JoaMat

Next build – remove R1 ( don’t understand why I put it there – maybe because I’m an amateur) and R2 value is far too low, unless you want 40 mA through LED, so I switched to 1K. Small board 19mm x 15mm with the 555, a small PNP , three resistors and of course the bi color LED. Works perfect.

Nightly build Red LED indicates disengaged headphone. The green LED indicates power is on. Here red is out and headphone is connected. Next build… …a bi-color LED to replace the two above LEDs.

Headphone protector installed and working. Delay time is 15 seconds, and it disconnects when offset is more than approximately +/-70 mV.

Yes, very much.

Thanks James, your schematics gives a clear picture how to switch to KSA1220 and KSC2690. Unfortunately, it seems that KSA1220 is out of business. Fortunately, TTA004 and TTC004 can replace KSA1220 respectively KSC2690.

Kind of, mains in at blue tblock and and +/-24V out at the other corner. Can’t be easier.

Just move the two right legs on step to the left and swing the left leg all the way to the right…

SMPS300R , bought from Audiophonics - nice company, next day delivery from France to Sweden.

My CFA3smd something, now powered from a switched mode power supply and equipped with a headphone protector. I’ll test this for a while and if I like it I might build a decent cage for it. Else I’ve a growing "good to have" closet.

It’s soldered by hand. I’ve tried hot air, but I prefer a solder pen and tweezer - gives me better control I think.

Seems to work. The red LED turns off and on correctly. Red light means everything is OK – off means something is bad. A green LED might be more appropriate. The short uninsulated wires, one each side, is not to correct a mistake. It was the only way I find to get it working. The board has 19 vias. I did one mistake though. I gave the mosfet driving the relay a wrong footprint, but fortunately it was possible improvise… now it works as it should. I’m waiting for the relay. Omron G6S-2G – surface mounted, good for 2 A.

Popped up at Qobuz grand selection. I enjoyed it.

Here is a rebuild Dynahi, now a CFA3 something. CFA3smd engraved on back side of the Dynahi front panel. A green LED in the small S. Diagram of bias (in mA for the first 40 minutes from power on) for servo respective no servo. I think that with the servo it’s possible to build this with just 4 transistors instead of 14 (per channel) on heat sink – time will tell.

Happy Birthday!

A working stereo CFA3 something. I’ll wait with chassis until I’m confident it won’t “runaway”. So, now it’s on the floor in our living room. My wife is a very understanding woman.

Issue with bais above solved. Reason was a misaligned 600pF smd capacitor shorted a trace to ground. When powering the amplifier, it takes some seconds until the bais raises to set value. One side tends to wait much longer than then others. Offsets all channels are close to zero – a few mV at most. No hurry with headphone protection...

Still too early say anything about stability. Yesterday I built another board. One side worked as supposed but the other side’s bais was stuck at zero whatever I did. When I touched a few places on the board with a test pin the PSU’s current raised so the current limiter kicked in. This happened even with an unconnected test pin. I can build very odd things… that I don't understand. Bottom line: JoaMat should build himself a Headphone Protector.

Here is result of today’s work. The board was milled yesterday. Schematically it’s similar to CFA3. Two of the triple Darlingtons transistors are to-126. All other transistors are sot-23 and sot-26. To early to say how stable this thing is…

tta/ttc and kca1220/ksc2690 are, in my opinion, reliable. I've used them for years as substitute for j79/k216. Next step is the 37 vias. Board, 0.5mm wire and tools. Anyone prepared to pay a fortune for handmade printed circuit board?

That panel looks good. Is it for an original DIY T2 or a Modified DIY T2? Me to have done some milling. 0.38 mm end mill, 18000 rpm and 300 mm/min. Two sides, 121 holes (5 diameters) and cutout took a little less than 2 hours.

Thank you, wilco (will comply).

Thanks, then I’ll give it a try.

Seems to work in LTspice. Too simple to be true?

Thanks Kevin! Working on an all heatsink version. Left side is almost ready...