100W Ultimate Fidelity Amplifier

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#13,886
clpk said:
Hi XRK, thanks, on a quick look I see that there have been changes in the differential pair collector resistors (680 to 1k2). Is it okay if I update PCB FH11 as per your schematic to build it? Greetings!!
Click to expand...

Sure, why not?

@Still4given,
Indeed, I made the FH9 to avoid having to use hard to find and expensive lateral FETs. But it turns out, I like the bass authority of the hexFETs more.
 
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#13,887
xrk971 said:
Sure, why not?

@Still4given,
Indeed, I made the FH9 to avoid having to use hard to find and expensive lateral FETs. But it turns out, I like the bass authority of the hexFETs more.
Click to expand...

Hmmm, I never built the FH9 so I can't compare but the FX8 was a beast for it's size. Way simpler to build though if you have the Laterals, which I do. You only need to fit the outputs to the heatsink. I would surprise me if the bass is actually better. Did you A/B them?

Blessings, Terry
 
#13,888
Bangla H said:
Hello again
i have done a bit homework and put a little board.
Hope it works.
Please take a look to correct contacted traces.
Inspired by following posted schematic, pic and layout
i came up to this one.
If it is OK i will share gerbers as next.



And mostly cloned Prasi's AA9MD board without fuses.
Thanks for sharing Prasi.


Best Regards. 🙂
Click to expand...

Have you finished your tests? If it works, can you share the gerber file?
 
#13,889
still4given said:
Hmmm, I never built the FH9 so I can't compare but the FX8 was a beast for it's size. Way simpler to build though if you have the Laterals, which I do. You only need to fit the outputs to the heatsink. I would surprise me if the bass is actually better. Did you A/B them?

Blessings, Terry
Click to expand...

Yes, I had the Bimo Mod FX8 and the FH9 side by side. It’s very apparent the difference. It’s only an extra TO126 and a pot plus a few resistors. The FH9 is really something special. You might want to give it a listen. I’ll even send you some PCBs of the FH9HVX if you are up for it. This is the 100w version.

Here it is on my Griddle Amp:
849179d1591003996-cast-iron-griddle-amp-budget-conscious-heatsink-solution-griddle-amp-final-01-jpg


@kozard, I am not sure if more has been done to the FX8, but I believe the Bimo mod was the latest and widely agreed to be excellent. I have even run the Bimo mod in full Class A. 🙂
 
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#13,890
kozard said:
So which version of the FX8 is the recommended version? Bimo Mod?
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If you like bass, you should choose Vertical mosfet as output rather than lateral mosfet if input and VAS stage is same. Vertical mosfet will have lower distortion at low frequency. But vertical mosfet is difficult to get low distortion in high frequency because gate capacitance is bigger.

According to person who built FX8 mod, they like the mid frequency.

This topology is simple but can have good enough quality.
 
#13,897
still4given said:
Funny, this is the best looking 100hz square waves I've ever recorded and they are on the FX8. I guess I will have to build a FH9 to compare.

Did you actually build and test a FX8?
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Yes, regular FX8 and FX8 Bimo Mod.

FX8 built about 5 years ago in this thread Post 6918:
542400d1460095341-100w-ultimate-fidelity-amplifier-fx8-first-sound-2.png


FX8 Bimo Mod:
831567d1586286113-100w-ultimate-fidelity-amplifier-fx8-bimo-class-ab-test-closeup-jpg


A square wave doesn't show bass authority as well as measuring damping factor at 50Hz between the two amps.

Lateral FETs typically have RDSon circa 1.5ohm and hexFETs are typically 0.06 to 0.1ohm. So the amp output impedance will be much lower, and this translates to better bass authority.
 
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#13,898
xrk971 said:
Yes, regular FX8 and FX8 Bimo Mod.

FX8 built about 5 years ago in this thread Post 6918:


FX8 Bimo Mod:


A square wave doesn't show bass authority as well as measuring damping factor at 50Hz between the two amps.

Lateral FETs typically have RDSon circa 1.5ohm and hexFETs are typically 0.06 to 0.1ohm. So the amp output impedance will be much lower, and this translates to better bass authority.
Click to expand...
Did you measure the damping factor of the two amps?
 
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