rumina

finished my cfa3 this week, thanks kevin gilmore for the desing and the support from the forum members. running on +-30v with moderat bias, changed the gain resistors to 3.2k for lower gain. needed some 3d printed parts so that all fit fine, a cfa3 in a quad 405 chase. no pot this time, i use a dac with volume control or a preamp. after all amps i build i think the best solution for a 1 case build ist mounting the trafos outside in vertical position, absolut no magnetic hum inducted. i also added grain oriented metal band around the trafos inside the trafo cases.

thank ang728 for the info, then im ready to order parts 🙂

i habe some current mirror amplifier ss/zf version 1.21 here that i like to use for the amp build. may i ask about two points on the underside of the board (orange marked) look liks place for a jumper on the front siede the are between the two 82ohm resistors. are they for jumper and/or what are they used for. thx

it's a BRZHIFI BZ2607 case from aliex..., size is 260*311*70mm. i have to many silver boxes so i like compact sizes even if the layout isn't perfekt. the trafo is a 100va /24volt from triad magnetic VPT24-4170 (mouser), with a bias of 200ma the amp needs only around 40va so a lot of reserve here, next time i would chose one that is a bit smaler.

finished today my cfa2, was a trouble free build beside that i like small case (think is a tetris disorder i caught in my teenage years ;-). once again, these trafo covers look nice but the shielding effect is near zero, to get ride of a small hum i needed to add some grain oriented bands. heatsinkt of the case seems a bit overdesingned, gets only a bit warm. offset without servos was surprising low at around 10-15mv, could use nice matched mje15030/15031 from my previous dynahi project. the amps sounds very nice, one of the few amps that are neural and speedy that i like, really a "wire with gain" type of desing. thanks a lot for the design kevin gilmore and all of you for the help from this forum :-).

my pcbs arrived today here in switzerland, thanks for the work 🙂

payment sent, thanks

i go for partial assembled boards, thanks for your work 🙂

these cover are mostly cosmetic but i like to use them, the only shield a tad vs grain orientated metal or mu metal. place the trafo near the big transistors with heatsink and you have a silent amp like in this pic (the 3th i made). my first version had some inducted hum because the trafo was on the other side near the small transistors. good luck with your build :-).

nice to see your success, it's the amp i like a lot with my power hungry magentoplanar headphones. after the that340 i tested the trendsetter lsk489/ls689 but at the end i enjoyed the 2sc3381/2sa1349 the most, quite shure that with the 2SK170/2SJ74 this amp performs superb. let us see the amp when it in its chase ;-). well done

oBravo Ra C-Cu

superb that are some nice amps :-), well done

great please add me with: 2x grhv, 4x grlv78xx, 4x grlv79xx, 1 main board, 1 mini t2 thanks

if the case is high enough you can try to mount the transformer standing up, base parallel to the back plate (or mount it direct to the back plate). i would remove the screw of the trafo, turn it up whitout fix mounting to test if the hum is less (if less thats a least one part of the problem).

this is the case i used: https://de.aliexpress.com/item/143-40-4-180mm-WxH-D-aluminium-elektronik-pcb-geh-use-6063-extrusion-fall/32857644347.html?aff_platform=api&cpt=1549182007927&sk=ZVxRRvI&aff_trace_key=807df99551d348b39035d168c5f73204-1549182007927-05033-ZVxRRvI&terminal_id=1183572cd19e4eb0be580194ccaeaa77 the pcb slides in the grooves (some tap around the edge for isolation). but you need make some place for the top cinch connector (grind the topcase a bit with a dremel or similar tool, shorten the silver latch). then do the same thing for the two caps underneat he pcb, they need 2 mm more space on the side of the pcb. now you can slide in the pcb from the top (not sliding the pcb in) in the groove opposite the caps underneat, push down and the pcb holds in place. for the topcase to fit you need to grind down the ac socket a bit, easy done with a dremel. due the case is a tad longer then the pcb i printed two case holder plates that hold the pcb in place, so you can also use the orginal alluminum plates, sadly the topplate is realy thick and i was to lazy and printed the two top plates also. i attache the freecad files and stl files so everyone can use them (missing are the holes for the pot/4.4mm plug and vents if you need them, easy to add). the case is thight but works fine with some work and patience, take care of the heat, venting is not easy for this case. smd_dynalo_roundcase_front_back_v2.zip