BiggerIsBetter

No cable, and I ended up disconneting everything so the only thing I had connected was the xover outs to the amp in, both are balanced and XLR. Both where plugged into my power conditioner (panamax) and I also tried plugging them both directly into the wall. With the crossover I was able to determine that the buzz is between 400-800hz. I also don't thing the impedance mismatch is the problem, even though 100 to 200000 is way over 10:1, the Audio Research BL1 (designed to convert unbal to bal into the VT-150 amps I am using has a 60ohm output, even lower than my xovers 100). I'm going to try other devices (like the BL1) directly hooked to the amp to see if there is the same buzz. Is so, it might just be amp noise exacerbated by the fact that I am using 116DB sensitive horn drivers with HUGE horns. Since the xover is pro and the amp is commerical I expect they are looking for different signal strengths, but I just dont get how that results in a buzz and if so what to do about it (I have not seen a balanced to balanced interface box)

As background: My chain is sources (mixed bal and un) to a Carver lightstar passive to an Apogee CRQ-12 parametric to a pair of BSS FDS-310 X-overs to 3 amps (2 bal, 1 not), to the speakers. All connection between the pre and xover are balanced XLR. I have a buzz, not a low hum. After hunting grounding loops and the like, I ended up with just the xover (no input), directly hooked to the amp with the worst buzz (the mid). Since the buzz was the same with no source connections, and I am going balanced to balanced and tried directly grounding the chasis of the 2 component and lifting the ground of the xover I have concluded that I do not have a grounding problem rather an impedance or sensitivity mismatch. The xover has an output impedance of 100 ohm and the amp (AR VT-150) has an input impedance of 200K ohm with a sensitivity of 2.3 v P-P. In order to get the buzz down to a barely acceptable level, I need to turn the xover output level to around -12DB. As a result, given that I am driving this with a passive, I have limited "juice" to drive an acceptable output level. Is this high noice floor (buzz) due to the impedance mismatch? If so, what are some options....I have a soldering iron and I'm not afraid to use it... Thanks!

Yep, It is likley somewhere in the laws of physics I replaced my 11.25" round tractrix horns with 27"x31" CD horns less than a week ago. Man are these things HUGE. This morning I walked by them and thought, if I skoot them over a bit I could get that big Jub horn in there no problem.

Very Interesting. I have a transformer hum on my citation 5.1 amp ONLY when the light in my room is in the dimmest of the 3 settings. I can solder and have lots of caps around, but am not exacle sure where those caps/diodes go, can you elaborate/simplify?

This is the same dilema that comes up a lot in conversatino about the Behringer digital unit. In summary, you want the highest level input (without climping) in order to maximize the amount of bit available. The best solution requires a volume control after the processor (which means know you need 2 since you are biamping)....hense the whole dilema. Either, do the best you can with the adjustment you have on your amp (i.e set to minimum and maximize the input to the processor) and put your head in the sand OR read everything that has been written about this for the Behringer on the various forums, prepared to be fustrated and have a head ache.

For the amperex, unless you bought them from a credible source as true NOS, I would check them often for emissions. I have had a large number of the amperex 6dj8 (various "version" from several sources), which tested just fine when I put them into use, go gassy....one taking a rather expensive amp with it....

How about one of you really smart guys read it and provide a reader's digest for the wanna be's llike me.

those things can have a "significant" amount of resistance. I would use a price of poper guage copper wire, it's cheap and easy....

Yep, Walnut, oiled finsih. From the pics the Ser Num shows 1985. Looks like GREAT deal for $500, and a fair price up to around $750. Looks more like sun fading than dust. The only quesiotn they raise is I thought that 1985 was a cornwall II, but in the pics the drivers are mounted from inside the cabinet (i.e. like a corn 1). I must be wrong on that, I'm expect someone knows the real answer...

You are likely to get lots of opinions. I expect you will get a good solid 100DB with that setup. Unless you want concert realistic levels and bass impact you should be fine. ....to me, the cornwalls don't provide concert realistic levels (limited by the bass abilities) with any level of power so if you are trying to get there you have more issues than just your amp.

Thanks Duke. After looking at all the options, looks like I am going with the P.audio C18-650LF. I was hoping to get 2240's, but got screwed on that deal and the 2240s are not that easy (or cheap) to come by.

For horn scoops, what is the criteria for a good woofer (18" and xover of up to 700hz if it matters)? My understanding is low Qts and high Fs (preferably Fs/Qts> 120) and low diaphram mass. Is that right, is there more?

The decision may also affect your level matching, i.e. if the mids and high are much more efficient the the low end driver, using a 16 ohm driver would be one way to close the gap.

djk, thanks for the info. Not sure I completely get it, but did have a specific question on the formula's under Fig. 6. If you take a 2240 with a Qts of .24 and a fs of 28 hz for example, we would get: flc = .24 x 28/2 = 3.36 fhm = 2 x 28 / .24 = 233 That seems right for the high cutoff, what wrong with the calc for the low (i.e. 3.36). I would have expect a low cut of around 40hz.

The 18A-2 has a Fs of 28 and a Qts of .29. Now I'm really not sure what several places are advertising as an Omega Pro 18 with a Qts of .24, it's not the 18A or A or the 18A-2. As an example, here parts express lisitng (they call it an 18A) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-428 I doubt it is a typo since most places list the spec as 28 Fs and .24 Qts Right now I am using a 400 hz round tractrix, crossed over at around 700hz. If/when I get a bigger horn I would like to try to go as low as 225hz on the crossover with the BMS 4592. Everyone is telling me the compression driver will sound like crap that low, but I think these drivers will do it with no problem so I need to hear it to believe it.