02:34 PM   #551
TboneAK is offline TboneAK  United States
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Thanks ZenMod! Yes I did build as per papas sch, but without cascodeing the FE. I’m using the Hifi 2000 400mm deep 5U chassis. Would think we want to stay below that point at which the thermistors save the day. I’ll build the load bank and hook it up and see how it behaves at .38vdc. My ACA runs just under 55c, so I keep thinking the F5T isn’t very hot. Hitting .4vdc won’t be hard, the pots aren’t super touchy yet, and I don’t think the heat will rise considerably with .02vdc more.
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Old 17th April 2019, 03:05 PM   #552
BigE is offline BigE  Canada
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TboneK the, 0.4 is the point when the diodes start conducting. This takes the source resistors out of circuit. Please be aware that Nelson Pass warns against building an amp without source resistors.
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Old 17th April 2019, 04:36 PM   #553
TboneAK is offline TboneAK  United States
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BigE, I’m not going to test the limits. I’m just getting feel of how this all works and the amps behavior. All this input from you guys is great!

I will most likely set it to .35 and enjoy it. Next thing is to start designing and building speakers for it to drive. The drivers will be here Friday!
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Old 18th April 2019, 02:14 PM   #554
TboneAK is offline TboneAK  United States
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I have the load bank on the rt channel. 8, 10 watt, 33ohm resisters in parallel for 3.8ohm measured load. The bias has settled to .394 to .389vdc with the load connected. This heat soaking is a slow process. Thereís a bit of oscillation, very slow, about .005vdc over about 2mins. Is that normal? I know itís pretty small and the offset is holding steady. Heatsink temps are still 45c and less. Ambient room temperature is 17-18c. Iím inclined to leave it be at this point.
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Old 18th April 2019, 02:26 PM   #555
Zen Mod is offline Zen Mod  Serbia
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F5Turbo Illustrated Build Guide
slow changes are ok , no worries

though , input shorted , no load - for all settings

dummy load is needed only when you need to observe dynamic behavior of an amp

load is not needed and not condition to have , for amp to settle where it needs to be settled
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Old 18th April 2019, 02:35 PM   #556
TboneAK is offline TboneAK  United States
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Thanks Zen Mod! I will proceed unloaded, input shorted. I have a few things to tidy up and it’s time to play some music!
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Old 18th April 2019, 04:02 PM   #557
BigE is offline BigE  Canada
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TboneAK,

Are the values you've reported for how the bias was set with amp case closed or open?

When you close the case, the internal temp will rise, along with the bias voltage.

How long a time has the amp been continuously on at that bias setting? I find that the heat and bias can continue to rise for 24 hours or more.....when I biased, I would bias for a couple hours on the bench, then play music and continue to watch the bias. It is suggested to revisit the bias after 1 day and 1 week.

Note that as you play music, the diodes will be conducting and contributing to the heat gain in the sinks, which therefore will contribute to more current flow through the outputs....
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Old 18th April 2019, 09:37 PM   #558
TboneAK is offline TboneAK  United States
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BigE thanks for the insight. I was already considering that I should back it down some and let it cook over night. It’s now my plan for this evening. The numbers reported are with the covers on.
I have some new drivers showing up tomorrow that will need braking in. Seems like a good opportunity to let the amp cook while driving them.
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Old 20th April 2019, 06:29 AM   #559
TboneAK is offline TboneAK  United States
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All is stabile. Dropped it to .37vdc to tonight. I plan on cooking it until I get the cut outs in a OB for a brake in session for my new drivers. They arrived today!
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