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Premium ACA with CapMX PSU


I have been asked to offer another round of groupbuy for my layout of Nelson Pass ACA amplifier - modified by TungstenAudio.
I will do - but: be sure - this will be my last contribution to the ACA.

Find attached an image of my PCB offer.
It contains of:

- a LT4320 based rectifier on the left side of the image
- Nelson Pass' ACA (with slight modifications done by TungstenAudio), on the image right side
- being driven by JasonKuetemanns CapMultiplier
- if you will ever read Rod Elliotts recommendations for a (small) ClassA PSU: here we are!

I will offer you 2 pairs of my PCBs (2xLT4320, 2xACA) as unregistered mail for 20€.

Tell me if you like to have.
Best regards - Rudi

P.S.: I am currently busy building a new desktop-PC for my own needs. It will consist of:

- BeQuietPure 500 Case, MSI X470 Gaming PLUS Mainboard (from time to time I like (?!) to play "Age of Empire" or "Stronghold", or even GTA)
- 16GB PC3200 DDR4 RAM, Radeon RX580 8GB graphic card, ..

Please have a look at my setup on image2.

An USB attached ASUS "soundcard" misses any heights!
The onBoard RTC892 does not " sound any better".

How shall I go on? Do you have any recommendations?


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It is still fun to see a new ACA board variation. I like the idea of a capacitance multiplier and the CRC section before the CapMX is good in order to reduce the dropout voltage.

As I have been working with other LT4320 and CapMx designs recently, I have some experience that I would like to share: F6 Amplifier. The PCB layout could be modified to add some simple connectors to allow a large screw terminal cap to be added in parallel with the 1000 uF cap on the output of the CapMx section.

Even though the amp I refer to is an F6, the bias current is similar, so some of the other measured parameters should be close to an ACA built with these new boards. I would suggest a 300VA power transformer with either 22V or 24V secondaries. In this case the 200 Ohm resistor to the left of the LSK170 could be increased to 499 or 1k Ohms to reduce the power dissipation in that expensive little JFet. A pair of IRFP140 Mosfets also will do a fine job with higher power supply voltage.
Gentlemen, the build of the LT4320-based rectifier PCB is not necessarily needed to power the ACA.

I suppose that you have already noticed the KBU8B - bridge rectifier, which is located on top of the speakers output connector.
The rectifier itself must be mounted beneath the PCB, on the heatsink to keep it cool. I myself am using a Vishay KBU8B.

The LT4320-based rectifier is "technical overkill" in my eyes (the ACA is "only" consuming 2A of current at its maximum),
but since I know that some of you are curious and only want the very best (?), …
In case you intend to use the LT4320 - based rectifier instead of the onboard bridge-rectifier:
Run a pair of wires from the OUTN / OUTP poles of the 4-pole LT4320-connector to the 2-pole "AC" - labelled connector on board
of the ACA PCB and solder 2 wires from "~" to the adjacent "+" resp. "-" PCB - holes.

The following members are currently interested in my offer:

Vasilis, cl00sed (?), shattered_dream, lordoff (2x), manniraj (?), gary_s, gwrskien, yoaudio, Dennis Hui

I will order on Sunday evening. It will then take about 3 weeks, until I have the PCB in my hands.
The price of 20€ includes worldwide shipping (unregistered- so you will not have a tracking ID) of 2 ACA- and 2 LT4320 PCBs.

I will summarize the order on Sunday evening.

Regards - Rudi
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