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Virtual Audition of Very Simple Quasi MOSFET Amp
Virtual Audition of Very Simple Quasi MOSFET Amp
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Old 9th August 2016, 05:53 AM   #1
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
Default Virtual Audition of Very Simple Quasi MOSFET Amp

If you are like me, you have probably wondered what the Quasi amp from this thread sounds like and what all the hub-bub is about. You can either be lucky enough to have someone give you PCB's, or be very handy and etch your own like some. Then build it, and then debug, then listen.

I built the amp from a PCB given to me by BanglaH, it was tough going as it had some problems with DC offset, and these problems appear to have not been completely solved as of yet. However, the amp still sings and it has been pretty much loved by all who have built it and heard it.

So I used my experience in recording carefully-crafted sound clips from my previous 6 "Subjective Blind" driver test threads to make the following sound clips of this amp, and also compared to several other amps that I have. The conditions were identical for all amps in that the speaker, microphone, DAC (CS4398 with Burr Brown OPA2604 via USB at 48kHz), and source were all the same with the only difference being the amp was changed. There are 3 sound clips each which have been re-normalized to -3dB peak value. Sound was recorded with the same measurement mic (UMIK-1) at the measurement position as 48kHz wav files. The data was then converted to 320kbit MP3 so that it would fit as an upload to DIYA servers for you to download.

The speaker was my reference 2-way FAST with passive transient perfect cross-over and ScanSpeak 10F/8424 mid-tweeter and Dayton RS225-8 woofers in a sealed 24 liter box. The speaker is described here:

10F/8424 & RS225-8 FAST Ref Monitor

Click the image to open in full size.

Here is measured impedance of this speaker:
Click the image to open in full size.

Here is my simple Quasi amp build:
Click the image to open in full size.

I will post the sound clips for this amp plus the following amps:

1. VHEX+ by vzaichenko (this is the only amp that used a different power supply, a 53v SMPS vs a linear 35v rail supply that all the others used in this test). This is currently my reference amp.

2. Inverted JFET Circlophone by Piersma (BJT output version)

3. Apex FX8 Bimo mod (lateral FET outputs)

4. Apex FH9 xrk971 mod (hexFET outputs)

Edit: 5. Jason K's thru hole VSSA amp (lateral FETs)

http://www.diyaudio.com/forums/solid...ml#post4798137

Edit: 6. Inverted JFET Circlophone with hexFET output:
http://www.diyaudio.com/forums/solid...ml#post4799986


Edit: 7. CFH7 amp "http://www.diyaudio.com/forums/solid-state/295286-virtual-audition-very-simple-quasi-mosfet-amp-14.html#post4811896"]http://www.diyaudio.com/forums/solid-state/295286-virtual-audition-very-simple-quasi-mosfet-amp-14.html#post4811896

Edit: 8. Pass M2 amp


Edit: 9. FH9HV with 44v rail supplies and KSA/KSC drivers vs BD139/140's - super sound quality improvement vs standard FH9.

Edit 10. F5 Juma http://www.diyaudio.com/forums/solid...et-amp-27.html

Here is the combined frequency response measured from all amps (mic and speaker untouched):

Click the image to open in full size.

This is what the measured harmonic distortion spectrum looks like from the speaker with the Quasi amp - in general, it's lower than the speaker's HD so really doesn't intrude - but higher order distortion components vary somewhat between amps:

Click the image to open in full size.

Here is the measured impulse and step response for the Quasi amp:

Click the image to open in full size.

Please use good quality headphones to listen to the clips. They will have less coloration and room effects.

The three soundclips represent some high dynamic range instrumentals/jazz, pop and jazz vocals and are saved as .asc files to use the max filesize limits. Once you download it, rename the extension to .MP3 in order to listen.

Let me know what you think, or which one sounds good to you and why. Have fun!

Sound clips for Quasi amp are attached below.

Edit 8/9/2016: the sound clip sources are mono versions of their original self so that a mono setup can be used to capture both left and right channel content and not suffer from stereo layout anomalies and also to reduce room effects by having mic 0.5m away. Recording is of mono amp with single speaker with mono mic. The sound recorded precisely matches the frequency response curves presented here as the same mic at the same position was used. Ultimately, the mp3 generated is mono as well but played in both ears.


Hopefully, I will be able to post virtual audition clips for all of these amps that Inhave built:

Click the image to open in full size.
Attached Images
File Type: png Amp-comparison-all-freq-response.png (68.3 KB, 3641 views)
File Type: png Amp-comparison-all-freq-response-HD-Quasi.png (152.9 KB, 3617 views)
File Type: png Amp-comparison-all-freq-response-IR-Quasi.png (55.8 KB, 3382 views)
Attached Files
File Type: asc Quasi-Clip-1.asc (1.73 MB, 225 views)
File Type: asc Quasi-Clip-2.asc (1.67 MB, 114 views)
File Type: asc Quasi-Clip-3.asc (1.76 MB, 121 views)

Last edited by xrk971; 18th November 2016 at 02:46 PM.
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Old 9th August 2016, 05:54 AM   #2
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
Default Sound clips from VHEX+ reference amp

Change to .MP# in order to listen.
Attached Files
File Type: asc VHEX-Clip-1.asc (1.73 MB, 201 views)
File Type: asc VHEX-Clip-2.asc (1.67 MB, 103 views)
File Type: asc VHEX-Clip-3.asc (1.75 MB, 112 views)
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Old 9th August 2016, 05:55 AM   #3
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
Default Sound clips from FX8 Bimo Mod amp

Rename extension to .MP3 to listen.
Attached Files
File Type: asc FX8-Bimo-Clip-1.asc (1.73 MB, 228 views)
File Type: asc FX8-Bimo-Clip-2.asc (1.67 MB, 120 views)
File Type: asc FX8-Bimo-Clip-3.asc (1.76 MB, 140 views)
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Old 9th August 2016, 05:56 AM   #4
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
Default Sound clips from FH9 xrk971 Mod amp

Change extension to .MP3 to listen.
Attached Files
File Type: asc FH9-Clip-1.asc (1.73 MB, 167 views)
File Type: asc FH9-Clip-2.asc (1.67 MB, 88 views)
File Type: asc FH9-Clip-3.asc (1.76 MB, 89 views)
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Old 9th August 2016, 05:57 AM   #5
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
Default Sound clips from Inverted JFET Circlophone amp

Change extension to .MP3 to listen.
Attached Files
File Type: asc C-phone-Clip-1.asc (1.73 MB, 140 views)
File Type: asc C-phone-Clip-2.asc (1.67 MB, 72 views)
File Type: asc C-phone-Clip-3.asc (1.76 MB, 81 views)
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Old 9th August 2016, 08:03 AM   #6
Jay is offline Jay  Indonesia
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Hmmm... interesting. Listening for the clip-1 instrument, I like the FX-8 Bimo mod...

In general, the variables are (1) dynamics (2) distortion (3) richness/details (4) naturalness...

Those with good dynamics (like the hex fet amps) tend to lose details/richness and naturalness... This could be related with distortion as I found FH9 has the highest distortion (and sounds "louder" than the others)...

Those like the circlo-phone lacks dynamics...

FX8 is good in every variables. May need a reference file to know more.

Last edited by Jay; 9th August 2016 at 08:08 AM.
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Old 9th August 2016, 08:05 AM   #7
Samuel Jayaraj is offline Samuel Jayaraj  India
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xrk971, thanks for the clips. Hands down the Quasi Mosfet-BJT has more Air, better tonality, Depth of stage and PRAT is tops. Overall, engaging from the word 'go' compared to the rest of the pack.

Hats off to the development team; Hugh's contribution here is phenomenal. Special thanks to him, despite the challenges he is facing.
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Old 9th August 2016, 08:34 AM   #8
Samuel Jayaraj is offline Samuel Jayaraj  India
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Also noticeably less sibilance, though some may hear it as a loss of sparkle in the music. Voices have more 'chest'. Dynamics are very good; the same passage sounds like 'pumping' (compression/expansion) in some of the other amps.
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Old 9th August 2016, 09:20 AM   #9
xrk971 is offline xrk971  United States
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Virtual Audition of Very Simple Quasi MOSFET Amp
These are some great comments and surprising interesting results. I never got a chance to listen to the clips except coarse listening to make sure recording worked and level was about acceptable. I wonder if a Subjective Blind test would have been better to avoid bias?
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Old 9th August 2016, 12:06 PM   #10
Elias is offline Elias  Finland
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Speaker impedance plot ?


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