50w Single-Ended BAF2015 Schade Enabled

[cubicincher]

to dantwomey

Hello dantwomey,


I use the 'oldtimers' LM317 / LM337 pretty often. I often add a CRC filter in front of the LMs. There are more modern voltage regulators which produce lower noise.
But I used the LM317 for my 50W-SE-Schade-amp to adjust the bias voltage.
This is a great amp!



Greets
Dirk

 

[Zen Mod]

yup

even Mighty ZM chose to use them in Singing Bush , for biasing and FE

 

[dantwomey]

Hello dantwomey,


I use the 'oldtimers' LM317 / LM337 pretty often. I often add a CRC filter in front of the LMs. There are more modern voltage regulators which produce lower noise.
But I used the LM317 for my 50W-SE-Schade-amp to adjust the bias voltage.
This is a great amp!



Greets
Dirk

Keep in mind I am only .1% of ZM. Or maybe .01%?

 

[Zen Mod]

no fret, even I can't always fill Enormous Mightiness of Mighty ZM

 

[cubicincher]

Then I am 0,0001% of ZM.


I am still working on the project to find the holy grail of dumbness!


Greets
Dirk

 

[Soundhappy]

Texas Instruments make new model of TL431

https://www.mouser.fr/ProductDetail/Texas-Instruments/TL431CLP-Z?qs=byeeYqUIh0P3%2BPlwAfHTLA==

https://www.ti.com/lit/ds/symlink/t...ll-mousermode-df-pf-null-wwe&ts=1597441032452

Perfect for Papa bias circuit

 

[dantwomey]

Texas Instruments make new model of TL431

https://www.mouser.fr/ProductDetail/Texas-Instruments/TL431CLP-Z?qs=byeeYqUIh0P3%2BPlwAfHTLA==

https://www.ti.com/lit/ds/symlink/t...ll-mousermode-df-pf-null-wwe&ts=1597441032452

Perfect for Papa bias circuit

Thanks to all the posts here I have completed my bias circuit, made the PCBs, and it works perfectly!

Regards,
Dan

 

[Ben Mah]

Soundhappy, the circuit that you posted has minimum output of 6.25V - too high.

Dan, your circuit has minimum output of 4.54V. That may or may not be low enough for IXFN140N20P. For THF-51S, that is probably too high for a large percentage of samples as the variability of Vgs is high. I used a 5K pot in my build (otherwise same circuit) and that outputted a minimum of 3.0V.

 

[Soundhappy]

@ Ben Mah

From article is adjustable 4v~12V bias circuit
Source : http://www.firstwatt.com/pdf/art_sony_vfet_pt1.pdf
I like very much precision of multiturns trimmer

 

[dantwomey]

Soundhappy, the circuit that you posted has minimum output of 6.25V - too high.

Dan, your circuit has minimum output of 4.54V. That may or may not be low enough for IXFN140N20P. For THF-51S, that is probably too high for a large percentage of samples as the variability of Vgs is high. I used a 5K pot in my build (otherwise same circuit) and that outputted a minimum of 3.0V.

I have a half dozen PCBs so if I run into trouble I can make up a spare with a 5k pot. Thanks for the info.

Regards,
Dan

 

[Ben Mah]

According to my calculations based on Ti datasheet:

Vmin = 2.5V(1 + 7500/5000) = 6.25V

See page 19 Figure 21:

https://www.ti.com/lit/ds/symlink/tl431.pdf?ts=1597519339702&ref_url=https%3A%2F%2Fwww.google.com%2F

Vref = 2.5V
Iref = 0.000002A so Iref x R1 = 0.000002 x 7500 = 0.015V, not significant

 

[MEGA_amp]

I initially used the same exact circuit with those exact values in post #1267. I was not able to go lower than 4.5V, which in turn prevented me from setting D-S at 28V on the lower IXFN. The 5k pot was the only change I made which remedied this.

 

[Soundhappy]

I build TL431 circuit long time ago...
and from my experience 4.7V is a perfect bias voltage for Schade 50 mosfet.
Work like a charm

 

[MEGA_amp]

I build TL431 circuit long time ago...
and from my experience 4.7V is a perfect bias voltage for Schade 50 mosfet.
Work like a charm

I should have put the caveat 'YMMV'.... my fets must've been made on Friday

 

[dantwomey]

Inspired by ZM is my Singing Shrub CCS!

Regards,
Dan

 

[ggetzoff]

Dan, nice work. I suggest you change the name to “a singing shrubbery”

 

[dantwomey]

Here's my initial shot at the second half of the shrub. I still have to make sure I have drain, source and gate in the right order on the JFETs.

Regards,
Dan

 

[Itsmee]

I may be missing something but your O/P & feedback don't look right.

 

[dantwomey]

I may be missing something but your O/P & feedback don't look right.

You'll have to be more specific for me to catch on.

Regards,
Dan

 

[MEGA_amp]

Looks correct to me. The speaker outputs from the CCS PCB and Gain PCB will obviously need to be tied together off board before going to +SPKR.