A Directory of Apex Audio Amplifiers

This thread is a consolidation of the numerous amplifier designs that member Apex Audio has generously provided the DIYA community over the past several years. The designs mostly come from the enormously popular (and large) thread 100W Ultimate Fidelity Amplifier - diyAudio which has become a bit unwieldy to use as a reference for designs. It is my hope that this thread will become a repository for Apex Audio's amplifier designs that is in an easily usable and searchable format. There are also several threads by Apex that have PA amps, etc - please consider providing links to those amps as well.

Note: click "Reload" page on your browser to auto scale the rather large image schematics. These are the original images as posted by Apex Audio. I only point to them.


To start things off, I have included below an initial list of amp designs that I could find using the search feature (I simply did a search for "AXn" where n is an integer representing the number of active devices). The problem is, there are amps named FXn, Bxn, An, Bn, ANn, etc. So it would be helpful if other members can point out designs that need to be added by posting here. From time to time, I will go in and update Post #1 to be an index pointing to the locations where the PCB layouts are located, the BOM, photos of working examples, etc.

When posting a suggestion for me to add to the index, please include the following in this order of importance:

1. Name of the amp, ie,, "AX11TEF" and rated watts and a note if special application like (uses lateral FETs or is fully-symmetric, etc)

2. An image of the schematic as drawn by Apex Audio (link to the image is fine), or if the amp is a mod by another member, a link to the member's schematic. Such as the FX8 Bimo Mod...

3. A link to the post or location where the amp design is discussed (either first mentioned or a key development where a working design is produced).

4. A link to the PCB layout sprint file or Gerber files if available

5. A link to the LTSpice/Multisim/TINA simulation file if available

6. A link to a photo of an actual amp that has been reduced to practice

7. A link to measured performance (FFT distortion plots, O-scope traces, etc.)

Thanks in advance for contributing to this index, and I hope you all find it helpful.

Finally, a huge thanks to Apex Audio for his tireless creativity and help in giving us so many great sounding designs to play with. :cheers:

Regards,
xrk971

Update June 20,2016: Miro provided a nice table of 68 schematics here A Directory of Apex Audio Amplifiers - Page 5 - diyAudio




Here is what I have so far for the Index. I will add links to the above items as time permits and as people provide feedback.

#### AN INDEX OF APEX AUDIO AMPLIFIERS ####

Quasi for Beginners - added Aug 6, 2016:
172638d1274698453-quasi-amplifier-beginners-apex-550w-classb.jpg


QUASI Amplifier for Beginners - diyAudio

SF3.1 AllFET preamp 470k input impedance - added 7/14/2016:

100W Ultimate Fidelity Amplifier

165430d1270331111-100w-ultimate-fidelity-amplifier-apex-fet-preamp.jpg


SB3.1 BJT preamp 47k input impedance - added 7/14/2016:

100W Ultimate Fidelity Amplifier

165433d1270333407-100w-ultimate-fidelity-amplifier-apex-bjt-preamp.jpg


PSU + Protect - added 7/14/2016:
166975d1271268112-100w-ultimate-fidelity-amplifier-apex-psu-dc-protect.jpg



Headphone Amp - added 7/10/2016:
542316d1460041518-100w-ultimate-fidelity-amplifier-apex-headphone-amplifier.jpg


Class A preamp power supply 24v - added 7/8/2016:
http://www.diyaudio.com/forums/power-supplies/164365-class-preamp-psu.html#post2140391

165267d1270226399-class-preamp-psu-apex-2x24v-aclass-psu.jpg


PDF transfers:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-791.html#post4768785

SF1 all FET buffer - added 7/7/2016:
http://www.diyaudio.com/forums/solid-state/173462-studio-reference-amplifier-33.html#post2596440

226001d1307363032-studio-reference-amplifier-apex-fet-preamp-buffer.jpg


PP8 SR Preamp - added 7/7/2016:
http://www.diyaudio.com/forums/solid-state/173462-studio-reference-amplifier-178.html#post4180772

458406d1420900146-studio-reference-amplifier-apex-sr-preamp.jpg


Regulated PSU, output voltage with this PSU can be set from 35V to 65V 5A with single pair 2SA1943/2SC5200 - added 6/29/2016:
188157d1284671254-studio-reference-amplifier-apex-regulated-psu.jpg


PCB: http://www.diyaudio.com/forums/solid-state/173462-studio-reference-amplifier-2.html#post2305489

4 Output version for 55v to 90v rails:
188172d1284677123-studio-reference-amplifier-apex-regulated-psu-10.jpg


More info (post #6):
http://www.diyaudio.com/forums/solid-state/173462-studio-reference-amplifier.html

Simple Stereo Protect - added 6/22/2016:
457759d1420567023-100w-ultimate-fidelity-amplifier-apex-simple-protect.jpg


PCB:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-406.html#post4176074

A3 - added 7/12/2016:
An externally hosted image should be here but it was not working when we last tested it.


FX7 - added 8/11/2016:
545562d1461618484-100w-ultimate-fidelity-amplifier-apex-fx7-sch.jpg


100W Ultimate Fidelity Amplifier

FX8 (50w) - uses lateral FETs:
347359d1367965695-100w-ultimate-fidelity-amplifier-apex-fx8sch.jpg


(FX8 links provided by Jeshi on 6/2/2016)
50watt, NPN differential input, complementary NPN/PNP VAS, lateral MOSFET output.
APEX FX8 post 2125, APEX layout post 6174
Prasi initial PCB layout post 6160, Prasi/Sonal edited layout post 6184
Bimo-mod version with simulation post 6483 using 2SC1845 input, 2SA1381/2SC3503 VAS, 2SK1058/2SJ162 output.
Prasi layout of bimo-mod post 7146
FX8 Bimo mod build with speaker test results:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-775.html#post4755887

FH9 (50w) - xrk971 mod for vertical FETs:

http://www.diyaudio.com/forums/solid-state/292226-directory-apex-audio-amplifiers.html#post4733400

Edit March 31, 2020: Updated Gerbers with solder pads on both sides here:
100W Ultimate Fidelity Amplifier

550019d1463581537-100w-ultimate-fidelity-amplifier-fx8-xrk971-hexfet-vbe-schematic-v2.png


Tina Sim, Sprint and Gerbers:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-746.html#post4718255

PDF's:
http://www.diyaudio.com/forums/atta...e-fidelity-amplifier-fh9-ver1.04-top-view.pdf

http://www.diyaudio.com/forums/atta...ier-fh9-ver1.04-toner-transfer-silkscreen.pdf

http://www.diyaudio.com/forums/atta...er-fh9-ver1.04-toner-transfer-copper-side.pdf

BOM:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-799.html#post4774271


FH9 fully built and tested by xrk971 using Sonal Kunal's Gerber files:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-784.html#post4764003

Note that I substituted 20k for 22k and 550R for 680R for resistors as shown in silkscreen. Also, final version uses BD139 as Vbe multiplier rather than MPSA42 as shown in Tina diagram.

FH9 HV - 120w (8R) output single pair vertical hexFET amp (requires swapping BD139/140's for KSC3503/KSA1381's):
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-790.html#post4768191

A9 CFA:
449041d1416219044-100w-ultimate-fidelity-amplifier-apex-a9sch.jpg


PCB pdf:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-357.html#post4133456

A10:
487833d1434017237-100w-ultimate-fidelity-amplifier-apex-a10.jpg


CA10 - added 8/11/2016 (untested as of this date):
564361d1470875954-100w-ultimate-fidelity-amplifier-apex-ca10.jpg


http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-834.html#post4799153

N10 - 150w MOSFET amplifier with IRFP250 x2 - added 7/8/2016:
http://www.diyaudio.com/forums/solid-state/163159-150w-mosfet-amplifier-irfp250x2.html

162499d1268565289-150w-mosfet-amplifier-irfp250x2-apex-nmos-amp.jpg


AX11 (50w):
342757d1366040499-100w-ultimate-fidelity-amplifier-apex-ax11sch.jpg


AX11TEF (50w):
536257d1457475704-100w-ultimate-fidelity-amplifier-apex-ax11tef.jpg


AA11 (class A):
537337d1457974999-100w-ultimate-fidelity-amplifier-apex-aa11sch.jpg


FH11 (250w 8R with 60v rails hexFET amp) Mod by xrk971 based on FH9HV design - added July 19, 2016:
560704d1468819884-100w-ultimate-fidelity-amplifier-fh11-schematic-v1.0.png


http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-805.html#post4777079

Simulation:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-801.html#post4775467

Verified build tested by Andrewlebon (note typo on MJE350 layout in middle of board - legs are ECB not EBC):
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-809.html#post4778364

Built and tested by Still4given:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-810.html#post4778451


FH12 (mod to reduce dissipation on current mirror) - 0.039% THD at 1kHz 60v p-p output in simulation, not yet tested - added July 22, 2016:

http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-816.html#post4780667

561303d1469190988-100w-ultimate-fidelity-amplifier-fh12-schematic-tina-v1.0.png



AX13 (50w?):
347374d1367973319-100w-ultimate-fidelity-amplifier-apex-ax13sch.jpg


A14 (CFA 35v rails) - added 6/22/2016
456005d1419793552-100w-ultimate-fidelity-amplifier-apex-a14.jpg


Successful build and tested by Olafk:
100W Ultimate Fidelity Amplifier

PCB Files:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-400.html#post4168322

Sprint Files:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-400.html#post4168814

AX14 (80w):
167581d1271628000-100w-ultimate-fidelity-amplifier-apex-kelvin-v2.jpg


AX14 with dual outputs - mod by Vargas Mongo:

http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-772.html#post4753185


FX14 vertical MOSFET (80w):
178830d1278159595-100w-ultimate-fidelity-amplifier-apex-fx14.jpg


NX14 NMOS amp (80w):
179301d1278422412-100w-ultimate-fidelity-amplifier-apex-nx14.2.jpg


A15:
552740d1464834882-directory-apex-audio-amplifiers-apex-a15.jpg


AX15 (80w full symmetric amp):
246036d1319407815-100w-ultimate-fidelity-amplifier-apex-ax15.jpg


AX16 (80w):
179202d1278348376-100w-ultimate-fidelity-amplifier-apex-ax16.jpg


AX17 (80w):
246444d1319579956-100w-ultimate-fidelity-amplifier-apex-ax17.jpg


AX18 (80w):
246153d1319466566-100w-ultimate-fidelity-amplifier-apex-ax18.jpg


AX20 (120w):
246443d1319578391-100w-ultimate-fidelity-amplifier-apex-ax20.jpg


BX20 (w?):
536674d1457638070-100w-ultimate-fidelity-amplifier-apex-bx20.jpg


BX22 - added 6/24/2016:
561589d1469373906-100w-ultimate-fidelity-amplifier-apex-bx22.jpg


100W Ultimate Fidelity Amplifier
MM22 (phono preamp) - added 6/22/2016:
457735d1420560709-100w-ultimate-fidelity-amplifier-apex-mm22.jpg


HV23 (750w into 8R) quadruple vertical MOSFET amp - added 6/2/2016:

http://www.diyaudio.com/forums/soli...mplifier-irfp240-irfp9240-47.html#post2802550

252508d1322772159-mosfet-amplifier-irfp240-irfp9240-apex-mosfet-hv23-sch.jpg


AX30 (w?):
519308d1450126875-100w-ultimate-fidelity-amplifier-apex-ax30.jpg


P30 preamp (24v rails, 300mV in 2V out) - added 6/22/2016:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-405.html#post4175807

457723d1420554364-100w-ultimate-fidelity-amplifier-apex-p30.jpg


A33 - edit July 26, 2016 - note that resistor at offset trimpot is 470k not 470R per Apex.
451846d1417544972-100w-ultimate-fidelity-amplifier-apex-a33.jpg


A40 (?w):
461233d1422093709-100w-ultimate-fidelity-amplifier-apex-a40.jpg


F100 (80w into 8R) dual vertical MOSFET amp with DC servo - Apex says over 400 units installed and working reliably in bars/nightclubs etc, added 6/2/2016:

DC Servo MOSFET Amplifier

163352d1269048660-dc-servo-mosfet-amplifier-harissonsch.jpg


H100 (80w into 8R) high efficiency class H amp - added 6/2/2016:

DC Servo MOSFET Amplifier

178981d1278236637-dc-servo-mosfet-amplifier-apex-h210-sch.jpg


HV250 - added 6/7/2016:
553583d1465301961-directory-apex-audio-amplifiers-apex-hv250-sch.jpg


H900 (900w into 8R) Class H high power PA amp output stage for use with separate VAS stage - added 6/3/2016:
900W H-class PA Amp with Limiter

161327d1267886205-900w-h-class-pa-amp-limiter-apex-h900-output.jpg


More info on VAS stage and PCB here:
http://www.diyaudio.com/forums/solid-state/292226-directory-apex-audio-amplifiers-2.html#post4735042

BA1000 (1000w into 8R pro sound amp) - added 6/7/2016:

http://www.diyaudio.com/forums/solid-state/292226-directory-apex-audio-amplifiers-2.html#post4738805

348292d1368399671-1000w-simple-pa-amplifier-apex-ba1000-sch.jpg


B2000 - added 6/15/2016:
554795d1465895287-directory-apex-audio-amplifiers-b2000-2.jpg
 
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I will start things off with the FH9 - Xrk Mod, a 50w vertical MOSFET variant of the FX8 with a Vbe multiplier for thermal control. The circuit was something I modified in an effort to get away from the more expensive and harder to find Renesas lateral MOSFET used by the FX8. I simulated it on Tina and all looked good so I modified my existing FX8 and it worked well. It has since been built by another member.

Apex Audio named it FH9:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-733.html#post4702198

Schematic (note that Vbe multiplier was originally MPSA42 but that was changed to BD139 for convenient mounting hole):
550019d1463581537-100w-ultimate-fidelity-amplifier-fx8-xrk971-hexfet-vbe-schematic-v2.png


PCB layout:
550058d1463590661-100w-ultimate-fidelity-amplifier-apex-fh9.png


PCB pdf's:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-746.html#post4718306

PCB Gerbers:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-746.html#post4718422

Build photos:

Prototype mod from FX8 with Vbe multiplier on daughter board:
546819d1462252838-100w-ultimate-fidelity-amplifier-fx8-xrk971-hexfet-vbe-build-4-no-flying-leads.png


Real PCB build by Zoky2:
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-744.html#post4717829

549917d1463552447-100w-ultimate-fidelity-amplifier-fh-9.jpg


This amp PCB has been confirmed to work as shown by Zoky2.
 
Last edited:
Just a quick comment:

Embedding the images as you have done makes the thread slow loading and impossible to view on some devices. Perhaps just a name, description and the relate to links to the main thread would have been better.

I am simply linking the images as they exist in the main thread - not embedded really. You would have the same problems just browsing the main Apex Audio threads because they are full of images. Images are what make it easy to find and use - and visually interesting. I don't have any issues with the images causing slowdown or bogging down my browser. I think the problem may be that some images are wider than the recommended maximum 1024 pixel wide limit as posted previously. If other members have the same problem with images being linked to display I will reduce to just url's. But this is the first I have heard of accessibility issues. Maybe I have really high speed reliable internet ? This was all done on my iPhone.
 
no accessibility issues. only some schematics are too big a size.

I might have to take Apex drawings and rescale the bit maps to 1024 wide. Then upload as an attachment and then link it. Thanks fine pointing it out. It is big for me too but my browser automatically rescales to for if I click reload.

However, I am having trouble knowing where intersects occur.
Some of the intersect dots are too small.
This makes reading the schematic very difficult

I have seen much worse and I think Apex's drawings are perhaps the best in this forum as far as readability goes.
 
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this theme should be sticked up. if anybody contributed with a large scale of amplifiers, preamplifiers,power supplies, helped and explained all that he could than Mile Slavković APEX is the one. his three themes have over 5 million views and several thousands of posts,so,I believe that he deserves this theme to get it's topic sticker.
 
this theme should be sticked up. if anybody contributed with a large scale of amplifiers, preamplifiers,power supplies, helped and explained all that he could than Mile Slavković APEX is the one. his three themes have over 5 million views and several thousands of posts,so,I believe that he deserves this theme to get it's topic sticker.

You mean make it a "Sticky"? It's up the mods.