Virtual Audition of Very Simple Quasi MOSFET Amp

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donovas

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Joined 2014
xrk971, thank you for this wonderful test. even on my speakers i can hear the difference between the files, and im using baksa 55 for the amp.

i agree vhex seems to add more dynamic to the music. very uncanny. i have no theory as to why.

was vhex ever taken out of the case and compared with a same psu as the other amps? if not this would've made a lot of difference, i would think.
 
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thimios

Member
Joined 2009
donovas said:
xrk971, thank you for this wonderful test. even on my speakers i can hear the difference between the files, and im using baksa 55 for the amp.

i agree vhex seems to add more dynamic to the music. very uncanny. i have no theory as to why.

was vhex ever taken out of the case and compared with a same psu as the other amps? if not this would've made a lot of difference, i would think.
Click to expand...
Please can you do it clear,what is the vhex?
 
xrk971

xrk971

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Thank Donovas, glad you found it fun and useful. I never tried the VHEX with a different PSU since it needed 50v rails and the SMPS was the only one I had capable of that.

Thimios, VHEX is the VHEX+ designed by Valery - similar to the one you are building now but yours has a ton of Sankens.

Virtual Zero Audio - power amplifier products

Very nice amp.
 
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thimios

Member
Joined 2009
xrk971 said:
Thank Donovas, glad you found it fun and useful. I never tried the VHEX with a different PSU since it needed 50v rails and the SMPS was the only one I had capable of that.

Thimios, VHEX is the VHEX+ designed by Valery - similar to the one you are building now but yours has a ton of Sankens.

Virtual Zero Audio - power amplifier products

Very nice amp.
Click to expand...
Aha,agree,excellent amplifier!
Unfortunately not boxed yet...I will go for monoblock configuration when i have the money.
 
ggetzoff

ggetzoff

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Joined 2004
xrk971 said:
Hi Prasi,
Thanks for your observations. The point of the test and listening by the remotely located auditioner is that the whole recording and source chain and listening chain (your DAC, amp, headphones) are identical. The only difference being the amp under test. So any perceived differences must come from the change in the amp. I agree they all sound very similar and it means that people will probably be happy with any of these amps as they are quite good, well excellent sounding really compared to much commercial stuff at usual stores under $1k. There is some unavoidable room effects which I try to minimize with mic placement at 0.5m from speaker. The sound you hear is exactly represented by the measures frequency response posted which is pretty much flat within 5dB over 50Hz to 16kHz (or wide range of our hearing).

My in-person reactions to the sound are different than what the recordings show because I do get more room effects by listening farther away at the listening position and I get benefit of stereo separation and sound stage.

I do agree FX8 Bimo is very HiFi sounding. In person though, the amp that seems to get me to take notice are the Quasi, Circlophone (BJT), and the FH9. The Quasi has a totally different sound signature - it's probably difference in H2 vs H3/H4 but dynamics seem very lifelike. FH9 has a very pleasing engaging and powerful sound. The Circlophone (BJT) seems to do everything right - overall very balanced, low distortion, great dynamics. For critical listening and lowest distortion - probably the Jason K VSSA and VHEX+ are what I would say as most accurate. If I had to pick one amp as the only amp I had to live with for a long long time...

The VHEX+ gets the nod. In the end, neutrality, great dynamics, and midrange and high range resolution keeps me listening to all genres.

But, what's the most "fun" amp to listen to that will make you, as Hugh said, "get your feet tapping", the Quasi and the FH9.
Click to expand...

What is your current overall favorite? Still the VHEX+?
 
xrk971

xrk971

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It's hard to say one particular is a favorite. I switch amps a lot. I am currently listening to FX8 Bimo mod in full Class A with bias at 1.2amps and +/-24v PSU. I seem to go back to the Quasi or the VHEX with my SE Class A CFP 2SA1837 headphone amp as a preamp though. Actually, that preamp makes almost any low distortion amp sound like a SE Class A amp.

I have a similar thread on virtual audition of headphone amps. It's not surprising which ones were favorited in a blind test... SE Class A of course. And the 2SA1837 CFP was the top dog.
 
ggetzoff

ggetzoff

Member
Joined 2004
Brilliant thread. I have a full set of boards coming from vzaudio for a vhex+ build. To my ears the vhex+ is the flattest, open, most tone-correct of all the builds. Some of the other amps do things better, but overall the vhex+ is the amp you can live with the most. Plus, it's a well supported build.

There are a lot of good amps here. I need to do a full listen again. Awesome thread. Thank you. :D

Cheers,

Greg
 
ggetzoff

ggetzoff

Member
Joined 2004
fab said:
Just an advise that One must pay attention here that the setup is the one of xrk971 and limitation of microphone and positioning plus size of room... the subjective sound might be different once you hear it in your room with the rest of your system...

My 2 cents
Fab
Click to expand...

You are correct. It is an all things being equal comparison and the closest many of us will come to being able to hear these amps (like your USSA amps).;)
 
xrk971

xrk971

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fab said:
Just an advise that One must pay attention here that the setup is the one of xrk971 and limitation of microphone and positioning plus size of room... the subjective sound might be different once you hear it in your room with the rest of your system...

My 2 cents
Fab
Click to expand...

True and good point to remind folks of.

In my other virtual audition thread of a headphone amp, the room is not a consideration as the "sound" is just the recorded voltage across a load resistor. But the source, DAC, and ADC all play a role as they do here.

Blind Virtual Audition of Several Headamps

Funny thing is since that thread, I have built about another dozen headphone amps so may have round 2 soon. Will have a new commercial amp (Schiit M3) in comparo plus an ESP HPA and THAT1646 based design.
 
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nigelwright7557

nigelwright7557

Member
Joined 2008
murtonpikesystems.co.uk
The DC offset problem is due to quasi topology.
The feedback capacitor to ground is wrong polarity.
On all my amps there is a negative voltage on top of that capacitor so the capacitor is wired other polarity and they all work fine.

I always add a current mirror on the front end and have one resistor in one leg and a pot in the other to set DC offset. Or even a pot across LTP tail to set DC offset.
 
maty tinman

maty tinman

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Joined 2012
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I heard ALL 14 amps.

1º F5 Juma. I love the sound.

2º VHex+ . It seems doped. Much bass, some anecoic sound. Maybe is the ideal with orchestral music.

3º Quasi. Sweet, warm. It needs more energy and highs. To listen vocal music.

I think that F5 Juma has the best of VHex+ and Quasi. Problem, to me, it has very little power to move my KEF Q100 speakers (86dB and 4.7 Ohms minimum). Am I wrong?

And yes, your speakers sound very bad with orchestral music.
 
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Hikari1

Member
Joined 2012
maty tinman said:
I heard ALL 14 amps.

1º F5 Juma. I love the sound.

2º VHex+ . It seems doped. Much bass, some anecoic sound. Maybe is the ideal with orchestral music.

3º Quasi. Sweet, warm. It needs more energy and highs. To listen vocal music.

I think that F5 Juma has the best of VHex+ and Quasi. Problem, to me, it has very little power to move my KEF Q100 speakers (86dB and 4.7 Ohms minimum). Am I wrong?

And yes, your speakers sound very bad with orchestral music.
Click to expand...

I have the f5 with 2 pair Toshiba 2sj201/2sk1530...so similar to Juma's amp but not the same although it is probably more similar to Juma's than a stock F5. At 25W it would drive my KEF R700's (87db, 3.2Min) fine as long as you don't listen loud (over 85db).

It just depends on how loud you listen and how big your room is.
 
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Hikari1

Member
Joined 2012
Well juma f5 and my f5 are using rare toshiba mosfets...they are vertical mosfets but designed for audio. They are expensive and hard to find and are often faked.Most f5 are using IRF mosfets which sound different but are readily available.

Iam not familiar with the ussa 5. I have seen the vssa amps which are f5 with but input and lateral mosfets. Can you post a schematic of ussa?

Laterals might sound sweeter but have less current capability. Part of the charm of the toshiba mosfets is they kind of sound like laterals with more current...so maybe best of both worlds? That’s what I have heard although I haven’t heard an amp with f5 topology and laterals.

If you listen to large scale music loudly you want more watts I would think. If you listen at lower levels jumas amp will be fine. There is an f5 turbo project as well (50w). Dual pairs of mosfets. That’s what Iam using now.
 
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Hikari1

Member
Joined 2012
Also, I have never heard juma’s f5. He also has another design called “cubie” which has lateral mosfets. Might want to ask him for a recommendation if you like his designs. I believe the cubie is 50w class a/b so it might be more appropriate for you if you are into big orchestra music.
 
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