A bit of guidance: Valencia crossovers

[doodlebug]

I picked up my Valencias a couple of months ago and they're quite nice with the tube gear I'm using. I have been attempting to get a bit better bass out of them. Bass much below 100hz is muddy and rolls off rather quickly - at least to my ears and some rather crude measurments with a signal generator, mic and a recorder via high-end DAC/ADC. These are 16 ohm Valencias and the use of different taps on the amps (HK Citation II or Mac MC-225s) have not changed this characteristic.

The crossovers, N-800-Fs, were reworked prior to my ownership by replacement of the caps with polys. These had been removed from their aluminium cases and hand-wired to a small piece of hardboard along with some of the original chokes.

I've begun to suspect that, perhaps, these were not rewired correctly during the rebuild. For one, there are 2 of these chokes still in the original cans and not wired into the existing circuits.

Can anyone point me to the schematic for the N-800-F? I've checked the excellent archives but do not find this exact model there.

Thanks for any help.

Cheers,

David

[spkrman57]

2nd order Butterworth and L-pad @ 800hz

Ron

[spkrman57]

18 ufd and 2.2 mh is what online calculator came up with for me with 8 ohm drivers @ 800hz


Hope this helps

Ron

[doodlebug]

Ron,

Thanks for the calculations. Looks like there may be a problem, then. Think I'll just rebuild the things with new parts altogether. What's the URL you're using?

Cheers,

David

[spkrman57]

Try that out and see if you get what you need.

Not factory, but I like a 2nd order on the bottom and a 3rd order on the top(horn), you can attenuate with a pair of resistors and add a cap for HF compensation(ala Pi speakers).

Ron

[doodlebug]

That should be a fun project. I appreciate the help.

Cheers,

David

[spkrman57]

The 1st resistor is parallel across the HF output of the crossover (15 ohm/10 watt is fine) and take a series resistor from the positive leg of the HF output in series with the horn (30 ohm/10 watt). Parallel a .33 ufd or .47 cap in parallel with the 30 ohm resisitor and you should be close in the ballpark.

This eliminates the L-pad and the lower value cap(.33 ufd) brings in the HF compensation later and higher, the higher value cap(.47 ufd) brings it in sooner.

Basic attenuation is approx 12 db and works well for me. But I use 2226 JBL 15" drivers for the bottom end, so your results may differ slightly.

Great tweaking abilities if you have different value resistors and caps to play with.

See the Pi speaker forum for more info if interested. Search for "audioroundtable" and select "Pi speakers" (on lower right of main forum page)

Ron

[DonM]

Could you explain why you used a second and third order crossover?

I'm researching a similar project for the Altec 416A & 806A.

Thanks,

Don

[spkrman57]

The reason for the 3rd order for the hi-pass as it was explained to me was to better oad the "Q" of the HF compensation circuit. I am not that deep into the "Q" factor and such and just know it works very well on the 811B horn setups I have used.

PS: I also used 1600hz for crossover point as it allows the HF to have a slightly better top end response.

Wish I had more time on this subject, but going out of town for a few days. Send me a PM and I will try and elaborate further next week.

Pi speaker forum has most of this info and you can search for more specific info. I and others have posted about the use of 811B horns and 806/802/902 drivers in the forums and might be a good starting point to search there.

Ron