MASantos

Apparently mouser forgot to send me the opa134 needed so I plugged a pair of opa445 for the CFA servo. No smoke. Voltages are +25.02 and -25.11 I didn't match any of the LEDs or resistors so this seems pretty good to me and probably won't make a difference in real life.

I had the under switch in my power amp, but this one wont have feet high enough to reach under. I'm ordering a latching anti vandal switch and will be using a 4 pin xlr even though the amp is single ended. I already have my hd650 with a balanced connector so I wont have a need for adapter cables.

Looks great!! I got my case today. The power switch is rubbish and I'll try to get an illuminated pushbutton with European approval that fits the hole. Does anyone know of nice looking 1/4 Jacks other than neutrik?

Thanks.

Ok. My case in in customs, might as well wait a couple more days and test it in place with output thingies in the heatsink.

Received my transformer today from toroidy.pl. As always great quality. Any special startup procedures I should be looking for? Should I power on without voltage references, opamps or output transistors first?

WIP: Angle bracket for my cfa amp.

I settled on this case: width 320, height 70, depth 248, plenty of space for a single ended cfa and I might even be able to fit a coilcraft COMOCO choke filter (comon and differential filter in the same choke.) Transformer will be a 100VA from toroidy.pl, used them in other projects and quality is top notch. Now on to find a suitable 10K volume control. Would like something a little better than a RK27. stepped attenuator or a relay based one. Any ideas that don't break the bank?

I've read a few parts of this thread but would like to confirm the following: For a 24VDC output to power 2CFA boards I should use a 22-24VAC 50-60VA transformer right? How important is led and resistor matching? Do I really need 5 decimals of precision in the output voltages?

I am building a single chassis single ended version. I thought about something like this: It could be a small cube about 14-16 cm sides. everything bolting to the heatsinks. I would have to make it myself though. Commercially I found some aceptable options: https://www.audiophonics.fr/en/aluminium-boxes-cases/diy-case-amplifier-100-aluminium-271x240x90mm-p-9499.html

What case did you get for yours? Looking around for options but I either find too big or too small

One CFA board done. Small BJTs were incredibly close matched in the tape reel. A few decimals of mA between them. RN60 resistors, and 3W CMF at the outputs.

I started matching transistors today for my cfa build but quickly started scratching my head. I'm using Amb.org bjt matching circuit with a 110K resistor for the MJF1530/1531. I got between 9 and 15 mA for the 1530's and ~30mA range for the 1531's. Shouldn't I get closer readings between N and P devices?

You can also check the bluesound devices. One of the best interfaces in the market IMO and they have a unit with built in storage. I've had the Node for some years now to use with LAN stored music and tidal and it is reliable, fast and easy to use. I had tidal until recently but changed to spotify family plan. Easier UI, controls the amplifier and wifi speakers around the house directly and for casual listening I can't hear the difference between spotify and tidal.

I plan to use this side panel, it is 10mm thick and is able to cope with a few watts. Should be similar to a bottom panel some others have used I believe.

So I just ordered some of the parts to start building my single ended CFA and some decisions need to be made before I continue for which I ask your help: 1. KG recommends +-24V, is there any real benefit in going up to 30V for "regular" cans such as HD650. I do not see myself buying a pair of orthos in the near future although I would like to try them at some point. I am looking to build a single chassis in a somewhat small footprint so having to deal with the extra heat might be a problem. 2. What heatsink size would you recommend for this? I am thinking of placing both boards on a 200x120x40 heatsink from modushop to make a single heatsink enclosure like the one I sketched. 3. Any suggestions regarding stepped attenuators or volume pots that don't break the bank? I'd like some better quality than a RK27... I'll probably have some more doubts before I finish so you'll have to bear with me on this one.

Starting to gather parts for a GRLV and found a pair of 4700uf 63V nichicon UKW capacitors. They are leaded not snap in. Any issue with using these in the PSU? Comparing to regular snap in caps I get higher ripple current but rated only for 2000h vs 3000h.

No offset between positive and negative sides on the same channel!! Cool!!

I was measuring L+ L- to GND. I didn't measure between L+ and L- I'll check that quickly. No single ended phones atm so I'm safe there.

Success! I managed to get offset to within +-1.5mV on both channels. Installed the servo jumpers and music is great! One question: I let the amp cool down and then measured offset during startup. It got very high, above 150mV and descended in about 20-30 seconds to +-1mV, is this behaviour normal even with the servos in the circuit? MIght this damage the headphones if plugged during startup?

This might be a dumb question, should I short the inputs?

Thanks!! Today was outside DIY with my 6yo, recycling some wine crates.

Channel to GND DC yes. So you just play with the 2 trimpots close to the LED's to adjust offset? I'll reset the 4 trimpots close to the input transistors to midpoint and go from there. I'll need to remove the 0 ohm resistors first.

I measured the bias across all the 20R resistors and they're all flowing between 270-340 after a few hours with the top plate on. there are some variations in each channel between the 20R resistors, some might go to 340 and the one next to it only to 310. could this be transistor variation? I had the DC offset dialed to about +-5mV before installing the jumpers on the back side of the board. I'll remove the jumpers tomorrow and reset the trimpots.

So I finally got to finish my dynalo mini build. It is playing nice with 2SK170/2SK79 input jfets, 420ohm led resistors and 255 bias resistors. Temperature with cover on is 103C on left side (- channels) and 81C on right side (+ channels) transistors, is this sort of difference normal? I checked bias and L- is around 340mV while R+ is around 290mV. could this have anything to do with the offset trimpots? All the bias resistors 255ohm and led resistors (420ohm) measure within spec. Voltage drop on the leds around 1.65V When I remove the lid the temperatures drop quite a bit to around 60C-75C which is understandable. Sounds great though with my sennheiser HD650 recabled with 4 pin XLR. I would just like to understand this diferrence between plus and minus channels