Class A amplifier for my speaker testing and Audition

[Hari Iyer]

At last i will be building my Class A amplifier from today for my speaker testing and audition. This is based on the already published design from the DIY community. Check out the link here The β22 Stereo Amplifier

 

[spirovious]

Congrats Hari, will come to hear it later.

 

[darshanjoshi]

good going hari
congrats

 

[iaudio]

Heard a lot about Beta 22 on various forums, it is known to be quite transparent. Good luck with the build Hari.

 

[Hari Iyer]

Yesterday started assembly of the power supply board and finished few resistors and transistors. Will complete the power supply board by this Sunday and post images.

 

[bibin3210]

Congrats Hari, Waiting to see more photos of the finished board.....

 

[Hari Iyer]

Almost 2 months of getting my PCB, have now finished the challenging Class A power Amplifier. The SQ compared to my Sony Vintage Amp and the Beta 22 is huge difference and as per me Mind Blowing. Could get every detail from this amp without any effort or increase in the volume. At 9 o'clock position this amp is quite loud without even the pre-amp board. After connecting the pre-amp should be able to control the volume much better. Now after building this amp all my perceptions about wattage is gone and this modest 18W rms amplifier sounds louder by atleast 4 times my 40W Sony amplifier.

Some technicals - I have now set the quiscent current to around 120mA and the amp is under test mode. It gets only warm and not hot as lot of other class A amps get. May be once the top cover is installed it may become hot.

Will await audition from Denom, Santy, Spiro next week for justifying my claims about the SQ.

Some images during the work in process-

 

[spirovious]

So the time has come to visit to your place & hear,compare the amp.cheers.

 

[Hari Iyer]

So the time has come to visit to your place & hear,compare the amp.cheers.

I have sent our team a mail with more images. You can drop in next week for a listen (even Thursday should be fine with me).

 

[avidyarthy]

Also, buy a Topping ....

 

[bijinmb]

Hari, Really appreciate your effort and research behind Beta 22's work.

Hope to hear more from you and also the guys who gonna do real audition there.

Flamboyant work...

 

[aks07]

Respected Sir,

Congratulations on a very neat build.

For 18 WPC at Class A, this seems a v-e-r-y efficient amplifier. I noticed the standing current is 120mA. What is the main rail voltage? Also, what type and impedance of loudspeaker you are using?

I am very keen to know how it all happens.

Thanking you

Warm regards
AKS

 

[Hari Iyer]

Respected Sir,

Congratulations on a very neat build.

For 18 WPC at Class A, this seems a v-e-r-y efficient amplifier. I noticed the standing current is 120mA. What is the main rail voltage? Also, what type and impedance of loudspeaker you are using?

I am very keen to know how it all happens.

Thanking you

Warm regards
AKS

Yes, 18 WPC seems more than sufficient for my room. The main supply voltage is +/- 30Volts. I am using a TL BS speakers build by me and has a relatively flat impedance curve even at resonance of the woofer. Hence the load will not vary much for the amplifier and drives it very easily without even getting too hot. Infact without fan too the amplifier is just warm which is quite a surprise for me about what i have heard about class A amps. I am using a heat sink for 30Amps load though.

 

[Hiten]

Nice build Hari.:thumbsup:
From Pics it looks like Heatsink are small and upside down. Hope this is temporary. I don't understand bias settings and I don't know technical things of Class A but if it is not producing heat it is only working in class A for first few watts. For sustained dynamic music it will clip and will not be good for speakers.
May be experts would chime in. But once again nice build.
Regards

 

[keith_correa]

Nice work Hari. Where did you get all the components from?

 

[captrajesh]

Great work Hari Iyer. I see that the original amp has a separate chassis for the power supply for isolating the amp from the power supply which generates considerable EMI. Hope you are addressing the issue adequately since the whole thing is in one box.

 

[Hari Iyer]

Nice work Hari. Where did you get all the components from?

99% of components are available at Lamington Road. The only component not available are the current regulator diodes. There were 8 current regulators in the power amplifier and 4 in the regulated power supply. I modified the circuit to use an JFET as a current source instead of using the current regulator diodes. This was the most challenging part of the amplifer to find the correct component value to get the correct current regulation across the power amp and the amplifier. In the process burnt quite a few BJT's but finally got the right combo.

 

[Hari Iyer]

Great work Hari Iyer. I see that the original amp has a separate chassis for the power supply for isolating the amp from the power supply which generates considerable EMI. Hope you are addressing the issue adequately since the whole thing is in one box.

The amplifier has a virtual capacitance to the order of 60,000 microfarad and negates the need for bulky capacitors. Also the power supply is regulated one and uses MOSFETs for regulation which again is a low noise device. Also there are couple of current sources in the power supply and the amplifier which reduces any stray EMI induction and helps in reducing the noise figure. The power supply ground and the chassis ground is isolated and the chassis will in turn be connected to the wall unit earth. This will make the amplifier immune to the any Stray EMI / RF noise. I am also planning to add an external EMI/ RF filter to the AC input before the power transformer to prevent any stary pick-up if any. I am now using this amplifier since past 3 days and have not noticed any hum/ hiss or RF/EMI noise.

 

[Hari Iyer]

Nice build Hari.:thumbsup:
From Pics it looks like Heatsink are small and upside down. Hope this is temporary. I don't understand bias settings and I don't know technical things of Class A but if it is not producing heat it is only working in class A for first few watts. For sustained dynamic music it will clip and will not be good for speakers.
May be experts would chime in. But once again nice build.
Regards

Infact what i noticed is something different. For the first few minutes about 10 minutes the amplifer SQ is not that smooth. But after the amplifier heats up it sound very very open and smooth and the entire sound stage has lot of presence and warmth. I feel after getting warmed up and after the quiscent current is stabilized it becomes class A. Before the warm-up it works in class B as the current is yet to build-up in the circuits.... just like a Tube amplifier.

The heat sink is kept up-side down because the entire bottom portion is ventilated and the heat sink is directly touching the chassis. Hence the chassis also acts like an heat sink and the heated chassis escapes the heat to the ambient. This could be one of the reason the amplifier not getting hot.

 

[arj]

Respected Sir,

Congratulations on a very neat build.

For 18 WPC at Class A, this seems a v-e-r-y efficient amplifier. I noticed the standing current is 120mA. What is the main rail voltage? Also, what type and impedance of loudspeaker you are using?

I am very keen to know how it all happens.

Thanking you

Warm regards
AKS

Hi AKS did you mean efficient in terms of the conversion to output power by the amp ?. From the little I know the pure class A efficiency is less than 15%.. Hence input power should be at least 120 w consumption..am I right ?


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