Need amp that's stable into 2 ohms [Archive]

nightflier

03-20-2009, 03:03 PM

I'm trying to help out a local school with the purchase of a new amp for their exercise room. They were originally using a Harman Kardon 3480 Receiver to drive 6 Infinity Primus 160 Speakers using a speaker selector box. Well after a year the amp in the receiver died. I considered these speakers pretty easy to drive (90dB/8Ω), but the HK amp couldn't do it, I guess. The space is about 2000 sq. feet, so they probably turned the volume up pretty high.

Anyhow, I gave them an old preamplifier I had and I am now trying to find them an amp that can drive the Infinity speakers. I presume the amp has to be stable down to 2 ohms to do this, but I really don't know. The problem is that they have a budget of around $200, which I know is very little. I've looked at pro amps like the Mackie FR800, but I really am not sure if this is what I should be looking at. Any help?

02audionoob

03-20-2009, 03:49 PM

You could perhaps try an Adcom GFA-545 or 545II with that budget. Maybe you could even find an Adcom speaker switch. They have a 'protection' button for amps not designed to handle the low-impedance loads.

Edit: I didn't realize those commercial amps are actually fairly inexpensive. That does seem like a better idea.

Kevio

03-20-2009, 04:46 PM

Yep, this is a commercial application blows that consumer right stuff up. I'd be looking for a commercial or MI amp. QSC GX3 (http://qscaudio.com/products/buy_now/buy_now_family.php?family=GX) might be a more robust choice.

blackraven

03-20-2009, 07:45 PM

You could try find this amp used http://www.audiophileliquidator.net/product_info.php?cPath=35_24_51&products_id=1206

or this one which sells for under $400 http://www.audiophileliquidator.net/product_info.php?cPath=35_24_51&products_id=532

Mr Peabody

03-20-2009, 07:47 PM

I don't know their price but Sherbourn makes some multichannel amps with switching designed for multiroom systems that would be perfect. I don't know if they are stable to 2 ohms but with this design it wouldn't need to be.

blackraven

03-20-2009, 08:12 PM

Here's an 8 channel amp http://www.speakercraft.com/files/files/file/267.pdf

Any multichannel amp is going to cost a bundle.

RoadRunner6

03-20-2009, 09:03 PM

I think you will find that with a reasonably decent switching box the impedence will not drop below 4 ohms with 3 sets of 8 ohm speakers (the impedence thru a switching box does not drop to the low impedence levels like it would if you had all six speakers hook up in parallel). That said, you would think that the HK receiver which has a fairly decent amp as far as stereo receivers go would be OK driving a 4 ohm load thru the swithing box.

On the other hand, these are not PA speakers. They are medium sized bookshelf speakers designed for homes. They should be OK at reasonable levels. However, they do not put out low bass. They probably start rolling off about 60-70Hz and are down to about -3dB's at 50Hz or so. I can imagine that in this circumstance somebody might have been boosting up the bass contol to try and get more bass from the speakers. This would play havoc on the amp in that receiver. I've seen this happen many times at parties, etc. where some idiot cranks up the bass or "loudness" control to get more bass. Of course, this will soon overtax the amp. If this is the case, I can see why it didn't last long with this type of abuse. In home speakers something much more efficient like Klipsch speakers would have been a better bet.

I suggest that the solution for this school would be to make sure they understand not to touch the bass control, leave it at the medium setting and to leave the loudness control off. Make sure the amp has adequate ventilation.

I would stretch the budget a little and go for a quality amp. This UPA-2 amp from Emotiva should have no problems at 4 ohms and is a steel for $299.

http://emotiva.com/upa2.shtm

The pro amps linked by Kevio might be the heavy duty way to go. Also, check that switcher box spec sheet and see how much power it will handle

RR6

basite

03-21-2009, 03:28 AM

I'd say 'Get a Mcintosh', but that budget sorta limits options :p

nightflier

03-23-2009, 11:33 AM

Thanks for the input. It looks like the only way I can squeeze this into their budget is to buy used. The QSC amp might be a good bet, but the specs say it is only good into 4 ohms (correct me if I'm wrong). The speakercraft amp is another option, but well over the budget I have for these. If I go used, any recommendations on places that are reputable (as opposed to eBay and that sort of thing)? Pro amps tend to suffer a lot of abuse already, so buying used is lot more risky. Adcom would be nice, but I don't know how well they would handle a 2 ohm load. And older NAD maybe, since they have decent protection circuits?

Regarding the bass, that's something that I can tell them, but eventually someone, at some point is going to turn up the bass, so I need an amp that can handle it. Sound quality isn't really an issue, especially with all the ambient noise in the exercise room. Maybe I can find an old sub that we can pass the signal through at a later date, but for now this is what it is. Yes, Klipsch speakers would have been better, but they're not going to swap out these speakers.

markw

03-23-2009, 12:34 PM

that's a lot of room to fill with sound, even with six speakers. Unless they only want dentist's offict style background muzak, odds are that any consumer stereo amp will be driven pretty hard. I think smaller amps for each speaker would be a less volitale, more permanant soution.

I don't know how you're gonna do this for under $200, but sometimes you simply can't get there from here. Maybe three beater stereo receivers from garage sales?

If you shop carefully and they are somewhat flexible (realistic?) with their budget, three Audiosource AMP-100's would be ideal.

RoadRunner6

03-23-2009, 02:24 PM

Regarding the bass, that's something that I can tell them, but eventually someone, at some point is going to turn up the bass, so I need an amp that can handle it.

Handle it???

Let's say for the sake of argument that you have an amp that puts out 150 watts per channel and it dies after a year (sound familiar?).

Now lets say that one of the little bastards turn up the bass and or loudness control to +12dB's. This is entirely possible. With a 12 dB boost in the bass frequencies you now need an amp that puts out aproximately 1500 WATTS per channel! all things being equal.

Find one of those for $200.

RR6

nightflier

03-23-2009, 03:19 PM

Multiple amps. I hadn't considered that. OK, let's say I purchase a solid amp for four of the speakers and then add a second amp later. That does ease up on the requirements. What can I get for around $200 that will drive 4 infinity speakers? And yes, I do need an amp that will "handle" the occasional stupid kid turning up the bass?

I know this is a tall order, but times are tough and schools just don't have big budgets these days. I really would like to help them out, if I can.

02audionoob

03-23-2009, 03:37 PM

I like the idea of the multiple AudioSource AMP-100 amplifiers.

Back on the Adcom idea, though...I downloaded the manual for the GFA-545II just now and it was clear in saying it could drive two or more sets of speakers and referred to loads like this. I also checked the manual for their speaker switch and it indicates the protection button is for amps other than Adcom, which might not be able to handle the load. It seems to be saying an Adcom can handle it.

That said...I've seen AMP-100 amps going for less than $100 new on Amazon.

Feanor

03-23-2009, 03:40 PM

Thanks for the input. It looks like the only way I can squeeze this into their budget is to buy used. The QSC amp might be a good bet, but the specs say it is only good into 4 ohms (correct me if I'm wrong). ...

Yep, you're wrong. Or at least, the majority of QSC amp series come in 2 ohm versions. Check out their website (http://www.qscaudio.com/products/products.htm).

Mr Peabody

03-23-2009, 06:02 PM

I was checking Amazon for Sherbourn just to see how much they were and oddly enough I didn't see any product. However, I did see a bridgeable AudioSource starting used at $70.00.

Kevio

03-23-2009, 07:27 PM

Yep, you're wrong. Or at least, the majority of QSC amp series come in 2 ohm versions. Check out their website (http://www.qscaudio.com/products/products.htm).The GX series are the bottom of the line (and the only thing that comes close to fitting the budget). Corners have to be cut to meet these price points. The GX amps are only spec'd at 4 and 8 ohms. On the bright side, the specs don't specifically prohibit lower-impedance loads.

The reason amps have a hard time with low impedance loads is because they require a lot of current to drive them. It is current, not voltage that generates heat and fries things. Amps that can drive low-impedance loads have overbuilt power supplies good cooling and protection circuitry.

I'm sure the QSC amp will be an improvement over the Dennon because at least the QSC has a fan. The GX amps do not have appear to have overbuilt power supplies. They have an overdrive prevention circuit but do not appear to have thermal protection. If the former is well-designed, the latter may not be strictly necessary. A real commercial amp would have both though.

Other suggestions: Use a preamp without tone controls or build the system without a preamp. Use a fancy speaker selection box that will connect multiple selected sets of speakers in series rather than in parallel. It won't be optimally loud or sound great with this configuration but neither will anything blow up.

Feanor

03-24-2009, 02:35 AM

The GX series are the bottom of the line (and the only thing that comes close to fitting the budget). Corners have to be cut to meet these price points. The GX amps are only spec'd at 4 and 8 ohms. On the bright side, the specs don't specifically prohibit lower-impedance loads.

The reason amps have a hard time with low impedance loads is because they require a lot of current to drive them. It is current, not voltage that generates heat and fries things. Amps that can drive low-impedance loads have overbuilt power supplies good cooling and protection circuitry.

I'm sure the QSC amp will be an improvement over the Dennon because at least the QSC has a fan. The GX amps do not have appear to have overbuilt power supplies. They have an overdrive prevention circuit but do not appear to have thermal protection. If the former is well-designed, the latter may not be strictly necessary. A real commercial amp would have both though.

Other suggestions: Use a preamp without tone controls or build the system without a preamp. Use a fancy speaker selection box that will connect multiple selected sets of speakers in series rather than in parallel. It won't be optimally loud or sound great with this configuration but neither will anything blow up.

'Flier's problem is that he has a "professional" application for which a pro amp is the best solution. Hooking the speakers in series will keep the impedance under control but cause people to crank the volume control with the result that the amp will still be strained.

A new QSC ISA280, which will do 2 ohms, can be had for $460 plus shipping. Maybe he can get one used. But when you start talking about multiple amps or the likes of an Adcom 555II -- a nice amp that will do 2 ohms -- you're getting into that price range.

Kevio

03-24-2009, 05:57 AM

'Flier's problem is that he has a "professional" application for which a pro amp is the best solution. Hooking the speakers in series will keep the impedance under control but cause people to crank the volume control with the result that the amp will still be strained.I agree, it is a pro application but there's a decidedly no-pro $200 budget. You can go ahead and say it can't be done but I'm trying to put some options on the table.

Yes, you'll definitely have to turn the volume control higher to get the same loudness driving a higher impedance load. But, so long as you stay below the clip point (the GX amp has clipping protection circuity and indicators), at the same power output level (loudness), an amp will be less strained driving an 8 ohm load than 2 ohms. Less strain means less heat, less distortion, lower opportunity for component failure.

Rich-n-Texas

03-24-2009, 07:42 AM

10% off all in-stock items at www.emotiva.com (http://www.emotiva.com)

Feanor

03-24-2009, 08:06 AM

I'm trying to help out a local school with the purchase of a new amp for their exercise room. They were originally using a Harman Kardon 3480 Receiver to drive 6 Infinity Primus 160 Speakers using a speaker selector box. Well after a year the amp in the receiver died. ... I presume the amp has to be stable down to 2 ohms to do this, but I really don't know. The problem is that they have a budget of around $200...

It's a skimpy budget. Could be this is as close as you'll come, new, for a 2 ohm amp ... Behringer EP2500 for $270 (http://www.bhphotovideo.com/c/product/280617-REG/Behringer_EP2500_EP2500_2_Channel_Rackmount.html#s pecifications) plus shipping: 1200 wpc into 2 ohms(!)

Or a little less power for a little more money, the Mackie FR-800 (http://www.bhphotovideo.com/c/product/485506-REG/Mackie_FR_800_FR_800_Rack_Mount.html#specification s).

Kevio

03-24-2009, 12:23 PM

It's a skimpy budget. Could be this is as close as you'll come, new, for a 2 ohm amp ... Behringer EP2500 for $270 (http://www.bhphotovideo.com/c/product/280617-REG/Behringer_EP2500_EP2500_2_Channel_Rackmount.html#s pecifications) plus shipping: 1200 wpc into 2 ohms(!)

Or a little less power for a little more money, the Mackie FR-800 (http://www.bhphotovideo.com/c/product/485506-REG/Mackie_FR_800_FR_800_Rack_Mount.html#specification s).
Nice options!

markw

03-24-2009, 12:33 PM

I'm just curious how, working with three pairs of eight ohm speakers, you arrive at a two ohm impedance.

I can envision a configuration where 5.3 ohms overall is possible.

nightflier

03-24-2009, 12:55 PM

Mark, the Ohm measurement is variable, so it's just a guess. Since the HK amp was able to drive 4 ohm loads, I presumed that the impedance during loud passages would have dipped well below that to fry the amp, as RoadRunner suggested.

Feanor, I like the Behringer amp, especially with the bass cut-off options. It may be just what I'm looking for. Regarding the inputs, I'll be using RCA to TS connectors. The manual mentions that the 1/4" jacks can take unbalanced inputs (i.e. TS 1/4" connectors), so using mono RCA-TS converters shouldn't be a problem, correct?

markw

03-24-2009, 01:37 PM

Feanor

03-24-2009, 03:34 PM

...

Feanor, I like the Behringer amp, especially with the bass cut-off options. It may be just what I'm looking for. Regarding the inputs, I'll be using RCA to TS connectors. The manual mentions that the 1/4" jacks can take unbalanced inputs (i.e. TS 1/4" connectors), so using mono RCA-TS converters shouldn't be a problem, correct?

Should be no problem with RCA to unbalanced 1/4" TS -- see the manual, page 11 (http://www.behringerdownload.de/EP1500_EP2500/IMPL%20Tech%20GLOB_P0183_M%20Web%20EN_2008-01-25_Rev.6.pdf).

RoadRunner6

03-24-2009, 03:37 PM

That is why you have the speaker selector box to keep the impedence from dropping to 2.34 ohms!

markw

03-24-2009, 03:59 PM

That is why you have the speaker selector box to keep the impedence from dropping to 2.34 ohms!Watts the rated power capacity of said switchbox? Power has to be dissipated somewhere in order to maintain a constant impedance.

(pun intended)

nightflier

03-24-2009, 04:20 PM

150W, I believe.

markw

03-24-2009, 04:38 PM

150W, I believe.What kind of power does the amp put out?

RoadRunner6

03-24-2009, 10:28 PM

10% off all in-stock items at www.emotiva.com (http://www.emotiva.com)

Rich, that drops that UPA-2 amp to $269, what a deal! They also have their small 5 speaker package for $761 with free shipping. That is an outstanding set of speakers for an amazing price. If I didn't have the Axiom's I would jump on that deal.

Rich-n-Texas

03-25-2009, 07:34 AM

Yeah, Cathy at Emotiva said "Hurry, before (Dan) comes to his senses."

nightflier

03-26-2009, 08:33 AM

markw

03-26-2009, 09:08 AM

http://www.newegg.com/Product/Product.aspx?Item=N82E16882180022&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Receivers-_-AudioSource-_-82180022

You do the math.

Rich-n-Texas

03-26-2009, 10:40 AM

Three of us have reviewed our Emotiva amps in this and other forums, and in each review it was agreed that these babies can handle just about anything you throw at them without the slightest amount of strain. My B&W's have a minimum 2 ohm impeadance and my amp doesn't even flinch, even at 90dB. It sits at the bottom of my audio rack, behind a closed door.

Again, Emotiva's running a sale on their products. Look 'em up!

Feanor

03-26-2009, 11:51 AM

Well I need to make a decision. I've been given up to $300 for the budget, a little better but still slim pickins. Anyhow, should I go the Emotiva route or the Behringer? With the emotiva, my question is whether it will handle 2 ohms and if it will run hot. Also, will it handle the occasion dumb-a$$ turning the bass up. What is the warranty on Emotiva amps, anyhow?

For the Behringer the concern is about the unbalanced 1/4" to RCA adapters. Theoretically it should work, but I'm since pro amps aren't my forte, I just want to make sure I got it right. The other question I have is whether Behringer makes decent amps and if they stand by their products.

(the amp will be connected to a speaker switch box that should handle 150W per channel).

If you're concerned about 2 ohms, forget about amps that aren't speced for 2 ohms, (dah!) In response to Rich: maybe you speakers dip to 2 ohms but the average level is likely significantly higher, and the average is what actually matters.

Neither the Emotiva nor the Audio Source are speced for 2 ohms, although I guess you could buy two Audio Source.

Behringer stuff is "prosumer" and not necessarily as robust as full-blown pro equipment, however I have seen a good many endorsements for it. I'd take them over Audio Source any day. The RCA to 1/4" unbalanced (TS) is OK per the Behringer manual (http://www.behringerdownload.de/EP1500_EP2500/IMPL%20Tech%20GLOB_P0183_M%20Web%20EN_2008-01-25_Rev.6.pdf)-- see page 11 where they are mentioned. Get hybrid 1/4"TS/RCA cables from Markertek (http://www.markertek.com/Product.asp?baseItem=TN%2DSR%2D3&cat=CABLESCONN&subcat=AUDIOCAB&prodClass=ASPRCA&mfg=&search=0&off=).

The 150 watt switch box will take a lot more power than that on a peak basis, so don't worry about that.

Hyfi

03-26-2009, 12:16 PM

Sunfire amps always boasted they can handle anything down to 2ohms

markw

03-26-2009, 12:19 PM

Neither the Emotiva nor the Audio Source are speced for 2 ohms, although I guess you could buy two Audio Source.Actualy, my original propsoal was three Audiosource amps. One channel for each speaker.

Rich-n-Texas

03-26-2009, 12:30 PM

Actualy, my original propsoal was three Audiosource amps. One channel for each speaker.
Just don't... tri-amp them like that other guy did. :eek6:

Feanor, I agree. I assume *minimum* is the same as *dipping* down to 2 ohms.

RoadRunner6

03-26-2009, 12:55 PM

As I mentioned before, I think your presumption of 2 ohms using a speaker connection box is incorrect and you probably won't see it dip much below 4 ohms even with three sets of 8 ohms speakers.

Why don't you give the gang at Emotiva a quick call. They are very friendly people and extremely knowledgeable. Talk to Lonnie or Big Dan if he is in. They will definitely be able to address your concerns.

nightflier

03-30-2009, 11:09 AM

MarkW makes a good point on the cost issue: three Audio Source Amps @ 89.00 each, one for each pair of speakers is the best deal. This would eliminate the need for the switchbox altogether since these amps have their own volume controls too. A couple of other advantages: no need for TS>RCA adapters and (this is my computer background influencing me), being separate, if one fails, there's still two other ones to keep plugging along.

Does anyone know if these amps run hot? They'll be running just one pair of speakers each and these are 8 ohm speakers, so I'm going to guess they'll handle that just fine, right?

blackraven

03-30-2009, 12:52 PM

Nightflier, here's the Speakercraft BB275 amp that is on sale at Amazon for $299. Its rated at 2ohm and you can daisy chain them togther if needed.

http://www.amazon.com/gp/offer-listing/B001TK3EE4/ref=asc_df_B001TK3EE4756722?ie=UTF8&condition=new&tag=dealt15905dealt&creative=380345&creativeASIN=B001TK3EE4&linkCode=asm

Here's another site for $329 which includes the shipping price.

http://www.buy.com/prod/speakercraft-2ch-amp-75w-ch-rms-rack-mnt-nic/q/loc/111/209869979.html?dcaid=15891

blackraven

03-30-2009, 12:57 PM

I would strongly consider the speakercraft. It appears to be made for commercial applications such as yours. High current and rated at 2ohms with the ability to daisy chain multiple amps together.

02audionoob

03-30-2009, 01:38 PM

Does anyone know if these amps run hot? They'll be running just one pair of speakers each and these are 8 ohm speakers, so I'm going to guess they'll handle that just fine, right?

I have one of these and it doesn't run hot. However...It does not sound nearly as powerful as an Adcom GFA-535.

Mr Peabody

03-30-2009, 05:58 PM

How do you plan to get the signal to the 3 amps? A "Y" adaptor may work for two but you have 3.

markw

03-30-2009, 06:43 PM

How do you plan to get the signal to the 3 amps? A "Y" adaptor may work for two but you have 3.They can be daisy-chained.

http://www.mcmelectronics.com/content/ProductData/Manuals/50-6062.pdf

My last comment here : Three of these amps,with six channels loafing along while putting out at least 50 wpc with easy 8 ohm loads on each, will be a more conservative solution than two channels working hard to feed a power-wasting, heat generating, impedance matching, speaker selector.

blackraven

03-31-2009, 09:16 AM

The speakercraft is made to hook up multiple speakers according to their web site.

nightflier

04-09-2009, 02:57 PM

Well we decided on the AudioSource Amps, but we'll buy one first and see how it performs on one pair of speakers. If it works OK, then we'll get two more, if not we'll get a second amp from another manufacturer for the other 4 speakers, although that will be more expensive overall.

I'll report back after we get the first one connected about how it performs.