Welcome! Need support, you got it. Or share your ideas and experiences.
Return to Planar Speaker Asylum
69.65.66.188
In Reply to: RE: PLLXO question related to LDR posted by johnvb on February 26, 2012 at 09:51:24
John, I would have to agree that LDRs have improved greatly in stability. After you mentioned your plan in another Asylum forum, I dusted my old research and then looked at what you saw. This was weeks ago and I am still keeping track of it for the future.
By and large, it looks promising. Too much, perhaps. I asked and the kits are not being made available anymore, or at least for now. They seem to be selling all the selected LDR paired sets that they can get as finished product.
As Davie and Neo suggest, insertion losses could be a problem. The thing I liked about this LDR design is the low input impedance. It appears that my existing PLLXO setup would hardly be affected by being right after the attenuator. If you consider that my LP is currently being set as 2nd order, I already have the bulk of losses accounted for. I can still go to 1st order on it and remove impedance.
BTW, this may work just as long as I don't want to add a properly timed subwoofer. Things get trickier for this and Davey may have a good perspective on this also.
Follow Ups:
I've read the Warpspeed is no longer offered as a kit form, but Uriah Dailey is still selling a kit (actually you can get the parts, or the boards pre-assembled). AFAIK, he made an agreement with the original Lightspeed designer, George Stantschleff, not to sell completed units. See the link below.
The problem with having a passive pre (regardless if it is an LDR or not) is that the output impedance varies if you change the volume. This means the the fc of the filters and the xo point of the PLLXO will also vary everytime you change the setting on the passive. You could put an opamp buffer between the passive and the PLLXO but then you might as well go to an active crossover.
On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
Edits: 02/26/12
Neo, I may have failed to realize this. It could mean that my UBS DAC and the pre-amp have the same output impedance, which I don't know for a fact. I can plug into each separately and measure no change in xover points.
I never saw a spec call for it while designing the PLLXO filters and simply assumed that input impedances was all I had to worry about.
Well, time to start lining up the active stage ducks, then. It was in that "future projects limbo" for when a proper subwoofer integration became a need anyway.
You have to consider/include 'everything' when designing PLL's. :) Even interconnect capacitance might be an issue.
You can measure output resistance of a source fairly easily. Take a voltage measure unloaded and also with a 1k resistor attached.
Rout = 1000 times (Ropen-Rload)/Rload
You'd be surprised how high the source resistance is on many components.
Cheers,
Dave.
Shouldn't that be Z = 1000*(Vload-Vopen)/Vopen?
On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
So is it's OK to place the pot after the PLLXO? I'm thinking of a dual deck (4 channel) stepped unit.
Edits: 02/26/12
Thanks Davey! Where do I find the impact relative to changes in Rout in a given configuration?
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: