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In Reply to: Sweeet posted by magnetar on December 11, 2003 at 17:11:04:
Very encouraging. I'll start looking for a pair and have another look at the schematic which White so kindly provides on their site.
Follow Ups:
My system puts out tremendous energy below 20 cycles -- they are rolling it off. I'm going to take them out of the tape loop and put them in line with the everything but the sub amp and let the sub amp get back to doing business.I'll open one up when I make the switch and take a look under the hood.. hehe
Magnetar
The lowpass filter is 2-pole and comprised of C5/C8 and R3/R4/R22. If you are going to remove it, you might want to consider bypassing some of the unneccessary op-amps while you're at it. If your preamp has 600 Ohm output impedance, you can eliminate the first buffer (U1 pins 1-3 and R5/6). If not, you can either retain it or replace it with an FET source follower (maybe in the future?). I think you might be able to get away with eliminating the buffers between filter stages as well. Depending on how much gain the filters are set for, these buffers may be making up some gain. The resistor values aren't printed on the schematic, so I can't tell. Looking under the hood would answer that easily enough. If you do need the gain makeup, you have some options which are not limited to using op-amps. Add a little bit more gain on the front end, where the input buffer is now, and maybe some more on the back end. If you are lucky, you might get the circuit pared down to just the three op-amps associated with the filters. The DC offsets of the op-amps will add up, so you will need an output cap, but just one big cap at the output should be sufficient. I think the rest could be safely DC-coupled. There's potential to really make this thing sing!
Well, I have come to the conclusion I don't need these for my system. For one if you bypass the high pass filter in the front end you end up saturating the coils, this in turn compresses the dynamics and mucks up the sound. The other thing is when I use correlated OR uncorrelated pink noise and adjust the pots to smooth I make little 1-3 db changes and the spectrum analyzer displays a virtual flat target response -- THEN when I gate the room (OR LISTEN) and measure the system it ends up being wrong, wrong, wrong. I also gated and made the adjustments to THAT target and found (it was better) all I needed was a -2 db dip at 5k and a +2 db rise at 2k to smooth out the high end. With the EQ's in place and these adjustments made the bass loses definition and power, and the dynamics get crunched and the music get's confused-- time to just play a little with the passive network between the mid and high horns..
Magnetar
That's dissappointing, isn't it? But it's lucky you can get away without too much correction. I have been interested in the Whites because other 1/3rd octave eq's I have tried do all of the nasty things you describe. Actually, that's why I really would like to get my hands on a pair of 4004's.
My biggest problem was about a 15-20dB peak at 120 Hz. The Q is so high that an RTA hardly notices it, but your ears sure notice it. It was obnoxious. It's a room artifact that I can't do anything about, so I solved the problem with passive LC notch filters. UTC used to make a variable inductor that makes easy work of the filter. Just slap a cap across it, load it with the appropriate resistance to arrive at the right Q and depth of attenuation, then dial in the screw on the side to tune out the notch. There's precious little in the way of side effects.
If your 5 kHz peak is near a crossover point, you're lucky.
I'm not dissappointed. I thought it would be nice to try and fix some recordings and possibly smooth my horns further. I guess I'll just have to live with the recordings. The notch filter you use will probably due less harm at a lower expensive than a White EQ. IMHO the 4004 will still have serious problems in the bass - especially if your horns will do the bottom octave well.-
Magnetar
The notch filter I use should harm the overall sound less than any equalizer, that's true. It would be nice to address some other response problems, though. Are you sure that inductor saturation was your problem with the Whites? If so, I would think you could back the level off until you have a comfortable amount of headroom and make the gain up. I suspect there are other evils at work.The speakers I am using now are TAD studio monitors (1601c woofers in reflex cabinets), and pretty muddy in the bass. I'm looking forward to moving them out of here.
If you want to fix some problematic recordigs, how about a mastering equalizer like a Pultec? A little pricey, though.
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