FET-hex explendit amplifier

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#501
ashok said:
Acca's circuit is a class B amp. So the output stage is still in cut off mode. Adding a BD139 bias spreader will be required only if you want to run it in class AB mode. Then you will also have to deal with bias stability issues.

Acca's circuit is stripped down to a bare minimum and if that sounds good enough, then it's a great find. Has no adjustments and seems to be stable without additional components. This might be device specific I guess. So better use the circuit with parts as shown.

If you really want the bias spreader you could remove the diode string and put in the attached circuit.
Click to expand...
Hi Ashok!
After class AB has lower THD distortion in the relationship class B, because I want to ask this circuit to operate in Class AB!!😉
Otherwise like this audio amplifier is good for the subwoofer!
 
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#503
Yes,my stage is biased in class B,so not current on output transistors.
You can use this MJ's
I tried to use two diodes.I don't hear any changes in sound.
In voltage feedback amp,this is very big difference.
No good enough,only good sound 😉
You can add miller caps under board,if unstable.
I don't add this because it's stable (I watch on 'scope)
 
#507
Rreplacement with MJ11015/MJ11016?

Acca said:
You can change 27R to 18R in BD's emmiters
This will change VAS current from 7 to 11mA
Click to expand...

Hello Acca!
Is this amp is reliable in operation?
Is the sound of this amp is good for listening to?
Instead of Darlington transistors BDX33C/BDX34C be used MJ11015/MJ11016?
If you use them gave her some change in the schematics?
Thanks for your help!
 
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#509
Audio amp with mj11015/mj11016

So the schematics with Darlington transistors mj11015/mj11016 should be like this:😉
cheers!:cheers:
 

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  • New schematics MJ11015.MJ11016.JPG
    New schematics MJ11015.MJ11016.JPG
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#515
Post 503

Hello Acca,

What's the changes to the amplifier (output current, biase current?) in using 3 diodes and using 2? Can you calculate this?

Thanks,
WP

Acca said:
Yes,my stage is biased in class B,so not current on output transistors.
You can use this MJ's
I tried to use two diodes.I don't hear any changes in sound.
In voltage feedback amp,this is very big difference.
No good enough,only good sound 😉
You can add miller caps under board,if unstable.
I don't add this because it's stable (I watch on 'scope)
Click to expand...
 
#516
wponline said:
Hello Acca,

What's the changes to the amplifier (output current, biase current?) in using 3 diodes and using 2? Can you calculate this?

Thanks,
WP
Click to expand...
It's same.
Output bias is always zero.No current through output transistors.Maybe it can be calculated when use datasheet (Ube vs. Ic).I don't take care about it.Sound is good in both versions.I'll make another one amp today (with real heatsink,and tonight I'll post pictures).
 
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#517
BG1

borys said:
I am using e-mu 0204 at the moment, but it can be any sound card (integrated in laptop too), have to work in full-duplex mode (99% of them is working ok).
Load is let me say 8R so just put additional 2 resistors to divide voltage going to sound card (or use potentiometer), put the signal back to the line-in. Spectralab is what you looking for. You can use arta, rmaa software too.
Click to expand...

Thanks Borys.
I had try a number of such softwares in the past.
I'm looking to buy, arta, but i worry if it is the proper way to test power amplifiers in full volume.
Thanks and sorry for my late.
 
#520
It's stable now.This is not DC pulses,this is very low frequency output.
My phone is offender.This is not happened by amp.Use smaller input cap to remove this 😉
Today I worked on very simple amplifier.Tomorrow I'll upgrade it and maybe post new topic.It uses only two (maybe 4 for higher current) transistors on output and VAS is changed with transformer.
 
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