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VSSA Lateral MosFet Amplifier

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Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
I use Diffmaker or the Distortion Isolation script in Praxis.
I also use a variety of the Belcher test and various TIM and PIM tests.
When you go back to early MPP i showed some comparisons that used that measurements.
I use a specially modified DAAS professionally, i have a Klippel, Wandel&Goltermann, Audio Precision etc. I decided though not to show any measurements with such expensive equipment any more on a DIY thread. It is just too frustrating, if you can not afford it.
The Quant Asylum Q400 is good enough i think for all practical purposes.
Bill Waslo tested the ICE-Power amps from B&O and found a huge null.
Problem is that i do not like the sound much. I do not know if he had connected a loudspeaker plus cable or not. Some amps that perform great on a dummy load do not like much to drive a loudspeaker with it´s complex load.
My friends at Stereoplay did a lot of research why certain amps that sounded good in the listening room did not measure super low distortion in the lab.
They found certain dynamic parameter, for example the amp should not change it´s distortion profile over level, frequency and complex load but this is too complicated to explain in brief.
I have long given up to find any exotic type of distortion that can explain in full what we hear.
An Enigma.
 
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Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
Here we go :
http://www.libinst.com/Detecting Differences (slides).pdf
I think Diffmaker is a free download so everybody can bring some high tech into the lab.
By the way, i can now make loudspeakers that have such low distortion that i can not hear them when i put the distortion residual in one channel of a headphone and the undistorted music in the other channel. It is simply masked so for me that red herring is from the table too.
For example the new Accuton Cell midrange performs that way, so does Michael Böressens Raidho ribbon.
 
Lazy Cat

Lazy Cat

Member
Joined 2007
Bigun said:
Well I have been watching closely - this is a fantastic result (amplifier design and pcb layout) LC. You kept it simple in layout and in physical form. I know you promised that you'd do this but it isn't easy and it turned out very well indeed.

I think this has turned out to be the 'F5' of the SS forum (meant as a compliment).

The LatFET is so well suited to this topology because of the ease of thermal compensation and ease of drive. The two-in-one package for the FETs was really the icing on the cake.
Click to expand...

Thanks Bigun, greatly appreciate your opinion. :)
 
Lazy Cat

Lazy Cat

Member
Joined 2007
Joachim Gerhard said:
Here we go :
http://www.libinst.com/Detecting Differences (slides).pdf
I think Diffmaker is a free download so everybody can bring some high tech into the lab.
By the way, i can now make loudspeakers that have such low distortion that i can not hear them when i put the distortion residual in one channel of a headphone and the undistorted music in the other channel. It is simply masked so for me that red herring is from the table too.
For example the new Accuton Cell midrange performs that way, so does Michael Böressens Raidho ribbon.
Click to expand...

Thanks Joachim, certainly very useful tool. I'm using my simple distortion magnifier made out of two opamps, it works down to -110 dB. By measuring VSSA I see only H2 diff signal others are just too low. :)

Looking forward to your build and final implementation, since you've decided to use SMPS. :up:
 
M

miksi

Member
Joined 2003
I've just finished two boards with nichicon KA and will put them in the box tomorrow but right now have a few questions.
My Hypex power supplies have voltages little over +-46V. I'm worried about two input transistors with Vce=45V. Can I use bc546 and bc556?
On my boards gate stoppers are zero ohms. Is this by design? I remember seeing 100 and 68 ohms on v1.4 schematic.
Andrej, your demo VSSA is really :cool:. Between those Hypex supplies you have switch and some orange ¨stuff¨, and you use unregulated positive supply from one board. Can you elaborate? I can see you didn't replaced those little samwhas (yet) only big ones. Did you glued them again like originals?
Regards
 
Lazy Cat

Lazy Cat

Member
Joined 2007
miksi said:
I've just finished two boards with nichicon KA and will put them in the box tomorrow but right now have a few questions.
My Hypex power supplies have voltages little over +-46V. I'm worried about two input transistors with Vce=45V. Can I use bc546 and bc556?
On my boards gate stoppers are zero ohms. Is this by design? I remember seeing 100 and 68 ohms on v1.4 schematic.
Andrej, your demo VSSA is really :cool:. Between those Hypex supplies you have switch and some orange ¨stuff¨, and you use unregulated positive supply from one board. Can you elaborate? I can see you didn't replaced those little samwhas (yet) only big ones. Did you glued them again like originals?
Regards
Click to expand...

Hi miksi :wave:

There's not full SMPS voltage on BC550c/560c Vce, so it should work. No need to change input BJTs.

Yes zero gate stoppers installed not by mistake. If you would like to experiment with higher gate values later on, first you would need to remove C22.

There's power on switch, Shrack RT033-12L relay and C-80 NTC forming inrush current limitter - soft start, since original NTC on SMPS400 is removed and replaced by jumper.

Little Samwhas will be replaced later, no glue. BTW this new amp is runing burn-in period and sounds gorgeous.

Regards Lazy Cat :cheers:
 
Lazy Cat

Lazy Cat

Member
Joined 2007
AKN said:
Hi LC,

Am I reading this right? If so, quite a departure from published schematic. Please explain further.
Click to expand...

Not a departure, they are still sitting there on PCB, just a value reset to zero. At any time you can higher their values according to Semelab ALF application or any other recommendations. My measurement and listening tests showed best result if they're zero. :yes:
 
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