KG CFA3 headphone amp

[audioguru1]

no definitely not.

but you could do output bias stage switching to go with the voltage switching. choice of lower voltage and higher bias current and higher voltage at lower bias current.

Thanks for this suggestion. Had not thought about that, I really like this idea. That's whats great about DIY, the exchange of ideas here. So cool.

Did a little testing and it seems that if I want to have low voltage and high bias (which I do), it sets up a scenario where when flipped to high voltage there is too much bias (was over 230mv). Easy enough to switch bias to low when setting voltage to high, but also easy enough to forget.

Maybe there is a way to do it with relays that trigger each other? Been a long day, need to think on this more with a fresh mind, but open to suggestions.


Thanks Kevin.

 

[kevin gilmore]

needs to be one switch that drives relays which do the voltage and the bias at the same time.
same as the ss/zf switch.

 

[audioguru1]

Still working slowly at improvements, been slow going with just life stuff. The time I have had to spare i've been listening at various voltages and gain settings. Two observations, at 30v power supply voltage the bc546/556 reach 70c (too hot IMO). I added heatsinks, and it helped some. Gain has a impact too, using the 4.2k gain resistors in the latest boards makes the 546/556 the hottest, 1.9k gain resistors isn't enough for my liking. I found 3.2k to be a good balance. So in case its helpful a) check temps on your 546/556 b) consider 3.2k gain resistors as one setting (if you have switching). I also found setting the power supply at 27.5 has helped a lot with heat with no downside in sound. Speaking of power supply, I have been using VS-VS-HFA08SD60S-M3 for the bridge (with heatsink) , with good effects. My overall goal has been 60c or less, which is hot but still less than 50% of the max 150c rating (should be safe?).

 

[johnwillmclean]

FYI
https://www.head-fi.org/classifieds/cf2a-dual-mono-fully-balanced-amp.76393/

 

[Rastloser]

I'm new to this thread and the CFA3 generally, but I like tinkering with DIY projects. My current DIY headphone amp is an AMB Beta 22 (4 board balanced), but since I keep reading great things about the CFA3, I'm thinking of making this my next DIY project.
I have found some files with partial schematics, with board designs, some BOMs and there are some boards listed on Ali, but most posts on other forums have been deleted or are unavailable, so I've come here to ask if someone has some compiled info or post numbers that detail important aspects.
I will probably work through the whole thread, but any hints are greatly appreciated since 122 pages are quite some effort...

Thorsten

 

[Pars]

I would look on head-case. Now for something completely different in the diy section. Tread lightly and you'll be just fine.

 

[pompon]

head-case ... it's a agressive forum ...very bad experience there.

 

[icnaiwhimor1975]

I would look on head-case. Now for something completely different in the diy section. Tread lightly and you'll be just fine.

They have closed registration there for several years now.

 

[kevin gilmore]

registration is definitely not closed. it was a bug. got fixed last month when someone said something.