those transistors has the same pinout as 2SA1930/2SC5171. so they need to be mounted with the backside out. the first prototype F5 turbo Boards had the pinout reversed for the cascode transistors. that may be the confusion.
F5T bias problem solved
hi friends,
problem solved, I changed the orientation of the cascode transistors and now I can perfectly fine tune the bias and offset,
but
I did not go further above 120 mv, because heatsinks became very hot, measured 42-45 degree celcius. I need to upgrade heatsinks, byt he way I did not know the MUR3020W not generate any heat. Should I remove them from heatsinks? because I need more space in my chassis.
I also did a sound test with a cheap 3" 10W 8Ohm full range speaker, sound is very fine, musically involving, make me listen tracks from beginning to the end with that cheap speaker.
hi friends,
problem solved, I changed the orientation of the cascode transistors and now I can perfectly fine tune the bias and offset,
but
I did not go further above 120 mv, because heatsinks became very hot, measured 42-45 degree celcius. I need to upgrade heatsinks, byt he way I did not know the MUR3020W not generate any heat. Should I remove them from heatsinks? because I need more space in my chassis.
I also did a sound test with a cheap 3" 10W 8Ohm full range speaker, sound is very fine, musically involving, make me listen tracks from beginning to the end with that cheap speaker.
Last edited:
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. ☹️
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. ☹️
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.
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.
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 .......
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 .......
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
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