kevin gilmore Posted December 26, 2012 Author Report Share Posted December 26, 2012 Its a operational transconducance amp, and the load is 105 ohms.Increase to 500 ohms for 10db of gain. add pot after the 105 ohmsand then a buffer. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 20, 2013 Author Report Share Posted February 20, 2013 So this one kind of came out in the mix. http://gilmore.chem.northwestern.edu/nfd.pdf unbalanced in, unbalanced out, about 8 watts into he6 gain programable with a single resistor (use a really good one) and Thd < .01% seriously sweet sounding. will start on the board soon. Quote Link to comment Share on other sites More sharing options...
spritzer Posted February 20, 2013 Report Share Posted February 20, 2013 Crap, just what I need... more stuff to build... Quote Link to comment Share on other sites More sharing options...
Kerry Posted February 20, 2013 Report Share Posted February 20, 2013 All in due time... This is fun, but agree it's hard pick the best. I'm very interested in an amp to drive planar headphones. It seems like this is going to make the list. Quote Link to comment Share on other sites More sharing options...
Horio Posted February 20, 2013 Report Share Posted February 20, 2013 (edited) So I'm a bit confused as it seems like this thread has wandered off to some other designs more recently. Where does the KGITSOJC stand these days? Edited February 20, 2013 by Horio Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 20, 2013 Author Report Share Posted February 20, 2013 The posted front end with a lower power output sage makes a kickass Unbalanced preamp. Still trying to match this performance in a fully balanced version Quote Link to comment Share on other sites More sharing options...
c12mech Posted February 21, 2013 Report Share Posted February 21, 2013 I was going to ask the same thing as Horio. In the end will this be able to do balanced/balanced, balanced/unbalanced, unbalanced/balanced, and unbalanced/unbalanced all in one unit. I know that is a lot to ask for but it would be my ultimate preamp solution. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 21, 2013 Author Report Share Posted February 21, 2013 That is what i want to acomplish. Quote Link to comment Share on other sites More sharing options...
c12mech Posted February 21, 2013 Report Share Posted February 21, 2013 If that is the case then I will keep waiting on this to materialize. Quote Link to comment Share on other sites More sharing options...
Pars Posted February 21, 2013 Report Share Posted February 21, 2013 This sounds really promising Kevin. Are you thinking of keeping the higher power output stage... for a headphone jack? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 21, 2013 Author Report Share Posted February 21, 2013 i sure wish some company (any company) could supplycurrent manufacture complementary jfets. Then thingswould be so much easier. Quote Link to comment Share on other sites More sharing options...
Pars Posted February 21, 2013 Report Share Posted February 21, 2013 Any news from our friends at linearsystems? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 21, 2013 Author Report Share Posted February 21, 2013 They are either liars, or completely incompetent or both.4 years to make a p-channel jfet, yeah right.Or there are huge quantities of 2sk389 and 2sj109 somewherethat none of us have access to that are preventing lsj109from being released. Ayre evidently has 10's of thousandsof parts in stock, yet stax had to resort to glueing singlestogether recently. Even the singles are not available. Quote Link to comment Share on other sites More sharing options...
spritzer Posted February 21, 2013 Report Share Posted February 21, 2013 I'm tempted to ask Fairchild how many parts we need to order to get them matched in a single envelope... Quote Link to comment Share on other sites More sharing options...
wink Posted February 22, 2013 Report Share Posted February 22, 2013 Tempt away. Quote Link to comment Share on other sites More sharing options...
c12mech Posted February 22, 2013 Report Share Posted February 22, 2013 I'm tempted to ask Fairchild how many parts we need to order to get them matched in a single envelope... If it meant being able to have available parts to design and build new circuits I would be willing to buy a fair amount of them myself. Is there no one that makes a decent SMD part that is equivalent to what is needed. It seems that everyone is going SMD now. I would hope they could make some good parts in those packages. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 22, 2013 Author Report Share Posted February 22, 2013 what i want is front end complementary jfets. Don't care if they are surface mount. Quote Link to comment Share on other sites More sharing options...
spritzer Posted February 22, 2013 Report Share Posted February 22, 2013 Yup, package doesn't matter. Fairchild does make a nice P-channel but I'd guess we'd need a lot of units for them to make complimentary pairs for us. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 23, 2013 Author Report Share Posted February 23, 2013 (edited) here is the unbalanced/balanced to balanced front end. http://gilmore.chem.northwestern.edu/ubaltobald.pdf really sweet sounding. 0 db of gain balanced, -6db of gain unbalanced. gain is controlled by R5,R32 so i could put a relay in that switches the gain to maintain 0db (or any other number) when you switch from unbalanced to balanced. still even better with the that340 replaced with jfets. mpsw06,mpsw56 replace 2sc2240/2sa970 when we can't get them. Edited February 23, 2013 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 24, 2013 Author Report Share Posted February 24, 2013 first cut at the board http://gilmore.chem.northwestern.edu/ubaltobald.jpg Quote Link to comment Share on other sites More sharing options...
Horio Posted February 24, 2013 Report Share Posted February 24, 2013 (edited) Dumb question, but is the intent to use this between the "multiamp" board and an input selector board? Or would the gain be taken care of on this se/bal board and the "multiamp board would be eliminated. Edited February 24, 2013 by Horio Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted February 24, 2013 Author Report Share Posted February 24, 2013 (edited) This is instead of the multiamp board. Input switching This board Pot of some kind Diamond buffer output There is nothing wrong with the multiamp, in fact it sounds great too. But the input impedance is lower due to supersymmetry. The idea on all of these is to eventually replace with jfets once they become available. As it is, this new board is without feedback of any kind, and is faster and more quiet. plus gain is a single resistor and compensation is unnecessary. Edited February 24, 2013 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
Horio Posted February 25, 2013 Report Share Posted February 25, 2013 That makes sense. Not to get greedy, but adjustable gain from the front panel would be a great feature. Quote Link to comment Share on other sites More sharing options...
spritzer Posted February 25, 2013 Report Share Posted February 25, 2013 Relays and a stepped switch would be an easy way to adjust the gain. Now if you want it to be a volume control then you are looking at KX-R levels of complexity though... Quote Link to comment Share on other sites More sharing options...
Pars Posted February 25, 2013 Report Share Posted February 25, 2013 Preamps such as the Pass Aleph P use a simple panel mounted pot for gain control, one per channel, separate from a volume control. Quote Link to comment Share on other sites More sharing options...
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