curious about DHA2 crossovers

[Daddy Dee]

Thanks Bruce. I had no idea about the DHA being John's brother.

[Marvel]

Thanks Bruce. I had no idea about the DHA being John's brother.

If that isn't correct, I hope he will let us know. As long as he doesn't drive down here and slap me.

I haven't seen him since I met him to give back his ALKs he loaned me. I used them whil I got the parts and built the DHA2 crossovers.

Bruce

[Deang]

Don't worry, they're the initials of John's brother.

If you'll at the look at the schematic closely, you'll notice that attenuation is fixed on that design. If you build it, be aware that you can't adjust the attenuation.

I later adjusted the design so attenuation could be changed on the fly (like the Universal). I dropped the idea of soldering a wire and disconnect to each tap, and just used two wires coming off of the barrier strip (Al adopted this on the second iteration of the Universal). At some point I changed the first order tweeter filter to a third order Butterworth, and thus the Super AA was born.

Greg Roberts of Volti Audio sells the modified DHA2 as the VTK-400. The network goes back to wiring individual connections to the autotransformer, with the addition of a second low pass coil, which from a technical standpoint, doesn't really work, since you would need the correct cap to go along with it. It does look nice though, his work is beautiful. It probably did take him a while to figure out the physical layout, routing and such - but there really isn't anything new going on here. My personal preference would be for less woodwork and bling and better sounding capacitors.

[erez]

build prototype of the DHA2. like @Marvel version.

I'm wondering if this is dangerous for the k55v mid?

the cutoff frequency is ~450hz and 6db/dec  😱

In any case, the sound is deep and with big soundstage 

Edited April 13, 2021 by erez

[Marvel]

It should be 400Hz...

 

Not a problem for the K55 at all. The LaScala and Klipschorn both have a 400Hz crossover.

[erez]

you're right.

k33 is 4 ohm and k55 is 16.

 

have SET amplifier.

need to decide between bi-amp with crown amp to the BASS 🤔

now i with mini DSP, and move to DHA2 crossover.

thanks

[Marvel]

I'm still using this crossover on my LS, and it worked great with my 2a3 amps. I recently sold those amps, though, and now use a small Crown D45.

 

The MiniDSP would give you more control.

[erez]

thanks Marvel

today i try only SET amp, feel to me little bright, maybe its because i dont have autotransformer?

how much 'db' down do you recommend?

in bi-amp, i just balance with MIC.

 

[JohnA]

You really need to change the 3.3 uF tweeter cap to 2.0 (2.2 OK) to tame a response hump in the K-77s from around 6k to 9k.

[tigerwoodKhorns]

13 hours ago, JohnA said:

You really need to change the 3.3 uF tweeter cap to 2.0 (2.2 OK) to tame a response hump in the K-77s from around 6k to 9k.

 

I have this in my server under DHA Notes.  I think it is one of Dean's old posts:

 

The autobulb has some resistance, so it's "a resistor". With the 65 ohm resistor, it acts as an L-pad. I believe it knocks a little over a dB off of the tweeter's output. The bulb doubles as tweeter protection. Faster than a polyswitch if I'm remembering right. After I built about a half dozen pair of these things I got it in my head to just use zeners and to forget about the L-pad. This is the only pair I built with zeners. After I did it, I realized I might have made a mistake. It's a first order tweeter filter and there's quite a bit of energy being sent to that driver. I was concerned that they might start activating too soon, cutting the tweeter's output when they shouldn't be. The customer never complained, and it's been over five years. By then I was building the Super AA, and only got one request (two if you count Bruce) for a pair of these. I got the idea to just built a first order Super AA and called it the Super A -- and built it so the attenuation could be adjusted. I also cheated and changed the 3.3uF to a 2.2uF to reduce a little of the tweeter energy. That was Bobby Crite's idea. I didn't want to use the bulb, zeners, or an L-pad. I'd thought about using another autoformer, but decided that was crazy expensive just to shave a dB or two off. So I called Bob for his thoughts. He said that since I'd already ruined the crossover by using a resistor, might as well go all the way and use the wrong cap. Seriously though, it was a good call -- sounded great.

[erez]

thanks for the help tigerwoodKhorns and JohnA.

my first setup is same DHA2 bi amp.

when i change to one amplifier, i here the brightness, so i thought its the bass power.

according to the mic measurement, the mid k55v is fall at ~5k, so change to 2uf is not good.

i try the L-pad