Breaking KX-5 VX-5 link
 

When I proposed inserting a fully balanced Bryston 10B between my KX-5 Twenty and VX-5 Twenty to high-pass to KEF LS50s, Charles Hansen objected, because it might compromise the zero feedback design. I've been discussing this matter on the Bryston board and wonder how to balance the sonic value of zero feedback against relieving the LS50s of low frequency duty. The 10B is sitting in the box unopened. Any thoughts?

db

Having inserted the Bryston 10B between the KX-5 Twenty and VX-5 Twenty for high-pass, the objections of Charles Hansen seem well founded. The high frequency sound is a bit too "HiFi" for my taste. One of the glories of the Ayre stuff is the music just seems to flow. That's no longer the case, so I'll be removing the 10B and work on low-passing the sub to reduce its overlap with the LS50. (The sub controller is driven directly from the unbalanced output of the preamp.)

db

Breaking KX-5 VX-5 link
 

Bad idea.

In addition to messing with the magic between your Ayre preamp and amp the 10B will introduce a phase shift in output signals. Best to do as you suggest and test the system frequency response with a sound pressure meter, eg Galaxy Audio CM-140 or better, and computer software such as REW. I found my ears alone cannot be used to setup bass. With sub setup it is best if you can adjust the crossover slope, volume, signal polarity, and crossover frequency. My sub is setup with crossover frequency of 30Hz, 12db/octave, and volume adjusted to blend into the low end of Quad ESL63s (using a 10B on a second output from the KX-5 twenty but you have sub electronics).

Ouch!

I should remove the 10B from the balanced preamp-amp link and try using the single-ended outputs of the KX-5 Twenty to drive the LF-pass section of the 10B rather than the the Velodyne SMS-1, perhaps sending the LF-passed output from the 10B through the SMS-1 for acoustic room correction.

I purchased my single ended 10B in the early 90s. There are 12 crossover frequencies from 30 to 1k and 6, 12, and 18 db/octave slopes. I ran a wire for each channel in the box to put the volume control on the low pass instead of the stock high pass. Just need to choose polarity so the sub and main speakers are in phase at the crossover. Choose slope for best blend.

I'm using KEF LS50s, so I expect to cross at 70 Hz* with 18 dB slope. I'll need XLR/RCA cables or adapters. Any guidance for choosing polarity?

* 70 Hz is the lowest crossover my 10B offers.

db

I suggest you contact Bryston to enquire about changing resistors to establish a lower crossover frequency. Schematics used to be available. An 18db/octave slope will need a polarity swap to the sub. 6 and 12 do not need a polarity swap. It was impossible for me to determine bass response by ear so I purchased the CM-140 and I run REW on a netbook along with a Presonus AudioBox USB.

I haven't soldered anything since I built Dynakits as an undergrad six decades ago. It appears as though KEF LS50s begin a mild rolloff around 70 Hz, so a 70 Hz crossover with a 12 dB slope might be a good match.

db