FET-hex explendit amplifier

[Gost22]

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.

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!

 

[ashok]

Never underestimate all classB designs !
Try it out before dismissing it !

 

[Acca]

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)

 

[Acca]

Never underestimate all classB designs !
Try it out before dismissing it !

Of course,not all class B amps have same audio output quality

 

[Acca]

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!

And very good for high tones.Because this I like it
First try with diodes,to see what i say

 

[Acca]

You can change 27R to 18R in BD's emmiters
This will change VAS current from 7 to 11mA

 

[Gost22]

Rreplacement with MJ11015/MJ11016?

You can change 27R to 18R in BD's emmiters
This will change VAS current from 7 to 11mA

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!

 

[Acca]

Yes,it's good,I used one module in my active speakers.
Very good for listening.
Yes,see post #503
No changes,only 18R in emmiters.

 

[Gost22]

Audio amp with mj11015/mj11016

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

 

[Acca]

Yes

 

[breizheau]

It's done, i just have finished to read this thread....
Marc told me to use this amp on my 2xboomers and use the VSSA with my tweeter.
I ordered 2 x SPMS 1000W at Connexelectronics to try.

I have to order on On-semi webshop...

 

[Gost22]

Acca, can be power supply for the amplifier Ucc = + /-40V?
thank you!

 

[Acca]

Yes,but change 15k to 18k

 

[bimo]

I want to modify current source like this. It should be improve a bit, but I am not sure if sound quality will be improve. Wit standard current source (without zener), is already

 

[wponline]

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

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)

 

[Acca]

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

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).

 

[thimios]

BG1

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.

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.

 

[Acca]

I tested my another amp today,and it's necessary to add 330pF on C and B of outputs.If no this,amp will oscillate and destroy.My first amp not needed this cap because transistors have low fT.

 

[BYRTT]

My first amp not needed this cap because transistors have low fT.

Hi Acca thanks for reporting, it is great for learning/knowlegde, at same i wonder if you got solution to the problem with the DC-like pulses that moved speaker cone, if you nailed it would you report solution ?.
Regards Ricky

 

[Acca]

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.