KG CFA3 headphone amp

[paradoxper]

In the interest of keeping this active, did some minor work on the amp today. Better rated umbilical connectors (higher amp rating and just better precision), and now have a separate power supply for the headphone protector and volume circuit. At this point i'm fully separate dual monofor each cfa3 board from power supply transformer, to board and have yet another power supply for the protector. Moving the headphone protector to its own supply did improve things quite a bit. There were a few threads about feeding the protector regulators higher voltage and asking them to drop the voltage down 10+ volts causing issues. At least the regulators certainly run cooler.

I still have yet to find a laser cutting shop that can for a reasonable price execute my vision. Anyone have any suggestions for such a place? I want to cut some lettering in the top as vents.

When Kerry and I did the first Nascent DIY T2, we used Anodize Inc. They offer various services. If not cheap, the quality is amongst the best.

 

[audioguru1]

When Kerry and I did the first Nascent DIY T2, we used Anodize Inc. They offer various services. If not cheap, the quality is amongst the best.

I will give them a try! The website doesn't list cutting, did they do cutting for you?

Maybe I just need to buckle down and learn fusion360 (or pay someone to coach me) and have send cut send do it... hm. I legit watched videos and tried for a little, but found it confusing.

 

[Satyrnine]

In the interest of keeping this active, did some minor work on the amp today. Better rated umbilical connectors (higher amp rating and just better precision), and now have a separate power supply for the headphone protector and volume circuit. At this point i'm fully separate dual monofor each cfa3 board from power supply transformer, to board and have yet another power supply for the protector. Moving the headphone protector to its own supply did improve things quite a bit. There were a few threads about feeding the protector regulators higher voltage and asking them to drop the voltage down 10+ volts causing issues. At least the regulators certainly run cooler.

I still have yet to find a laser cutting shop that can for a reasonable price execute my vision. Anyone have any suggestions for such a place? I want to cut some lettering in the top as vents.

I’m not sure what you have in mind, but I had my chassis done at modushop in Italy and was super impressed with the wntire process and end result. They can do quite a bit of customization that might not be obvious from their storefront. I’d email Gianluca there and see if he can help.

 

[paradoxper]

I will give them a try! The website doesn't list cutting, did they do cutting for you?

Maybe I just need to buckle down and learn fusion360 (or pay someone to coach me) and have send cut send do it... hm. I legit watched videos and tried for a little, but found it confusing.

We did anodizing, polishing and laser etching with the T2. If you look at my CFA3, the top panel was drilled by Modushop. I am uncertain if they still offer that depth of service as we were sure they undervalued the time declared.

 

[audioguru1]

We did anodizing, polishing and laser etching with the T2. If you look at my CFA3, the top panel was drilled by Modushop. I am uncertain if they still offer that depth of service as we were sure they undervalued the time declared.

I will check with them, thanks for this great tip.

I’ve got lots of things in my head I want to do but can’t execute. I also would love to do some Damascus steel. In my pen hobby some makers are doing that on nice pens. It looks amazing.

 

[paradoxper]

I will check with them, thanks for this great tip.

I’ve got lots of things in my head I want to do but can’t execute. I also would love to do some Damascus steel. In my pen hobby some makers are doing that on nice pens. It looks amazing.

Maybe a dama volume knob or some inlay work.

 

[Satyrnine]

Maybe a dama volume knob or some inlay work.

Ooh! I’d looove a dama vol knob as well.

 

[audioguru1]

I did some research and I can get 1" round stock pretty "reasonable". I need to find someone willing to mill it though. If I can get it going i'll be happy to make a few.

 

[kevin gilmore]

https://www.amazon.com/Diameter1-St...07f1c0d2d1f092c9774c01e&qid=1718925085&sr=8-3

all you need to do is drill 2 holes. the .25 inch one is very hard. the .025 inch side hole for the set screw is MUCH harder!
i know this from personal experience.

 

[audioguru1]

Did a thing last night - implemented a voltage switch to adjust the rails. What I did was stick a 3k resistor in the GRLV to set it at 30v, then put parallel resistors and a DPDT on / off / on to parallel resistors in and out. I ended up deciding on 30v (off setting) / 28 / 24.5. The bias points work out nicely, at 30v 195, at 28 185 and 24.5 155.

I've found I prefer the Caldera at 24.5, and the Susvara at 30 (but I need a new case to handle the heat at 30).

Going to bite the bullet and get a modushop custom milled case.

 

[rthomas]

Hello all,

Can somebody with electronics/electrical knowledge enlighten me as to which is the superior circuit? The Dynalo as used in the GSX Mk2 or the CFA3 circuit?

Has KG himself commented on this somewhere? I want to know any technical reason why one design may be superior to another.

 

[kevin gilmore]

Did a thing last night - implemented a voltage switch to adjust the rails. What I did was stick a 3k resistor in the GRLV to set it at 30v, then put parallel resistors and a DPDT on / off / on to parallel resistors in and out. I ended up deciding on 30v (off setting) / 28 / 24.5. The bias points work out nicely, at 30v 195, at 28 185 and 24.5 155.

yamaha did this very thing about 40 years ago. this is a great idea. i should have thought of it. makes stuff more complicated though.

dynalo vs cfa3. very different amplifiers. cfa3 is way more complicated with lots more parts. cfa3 can be zero feedback. both amplifiers sound quite different with different headphones.

 

[RudeWolf]

Can somebody with electronics/electrical knowledge enlighten me as to which is the superior circuit?

In my experience, a SuSy Dynalo vs CFA3 (NOS Toshiba JFETs+GRLV both) the CFA3 comes out on top. With that said, the difference can be surprisingly small. And I'd rather pit the Dynalo against the CFA2. In which case I've heard the latter also come out on top. Neither are less than excellent amplifiers and I like that I can build the Dynalo without having to dick around with tapping heatsinks.

I will add that the CFA circuit is more oscillation-happy, so care must be taken to keep it nice and stable.

 

[RudeWolf]

yamaha did this very thing about 40 years ago. this is a great idea. i should have thought of it. makes stuff more complicated though.

Class-G CFA3 coming?

 

[kevin gilmore]

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.