Active Crossovers

[Coytee]

Rudy,

Mike & these guys know have forgotten more about this stuff than I've ever known so take that reality into context here.

I also had some hum issues when I was first putting things together. I was mixing some RCA and XLR equipment (Peach preamp/DX38). I also had a mix of RCA and XLR amps.

One thing that was suggested I try was an Art Cleanbox http://www.bhphotovideo.com/c/product/288115-REG/ART_CLEANBOX_CLEANBOX_Bi_Directional_Level_Matching.html

There is another brand as well, I think it's called Rolls. Allows you to take your RCA and convert it to XLR while simultaneously, allowing an XLR to be reconverted back to RCA.

I tried it and it did get rid of a lot of my issues.

Just between you & me, it also seems that some dufas who soldered his own XLR cables, cross wired one of them and that was at least, partially responsible [:#]

I've hammered out most of my issues by now and one thing I did not want was yet, another item plugged into the wall so my Cleanbox is currently gathering dust. Although they're not terribly expensive, you are welcome to try it and see if it helps.

It also has some gain control knobs on the front so you have a bit of level matching ability with it.

I didn't use store bought XLR/RCA adapters although I now have a handful of them in my drawer. I have finally managed to kill most of my noise issues and that was done primarily by fixing the wire that was cross wired and then balancing the gains between my stuff. Oh.... something else that I would not expect to be an issue for you. I have my two Crowns plugged into a power strip. I think this is a cheap power strip as I will sometimes get a hum in the system and for the longest time, only knew that if I "wiggled the wires" that are amassed behind everything the hum would at times, go away. Today, I now know where it is. It's the power cord (plug) of one of the crowns where it goes into the strip. The strip isn't offering much of a contact in there somewhere and when the plug gets moved within the outlet, the hum comes back or goes away.

Now that I know exactly where the issue is I just live with it since I can fix it in a moment if need be and I'm not going to buy things to fix a problem upstairs that might not exist once I move things downstairs and have some dedicated outlets for each amp (instead of using a power strip).

All that to say..... if you want to fiddle with the Cleanbox, they're cheap enough.... and/or I'd be happy to send you mine.

[Rudy81]

Coytee, thanks. If I neet to try out the box, I'll let you know. Now I'm having to learn about grounding issues, pro gear racks etc. Like you, I don't need to plug more stuff into my power source behind the gear.

I really need to try to solve the issue by staying all balanced. I just need to figure out how to reduce the hiss when going strictly balanced. So close, yet so far....

[Rudy81]

Regarding the XLR to RCA cables, I have been reading this informative page http://www.rane.com/note110.html trying to figure out why these cables pick up so much RFI. I tested the cables and find that pins 1 and 3 are hooked together and go to the shield of the RCA connector. Pin 2 is connected to the center RCA pin. Oh, and the XLR case shield is also hooked up to the shield of the RCA connector.

Based on the diagrams on the linked page, that is cable setup number 6 for "cross-coupled" outputs only. Whatever that means.

Audio engineers need to make home and pro audio gear a little more compatible to make my life easier. []

[Rudy81]

After carefully reading the Rane paper, I decided to try the a home made XLR to RCA using the two combinations mentioned in the paper for XLR out to RCA in.

The results were the same noise problems for hookup as example six. Setup 4 in the paper is noisy during EV boot, but when it finishes booting, I get the same loud hiss I got as when using balanced only. Very strange and confusing for a novice.

[Rudy81]

Rudy it sounds like with the XLR to RCA cables installed you are probably experiencing grounding issues which needs to be solved if this is the amplifiers and hook-up you prefer.

The advantage of equipment being installed in a pro rack is it electrically ties all the equipment cases together resulting in less ground volatge differences between the equipment. These ground voltage differences can be picked up and amplified causing hum, hiss..etc... and that is why I have suggested that you experiment with running wire between the amplifier's cases and other equipment's cases in your system to see if this will eliminate your noise problem when using the XLR to RCA cables.

If you decide to stay with Balanced XLR connections which from what you have said so far indicates to me just a gain issue then we should be able to solve that with proper attenuaters.

Hang in there Rudy

mike tn

What attenuators do you suggest? BTW, I took apart one of my balanced cables and note that the G (case ground) is not connected to anything. What is the normal setup for the G connector in the XLR?

[Don Richard]

Setup 4 in the paper is noisy during EV boot, but when it finishes booting,

It is important in a bi-amped setup to turn the amps on last and off first. You should not have your amps even on while the EV is booting.

[Rudy81]

It is important in a bi-amped setup to turn the amps on last and off first. You should not have your amps even on while the EV is booting.

I did not have any problems having the amps on first with the balanced connections. With unbalanced, it picks up some strange noises. Problem for me is that I need my HT system to be pretty much totally automatic to turn on and off. I'm not always here when the family wants to watch a movie.

Regardless, for the time being, I can't get it to work properly either way without RFI or hiss, depending on how i hook it up.

[Coytee]

It is important in a bi-amped setup to turn the amps on last and off first. You should not have your amps even on while the EV is booting.

I turn mine on last and off first, however, I just hit the switch. Truth be told, they are usually powering up before my Dx finishes and EASILY do so before my Peach gets out of its 45 second protection circuit.

Not wanting to sound rude by why is it so important that even the crossover be past its boot stage?

[Rudy81]

I wanted to wrap this cabling thing up for the next poor enthusiast who has this type of cabling problem and stumbles onto this thread. BTW, I'm going back to edit my original post and make an index for this thread to weed out the superflous garbage that got away from the original topic.

1) Hooking up home and pro audio gear can be problematic. I have read many pro articles that warn of such problems, in particular the Rane article mentioned earlier.

2) Hooking up a totally balanced system if by far the best way to go to prevent noise, hum etc.

3) Using XLR to RCA cables can work, but can pick up noise that is avoided in a totally balanced system. I had some initial problems that I initially blamed on the XLR to RCA cables, but that problem was solved by following mike tn's advise to connect all the equipment chassis to each other.

4) Since we are using highly efficient speakers, it is very possible ( my problem right now) to pick up the noise floor in the mid and tweeter drivers....producing hiss.

Solution to the hiss is still under investigation. The optimum idea is to use amplifiers that offer gain attenuation. I will be looking into the possibility of getting some sort of XLR attenuator.

So, now back to using an active crossover with Khorns.

[cfelliot]

Rudy,

I was reading the DC-1 manual tonight and came across the following:

"Optimal signal-to-noise performance is obtained when the nominal (average), input level consistently lights the +3dBu (green) and/or +6dBu (Yellow) LED indicators."

This can't be done with the DC-1 when fed by a preamp/processor the attenuates the input via a volume control for different listening levels. The DC-1 has no master gain control and would require that one be constructed post processing.

These guys http://www.minidsp.com are working on a board that provides this feature. Their ADC and DAC sections are not the same quality of the DC-1, but they're on the right track.

I envision a system where I stay digital from the source through the DSP and then to the power amps.

Just FWIW,

Chuck

[Rudy81]

Chuck: So are you saying the problem is with my source pre/pro? I am not sure I understand. Is that different than the DX38?

[cfelliot]

No, not really! Your preamp is fine!

The issue is that as you lower the signal into the DC-1 via the volume control it gets less of an input signal to convert to digital.

So, it has fewer and fewer bits to work with and I think this is why you are hitting the noise floor.

Ideally, you could plug a CD player directly into the DC-1. That would give you around a 0db input signal. If it is above that this is the use of the -6db switch.

Now the problem is that there is no system volume control!

I'm not sure there is a solution with the DC-1 unless a ganged volume control is constructed.

I don'r really know anything about the DX38 and I'm pretty new to the idea of digital DSP crossovers.

Others may have some thoughts?

Chuck

[Don Richard]

Not wanting to sound rude by why is it so important that even the crossover be past its boot stage?

Devices with a CPU put out a lot of EMI/RFI when active, and that seems to be the source of part of his noise issues. I realize that the xover box mutes the outputs during this process, but his issue is "airborne".

[Don Richard]

I did not have any problems having the amps on first with the balanced connections. With unbalanced, it picks up some strange noises. Problem for me is that I need my HT system to be pretty much totally automatic to turn on and off. I'm not always here when the family wants to watch a movie.

On last, off first is standard operating procedure when using pro sound system, and that is the equipment and setup that you now have. This is to prevent driver damage because you have no filters or protection between the power amps and the drivers. If any low frequency energy gets to your tweeters, they are toast. For family operation there are power sequencers, such as the Furman PS-PRO II SMP 3 step sequencer and power conditioner. This will automate the process and allow all of the equipment to be plugged into a filtered and protected power source with a common ground. This should also help to clean up EMI issues that you are having.

Balanced is the way to go. You need attenuation at the amps to remove any hiss issues.

[Rudy81]

Don: I'm beginning to get the picture. Thanks for the lead on the power sequencers. Now the problem is the attenuation at the amps. Perhaps the way to go is to get pro amps rather than what I am using now. Any suggestions? I don't need a ton of power, just good sound.

[Coytee]

Now the problem is the attenuation at the amps. Perhaps the way to go is to get pro amps rather than what I am using now. Any suggestions?

You are welcome to borrow my Dx38 and see what you think.

You are welcome to borrow my Art Cleanbox and see what you think.

You are welcome to borrow my HP 400 thingy-do-which box and see what you think.

I ain't sending you my Crown amps!!! (point being that I'm not willing to give them up like I am the other items so maybe that will give you a hint as to my thoughts on them) []

[Rudy81]

You are welcome to borrow my Dx38 and see what you think.

You are welcome to borrow my Art Cleanbox and see what you think.

You are welcome to borrow my HP 400 thingy-do-which box and see what you think.

I ain't sending you my Crown amps!!! (point being that I'm not willing to give them up like I am the other items so maybe that will give you a hint as to my thoughts on them)

As always, thank you. You guys are too generous. I have decided to go totally balanced. I think I will focus on getting amps I can attenuate. What crowns do you use?

[Rudy81]

I finally finished hooking everything back up. Sitting here listening again. Very nice when music is playing. I will have to tackle the hiss thing in due time. I'm in too deep to give up now.

I decided last night to clean up that rat's nest behind my gear. It is now a little more tidy. All chassis are grounded to each other. Everything is hooked up balanced except for the rear and side effects speakers. For the time being, they are XLR to RCA.

Not to open up a can of worms, but am taking suggestions on pro amps. I don't think much power is needed to drive the tweeters and mid.

[Don Richard]

Now the problem is the attenuation at the amps. Perhaps the way to go is to get pro amps rather than what I am using now. Any suggestions? I don't need a ton of power, just good sound.

Crown D series amps are low distortion, low power amps often used in studios and for broadcast monitor applications. The D-45 is about 25 WPC and the D-75 is about 40 WPC.

[Rudy81]

Ahh, it pains me to admit it, but I give! I have spent the better part of a month thinking about, researching and putting together this active system. Problem came to a head last night when I finished putting together my system for the millionth time, turned it on and the darn hiss is just too much. Being anally retentive, I am used to a totally silent system when it is fired up and idling unless I stick my head in the horns. I tried again this morning and this afternoon only to be foiled again. I have tried various cables, balanced, unbalanced, etc. Nothing gives me the nice quiet system I have in passive mode.

This active setup creates such a gain problem with my amps that the hiss is clearly audible anywhere in the room. I figured I would just live with it for a while. I was wrong, I can't live with it for 10 minutes.

I really wanted to play with the active setup and think I would really like it. Sadly, the last three weeks have been incredibly frustrating. I never really got past the setup stage.

At some point later on I might try again with pro amps vs. home audio amps. For the time being, the stuff I purchased for the experiment is going back on eBay. This is so frustrating.

However, thank you guys for all your help. I certainly learned a lot.

[:'(]