100W Ultimate Fidelity Amplifier

And most probably ultra unstable too, Ive dug around, this design by apex is a clone of a yamaha amp, <snip>

Do some sims, and youll find it impossible to stabilise no matter how you try to compensate it.

I use a greatly simplified version of this amp ah-la LF351 (circa 1975 so it came before the Yamahaha), a very good sounding op-amp, which is the most stable amp I have ever seen by a country mile. That power version of the LF351 will drive any load I throw at it including using the second channel as a virtual ground for the first channel through any kind of load down to the transistors SOA limit. Mine has a parts count of 35 per channel not including the power supplies. So I really do not believe the basic idea is incorrect. Just the implementation.:geezer:
 
And most probably ultra unstable too, Ive dug around, this design by apex is a clone of a yamaha amp, only that yamaha used it as a subwoofer amp, thats why you see compensation done like that 330pf cap across the feedback resistor, there was no intention for this amp to operate to normal frequencies required for full range amp. From what I can read about the yamaha amp is that it was discontinued prematurely because of problems, I can guess what those were......

Do some sims, and youll find it impossible to stabilise no matter how you try to compensate it.
U can find similar design in Pioneer, InterM, Zeck, Yamaha... amplifiers. Yamaha use this design in all amplifiers in last 10 years, not just for subwoofer amps. Do some sims of newer Yamaha (AX-596), and youll find it impossible to stabilise.
Regards
 
Pcb ax-14

PCB size: 60x82,5mm
Zobel Network 4R7 and 100nF on speaker terminal.
 

Attachments

  • APEX KELVIN BJT PCB.jpg
    APEX KELVIN BJT PCB.jpg
    167.7 KB · Views: 13,771
I use a greatly simplified version of this amp ah-la LF351...
This amplifier is completely different to the LF351.
Below is the LF351 schematic from National's datasheet.

Perhaps if you actually looked at a design before commenting on it, your comments would make more sense.

I thought you might have learned that after the mess you made here.
Apparently not.
 

Attachments

  • LF351.GIF
    LF351.GIF
    13.3 KB · Views: 11,682
LF351 has FET however BJT may be used. This is very similar. The same general concept except much simpler.

Godfrey obviously knows the difference between the functional schematic of the design concept for the IC and the actual schematic as put on the die inside an IC, or maybe not.

The only company I ever heard of that built the schematic as found inside an IC was Analog Engineering in Kentucky or Tennessee.
 

Attachments

  • LF351.jpg
    LF351.jpg
    9.6 KB · Views: 12,779
I cannot say specific about ApexAudios amp but the "simplified" version more like a power LF351 has open loop: 85kHz -3dB bandwidth; gain of 95dB; THD 1%; symmetric slew rate; and output impedance of less than 1 ohm at 10kHz. That should leave plenty of room to find a compensation scheme which works. Would expect the ApexAudio amp to be very similar with possibly higher gain and possibly lower THD.

Please remember simulations mean almost nothing until the sim is tweaked to match the real world performance. At the very least this amp seems like an excellent starting point for a "ultimate" amplifier. It is intrinsically linear, has symmetric slew rates, and will operate without feedback if DC quiescent is such that the output is normal and near ground. Most of the amps seen here on DIY have none of these features.

An ultimate amplifier for audio music, yes. Not an ultimate amplifier for those who cling to the belief amplifiers in this power range need slew rates approaching 100V/µs, full power bandwidth of more than 1mHz, hash chokes in the output providing impedance coupled outputs, and to keep their "oscillators with gain" in check . There are a lot of those guys found here on DIY.

Yes strong agreement with ApexAudio on this one.
 
Last edited:
Bad expirience with stability of some design not mean that will be a problem with all similar circuit. I have bad expirience with stability of many amplifier which use OP amp on input stage, and I afraid to use this topology, but use it anyway in my PA amps.
Amplifier schematics is similar anyway. There is several topology, and any of them can be good starting point for " Ultimare Fidelity Amplifier " , implementation is most important for functional amp.