kevin gilmore Posted December 28, 2014 Report Share Posted December 28, 2014 been working on this one a while, with all the popular transistors disappearing, I hope that this one won't go obsolete before the boards are out. I don't think so because Fairchild has said that the bc parts should be available for at least 5 years but onsemi said the same thing. This one is a diamond transistor input set, used as a voltage to current converter. A pair of Wilson current mirrors with input and output cascade as the VAS and a triple darlington output stage. http://gilmore.chem.northwestern.edu/cfa2.pdf if someone knows of better surface mount parts to replace the bc series, I might as well do that from the start. ft >150mhz, hfe >100 Vceo >50 etc 1 Quote Link to comment Share on other sites More sharing options...
spritzer Posted December 28, 2014 Report Share Posted December 28, 2014 I think the BC stuff is as sure a bet as we can have with semi's. They are old as the hills a a lot of companies make them. It's either that of throw an ECC83 in there. They will outlast all of it in production. Quote Link to comment Share on other sites More sharing options...
UFN Posted December 28, 2014 Report Share Posted December 28, 2014 Interesting as usual and agree on the BC-parts - if they disappear then I think we might as well close up shop BTW, isn't it the 549/550 and 559/560-versions that are supposed to be "audio" parts and the 546/547 and 556/557 are intended for switching? //UFN Quote Link to comment Share on other sites More sharing options...
PretentiousFood Posted December 28, 2014 Report Share Posted December 28, 2014 Rohm's got some new stuff that's not quite as good as the BC550/560 pairs with regards to ft, but the Hfe/Ic curves look a fair bit more linear and better matched between the P and N parts, going by the datasheets. 2SA1576 / 2SC4081 2SA1774 / 2SC4617 1 Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 29, 2014 Author Report Share Posted December 29, 2014 http://gilmore.chem.northwestern.edu/cfa2.jpg Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted December 29, 2014 Report Share Posted December 29, 2014 Cool Quote Link to comment Share on other sites More sharing options...
nopants Posted December 30, 2014 Report Share Posted December 30, 2014 does the output need sinks? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 30, 2014 Author Report Share Posted December 30, 2014 absolutely. angle bracket version Quote Link to comment Share on other sites More sharing options...
RudeWolf Posted December 30, 2014 Report Share Posted December 30, 2014 (edited) What's the situation with smd parts? Nothing too interesting there? Nevermind, must be the hangover talking. What about BC850C/BC860C? Also I'd love to have SMD options for lower dissipation resistors and maybe even ceramic capacitors. Nice design, btw. Looks like current feedback is all the rage nowadays. What's the predicted current draw on this thing? I've heard that CFA's are sensitive to power supply ripple, so I'm wandering how fancy can I go before it turns into space heater. Edited December 30, 2014 by RudeWolf Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 30, 2014 Author Report Share Posted December 30, 2014 transistors need to have a Vceo of 50v or more bias is 150 ma and the current mirror as the VAS means that the peak to peak voltage swing is 40V on +/-24v supplies absolutely flat to more than 5mhz Quote Link to comment Share on other sites More sharing options...
nopants Posted February 25, 2015 Report Share Posted February 25, 2015 What do you recommend building between this and the dynalo? My k401 feels neglected Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 1, 2015 Report Share Posted March 1, 2015 Have the files been posted for this one yet? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted March 1, 2015 Author Report Share Posted March 1, 2015 just posted cfp2 to the boards directory I have not had boards made yet, or tested, prototype works fine. someone needs to check the board. Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 2, 2015 Report Share Posted March 2, 2015 (edited) Hand traced and it looks ok to me. Subtle differences in the schematic vs the board: C2 is 100uf in schematic vs 47uf on board. C1 is 4uf in schematic vs 4.7uf on board. The top two tiers of the triple darlington emitter resistors float in the schematic and are output referenced on the board. Also noticed the ground in and out connections, the 100uf and .1uf cap grounds don't have thermals...not sure if you typically use them there or not. What's the gain set to on this one? I having trouble figuring that out. I plan to get a proto board spun when I have time...much more compact than the KSA5. Edited March 2, 2015 by GrindingThud Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted March 2, 2015 Author Report Share Posted March 2, 2015 (edited) The top two tiers of the triple darlington emitter resistors float in the schematic and are output referenced on the board. They float on the board too. not tied to the outputs. For power supply caps i like to do complete solder to ground as the thermals have some impedance, especially at higher currents. Edited March 2, 2015 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 2, 2015 Report Share Posted March 2, 2015 Doh...I Must have been dazed by staring at purple on purple for too long. They float on the board too. not tied to the outputs. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted March 2, 2015 Author Report Share Posted March 2, 2015 slightly updated board file Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 27, 2015 Report Share Posted March 27, 2015 Looks like a project weekend! Boards are in. I plan to do one set as throughole and one as SMD. Question...will it mind being run off the KSA 21V supply? My other alternative is the 30V from the Dynahi without modding it. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted March 27, 2015 Author Report Share Posted March 27, 2015 (edited) definitely ok on +/-20v Edited March 27, 2015 by kevin gilmore 1 Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 28, 2015 Report Share Posted March 28, 2015 Soldering under way. Possible error on board. In the schematic, the positive input of the opa445 is grounded. On the board, pin3 is not connected to anything. Pins 1, 3, 5, 8 are floating. I plan to run a short jumper from pin3 to the nearby .1uf cap ground if it needs it. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted March 28, 2015 Author Report Share Posted March 28, 2015 (edited) thermal on pin 3 is definitely missing. will fix on the layout in a few minutes. pin 3 has to be connected to ground. Edited March 28, 2015 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 29, 2015 Report Share Posted March 29, 2015 (edited) It lives! Without the servo (still need to add the jumper) it's only got a few mV offset and is dead quiet with cheesy iems Now I've got to figure out the bias....oh, I think I've got it. 150mA across the 1 ohm. Now I've got to get the second channel built. I think this one may be a winner. I'm observing interesting behavior...seems the bias current changes with input pot position. May be because the servo is out, or could be my input wiring. Driving my headphones in mono it sounds great! Edited March 29, 2015 by GrindingThud Quote Link to comment Share on other sites More sharing options...
eggil Posted March 29, 2015 Report Share Posted March 29, 2015 Man that was fast. You just got the boards! Quote Link to comment Share on other sites More sharing options...
UFN Posted March 29, 2015 Report Share Posted March 29, 2015 Looks good, keep us posted when you finish the other channel Just out of interest, which caps did you use for the 4.7uF/47uF positions? //UFN Quote Link to comment Share on other sites More sharing options...
GrindingThud Posted March 29, 2015 Report Share Posted March 29, 2015 http://www.mouser.com/Search/ProductDetail.aspx?R=RDEC71E476MWK1C03Bvirtualkey64800000virtualkey81-RDEC71E476MWK1C3Bhttp://www.mouser.com/Search/ProductDetail.aspx?R=FK20X7S1H475Kvirtualkey52130000virtualkey810-FK20X7S1H475KLooks good, keep us posted when you finish the other channel Just out of interest, which caps did you use for the 4.7uF/47uF positions? //UFN Quote Link to comment Share on other sites More sharing options...
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