Amplifier build

[KNielsen]

So... Finally took the opportunity to order a prototype PCB from JLCPCB. It's as cheap as it gets, but enough to start some testing of the layout without spending an enormous amount of money before the real build begins

Best regards

 

[Andersonix]

I see you kept on adding PS caps, now one set for each transistor! How are you deciding how much is enough?
A discussion at diyaudio.com made me conclude that those decoupling caps must be >at< the pins of the output transistor, which you seem to have accomplished pretty well.

 

[KNielsen]

I see you kept on adding PS caps, now one set for each transistor! How are you deciding how much is enough?
A discussion at diyaudio.com made me conclude that those decoupling caps must be >at< the pins of the output transistor, which you seem to have accomplished pretty well.

First design was 1x 220uf/2.7uf at each rail.
I looked it over and found that the space on the PCB allowed a much closer connection to the outputs (a good thing) if smaller value of caps were selected due to smaller diameter.
It's now 8x paralleled 47uf/0.47uf pr rail.
Soundwise or how much capactiance is needed??; to be honest I have no clue yet if this this is gonna sound "just right".. But generally I prefer some capacitance after the PSU, and found the new layout to fulfill this aspect

Edit: at one point I'm also afraid of adding to much uf after the fuse, making it useless

Regards

 

[KNielsen]

The proto PCB has arrived

 

[KNielsen]

Progress so far... Normally I'll start with the smallest parts and work my way up from there, finishing with the caps, but didn't have all parts right now and couldn't stop my soldering iron. The last parts will arrive Thursday

 

[KNielsen]

First "simpel test" after some swing in the megahertz region that needed attention!
I didn't manage to fix this with the DC-servo for now, so skipped it in favour of an RC-network so I could focus on the rest of the build.

R17 is pulled and replaced with a 2Kohm/470uF to ground to do the feedback. I actually wanted to use a 1Kohm/1000uF as RC, but didn't have the 1000uf in my office, so scrambled what I had to do this

All KSP42/92 has been replaced with KSA992/KSC1854 and the pre-drivers are now KSA1381/KSC3503.
R5 is 56K with the LED diodes currently installed.
R6/R7 is now 475ohm, but might try 511ohm to see if I overdoo the diff-current...
At the BIAS-circuit the PNP/R26/R27 hasn't been tried and still bypased.

I have no heatsink for the amp-module yet, so it's pretty low BIAS: 2mV at the emitters(!!), so I don't harm the output transistors due to heat...
All curves is 2mVpp from the signalgenerator, so also in the lower end of the scale:

1kHz Sine


50kHz sine


1kHz square




Original schematic


The rails are 64VDC for now, DC-offset is approx 8mV though the transistors hasn't been matched in this pre-build

Best regards

 

[KNielsen]

Waiting for 50ps of new output transistors then I'll continue testing, but the final layout pr proto pretest is on almost done if further adjustments isn't needed

 

[Hipocrates]

Very cool stuff!

 

[KNielsen]

Very cool stuff!

Some better pictures of the board

 

[Hipocrates]

Some better pictures of the board
View attachment 2794159 View attachment 2794160 View attachment 2794161

they look impressive, and open hardware too... do you have them on github as well, I could learn a thing or 2 studying the schematics.
What kind of PS are you going to use? If you don't mind the asking.
Thanks for posting them.

 

[KNielsen]

they look impressive, and open hardware too... do you have them on github as well, I could learn a thing or 2 studying the schematics.
What kind of PS are you going to use? If you don't mind the asking.
Thanks for posting them.

The open source logo is due to the fact that I'll share my final "fully working" project later. All schematics and layout (files pr Kicad) will be shared. You'll have to wait just a bit longer all Gerber's will be included for ordering at JLCPCB and other Gerber's for ordering at PCBWAY if one like this better.

Regards