Question for Pano: JB's 605 OB crossovers

I grabbed a copy of the schematic you posted on the crossovers
you used with John Busch's open baffle 605A speakers at LSAF
last May. I am using Jeff Markwart's design on my 605B OBs and
thought I'd try the fixed attenuation with HF compensation
you show in the LSAF design on the tweeter side. I'm curious why you
have the 10uf cap in parallel with the 4 ohm resistor on the ground
leg? It looks like it would have no effect as all frequencies that made
it though the 2nd order filter would be a good octave higher. Is this
intended to put a steeper, shelved cut from say 800 hz or so?

I've attached that schematic. Not sure how it will appear.

Thanks,

Skip

Hi Skip,
Sorry I haven't been on the forum in quite some time.
Let me study your question and get back to you.

Pano

Thanks for picking the question up. I just noticed the 'extra' cap
and was curious.

Skip

SKIP

The two RC networks " boost " the HF to the horn.
Below the frequencys the caps kick in the HF driver ckt looks like 14R in series with an 8 ohm driver . About -9dB ,a reasonable padding down of the horn to match the woofer . At very HF the 3R and 4R are bypassed and the ckt looks like 7R and an 8 ohm driver. -5.5dB ,or 3.5dB of " boost " split by the RCs for high freqs.
I read the values as : 10uF & 4 ohms res freq = 4 kHz, and 0.47uF & 3 ohms freq = 113kHz?? Could the 0.47 be 4.7?? Then the second freq = 11kHz.

Don

Bingo!

Thanks to you both. I was looking at the RC pairs as a series
attenuator with the capacitor acting has an HF bypass. I'll
need to bone up on them as a resonant circuit element.
Also, just to confirm, the cap marked in the diagram as
.47 uf should be 4.7 uf? I have both, so I probably should
start with the right one.

SKip

HI Skip
I would use a 4.7uF cap . Every one knows those drivers need all the help they can get.
When you build the XOs try them with all the resistors leaving out the 10 and 4.7 caps. Then add them in and tell us whsat you hear .
Don

Quote:

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Originally Posted by donaldpatten

When you build the XOs try them with all the resistors leaving out the 10 and 4.7 caps. Then add them in and tell us whsat you hear .

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That's a great idea. I have that basic crossover in effect already, with
the series cap and bypass inductor for the highpass, but with a big
pot for attenuation. I will ditch the pot and put in the series resistors
first to see how close the sound matches the pot (after measuring
the the legs on the pot), and then clip lead in the caps as a first
pass on the mod.

thanks,

Skip

Skip Pack

Good to see you on the forum.

The Jeff Marquart base crossover is quite good. However, after listening to it I felt it needed to be adjusted to the actual 605's, especialy considering the way I was using them.

They were not stock with the GPA upgrades and of course the OB aspects. So it came down to adjusting by ear with some measurement to keep things from straying too far. Text book traps just did not seem to improve things. They are general at best.

So much listening, adjusting, listen again in several rooms with a wide range of music and amplifier - CD and phono sources. It takes trial and error to get things to the next level. No other easy way around it. Know that Pano was doing some of this at LSAF too.

So, would be iterested in knowing what is working, or not working for you. Your 05's sounded quite good in Sarcamento. Wish we could have listened to them a bit louder in a more appropriately sized room.

Hello John,

Yeah, I figure it's parts box time. At least I have a pretty good
selection of cap values and varieties to try on these compensation
filter sections. It's the roomfull of coils that I lack. I'm currently
using the Erse Super-Q coils in these crossovers, but always wonder
what some big, quality air cores might do.

Skip

Skip

It will be interesting to see what works for you. Hope you let us know how it goes.

As for inductors, the very low power levels you will be using pretty much offset the alleged advantages air core coils have over iron core. In fact, with the lower DCR values typical of Iron core help preserve dynamics and lower insertion loses. I have some 8 ga. air cores and just can't hear all that much difference, with the exception of the lower mid-range. Once you are up above 750 Hz or so, the power levels delivered are usually less than a watt, way less. So the feared iron core saturation just is not a factor.

I know there are those who would take issue with what I am saying, but my empirical experience is hard to ignore.


John