100W Ultimate Fidelity Amplifier

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#6,824
xrk971 said:
This amp is super easy to build - went together faster than any amp I have built. I am still waiting for the output stages but have some 2SC5200/2SCA1943's slipped in their place to get a feel how big this amp is. It is small! Smaller than a typical TPA311x class D amp.

I am a bit impatient waiting for the MOSFETs to get here...

Is there anyway this amp can work with BJT's rather than MOSFETs? What would happen if I powered this up with the PNP on left and NPN on right.

The MOSFETs are G - S - D and the BJTs are B - C - E.

Would it be PNP on left and NPN on right given Vcc(+) is on left and negative is on right side.
Click to expand...
Nice work, if you want use 2SC5200/2SA1943 go to AX10.
 
#6,825
Apex i use PCB from AX14 to A100
2SD2389/2SB1559

And have DC in out... (43V DC)

If fast on-off trafo there is sound distorted ~ 2 second and quiet
0.33R - 1mV

Connected like that...
 

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#6,829
Hello Apex and friends,
This query is regarding the Apex FX8 schematic. I was wondering if a capacitor is required across the output stage biasing diode (1N4007) ? What is the function of such a capacitor and how do we compute it's value?
What's the final approach for the output stage biasing? Can I use just the diode, or should I consider a variable resistor (1K) ?
Thanks
 
#6,832
Jay said:
While waiting, why not (thermally) couple the LTP transistor pair? If the legs are already too small you can use copper plate in between the transistors.
Click to expand...

Would that help improve the balance stability? I am surprised they don't make dedicated LTP transistors with two on same die with 6 legs - I suppose 8 leg dip like an op amp package would work.

The two VAS(?) transistors BD139 and BD140 also show a metal plate should be attached to them but I wonder if that's for heat sinking rather than thermal coupling.
 
#6,833
xrk971 said:
Would that help improve the balance stability? I am surprised they don't make dedicated LTP transistors with two on same die with 6 legs - I suppose 8 leg dip like an op amp package would work.
Click to expand...

I think thermal coupling the LTP is more effective than using degeneration resistors.

In the past there are a lot of such matched transistors in one package (5-leg or 8 and 14-pin IC). I'm still using such transistors. Currently my FX8 is still using 2SC2240-BL, later will be compared with the 5-leg dual transistor which seems to be better on paper.

xrk971 said:
The two VAS(?) transistors BD139 and BD140 also show a metal plate should be attached to them but I wonder if that's for heat sinking rather than thermal coupling.
Click to expand...

The original design was using smaller transistors for the VAS (BC639/640).
 
#6,835
xrk971 said:
Jay,
How do you like your FX8?
Click to expand...

Still struggling with power supply sound... 😀 I have a different way to assess amplifiers...

xrk971 said:
I want to do a comparison thread where I keep the speaker fixed and swap out various amps and make sound clips.
Click to expand...

It is hard when the power supply has to be different... A power supply can kill the sound of an amplifier... (but only microscopic to most ears)

I'm very very curious to see how the amplifiers will sound like when recorded into a clip...
 
#6,836
Jay,
I know you have very sensitive golden ears but what I am talking about are very obvious audible differences going from class D to class AB (various flavors) to quasi class A (like Circlophone), to true class A (like Pass ACA or JLH). It may be possible to stick with same 35v dual rail supply from toroidal transformer followed by basic PSU circuit like the one Destroyer X designed for the Dx. To get the very low micro-ripple PSU will take an active transistor controlled linear circuit. Maybe I need to build one of those next. I can put a variable regulator to dial voltage to what is needed.

I hear very obvious differences in LM3886 vs Dx (and hopefully can add FX8 when I have it completed) vs Circlophone vs class D (IRS2092) and class D (TPA311x).
 
#6,837
xrk971 said:
what I am talking about are very obvious audible differences going from class D to class AB (various flavors) to quasi class A (like Circlophone), to true class A (like Pass ACA or JLH).
Click to expand...

Let's see if I can detect HF issues in the coming blind test. Better if you can include/reveal the distortion spectrum. Class-D has obviously HF issue. Class-B tends to have high order distortion (which I considered as HF issue).

xrk971 said:
It may be possible to stick with same 35v dual rail supply from toroidal transformer followed by basic PSU circuit like the one Destroyer X designed for the Dx. To get the very low micro-ripple PSU will take an active transistor controlled linear circuit.
Click to expand...

It is the issue with interference that I'm worry about. With the same power supply then it is fair for all amps.

xrk971 said:
I hear very obvious differences in LM3886 vs Dx (and hopefully can add FX8 when I have it completed) vs Circlophone vs class D (IRS2092) and class D (TPA311x).
Click to expand...

Your assessment was correct regarding 3886 and DX. But FX8 is IMO a much better amp...

Class-A like ACA will highly dependent on the speaker used. It will be an outlier...
 
#6,839
xrk971 said:
Great - looking forward to my FX8 then. It's amazing how small and compact it can be and still sound great. Which lateral Mosfet are you using for the output? I know you said certain parts are hard to come by where you are.
Click to expand...

Small and compact is actually a good recipe... I'm temporarily using Hitachi K2221/J352.

I'm just reading a thread where a fella found First watt's F6 sounded horrible and praised an LM3886 much higher than I think it deserved. What I'm saying is, people have different way/taste when judging an amp, so you cannot trust my taste (for example, I don't like DX amp like you do and many others) 😀
 
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