2stageEF high performance class AB power amp / 200W8R / 400W4R

Friends, I finally got around to replacing the internal cabling after a year. I replaced the cheap chinese cables with SUPRA branded ones.
1, for power connection SUPRA RONDO 4x2,5mm
2, for speaker connection SUPRA RONDO 2x2,5mm
3, for signal connection SUPRA DUAL

Old cabling
IMG_20241001_182555.jpg

Upgrade cabling
IMG_20250221_223440.jpg
 
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Some thicker copper can help to make the measurement figures look better beyond 0.00xxx percent 😎 and it would be very very difficult to hear a difference using SA2014 circuit ...
BTW: I am currently listening music using my 4 channel SA2014 built 2014 with more than 21000 operating hours. WOW
 
Evvo datasheet shows low transition frequency of 40Mhz vs 100Mhz Toshiba...
Onsemi discontinued the el-cheapo ksa940/ksc2073 that i use along with Toshiba 2sa1943n/2sc5200n in the stk clone
EVVO 🙂 sells both the ksa940/ksc2073 & A1837/C4793 for about the same price. MJE1503x are more expensive.
There is a cost saving using the isolated package, not needing the insulator, shoulder washer, but Pd is not as good as the exposed metal.

It's nice to see the new chassis heatsink brackets in use. A few threaded inserts in the back makes it easier.
Did you have fun with the bottom screws for the front panel? I used some studs inserted into the FP first, attach to the bracket using a flat/lock washer, nut or keps nut. A small wrench to tighten.

Wiring looks neater, what gauge original and after? #16AWG should be good enough.

21000 operating hours, cheers, let's hope the KEC parts are just as reliable.
 
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Transistors should last "forever" - only "electro migration" problem operating the parts near limits will kill them. Maybe the Voyager space probe has no lytics on board to stabilize the on board voltages (offered by nuclear batteries). This may explain the reliability of the electronics.

SA2014 may get problems after another 20000 - 50000 hours of operating when some lytics going the path to death (dry out). But thats maybe beyond my personal lifetime and it is very likely that I can never report this event to the DIY community 🤣

Have fun, Toni

P.S.: The EVVO A1837/C4793 are looking not to be a good replacement for Toshiba A1837/C4793. The Unisonic (UTC) or KEC variants are closer to the original
 
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Dear Roman,

what I can't clearly see if the speaker output minus is as short as possible connected to the GND input stage... the new/second picture shows a small cable ...
(effectively minimizes dc offset and THD+N; case design and input/output stage placement and new cable routing allows you to get the best out of the design)
 
Second source for critical transistors: profusion. Got some KEC replacements from profusion today for testing ...
Have fun, Toni
Hi Toni,

I am still very curious about how your testing is going with KEC devices. Can't wait to see your results.
All my required devices have arrived except KSA1381. I got KTA1381 (only 3 pieces), since KSA1381 is EOL, it was "back order" when I ordered it, but went out of stock.
So I have following two alternatives with me, if I can use them!
O1, Can I use KSA1142 in place of KSA1381 (Q12,Q13 in sa2014_input_vas_stage), I know KSA1142 is a 180v, Ic=100mA, hfe=114, Pc=8W, ft=180Mhz and Cob=4.5-7pf with a good SOA.(also EOL)
https://www.mouser.com/datasheet/2/149/KSA1142-89939.pdf
OR
O2, Can I use KSA1156 is a 400v, Ic=500mA, hfe=145, Pc=10W.
https://www.mouser.com/datasheet/2/149/KSA1156-62023.pdf

Pardon my ignorance I am a beginner and trying to learn.
Regards,
Arshad.
 

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SA2021 - NCH (New Class H) is now playing some weeks every day. My opinion: it's the successor to SA2014 (of course SA2014 has lower THD) with low idle power dissipation and more peak power. SA2014 is, was and will be the ultimate power horse in the context of maximum sound fidelity, but SA2021-NCH as a green variant of SA2014 is a wonderful replacement of all other power amplifiers in my home cinema. SA2021 pcb's for nerds are available - do you have the skills to build your own SA2021?
SA2021 tower design - absolutely noiseless. No hiss, no hum, no noise if input disconnected/shorted. All noise measurements reach the limits of my measurement device (VP7723D).

NOTE: SA2021-NCH - a team design by Dave Zan and me with many know how from the diyaudio community.

Have fun, Toni
 
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Hi Toni,

I seem to recall that you once said your NCH design is a self oscillating amplifier, acting similar to a class H one, but without requiring multiple supply rails. So, does it resemble a class D one? Would you like to share some details? Thank you!

Best regards!