Very simple quasi complimentary MOSFET amplifier

[xrk971]

It's in work, not functionally working yet. But I have high hopes that Thiamongi's build will have better luck than me.

 

[thimios]

It's in work, not functionally working yet. But I have high hopes that Thiamongi's build will have better luck than me.

Is Thiago in progress?

 

[xrk971]

Is Thiago in progress?

Yes, his progress photo from earlier post:

Nice looking amp

 

[thimios]

Yes Nice!
A piece of art!
Thiago....my hat out

 

[Algar_emi]

What is the recommended power transformer rating and specs for this amp, 2 channels?

I saw around +/-32-35Vdc supply, but no VA rating for the transformer.

Thanks
SB

 

[xrk971]

I am using 250VA 25vac transformer and qnty 6 x 4700uF caps per amp for 35v rails.

 

[thimios]

What is the recommended power transformer rating and specs for this amp, 2 channels?

I saw around +/-32-35Vdc supply, but no VA rating for the transformer.

Thanks
SB

This dependent from your pocket.😀
The bigger the better.

 

[Algar_emi]

Then what is the power rating of this amp, at 35V supply let say?

I was thinking to use a 500VA.

Thanks
SB

 

[prasi]

Then what is the power rating of this amp, at 35V supply let say?

I was thinking to use a 500VA.

Thanks
SB

300VA should be enough for a pair of amps.

 

[xrk971]

In Stereo, Finally

I now have managed to fix both channels. Both use 2N5401/2N5501 and MJE350. DC offset is stable within 10mV over hours of playing music. Sounds very nice - a nice sweet glass-like mids presentation with very substantial deep bass. Highs are very clear and non fatiguing, easy to listen to for extended periods.

I am running 100mA bias current and dual CRCLC PSU's with 250VA 25AC toroidal transformer for 35v rails.

Currently listening with my transient perfect ScanSpeak 10F/8424 and RS225-8 FAST two-ways. Very nice sound - surprisingly good clear bass.

Setup with power supplies visible:

Closeup of Unit 1 (left channel):

Closeup of Unit 2 (right channel):

This is the speaker being used:

 

[AKSA]

Hi XRK,

Now, for the best test......

1. Does the amp engage, does your foot tap and do you feel a heart string pulled from a particularly rendering musical phrase?
2. Can you listen intently without having to get out of your chair and walk away for a 'rest' over coffee.....
3. On sonorous tracks with double bass and deep piano bass, can you hear the real decay of the strings? It should be quite apparent, and needs a very low noise backgroup.
4. If you close your eyes, can you discern, on orchestral music, the rear drums, the right rear woodwinds, the front left and right violins, and the soloist out front? Can you assess their relative depth and width?

For this you need a very, very good CD. I often use the Linn Super Audio Surround Collection Vol 2, AKP284. I use an Oppo 105, stepped attenuator, and SEAS/Peerless speakers.

Very nice pcbs on the component side. Maybe since you have debugged the tracks and clean the grunge, maybe you should lacquer them to protect them from the summer moisture!

Cheers,

Hugh

 

[meanman1964]

How does he behave when you push it and cranking up the volume ?I hope no compressed sound?

 

[Ranchu32]

Congratulations XRK! Those modules look very neat an tidy.

Special thanks to you Hugh for helping XRK through his troubles...

 

[thimios]

I now have managed to fix both channels. Both use 2N5401/2N5501 and MJE350. DC offset is stable within 10mV over hours of playing music. Sounds very nice - a nice sweet glass-like mids presentation with very substantial deep bass. Highs are very clear and non fatiguing, easy to listen to for extended periods.

I am running 100mA bias current and dual CRCLC PSU's with 250VA 25AC toroidal transformer for 35v rails.

Currently listening with my transient perfect ScanSpeak 10F/8424 and RS225-8 FAST two-ways. Very nice sound - surprisingly good clear bass.

Setup with power supplies visible:

Closeup of Unit 1 (left channel):

Closeup of Unit 2 (right channel):

This is the speaker being used:

Glad to see that your problem has gone!
DC offset is stable within 10mV over hours of playing music.
Do you mean that offset is stable between the cold and warm conditions?

 

[xrk971]

Hi XRK,

Now, for the best test......

1. Does the amp engage, does your foot tap and do you feel a heart string pulled from a particularly rendering musical phrase?

Yes, the amp has a presentation that is clear, lively, and dynamics are excellent. I listen to known test tracks with well recorded live jazz trios (piano, stand up bass, drums), also vocals from Melody Gardot, Anne Bisson, Diana Krall, pop from various sources, and my favorite classical is Dittersdorf concerto for double bass.

2. Can you listen intently without having to get out of your chair and walk away for a 'rest' over coffee.....

Most definitely, it's the opposite - you don't want to leave or stop listening.


3. On sonorous tracks with double bass and deep piano bass, can you hear the real decay of the strings? It should be quite apparent, and needs a very low noise backgroup.

Imaging and soundstage are excellent. I can definitely place instruments on jazz trio. I don't have speakers that recreate large orchestral music well (2 way FAST with transient perfect XO) but for Dittersdorf double bass the attack is very good. Another great source of tests for attack on bass is stand up bas from Chick Corea's trio.

4. If you close your eyes, can you discern, on orchestral music, the rear drums, the right rear woodwinds, the front left and right violins, and the soloist out front? Can you assess their relative depth and width?

Need 3-way big speakers for orchestral but for simple chamber music and jazz groups, yes - spatialization is excellent. Separation of channels with monoblock amps and PSU's gives excellent soundstage.

For this you need a very, very good CD. I often use the Linn Super Audio Surround Collection Vol 2, AKP284. I use an Oppo 105, stepped attenuator, and SEAS/Peerless speakers.

I am using a DIY CS8398 DAC with BUrr Brown OPA2604 op amp output that I made (see photo):

I am using ScanSpeak 10F/8424 mid-tweets and Dayton RS225-8 woofers with my own passive 1st order transient perfect XO. Here are some measurements of this speaker (not with this amp):

HD:

Step & Impulse:

Phase:

Very nice pcbs on the component side. Maybe since you have debugged the tracks and clean the grunge, maybe you should lacquer them to protect them from the summer moisture!

Thanks for compliments on construction. Thank you for all your help to make it possible

Cheers,

Hugh

Final verdict is this is an excellent, engaging, muscially pleasing and very dynamic amp. I really like it. Given how many amps I have - this one deserves a real case. 🙂

 

[xrk971]

Glad to see that your problem has gone!
DC offset is stable within 10mV over hours of playing music.
Do you mean that offset is stable between the cold and warm conditions?

On initial cold start, offset is about 25mV. After 10min it is within 10mV over hours of music playing.

 

[AKSA]

Thanks XRK,
A really smart analysis.
What is perplexing to me and a few like-minded folks is this:
Why has the quasi topology been cast aside with contempt for about 20 years? This amp does about 0.07% (99% is H2+H3+H4) and on this version this spec is held to 20KHz. In fact with fast bipolars it is 1dB down without LP filter at around 200KHz.
This approaches avoids most of clip issues by using a quasi npn and a bootstrapped nmos. I noticed in sims that the nmos output
stays conducting down to -15Vp. This amp has some very significant features - long live quasis!
Great work XRK!

Hugh

 

[still4given]

On initial cold start, offset is about 25mV. After 10min it is within 10mV over hours of music playing.

Does it ever get to zero?

 

[xrk971]

Does it ever get to zero?

Yes, centered at zero and drifts to either +/- 4-5mV. Pretty good considering it's a singleton input.

 

[thimios]

Yes, centered at zero and drifts to either +/- 4-5mV. Pretty good considering it's a singleton input.

Post your circuit as built😉