Pro amps for HT

**Ayreonaut** · **07-15-06, 11:48 AM**

Has anyone here had experience using pro amps for HT? I've seen it recommended in a couple of places. The watts/dollar and reported perfomance is very enticing. Right now I'm looking at a two channel amp to drive my mains.

The one concern I have is using unblalnced pre outs from my receiver to signal balanced inputs on a pro amp. Has anyone tried this? Would using a transformer isolator to eliminate hum comprimise the signal quality in any way?

**brucek** · **07-15-06, 01:12 PM**

Quote:

The one concern I have is using unblalnced pre outs from my receiver to signal balanced inputs on a pro amp.

The only proper way around this is with an unbalanced to balanced converter. This of course adds a device in the chain (and noise).

The higher the cost, the better the specs usually on these devices. I've seen them in the $300US range.

here's one
here's another. The specs on this one aren't as good as the first one.

I would go with an amplifier that had the same interface as your receiver/processor has and not go through the conversion.

brucek

**Ayreonaut** · **07-15-06, 01:41 PM**

Well, they can be had as cheap as $16.99 from Radio Shack. Behringer has a much nicer one for $99. But I suspected what you have voiced: A transformer in the signal path has got to affect the sound, maybe significantly.

I wonder what all the raves are about from enthusiasts who have had good luck with pro amps. They haven't mentioned this problem in their posts.

**brucek** · **07-15-06, 02:31 PM**

Quote:

they can be had as cheap as $16.99 from Radio Shack

I hope you didn't want an opinion on that?

Quote:

Behringer has a much nicer one for $99

What's the model number?

Quote:

I wonder what all the raves are about from enthusiasts who have had good luck with pro amps

I suspect they have balanced outputs on their processors.

brucek

**Ayreonaut** · **07-15-06, 02:53 PM**

Quote:

brucek wrote:

I hope you didn't want an opinion on that?

Yeah, just kidding around.

But not kidding around, what are the chances of avoiding a ground loop if the amp and receiver are plugged into the same power strip? If that doesn't work, what about a cheater plug? Some people claim that there's really no problem with using one.

Here's the Behringer:

ULTRA-DI PRO DI800
Professional Mains/Phantom Powered 8-Channel DI-Box

The ULTRA-DI PRO DI800 is a professional mains/phantom powered 8-channel DI-box. It converts unbalanced line inputs into balanced outputs, featuring optional mains or phantom powered operation. Its servo balanced operation assures ultra-flat frequency response. Additionally, it allows direct connection to speaker outputs with up to 3,000 Watts. A ground lift switch as well as input attenuation/gain per channel round off this powerful device.

**brucek** · **07-15-06, 03:30 PM**

Quote:

what are the chances of avoiding a ground loop if the amp and receiver are plugged into the same power strip? If that doesn't work, what about a cheater plug? Some people claim that there's really no problem with using one.

Do you have a ground loop that is causing a problem?

With regard to cheater plugs, I have a standard speech I make that is part of the BFD Guide and goes like this:
"The cheater plug effectively eliminates the third prong on the AC plug. The 'third prong' is the electrical safety ground and is there to protect you and anyone who uses your equipment from electrocution. This safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment when equipped with the three prong plug. The third prong connects back to your service panel (where it is bonded to the neutral wire), and from there is connected either or both to your house plumbing or external ground rod. On equipment with a third prong, the metal case and external metal parts are all connected to this safety ground when you plug the electrical cord into the wall. If a component fails inside a piece of equipment and the 120 volts shorts to the equipments case, then that case is now live and can electrocute you. If the safety ground was attached, then a breaker would trip to indicate you had a fault."

Use cheaters at your own risk.....

Quote:

Here's the Behringer: ULTRA-DI PRO DI800

Yeah, that's a standard DI box (as they're called). The better quality ones don't add too much noise. You'd really have to test it out and see how it sounds to you first.

Why are you bent on a PRO amp? There are lots of regular amplifiers around that do a great job and don't cost too much. There's nothing special about a PRO amp other than it has balanced inputs and requires levels that a lot of regular receivers won't match...

brucek

**Ayreonaut** · **07-15-06, 03:45 PM**

Quote:

brucek wrote:

Do you have a ground loop that is causing a problem?

No. I was just wondering if this would be a deal breaker.

Quote:

brucek wrote:

Use cheaters at your own risk.....

Yes, they scare me too. I don't know if it makes a difference, but a cheater on an 1800W amp scares me more than a cheater on a line level BFD.

Quote:

brucek wrote:

Why are you bent on a PRO amp?

Oh, I'm not really. I'm just poking around and exploring my options. The watt/dollar value is pretty tempting on the pro amps and its hard to ignore.

Got any budget amps you'd like to recommend?

**brucek** · **07-15-06, 04:37 PM**

Quote:

I don't know if it makes a difference, but a cheater on an 1800W amp scares me more than a cheater on a line level BFD.

No difference. It's the AC line voltage that is the culprit...

Quote:

Got any budget amps you'd like to recommend?

Not really, I do like Rotel and Outlaw. They're both conventional amplifiers with decent specs and good bang for the buck.

brucek

**Wayne A. Pflughaupt** · **07-16-06, 04:46 PM**

Quote:

Ayreonaut wrote:

Here's the Behringer:

ULTRA-DI PRO DI800
Professional Mains/Phantom Powered 8-Channel DI-Box

The ULTRA-DI PRO DI800 is a professional mains/phantom powered 8-channel DI-box. It converts unbalanced line inputs into balanced outputs, featuring optional mains or phantom powered operation. Its servo balanced operation assures ultra-flat frequency response. Additionally, it allows direct connection to speaker outputs with up to 3,000 Watts. A ground lift switch as well as input attenuation/gain per channel round off this powerful device.

Daniel,

You have to keep in mind that a direct box is typically used, and designed for, musical instruments, not hi-fi listening. I don’t know if I would expect it to have audiophile-worthy specs. Also keep in mind that the instruments DI’s are intended for – guitars and electronic keyboards - have extremely low signal outputs. Feeding one a signal from a home theater pre-pro might overload it. Don’t assume that the speaker-level capability of this Behringer means it has miles of headroom. It probably has separate inputs for that, or a switch enabling that function (i.e., to pad down the signal).

I’ve had bad experiences using pro gear in my HT system in the past, so I’d be wary of anything you’d want to use. Don’t automatically expect that it will be clean or accurate until you give it a careful listening evaluation. I think I’d look first at pro amps that other audiophiles have used successfully. Also, see what kind of gear they have in the rest of their system to gauge how reliable their recommendation is. For instance, I wouldn’t be terribly impressed with a rave review of a pro amp if I saw they bought their speakers at Best Buy.

Also note if they’re feeding it a balanced or unbalanced signal. It may not be an issue at all, as many pro amps carry 1/4” inputs labeled “Balanced or Unbalanced.” I’ll let brucek comment on the legitimacy of using these inputs as unbalanced.

Regards,
Wayne

**Ayreonaut** · **07-17-06, 11:39 AM**

Thanks for your informative answers guys. Even if the pro gear did sound good, it may be more trouble than its worth, huh? I'm certainly not going to pass the signal through a transformer. I'd rather spend the money on the amp.

**Ayreonaut** · **07-17-06, 08:01 PM**

Quote:

Wayne A. Pflughaupt wrote:

I’ve had bad experiences using pro gear in my HT system in the past, so I’d be wary of anything you’d want to use. Don’t automatically expect that it will be clean or accurate until you give it a careful listening evaluation. I think I’d look first at pro amps that other audiophiles have used successfully. Also, see what kind of gear they have in the rest of their system to gauge how reliable their recommendation is. For instance, I wouldn’t be terribly impressed with a rave review of a pro amp if I saw they bought their speakers at Best Buy.

Wayne,

I was searching around some forums for information on amps. I traced this pro amp idea back and it leads to you!

Last July (on another forum) you recommended Carvin amps to Steve Callas for his subwoofer. He bought one and last November he pitted his Carvin HD1800 full range in a blind listening test against the PS Audio HCA-2. He and his friends could tell no significant difference between the two. And that got me turned on to trying a pro amp to drive my mains.

Small world, isn't it?

Daniel

**JimPeitersen** · **07-20-06, 01:50 AM**

I use a pro amp for subwoofer duty, but I have tried them full range and to be honest didn't notice any difference from "home" stereo amps. The input sensitivity of some pro amps give people problems, and fan noise is an issue. If you were to pick a nice "studio" amp or one of the Crown K series I don't think you would have any problems - and the headroom from the extra power is always good

JP

**Ayreonaut** · **07-20-06, 02:30 PM**

I went ahead and ordered the Carvin HD1800 just to try it out.
This is the one that Steve Callas found very similar to a PS Audio amp.
It does accept unbalanced 1/4" tip-sleeve inputs.

Price - $319 + S&H
Power - 2 x 600W RMS into 4 ohms
Fan Noise - 53db at 1 inch away
Sensitivity - (4Ω, Vms) 1.0V
Damping Factor - >500
Slew Rate - 45v/us

I'll let you know how it works out!

**Sonnie** · **07-21-06, 01:29 AM**

Interesting... will be looking forward to your thoughts. Sounds like a good price too.

**Mark Seaton** · **07-21-06, 01:12 PM**

Hi Guys,

Better pro amps can function very well in the home with some attention to gain and noise issues. One of the biggest problems that I see so many blow off (pun intended) is fan noise. Dismissing the importance of the noise floor in a home audio system is a major oversight. Remember that "quiet" is the other half of your dynamic range. If you have your equipment in a sealed/enclosed rack or in an equipment room, pro amplifiers can be great options. While they have discontinued the line, QSC's SRA amplifiers were killer options for home theater. The DCA line and I think some of the new PLXII amps are similar, but with louder fans.

If you are looking for big power that you can't really find or can't find at a realistic price for home theater, some of the best sounding amplifiers in the pro market are from LAB GRUPPEN. Their fP series and newer 4 channel amps are ones I've been seriously looking at for use in theaters with equipment closets. They are in no way bargain amps, but the do have very good value to any other options that provides honest power at very low distortion as they do.

**brucek** · **07-21-06, 01:54 PM**

Quote:

Remember that "quiet" is the other half of your dynamic range

Completely agree Mark.

It's the one real problem I have always had with Pro-Amps, HTPC, Projectors, etc. Those pesky fans.

That extra dollar you pay to have a high end audio system can be quickly eliminated when you introduce outside noise.

In critical listening, the subtle sounds that separate high end from the rest of the pack is eliminated when your fridge in the kitchen turns on......

brucek

**Ayreonaut** · **07-21-06, 02:57 PM**

My DVR emits a very quiet hum, and my rather quiet fridge is in the next room with an open doorway. The HVAC system is by far the loudest when it's on. Such are the comprimises of domesticity for the average listener.

I'm a fire protection engineer, and my work includes designing systems for theaters and performing arts centers for universities. I work with acoustical engineers and architects and have observed the lengths they take to isolate the auditoriums from external noise. Beyond room treatment, those measures include structural isolation and low velocity air ductwork to name just two. It's absolutely critical to have virtual silence when you're listening to an unamplified actor in a large hall.

Such measures seem too extreme to even mention in the context of HT. But I can see myself taking mechanical systems into consideration in a future construction of a dedicated HT. At least I could minimise the noise coming from the HVAC ducts and put any equipment with fans in a dedicated closet.

Back on topic, I chose one of the quietest budget amps I could find. Even so, one has the option of a fan modification if necessary. You can reduce the noise by replacing the fan with a quieter one or simply installing a resistor to reduce the fan speed.

**Sonnie** · **07-22-06, 12:42 AM**

In our HT room... you can hear a pin drop on the carpet. Well... maybe I couldn't but Superman could.

Generally you can mod those fans with quieter ones with no adverse effects. I wanna say I've read something on the Behringer EP2500 I have, where you can rewire it to slow it down. Mabye it was at the CULT where I read it, but a lot of people have done it and again, absolutely no adverse effects that I've heard of anyway.

**Ayreonaut** · **07-26-06, 04:33 PM**

Well, gentlemen, I have taken possesion of my new amplifier.

I connected the pre-outs of my receiver (Denon AVR1905) to the inputs of the amplifier (Carvin HD1800) with RCA to 1/4" unbalanced cables. I plugged the amp into the same power strip as the reciever. There was no ground loop hum; I shouldn't have worried so much about that.

I read two ideas about how to set the level.
1. Set the reciever's pre-out to +0 and turn the amplifier gain down.
2. Set the amplifier gain to the max and adjust the receiver's pre-out down.

Option 1 is supposed to protect the speakers. If the reciever throws a spike, the amp output is attenuated and won't blow my speakers which are only rated to handle 150W. This amp is supposed to deliver 600W into 4 ohms, so being careful sounded like a good idea. I set it up this way, with the receiver at +0dB and the amplifier gain at -15dB.

I really wasn't that thrilled. I think the bass sounded a bit punchier and better damped. But my litmus test is the explosively dynamic orchestral soundtrack from Spirited Away. (In the store, I heard a Musical Fi amp and Revel Concerta speakers pass this dynamics test with flying colors. I just have to get there.) Just before I installed the new amp I listened the track "Dragon Boy" one last time from the receivers's speaker outputs for a comparison. With the new amp installed I listened to it again. Not really that much different. At the level I was listening to (-6dB) the horns glared and the cymbals sizzled. Just like they did before. I went to bed with doubts about keeping the new amp.

The next day I decided to try setting the level the other way. I turned the pre-out level all the way down to the minimum -12dB. I turned the amplifer gain up to -1dB to match reference level. I've heard not a hint of click, pop or thump when powering up the amp or receiver, so it seems safe enough to try it this way.

BINGO! I played "Dragon Boy" again at the same volume level and the difference was a revelation! I played it again at Reference Level, and still amazing. All of the hash, sizzle and blare is gone. At reference levels its incredibly easy to listen to.

My guess is that the reciever's pre-outs were clipping when asked to reproduce reference level. At -12dB there is no problem. Now I can listen to the amp unhindered.

While my wife was out I popped in a bunch of action movies and listened to them all at refence level very comfortably. It seemed so natural, I wondered why I had ever listened at levels below this. (Except LotR FotR. That movie is recorded HOT.) When my wife came home I played part of the DVD Spirited Away for the kids. Incredible. My wife walked into the room and began watching it with us, smiling. After a minute I remarked to her that we were listening to this at reference level. The volume is set to 0. She hardly believed it. "Really?" She knew that 0 was unlistenable, yet here we were listening to it and it was completely natural. I'm still astounded. We watched Star Wars III last night at reference level. Awesome, awesome, awesome. She never asked me to turn it down.

OK, I know the experienced among you are rolling your eyes,

since you've been enjoying this for years and have moved on to other considerations. But my system is just now reaching tonal neutrality and high levels without distortion. I'm thrilled to be at this point and excited about what lies ahead.

For $319, how can you beat that?

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