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F5Turbo Illustrated Build Guide
F5Turbo Illustrated Build Guide
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Old 12th July 2018, 06:12 AM   #451
recepky is offline recepky  Turkey
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Hi
I placed fans and put the everything back. Turn on the electricity butt
Bias was 2.5mv. I measure the tp 1 2 and 3 4. Just for cruosity. There was no any signal between tp 1 and 2. And cut the electric off. Then turn on again. Now tp 1 and tp 2 was back. ????
I read 730 ohm between. Everything normal again. What hell is happening???

By the way I ran out off trimmer turns I Can not increase bias anymore above 170mv. ☹️
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Old 27th July 2018, 05:21 PM   #452
recepky is offline recepky  Turkey
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Hi everybody

i solved the problem. i changed cascode transistors with new ones. Sa1145y and c2705y. Now i can properly set the bias. ))
But i blow out b channel mosfets. ((
i could not set the similar mv output from p and n channel. There was 100mv difference. Also the trimmers are very responsive. By the way before everything I changed the r5 and 6 to 2.2k.
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Old 4th August 2018, 08:19 PM   #453
kpsthakur is offline kpsthakur  India
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Quick one folks, does this amp need a preamp? For running a Sony CD player
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Old 4th August 2018, 08:25 PM   #454
Zen Mod is online now Zen Mod  Serbia
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F5Turbo Illustrated Build Guide
try without , just with pot inbetween source and amp

if it's loud enough , just add decent buffer after the pot

if it is not loud enough , you need preamp with few times amplification factor
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Old 6th August 2018, 07:37 PM   #455
kpsthakur is offline kpsthakur  India
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I think my 2x(0-18) 600VA transformer seems anemic for v2, any chance I can try using 2(0-40) 600VA with Cascode for v2, I know we could easily use it for v3.
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Old 6th August 2018, 08:09 PM   #456
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possible , why not

though , it's always clever to keep voltage and current capability on same level ....... so just take care of having enough output parts
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Old 7th August 2018, 09:33 AM   #457
kpsthakur is offline kpsthakur  India
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Zen are you suggesting I increase the output MOSFET's, but then won't it become something like v3? Plan is to run it as v2 with standard P&N board pair per channel, possibly try biasing the amp a bit low
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Old 7th August 2018, 10:38 AM   #458
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I'm just saying that , depending of nature of intended load for them (speakers) , you must be aware of OS current capability ..... if load is tough - you need enough output pairs

if load is benign , do what you want ...... you're not in trouble

from personal experience - one of the worst things you can do is - to alter some construction , just to use something you already have .......
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Old 7th August 2018, 11:13 AM   #459
kpsthakur is offline kpsthakur  India
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Agree Zen, I will be using 4ohm speakers, which ideally should be good for v2's...again, I don't want to alter the construction stuff, just for the transformers sake.
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Old 11th September 2018, 09:28 PM   #460
kpsthakur is offline kpsthakur  India
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Default JFET Cascode options

Cascade query.

I am finally locking on slighly undervoltage transformers for F5T V2 version. 0-22V 300VA transformers for monoblocks, which technically means a total of 600VA for the entire project.

From 0-22V AC (this is rated, but the voltage is around 23..something Volts), I get about 30.8V DC, since this is a bit on the higher side for the JFET's, planning to cascode the JFET's & the formula I attempt to figure out Voltage available to JFET's post cascode is

CASCODE FORMULA: rail voltage / (R26+R28) * R28 = cascode voltage

so for 30.8V Rail voltage the following R26, R28 values and Cascode voltage combinations are arrived


R26, R28

1) 10K, 4.7K = 9.92V
2) 4.7K, 4.7K = 15.4V
3) 4.7K, 2.2K = 13.8 V
4)2.2K, 4.7K = 21.04V
5) 1K, 4.7K = 25.39V (which again probably reaches the threshold for the JFET's)

My personal choice would be combo 4- R25,26=2.2K & R27,28=4.7K, but wanted to check with forum if this is an optimum choice or should I move to either option 2 or 5 for better performance, or any other suggestion
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