and now for something completely different part 3

[Pars]

It looks like the NC pins of the relay on the board are floating. I wonder if tying these to ground would take care of it?

[Satyrnine]

53 minutes ago, Pars said:

It looks like the NC pins of the relay on the board are floating. I wonder if tying these to ground would take care of it?

If that were the case though, I'd get thump on headphones too, no? No thump with headphones or speakers, just the sub. Common denominator is the sub out is only thing that has a reference to PS Gnd.

Voltage divider for the sub out is: +out > 10k > 1k to PS Gnd. Sub out taken from junction of 10k and 1k. 

[xTr3me]

Can anyone help me? Some resistors in the schematic are 600R and 680R, while the 1.22 Gerber file is 300R and 600R. Some resistors are 4.2K and 50K, while the schematic is 1.9K and 25K. Which is the correct resistor value, and where can I find the latest CFA3 schematics? If I only keep SS, do I not need to populate the 4.2K and 600PF CAPs? Thanks

[justin]

600 or 680 can be used. 680 will be slightly higher front end gain

300 is correct

4.2k is just higher gain than 1.9k

I don't remember what the 50k and 25k are -- SS feedback resistors? if so also just higher vs lower gain

If only using SS, it's possible you can eliminate the 4.2k, as long as there is still another resistor in parallel with it. what you would do is measure the gain with and without the SS feedback resistors, and choose values so you have ~6dB less gain with the SS feedback resistors installed

[wudilmy]

Hello everyone, a question to Uberamp. Can i use Uberamp as a headphone amplifier for planar headphone such as susvara or DCA expanse if i add a pot before Uber3? Should i reduce the gain resistor? Thank you for your help😊

[audiostar]

And why not take the CFA3 for the Susvara or other planars?

[wudilmy]

I will also make a CFA3. Just want to try Uberamp on headphones, maybe it will be more impressive 😊 . Just want to know if it is possible use Uberamp as headphone amp with a pot

[wudilmy]

Btw How much is the gain of Uberamp?

[Satyrnine]

Been running my CFA3T at 150ma bias current per CFA2 board for quite some time. Just cranked it up to 200ma. I'm mounting the transistors direct to heatsink without an intermediary L bracket or such. After a few hours of on-time, I'm seeing about 55C on the cases of the hottest output transistors, so well within safe range once the junction>case temp math is done. Heatsink around 40-45C. Some of the bc555/6 are getting a bit warmer than I'd like though, so going to throw heatsinks on the hot ones as well. 

Sound wise, I think I hear more "speediness", highs/mids that are a bit more pleasing/engaging, and some increased weight and definition in the low end. Could just be my brain though.

I've had been driving my Ascend Sierra Luna V2 monitors directly from the CFA3T to great effect. I added a sub line out via voltage dividers from each + terminal, and ground taken from PS ground to feed a small sub for this desk setup. And it's been bliss.

[Shawn]

Working on a shrunk CFA3 layout this week, here is what it looks like. Haven`t tested it yet.

The dim is about 8.6 inches *  3 inches per channel.  Not small enough, but I bet someone can make it better by SMDing.

[RudeWolf]

On 5/14/2025 at 3:09 PM, Shawn said:

Working on a shrunk CFA3 layout this week, here is what it looks like. Haven`t tested it yet.

The dim is about 8.6 inches *  3 inches per channel.  Not small enough, but I bet someone can make it better by SMDing.

Good job! Almost mountable to one of these heatsinks! https://modushop.biz/site/index.php?route=product/product&path=284&product_id=733

[migo]

Hello, testing CFA3P here, seems to work fine, but it is running really hot at 150mA bias, wanted 250mA bias, but this impossible with used sinks. Powered with 30V PS. Do I need to change some values to run it with lower bias than designed 500mA? 

Thank you!

[tuodongyong]

On 4/22/2015 at 6:09 AM, kevin gilmore said:

the new verskon uses the bc parts

 

[bdinnev]

HI All,

After a long hiatus, I finally got back around to trying to spin up my CFA3 (rev 1.2) boards. After letting the magic smoke out of the output resistors a couple of times, replacing them, backtracking a few things / posts etc I finally got 1 side of one board to the reasonable point from both a dc offset and bias perspective without letting the magic smoke out. The other side of the board is still way off on DC offset (.4v) but nothing is smoking, so before I started probing that side of the board, I decided to plug my other one in to see where it was at.

After backing off all the pots and then plugging it in, the output resistors immediately went nuclear on one side. I de-soldered them and I think the heat from the meltdown coupled with me de-soldering those resistors a few times now weakened the copper traces on the board and I have now lost a couple of pads on the output resistors. I know I could make a fairly simple repair to try and get it working at least for proof of concept but coupled with the other issues I am having with the board I think it may be time to start from scratch rather that de-soldering all the transistors etc on the board and swapping them out trying to find the core issue. 

Does anyone have any headphone boards they can sell? I would either look for a single replacement 1.2 board or look for a pair / quad (?) of later boards and make a new complete pair. If anyone can assist, please dm me. I am based in the US but happy to pay freight from OS if needs be. 

Cheers,

Ben 

Edited 20 hours ago by bdinnev

[Pars]

The gerbers are available. Why not just get your own run?

[bdinnev]

47 minutes ago, Pars said:

The gerbers are available. Why not just get your own run?

Last time I checked it was during COVID and the figures just didnt stack for small runs up so had not thought about it this time round - but have just placed an order to get a batch made so will have a few spares - have gone with the CFA3 split boards and a whole new set of components so fingers crossed in the next week or so I have 2 boards working successfully. 

Edited 2 hours ago by bdinnev

[Pars]

Ordering from places like JLCPCB is pretty economical. I hope you did 2oz copper and at least 1.6mm PCB thickness? 10 boards for ~$90 shipped (this for the v1.2 full board).

 

Edited 2 hours ago by Pars

[bdinnev]

15 minutes ago, Pars said:

Ordering from places like JLCPCB is pretty economical. I hope you did 2oz copper and at least 1.6mm PCB thickness? 10 boards for ~$90 shipped (this for the v1.2 full board).

 

Yeah I did 2oz copper. Shipped for 5 pairs (split) boards (I know, 1 left over . . . . .) it came in at $135 - duties, sales tax etc . . . 

Edited 2 hours ago by bdinnev