100W Ultimate Fidelity Amplifier

[apexaudio]

I'm ready with my new A33 amplifier assembled ,soft start,DC protection, and factory PCB .
Sound it's very,very natural I like how it's sound . Thanks to Mr.Mile S for every amplifier posted on this forum .
Regards,Alex

Nice work,
Regards

 

[thimios]

I want to ask Mr Mile.
Why you choose this gain for AX14?
Mine give 18v rms out when inp.is 350mv rms.
(+/-35v power supply) .
I will post photos this afternun later.

 

[still4given]

I'm ready with my new A33 amplifier assembled ,soft start,DC protection, and factory PCB .
Sound it's very,very natural I like how it's sound . Thanks to Mr.Mile S for every amplifier posted on this forum .
Regards,Alex

HI Alex,

That looks really nice! May I ask what size transformer you are using?

Thanks, Terry

 

[apexaudio]

I want to ask Mr Mile.
Why you choose this gain for AX14?
Mine give 18v rms out when inp.is 350mv rms.
(+/-35v power supply) .
I will post photos this afternun later.

For use without preamp.

 

[alex mm]

Hi Terry,
transformer used 350VAC , 2X40V/4A and 2X14V /1A .......
Regards,Alex

 

[thimios]

For use without preamp.

It's imposible to drive this from a cd without clip.
I want to reduse gain so the amplifier clip when Vinp.=800mV.
NJW0281
NJW0302
+/-32V
Offset=18mV
BIAS=18mV/0.33R=54mA

 

[thimios]

AX14

The rest.

 

[still4given]

It's imposible to drive this from a cd without clip.

50K pot?

 

[apexaudio]

It's imposible to drive this from a cd without clip.
I want to reduse gain so the amplifier clip when Vinp.=800mV.
NJW0281
NJW0302
+/-32V
Offset=18mV
BIAS=18mV/0.33R=54mA

Nice work, use 1k instead 560R (R8) to reduce gain.
Regards

 

[thimios]

Thanks Mr. Mile.

 

[still4given]

I just finished my A33 on my new boards. It's working but I see a little oscillation. Anyone else see any?

Thanks, Terry

 

[still4given]

Here are some scope shots.

The oscillation is not visible on the scope above 10khz. It is mostly around 1khz

 

[still4given]

A couple more bits of information to maybe help. The only places I varied from the schematic was to use a 5k trimmer for the offset and a 500R trimmer for the bias. Speaking of that, I have the bias set to 60mA per device and the trimmer is at 460R. I have a 4u7 in the input and I used MJL4281/4302 for outputs. Everything else is per the boards silkscreen. I am taking the reading from the speaker out. These boards have the zobel and thiele built in.

 

[overall feedback]

A couple more bits of information to maybe help. The only places I varied from the schematic was to use a 5k trimmer for the offset and a 500R trimmer for the bias. Speaking of that, I have the bias set to 60mA per device and the trimmer is at 460R. I have a 4u7 in the input and I used MJL4281/4302 for outputs. Everything else is per the boards silkscreen. I am taking the reading from the speaker out. These boards have the zobel and thiele built in.

You can try MJE340/350 base collector capacitor 22pF or higher.

 

[apexaudio]

Here are some scope shots.

The oscillation is not visible on the scope above 10khz. It is mostly around 1khz

Replace 100pF with 3,3nF in input RF filter.

 

[still4given]

Hi Mile,

3n3 in input filter did nothing for the oscillation. Still there on both boards. I am wondering if any of the guys who built this amp, tested it on a scope? The sound is nice so it may not be noticed unless played loudly. Still, I think it needs to be fixed.

Thanks, Terry

 

[apexaudio]

Hi Mile,

3n3 in input filter did nothing for the oscillation. Still there on both boards. I am wondering if any of the guys who built this amp, tested it on a scope? The sound is nice so it may not be noticed unless played loudly. Still, I think it needs to be fixed.

Thanks, Terry

Replace 470pF with 1nF... also you can try 'overall feedback' sugestion...

 

[still4given]

Hi Mile,

I put the 100pF back andadded the 22pF to the B-C of each of the pre-drivers and the Oscillation is gone. Of course I don't know what if any affect it has on the THD or anything else but sine and square waves are clean and the amp plays perfectly. The only other change I might want is to increase the gain a little. I don't usually use a preamp and this one is a little lower than most of my other amps. I did get a chance to hook it up to my A/B system and it it quite comparable to my other CFA amps. Great soundstage. Strong, punchy bass, clear highs and detailed mids. Really, really nice. Definitely worth the build.

Thanks for another great sounding amp.

Blessings, Terry

 

[sonal kunal]

Found oscillation of Apex AX9. It was mistake I made on layout, I connected 47pF to collector and emitter of BD139 and BD140.

I have changed 15v zener to 22v for LME49860. Love sound of this amp on my monitor speaker lots of detail in mids, NX-14 will be replaced with AX9.

Corrected Layout.

Regards

 

[apexaudio]

Hi Mile,

I put the 100pF back andadded the 22pF to the B-C of each of the pre-drivers and the Oscillation is gone. Of course I don't know what if any affect it has on the THD or anything else but sine and square waves are clean and the amp plays perfectly. The only other change I might want is to increase the gain a little. I don't usually use a preamp and this one is a little lower than most of my other amps. I did get a chance to hook it up to my A/B system and it it quite comparable to my other CFA amps. Great soundstage. Strong, punchy bass, clear highs and detailed mids. Really, really nice. Definitely worth the build.

Thanks for another great sounding amp.

Blessings, Terry

You can increase gain, just replace 100R in feedback circuit with 47R
Regards