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Discussion Starter #1
I have a question/problem....

I have a new Mackie FR 800 amp to run my dual subwoofer system. I have two RCA style jacks on the back of my home theater processor labeled as "Sub 1" (out) and "Sub 2" (out). I have built two cables, each with a RCA plug on one end of the cable (for the processor sub outputs) and a 1/4" TRS phono plug on the other end for the amp input.

My question is this....the back of the amp has two "balanced" inputs where the plugs go in. The issue I am having is that the signal from the processor is probably a mono "unbalanced" signal. It is going into the "balanced" input of the amp. I have it hooked up and it sounds horrible. The sound is very low and muffled. I have to turn the gain (on the amp) to max level just to get it to an acceptable level.

If anyone can offer me the solution to my problem, I would be extremely grateful.

Thanks in advance for any help offered.....
 

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Does your HTR actually have 2 sub preouts? Have you checked the settings in your HTR? Also try using only one of the preouts if you have a splitter lying around and see what happens.
 

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Discussion Starter #3
Yes, my processor has (2) outputs designated for subwoofers. I have not tried a splitter yet.....what would the splitter do to solve my problem?
 

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I have a similar amp with balanced 1/4 mono inputs ..the connector determines whether it will be balanced or not.. and that IMO is not whats your problem. Have you done an ohm test on the cables you build?
 

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Elite Shackster
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What HTR are you using?

Running pro audio amps at full gain is not uncommon, in fact in industry it is usually set at this level unless there is some need for attenuation. If not set at full, the amp can never put out it's rated number of watts.

There is the possibility that you may require a line boost between the receiver and the amp. Home audio uses levels that are about 14db quiter than pro audio, but this issue is not common. Check the settings on the receiver and make sure that LFE is being sent to the sub and dynamic range compression is off. Muddy sound would not be attributed to a balanced vs unbalanced connection. If you had a 60hz hum that wouldn't go away or radio stations playing through your sub it would be a different story. ;)
 

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Discussion Starter #6
Thanks very much for all of your feedback....

I am running a Sherwood Newcastle P965 for my processor.

I have triple checked the cable I made with a meter and everything looks good with it.

The settings on my processor are the same as they have always been...there is a difference that I did notice though. The processor allows me to determine the cross over point for the subwoofer. I have always left it at 80hz. Just to test it out, I switched it to 60hz, with no change and also to 40 hz with no change. The processor does not act like it is sending the crossed over signal to the subwoofer. It sounds like a straight signal.

At 40 hz, I am guessing you should only hear deep bass. I can hear voices and sounds of all kind. It sounds like full range music coming through.....I'm really puzzled. I thought hooking this amp up would be a piece of cake.
 

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The processor's 80 Hz (or 60 Hz) low pass filter output for a subwoofer is not a brick wall filter. It should only slope at 6 dB per octave.
 

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The filter in the Sherwood pre-processor is not steep. It will allow some of the midrange frequencies through (although greatly reduced) so you can hear some vocal voice sounds in the sub.
 

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Discussion Starter #10
Thanks for the feedback. But, that's not good to hear....

What are some possible solutions for the low signal volume and crossover issue?

Any suggestions?
 

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You will have to try another HTR with that amp to see if it works right. I know there is a subsonic filter in the back of it... did you try playing with that?
 

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Discussion Starter #12
One more thing....

My subwoofer drivers for my final build are on order and have not come in yet. There are each rated at 4ohm's. I do have the option of ordering the same subs rated at 2 ohm's each. This would give me some more out of my amp.

At 4 ohm's my amp generates 300 watts stereo.

At 2 ohm's my amp can put out 480 watts stereo.

This way I can get more power to my subs and maybe solve the low volume signal issue?

I'm not sure.....

Do most people on this forum run 2 ohm subs?
 

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Discussion Starter #13
I do have a sub sonic filter....I have it set on the "off" position based on the manufacturers recomendation..... I figured my subs can easily play below 30 hz.
 

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I would not think that there is any crossover issue. Bet it is working as designed/intended.

For low signal volume, many of us use an ART Cleanbox or equivalent to boost consumer line level audio (-10 dBV) to pro line level audio (+4 dBa).
 

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For low signal volume, many of us use an ART Cleanbox or equivalent to boost consumer line level audio (-10 dBV) to pro line level audio (+4 dBa).
Quick question:

I been told that if the pro-amp has the RCA connector is just plug and play ... and I'm wondering (I'm not an expert, so please explain); If all consumer audio use a -10dBV signal and pro-audio +4dBA; when you get a pro-amp with RCA's (no ART cleanbox is need it)... Do this mean that the amp will get the -10 signal and do a conversion internally to use as if a +4 signal is used and will output the maximum that is capable???
 

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Elite Shackster
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Quick question:
Do this mean that the amp will get the -10 signal and do a conversion internally to use as if a +4 signal is used and will output the maximum that is capable???
Yup!

If possible you should avoid the ART Cleanbox as the frequency response rolls off on the lower frequencies. Only use it if you have no other choice.

This doesn't sound like a level matching problem as much as a frequency response issue. You say your woofers are on their way, what are you using now? What was in your setup before and what has changed?
 

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Discussion Starter #17
Well...let's see. I was running a pair of powered HSU subs and I decided to buid my own subs. The cabinets are built and the drivers are on their way (I will be running these subs passive). The amp came in this weekend and I hooked it up. I had a pair of 10" subs (wired to 4 ohms) from my car that I hooked up just to hear how well the amp would perform.

My processor was setup and running like it has for the past several years (with the HSU subs). Nothing changed there...

The 10" pair sounded absolutly horrible. The amp was set to "max" just so I could hear the sub over my main speakers. The "clipping" light kept flashing. It was the poorest performance I had ever heard. The whole experience was a big disappointment. This amp on paper is supposed to knock the fillings out of my teeth. This amp, the way it is currently running, would not wake my dog up.

You mentioned a frequency respsonse issue...what is that? What would that mean?

Thanks for your input!
 

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Discussion Starter #18
THXGoon....How do you have your AVR hooked up to your Behringer2500?

You are correct about the ART. I want to avoid it if I can.
 

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Elite Shackster
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Hmm, that's interesting on your experience with your 10" subs. I wouldn't expect a pair of 10's to compete with HSU, and being that they are from a car they may not have the proper parameters to perform the way you would expect in a home theater environment. Most of the time car subs are tuned higher than a HT sub. Are the 10's in any kind of box or are they just in free air?

Given that info I don't think there is anything wrong at all, you may just need to wait for your new drivers. The only thing that concerns me is the clip lights. Either the 10's are presenting a strange load to the amp or it's playing really really hard.
 
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