KEF Q300 crossover
Also one more question: can you tell if there is internal bracing in the cabinet? Thanks for the help.
New to Forum, hello. The Q300 driver is an amazing piece of engineering, backed up by a mediocre cabinet and horrendous crossover (parts).
Having played with literally dozens of caps, inductors and resistors for this speaker I can recommend the following:
Stock 19-20 ga. inductor says .65mh but actually measures .665. It is in series with + lead to the woofer Having tried values from .62 to .68 a value of .665 to .67 is ideal. Too low a number brings the mids to far forward IMO and to large a number makes the mids flat & hurts the soundstaging. Try an ERSE 16ga. .68mh and wind 10-11' off. Soak the inductors in clear varnish for a couple of hours and let them dry. This cuts down on ringing.
Capacitor is 4.3uf. This is in series with the + lead to the tweeter.I've tried the Sonicap and the Clarity Cap ESA series. I prefer the Sonicap because I like to play with and change the sound with various .01uf bypass caps. More on this in a minute. Pay the $ to have then matched.
Stock crossover has a 1 ohm resistor in series with the + tweeter lead after the capacitor. The stocker is truly a bad sounding ceramic! Have tried the following:
Dueland- Amazing, worth the money IMO- can be unforgiving with a bad frontend, BUT they run 3-4% high in value. This is audible. If you use a Dueland be sure to pay the extra $ to have then matched and have a value no higher than + 1-2%. Or do a parallel network (I use Mundorf's with the Dueland to get the value down to exactly 1.0-.01.
Mills- soft, boring IMO. You can parallel to get to .98 ohm rather than 1.0 ohm to open them up a little.
Mundorf- 1.0 ohm 5 watt are OK, 20 m-resist watt's are better if a little bright just above the crossover frequency.
Build a Zobel Network for the woofer. It removes the HF impedance peak and tames it 7-10K ringing; similar the going to a 12db crossover. I use a Mundorf m-resist resistor of 6.5 ohm and a 15uf Clarity Cap ESA of 15uf. This goes in parallel with the + and - leads of the woofer after the inductor.
Bypass cap for tweeter- You can completely change the sound & presentation of the speaker by bypassing the 4.3uf cap with a small bypass cap (it goes in parallel with the 4.3uf cap). I simply have a sort pair of wires coming off each side of the capacitor with small alligator clips so I can change the bypass at will. Here is what I use:
Jupiter .01uf- adds a little sparkle and improves soundstage. Very smooth but not real lively.
Mundorf .01 SIO- Not very "accurate" but very addictive midrange and adds a little sparkle at the extreme top, where the KEF tweeter is a little down.
VCAP tftf- VERY lively, very "lit up" as the reviews say. Exciting but can be too much.
Sonicap Platinum .01- nice, but not worth the $$ IMO.
Clarity Cap MR .01- Very neutral, very open, great soundstage, stays controlled at all times. One of my favorites.
AmpOhm PIO, alum. foil- Except for the tippy top of the treble (where it is to my ears just a little soft), this is my favorite bypass cap. Smooth, detailed, beautiful mids, nice open yet stable soundstage; can listen for hours at high volume without fatigue or strain.
Vishay .01- For $1 each they work well with the Sonicap and adds a little sparkle and opens the soundstage a little.
Caps do have directionality to them, and they do need a break-in/settle-in period. The VCaps being the worse, horrible & bity for the first couple hundred hours.
The port does not have an internal flange BTW. It does have only one brace running horizontal about mid cabinet.
If you're having a cabinet built from scratch, over-build the crap out of it! Make the front panel from 1" at least, brace it well, and line the inside with some form of Damping material. Sonicraft.com has some good stuff (black hole?). That's also where I got the Soniccaps & Mills resistors. Amp Ohm caps from thetubestore.com Erse inductors from erseaudio.com and most everything else from partsconnexion.com in Canada. BTW, I'm in the U.S.
Have fun.
Bruce in Tucson