Virtual Audition of Very Simple Quasi MOSFET Amp

[ben123]

Hello

Thanks for recording different amps.
I will give my personal opinion,
so to others if you don't want to be biased, don't read further.

I first thought difference would be easy to hear because I did some listening tests on source equipment and that was easy to hear. On amps I don't have that much experience.

For me 2 amps stood out; quasi and the apex fh9 xrk971 mod.
The quasi is slightly more softer and easier to listen, it has addictive qualities to it.
The fh9 is a bit more direct and has stronger bass, the fh9 is more present.
The quasi has a beautiful transition from note to note.
For me personally a like the more laid back sound of the quasi.

This is a very fine amp

 

[xrk971]

Hello

Thanks for recording different amps.
I will give my personal opinion,
so to others if you don't want to be biased, don't read further.

I first thought difference would be easy to hear because I did some listening tests on source equipment and that was easy to hear. On amps I don't have that much experience.

For me 2 amps stood out; quasi and the apex fh9 xrk971 mod.
The quasi is slightly more softer and easier to listen, it has addictive qualities to it.
The fh9 is a bit more direct and has stronger bass, the fh9 is more present.
The quasi has a beautiful transition from note to note.
For me personally a like the more laid back sound of the quasi.

This is a very fine amp

The Quasi strikes again! The FH9 got some credit too though - I actually like the sound of the FH9 a lot too. It's different than the Quasi though - more visceral. Quasi is more cerebral.

 

[Bigun]

This is a fun way to listen to different amps - just wish you had my TGM8 in the list

 

[xrk971]

just wish you had my TGM8 in the list

There's an easy way to solve that

Can you perceive the differences in how the amps sound? To first order, they all sound pretty good. When you look at the frequency response, they are almost identical. But dynamics and detail are another thing.

Note the crispness of the percussion in clip 1. In part, the transient perfect (TP) nature of the speaker resolves the clicks and clacks very well, more so than a non TP speaker. Here, an amp with clean square waves and high slew rate will outshine another amp that is not as clean on square waves.

 

[egra]

Thanks for the uploads X! All of these amplifiers are top performers therefore easy to fall in love with any of them. Listen to female voices I would choose Quasi, for percussion FH9, but in terms of neutrality VHEX wins the game. All in all I prefer FH9 mostly, head to head with VHEX which is a truly unique amplifier.

Equipments for test: JRiver Media Center -> AudioQuest DragonFly 1.2 DAC -> modded Sansui AU-217 amp -> SAL 2-way floorstanding loudspeakers + (a glass of) TAKLER Pinot Noir 2012

 

[xrk971]

Egra,
Thanks for the review and listening impressions. Glad you like FH9 - one of my favorites despite deceivingly simple design. The most important piece of equipment was the Pinot Noir!

You have all these great amps and you are now using a commercial Sansui AU-217? Isn't that the one that is like an AX11?

Cheers,
X

 

[mcd99]

Well I sat down with vodka in hand and listened...

Found the VHex the most pleasing overall. It had a more forward sound which is my personal preference. But the quasi had the most life especially in the treble. The difference was evident in the last third of clip 1.

Will have another listen with clip 2 in a bit. I need to listen to some of my music collection now.

This is an interesting exercise!

Paul

 

[egra]

Yes. Pinot Noir helps to open our mind to hear these differences what I mentioned above.

I have only modded Sansui and PeeCeeBee and countless Class-D amps (mostly from ebay) but none of them can reach the heels of these 2 Class-AB amps. I think the parallel push-pull VAS driver stage does the magical trick what I like so much. (FH9, FX8, AX11)

 

[xrk971]

For those not familiar with FH9, it is based on Apex FX8 (designed for latFET), and I modified by switching to hexFETs and added Vbe multiplier for temperature compensation. I simulated the concept in Tina first and it was good there so, I had PCB's made. Here is an FH9HV (uses HV VAS drivers) that can take 53v rails and put out 120w with a pair of hexFETs for outputs.

Here it is undergoing a 15min stress test at 34.5v rms into 10R load with 53v dual rail SMPS:

 

[mcd99]

X,

Which HEXFETs did you use? Can't tell from the picture. I like HEXFETs for their speed. May be candidates for my own homebrew amp.

Egra,

Agree, the use of alcohol works. But much like Pinot noir, need to treat the Vodka with respect.

Think all the amps are very good just that those two stand out as having something extra.

Paul

 

[xrk971]

Vishay IRFP240 and IRFP9240
Mostly purchased from China via Aliexpress, except the ones for VHEX+ were obtained as part of Digikey BOM. The cert sheet from Digikey however, says source of IRFP is from China. They look identical (Ali vs Digikey). Satin smooth pins and back metal tab, clean precise epoxy case, and of course, the moment of truth is when it can sustain 120w without blowing up.

I love IRFP240/9240's and would build all my amps with them if I could.

Two new amps coming up that will use them: allFET Circlotron designed by Kees52 and the CFH7. Also, on my list is a Pass M2 that also uses them.

 

[mcd99]

Vishay IRFP240 and IRFP9240

I love IRFP240/9240's and would build all my amps with them if I could.

Yes, me too. Although, if using sufficiently low enough voltage rails I like the IRFP240/9140 pair. Better complements as far as I can tell.

Two new amps coming up that will use them: allFET Circlotron designed by Kees52 and the CFH7. Also, on my list is a Pass M2 that also uses them.

Wish I could create amps as quickly as you. Stillunforgiven (sp?) has competition .

The beauty of this hobby is that once you have a decent PSU you can change amps at minimal cost.

Hopefully you can add clips of these two amps as well?

Paul

 

[xrk971]

I was thinking that this thread can just be a place where I add sound clips of all my amps as I progress. So certainly those will be added.

Yes, once you have a PSU and some heatsinks and supply of assorted resistors caps and transistors - additional amps cost under $5ea to make. Amazing really when you consider how good they can sound.

No one can touch Still4given for quantity and speed of builds.

 

[banat]

xrk971 thanks for nice music samples upload and in the same time for very interesting sonic experiment !,

I have listened all music samples ,but I was mostly concentrated mainly on music sample #3 , no alcohol , nothing like that ,
- all five amps sounds correct to me but , ...
- Quasy and VHEX amps sounds closest to what I like to hear ,...

- VHEX , far the best presentation of top octave with incredible overall micro-detail presentation , but just on some moments sounds almost little beat artificial to me .

- Quasy , the best bass octave presentation with overall most balanced tonal presentation ,it will be no ears fatigue effects on long listening session for sure , it is one small amp for 24/7 use .

 

[horst303]

I wonder if a Subjective Blind test would have been better to avoid bias?

ooh yeah, I can't see how one can avoid the confirmation bias trap.

For me, my bias was that I was expecting not to here any or much difference, and upon listening I have found that my bias was confirmed, okay so I haven't listened that carefully, but it's not like the difference between the drivers is it?



And my hat off to you Sir for doing the hard yards.

 

[xrk971]

xrk971 thanks for nice music samples upload and in the same time for very interesting sonic experiment !,

I have listened all music samples ,but I was mostly concentrated mainly on music sample #3 , no alcohol , nothing like that ,
- all five amps sounds correct to me but , ...
- Quasy and VHEX amps sounds closest to what I like to hear ,...

- VHEX , far the best presentation of top octave with incredible overall micro-detail presentation , but just on some moments sounds almost little beat artificial to me .

- Quasy , the best bass octave presentation with overall most balanced tonal presentation ,it will be no ears fatigue effects on long listening session for sure , it is one small amp for 24/7 use .

The Quasi is the only current feedback amp here and that may be part of the reason it has what is perceived to be good bass presentation. I have a JK VSSA that is also current feedback. Sound clips from that amp might be revealing - although it uses lateral FETs so there will be a difference there alone.

 

[xrk971]

ooh yeah, I can't see how one can avoid the confirmation bias trap.

For me, my bias was that I was expecting not to here any or much difference, and upon listening I have found that my bias was confirmed, okay so I haven't listened that carefully, but it's not like the difference between the drivers is it?



And my hat off to you Sir for doing the hard yards.

At first blush they all sound very much the same and in fact, are all fine amps that you would probably be fine living with for a while.

 

[banat]

The Quasi is the only current feedback amp here and that may be part of the reason it has what is perceived to be good bass presentation. I have a JK VSSA that is also current feedback. Sound clips from that amp might be revealing - although it uses lateral FETs so there will be a difference there alone.

Yes I know that Quasy is CFA(Singleton) amp but honestly I don`t care for that ,
I just have presented my personal impressions here , nothing else ,
btw ,wish to that Quasy to have touch of that top octave high definition of VHEX ,
and to VHEX to have much more of that easy-flow and overall balanced sonic presentation of Quasy .

JK VSSA variant need to hear before my comment is out.

 

[xrk971]

JK VSSA Sound Clips

This is for the Jason K VSSA amp. So now we have another current feedback amp.

Here is the measured frequency response in comparison to all the amps, and this is the only one that strays from the same basic curve that all the others have. It has fall-off at the high frequencies faster. I am not sure why this is as it uses similar lateral FETs that the FX8 Bimo uses (although they look like pulled Hitachi's rather than new Renesas). Note that the mic and speaker have not been touched since this experiment started so it's definitely caused by the amp:

Here is the measured harmonic distortion:

Here is the Impulse and Step Response:

Change extension of sound clips from .asc to .mp3 in order to listen.

 

[jkuetemann]

My choices of input filter may be a little more aggressive than some. Others seem to set the input filter fairly high, 1MHz+, where I set mine a little over 200kHz.