Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › d3a gyrator loaded parafeed design
New Posts  All Forums:Forum Nav:

d3a gyrator loaded parafeed design - Page 2

post #16 of 21
12/2/10 at 11:21pm
Thread Starter 
True but I am not one for fashion. The datasheet suggests a very low dynamic impedance and what is there looks more linear than an led. As you say, proof is in the listening.
Reply
post #17 of 21
12/2/10 at 11:47pm

Also might want try one of these http://www.fairchildsemi.com/ds/2N/2N7000.pdf  with the gate tied to the drain to the cathode would give about a similiar bias.

Reply
post #18 of 21
12/8/10 at 8:36am
Thread Starter 

update: I have it on a perf board ready to test

 

d3a gyrator.jpg

 

It'll find a test home in my tweakers amp which is currently a c3g parafeed. By the way, the c3g ccs loaded parafeed is currently biased by a tl431.... i think i prefer it to leds!!! the bass seems better... which could always be a small change in operating point.

 

test home

 

c3g parafeed.jpg

 

c3g parafeed 2.jpg


Edited by adamus - 12/8/10 at 9:21am
Reply
post #19 of 21
12/12/10 at 12:26am

Adamus is the tl431  adjustble under the cathode,  could you set it for 10V's or higher for tubes that require a lot of bias?

Reply
post #20 of 21
12/12/10 at 2:16am
Thread Starter 

its adjustable upto 36v (max rating) and achived using a couple of resistors - the datasheet explains better than i can. Watch the power rating though, it soon falls off with increased temp. Another thing to add is that i have a slightly increased noise floor with tle431, not noticable with senns but is with grados. I am looking for an osciallation but cant spot one, but my scope is a bit rubbish. The c3gs and d3a LOVE to oscillate, i doubt this would be a problem on non 'extreme' valves.

 

another method that would probably yield better reults is using a pnp in emitter follower.. you get the stable vref from the leds and the low dynamic impedance of the pnp - you can also scale power requirements with pnp type. cathode voltage = vref + Vce(which is about 0.7v)

 

pnpbias.jpg

 

Reply
post #21 of 21
12/12/10 at 2:37am
Quote:
Originally Posted by adamus View Post

 

pnpbias.jpg

 



Brilliant.   Thankyou very much adamus

Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › d3a gyrator loaded parafeed design