If VAS transistor not match on hFE in this design, H2 will be increase, may be DC Offset, too. But I think it is OK.
A1381 and C3503 can substitute with another low Cob transistor like A1360 and C3423. If it substitute with higher Cob, phase margin and gain margin will be reduce and it may need change the value of compensation's capacitors. Slew rate will be decrease and THD at high frequency will be increase.
The KSC3503D has Hfe range of 60-120 and the KSA1381E has Hfe range of 100-200, so there is a chance of finding reasonably matching devices in the overlap around 100-120 Hfe.
I guess if I am feeling lucky I could order some 2sc3503 /KSC3503 off aliexpress and see if I can get some in the 100-200 range and then order the KSA1381E from digikey to try to match that way.
From what Bimo says, we just need to get reasonable matching in the VAS and we are ok.
Last edited:
http://www.diyaudio.com/forums/swap...ors-sale-2sa1360y-2sc3423y-2sa1209s-2sc2911s-ksa1381e-ksc3503e.html
The input LTPs are massively unbalanced.
1.60mA/133mA = 120%
1.80mA/123mA = 146%.
You have to get these much closer to 100%
D.Self says better than 102%
But that is almost certainly not why you have the oscillation.
Try to find what is causing the overshoot after you fitted that 470pF slowing down capacitor.
Last edited:
Even if the Hfe is the same, two transistors with different Vaf will not behave as if "matched".
The KSA1381E has lower Vaf, but it also has higher Hfe. So it is actually better matched to the KSC3503D than if they had the same Hfe, if used in a symmetrical VAS.
The KSA1381E has lower Vaf, but it also has higher Hfe. So it is actually better matched to the KSC3503D than if they had the same Hfe, if used in a symmetrical VAS.
Dear ammel68,
Rochester Electronics has 1381E/3503E. You can order a mix of many difficult to source semis from them, but min total order is $100/
--gannaji
Rochester Electronics has 1381E/3503E. You can order a mix of many difficult to source semis from them, but min total order is $100/
--gannaji
Thanks for the suggestion, gannaji.
That $100 minimum order hurts.
Looks like ordering some from joshvi at $.45 ea. is a more viable option. I'll have to see what shipping to the U.S. is.
That $100 minimum order hurts.
Looks like ordering some from joshvi at $.45 ea. is a more viable option. I'll have to see what shipping to the U.S. is.
Thank you keantoken!
I was also guessing that fairchild/digikey must know something if they only sell the KSA1381E & KSC3503D and expect them to work in symmetrical pairs. I will just start with this and not worry about extra matching.
Last edited:
http://www.diyaudio.com/forums/atta...w-ultimate-fidelity-amplifier-apex-fx12dc.jpg
Here incorrectly includes capacitors 33 pF - to the emitters, at a low impedance point, and need - to bases. 470 pF must be connected in parallel with the 22 kilo Ohm, and its capacity reduced to units or tens of pF.
Check this circuitry and compensation in SIM, otherwise you can burn the transistors.
Hi!
You're absolutely right. But there is still a lot of similar transistors.
2SA1156 / 2SC2752
2SA1478 / 2SC3788
2SA1480 / 2SC3790
2SA 1353 / 2SC3417
2SA1540 / 2SC3955
KSC2682 / KSA1142
2SC2682 / 2SA1142
BF469 - 471 / BF470 - 472
2SA1381E / 2SC3503E
2SA1380 \ 2SC3502
2SB1110 \ 2SD1610
2SA1353 / 2SC3417
2SA1352 / 2SC3416
2SA1852 / 2SC4826
2SA1853 / 2SC4827
2SC2705 / 2SA1145
2SA1360\2SC3423
A little worse:
2SB1109 / 2SD1609
2SD1610 / 2SB1110
2SA1370 / 2SC3467
2SA1371 / 2SC3468
2SA1370\2SC3467
2SA1371\2SC3468
2SA1124\2SC2632
2SA1208\2SC2910
2SA1321\2SC3334
2SA1123\2SC2631
Living Index of Apex Audio Amps
Here is a collection of just some of the schematics from Apex Audio over the course of time in this thread. These were obtained from using the search feature and I am missing many but think it's a good start if others can add to this, and also add PCB layouts - use the quote feature so it is all intact. We can perhaps begin to use this as a "Living Index" to the profound productivity and good will that Apex has given us.
FX8 (50w) - uses lateral FETs:
AX11 (50w):
AX11TEF (50w):
AA11 (class A):
AX13 (50w?):
AX14 (80w):
FX14 vertical MOSFET (80w):
NX14 NMOS amp (80w):
AX15 (80w full symmetric amp):
AX16 (80w):
AX17 (80w):
AX18 (80w):
AX20 (120w):
BX20 (w?):
AX30 (w?):
AX40 (?w):
Here is a collection of just some of the schematics from Apex Audio over the course of time in this thread. These were obtained from using the search feature and I am missing many but think it's a good start if others can add to this, and also add PCB layouts - use the quote feature so it is all intact. We can perhaps begin to use this as a "Living Index" to the profound productivity and good will that Apex has given us.
FX8 (50w) - uses lateral FETs:
AX11 (50w):
AX11TEF (50w):
AA11 (class A):
AX13 (50w?):
AX14 (80w):
FX14 vertical MOSFET (80w):
NX14 NMOS amp (80w):
AX15 (80w full symmetric amp):
AX16 (80w):
AX17 (80w):
AX18 (80w):
AX20 (120w):
BX20 (w?):
AX30 (w?):
AX40 (?w):
Last edited:
incredible, the BX20 looks easy to build and to customize! I really like the simetrical output design!
How is the sound of this amp?
And can someone point me to the right post/doc about how calculate the amount of 2sc5200 / 2sa1943 i need for diferents outputs?
xrk971 point me to this thread and are really amazing!
How is the sound of this amp?
And can someone point me to the right post/doc about how calculate the amount of 2sc5200 / 2sa1943 i need for diferents outputs?
xrk971 point me to this thread and are really amazing!
well done,xrk971, I have a directory devoted to the Apex designs, incomplete I may add.
wish that this site/forum could have a means to create individual projects for proper sorting of documentation and related threads, I asked they did not consider my suggestions
wish that this site/forum could have a means to create individual projects for proper sorting of documentation and related threads, I asked they did not consider my suggestions