Opinion on the Behringer KM1700 Class-H amp

Hey everybody!

Since I just ordered a Behringer iNuke 3000DSP for my subwoofer, I thought I'd look at my options for an amplifier for my fronts. I stumbled across the KM1700 because I know that it's basically like Class A/B but with a variable and dynamic voltage rail. Correct me if I'm wrong!

They're slightly (and that's a mild expression) overpowered at 2x500w into 8Ohms. My speakers are barely 90 Watts RMS (if they're set as fullrange. They can take slightly more when not in fullrange, I suppose. Or less? Less movement is less cooling hmmmmm.)

Since I'm not very good with the specification-sheet reading, what would your opinion be? I can't actually find a specsheet. :(

Any input is greatly appreciated.

Cheers,
Anna

https://www.amazon.com/Behringer-KM1700-BEHRINGER/dp/B01MAY7S7W

Behringer KM1700
limiter is switchable
front-to-back ventilation
frequency response: 20 Hz - 20 kHz (@-10 dB), 10 Hz - 80 kHz (@-3 dB)
THD: <0.03%
signal-to-noise: >100 dB
sensitivity: 0.77 V/26 dB/1.4 V (switchable)
dimensions: 482 x 375 x 88 mm (w*d*h)
weight: 12.5 kg
 
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This looks like a very interesting amp to me, and I have mentioned this in another thread in the PA forum about it's little brother, the KM750.

The KM1700 reminds me of the EP2500. It's a class-H amp which, like you mentioned, is more like class AB than the class-D of the iNUKE series. It has two fans versus one on the EP2500 (I would do a fan mod if I bought one). The price is quite affordable at $199 for 500W/ch into 8R. While this might be "overkill" for your mains in terms of average power, it's not as overpowered as you might think for "peak power". You can think of it like a 100WPC amp with a good amount of headroom. This means your amp will not clip on peaks, unless you really listen to compressed music at very high levels. And yes, it does have the capability to fry your speakers, so don't play it too loud too long.
 
Thanks for your extensive reply!

The amp states an RMS wattage that I said. Is that an overrated spec?

I'm always very cautious with power. I have never accidentally damaged a speaker and I wish to remain innocent :)

I like having a good headroom anyway to allow for taking it to a rig or upgrading to more powerful speakers. Even though I doubt I've ever pushed these speakers over 40-60watts as they're already painfully loud at that power level.

Cheers,
Anna
 

PRR

Member
Joined 2003
Paid Member
product sell-page

"front-to-back ventilation"

You realize this means it has a FAN ?

On some amps, the fan lays dead until the amp gets hot. Others run the fan on full all the time. Others vary the fan speed as needed. No details on the sell-page.

This is a low-price PA amp, for bands and DJs. In a crowded room the fan whirrr is not an issue. In a home listening room, it may be.

Why are you looking at THIS amp?

Yes, it is covered with buzz-words. G-mode, ATR. Some of these may even be good ideas. For somebody. But any good idea can be done wrong.

Rail tracking.... do you listen to the rails?? What it really means is they get more output with less heat (and money). OTOH this is more Watts for your bucks. On the third hand, IMHO this is an insane amount of Watts for most homes.

Knowing B-ringer, I am sure it meets all specs and reproduces music fine. B-ringer got where they are by making low-low-price stuff that does work OK.

At $200 for 1000-1700 Watts it is at the lower end of what Watts cost today. There are enough other amps at this $/Watt point that I don't think B-ringer has done it especially good or bad.

General gripes against B-ringer tend to be that the pots and jacks don't last forever especially in hard use (traveling band). In fixed home use it may last 10-20 years no problem.

If you really want a Thousand Watt Amplifier, this is a safe bet and about as low-price as you can find.

If the fan turns out to be disturbing, you can probably pawn it for half what you paid; near-new kilo-watt PA amps have good resale value.
 
product sell-page

"front-to-back ventilation"

You realize this means it has a FAN ?

On some amps, the fan lays dead until the amp gets hot. Others run the fan on full all the time. Others vary the fan speed as needed. No details on the sell-page.

This is a low-price PA amp, for bands and DJs. In a crowded room the fan whirrr is not an issue. In a home listening room, it may be.

Why are you looking at THIS amp?

Yes, it is covered with buzz-words. G-mode, ATR. Some of these may even be good ideas. For somebody. But any good idea can be done wrong.

Rail tracking.... do you listen to the rails?? What it really means is they get more output with less heat (and money). OTOH this is more Watts for your bucks. On the third hand, IMHO this is an insane amount of Watts for most homes.

Knowing B-ringer, I am sure it meets all specs and reproduces music fine. B-ringer got where they are by making low-low-price stuff that does work OK.

At $200 for 1000-1700 Watts it is at the lower end of what Watts cost today. There are enough other amps at this $/Watt point that I don't think B-ringer has done it especially good or bad.

General gripes against B-ringer tend to be that the pots and jacks don't last forever especially in hard use (traveling band). In fixed home use it may last 10-20 years no problem.

If you really want a Thousand Watt Amplifier, this is a safe bet and about as low-price as you can find.

If the fan turns out to be disturbing, you can probably pawn it for half what you paid; near-new kilo-watt PA amps have good resale value.


I know these have a fan, yup! I have near dead silent fans laying around that I can put I'm, but they'll be behind the other wall anyway :)

I'm not per she interested because of the power input. Rather because no matter how cheap I go on Beringer, it'll be better than Logitech.

I have a 30day full refund warranty at the shop I'm buying my materials.


Perhaps I'm cheap because I'm not old enough, but for now cheap is fine. :)

Thanks for your reply, PRR.

Cheers,
Anna
 
Would like to see internal pictures.

Based on the weight of the amp, i would say the toroidal transformer is underrated somewhat.

Once someone posts some internal pics i would have a better idea.
Hopefully she has at least 10 150 watt output transistors per channel.

Certainly a great opportunity to have 8 subs on 8 bridged amps for 1700 per sub for only 1600

2 of these look like a much better value than inukes
 
Underrated somewhat? Understatement of the year. Most 'pro' and otherwise audio uses toroids (or switching supplies) designed only to deliver 1/8 power on average. Wall socket current ratings are based on the same assumption. It isn't a Behringer thing. The one in the QSC GX5 isn't much bigger.

To do it 'right' (deliver 500 per channel indefinitely, and more into 4 ohms) would require TWO 1.5kVA toroids weighing thirty pounds each. And a heat sink the size of a small car. And a 30 amp plug. As efficient as the inukes are even they will fold back the power after a few seconds at full sine output. Whether or not it is needed is subject of debate. Whether or not it sounds better done the old fashioned way is unmistakeable. But no one wants to pay $4000 for a 500 watt amp, do they?
 
The 2500va toroidals in all my amps weigh 31lbs. Seriously doubt a 1500va toroidal will weigh as much as a 2500. And you might need one 1500va toroid to do 500 rms sine wave forever, if the output stage could put up with that. I doubt it. On regular music signals no problem.

Im not a fan of SMPS at all and would agree with any deficiencies you describe.

However at a price of 200 bucks each, and based on the amplifier weight , I am betting on a 800 vA TO 1000 va toroidal.

Like i said i would love to see the amplifier channels on the inside. Even with the under rated toroidal in bridge mode this thing could actually do some amazing things into an 8 ohm subwoofer, but again have to wait for some internal pics. I really do not want to buy a couple, just to satisfy my interest as i almost did last week.
 
At that price point and weight I'm betting a 500VA. I did pop the hood on a GX5 (similar power class, $300) and that's what it was. 800's from Antek or Plitron are much (not just a little) bigger. And the heat sink looked like it belonged on a 1990's era Pentium or 80486 CPU. Being class H they are a lot more efficient than old Peaveys or BGWs. But you can't beat on these modern amps near as much. They count on you toasting the speakers long before the amp gives out, which is usually the case.
 
Hmmm...

FWIW, 1/8th power is pink noise with a 9dB peak-to-average ratio run so the amplifier is just clipping. Sine wave testing is still technically only half-power, since it has a 3dB peak-to-average ratio. If you want to really cook an amplifier, you'll need square waves, where the peak-to-average ratio is 1.

I happen to think the 1/8th power rating is just fine. It's pretty close for modern pop music. Live music will have a much larger dynamic range (and therefore average power draw will be low), while some EDM can have extremely compressed bass resulting in exceptionally high power draws.

The old iron amps (Macrotechs etc) are designed and rated for sine wave testing, which is very demanding and rarely occurs. Seems a bit silly to optimise for it, then.

I'd rather have an amplifier that'll do 500w sine waves and 5000w peaks than something that'll do 1000w sine waves. The first one is much more aligned with the program material I work with, and would offer more headroom in that usage. Someone that's doing raves would probably want the 1000w sine-wave-amp for their subs, but likely still the peaky amplifier for the mid-high range.

Chris
 
I looked at the schematic of the gx 5 ,,,,,,,,,, not impressed.
Definite no go with such a small power supply. Good little amps for general speaker use, but no subs.

5000 watt peaks on the other hand, I see as twice as useless, based on the ten times the power to double the sound rule. A lot of power dispersed for very little gain. Then the question comes as to the length of the peak, and then of course any peak that high will be 2 ohm loaded for sure.
 
I'm still interested in the KM1700... I just did a fan mod on my EP2500 so that I can use it in an active speaker project. To do the mod I chose a 12Vdc "quiet" 80mm fan with added series resistance to drop the 24V feed down to an appropriate voltage. The voltage across the fan that I chose was 8V. At this voltage I know that the fan will definitely start (rated to start at 6V and above). Also, at 8V the fan is so quiet that I can't hear anything unless my ear is 1 inch from the blades and even then it is very, very quiet. I used the Fractal Designs R3 80mm fan with 400R in series, blowing back-to-front. This does result in much less airflow compared to the stock fan, but I will be using the amp "lightly" compared to its rated output and so I don't expect to have to remove the amount of heat that it would produce in a pro application. I will be using the EP2500 to drive some open baffle subwoofers. Based upon some DIYer measurements I found for the EP2500 I know that the amp exceeds the rated power output at 20Hz into 4R and lower impedances at relatively low distortion (e.g. >600WPC into 4R resistive load with 0.015% distortion at 20Hz).

I would expect one could do a similar fan mod on the KM1700 and end up with an inexpensive, high-powered, essentially silent, non-class-D 800W/ch@4R home amp. I like to think of it as a 100WPC amp with a lot of headroom. The KM1700 has switchable input sensitivity (0.77V, 26dB, or 1.4V) which makes it more compatible with home audio signal levels. The KM1700 is currently selling for $199 new from lots of retailers - it's an amazing deal.

Because these amps are class-H they run cooler and require a smaller transformer compared to a class-AB amp.
 
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Chances are you will not run into issues with a fan mod. If two ohm loading your asking to blow your amp with the mod. I suggest using the lm2596 units for fan mods. For a couple dollars out of china you can vary the fan speed, not just be stuck at one speed.

One of my issues with these amps is the single tunnel vs twin tunnel design.

The km units look to be an outstanding value regardless of any limitations.
 
Chances are you will not run into issues with a fan mod. If two ohm loading your asking to blow your amp with the mod. I suggest using the lm2596 units for fan mods. For a couple dollars out of china you can vary the fan speed, not just be stuck at one speed.

One of my issues with these amps is the single tunnel vs twin tunnel design.

The km units look to be an outstanding value regardless of any limitations.
Not looking to drive 2 Ohm loads - sorry if I implied that. I threw out that spec to show that the amp is more than capable in terms of power and current. I am using two 4 Ohm nominal (3.2 Re) drivers that are connected in series and I will use the amp bridged. I might use up to 400W, and the amp is spec's at 1300W continuous in that configuration. As a result, I don't expect to need all that much cooling air flow, but I do plan to keep an eye on it closely until I am certain all is working OK.

I didn't think of using a buck-converter for the fan. Not a bad idea, but I am not sure how the amp controls the fan (according to the MFG literature, fan speed is adjusted to meet the cooling demand). If there is PWM control used or something like that the buck converter is not going to work.

A great solution would be a programmable PIC+thermocouple+LM2496 (or other way to vary voltage) fan-controller unit where you could set min and max voltages to vary the fan speed versus the temp on the thermocouple, which could be mounted to the heat sink itself. In this case, something on that level of complexity is not warranted.
 
Another neat idea, credit to someone else. is to mount one fan on the inside and another fan on the outside, doubling air floor with the quieter fan. If using 12 volt fans you would then wire them in series. A few extra nuts and bolts required for mounting the fans.

All my units are two speed fans as well. I never seen the second speed yet....... but it will still work with a buck unit. They tend to work better on the original fan or one of 24volt. this leaves more fan speed leeway. In any event , voltage is simply increased and the convertor will still work.
 
I always over-amp my PA speakers to a considerable degree. Sure, a 1200cc (73CI) VW Beetle (Bug) will do 70mph, but the Porsche beside it at the same speed has another 100+mph in reserve. I try to use amps with at least double the rms rating of the speakers. Power amps are so cheap these days it seems daft not to.

Cheers, Carl.
 
I'm still interested in the KM1700... I just did a fan mod on my EP2500 so that I can use it in an active speaker project. To do the mod I chose a 12Vdc "quiet" 80mm fan with added series resistance to drop the 24V feed down to an appropriate voltage. The voltage across the fan that I chose was 8V. At this voltage I know that the fan will definitely start (rated to start at 6V and above). Also, at 8V the fan is so quiet that I can't hear anything unless my ear is 1 inch from the blades and even then it is very, very quiet. I used the Fractal Designs R3 80mm fan with 400R in series, blowing back-to-front. This does result in much less airflow compared to the stock fan, but I will be using the amp "lightly" compared to its rated output and so I don't expect to have to remove the amount of heat that it would produce in a pro application. I will be using the EP2500 to drive some open baffle subwoofers. Based upon some DIYer measurements I found for the EP2500 I know that the amp exceeds the rated power output at 20Hz into 4R and lower impedances at relatively low distortion (e.g. >600WPC into 4R resistive load with 0.015% distortion at 20Hz).

I would expect one could do a similar fan mod on the KM1700 and end up with an inexpensive, high-powered, essentially silent, non-class-D 800W/ch@4R home amp. I like to think of it as a 100WPC amp with a lot of headroom. The KM1700 has switchable input sensitivity (0.77V, 26dB, or 1.4V) which makes it more compatible with home audio signal levels. The KM1700 is currently selling for $199 new from lots of retailers - it's an amazing deal.

Because these amps are class-H they run cooler and require a smaller transformer compared to a class-AB amp.

My EP2500 started to develop some problems so I pulled the trigger on a KM1700. Now I get to find out if it's any good, or not. Specs are:
  • 500W/ch @ 8R
  • 800W/ch @ 4R
  • 1700W bridged into 8R

Even if this is peak power and RMS is half of that I will be pleased since I picked up a refurbished unit at a very nice price. There is more to pure power, however. It is noisy (apart from the fans, which I will likely replace)? Does it run hot or cool (it's class-H, so hopefully on the cooler side). Etc.
 
Class H usually gets you around 80 to 85 percent efficiency

Class H will usually get you 80 to 85 percent efficiency depending if it is two
tier or three tier class H. Due to the size I would assume the km 1700 are two tier class H. One just needs to observe the power transformer winding's and check for how many stages of wiring are coming out of the power supply to confirm.

Class H amplifiers, generate more peak power than conventional AB class amplifiers with no staging. This peak power is generally not included in the normal manufactures specifications. If she is 500 watt she will peak a lot higher, as much as 800 watt for 22ms, which is the poor standard used by SMPS, that in general does not reflect useful output. They sell more class D and smps powered amps using inflated numbers at 22ms burst. Most of the SMPS supplies tank out, at the well known 500 watt level.

A welcome addition these amps are, in a world of toroidal amplifiers, that are being dropped, mainly because, more CASH can be made with the new tech.
 
My KM1700 arrived. So far I only plugged it into mains power on my kitchen countertop to hear the fans spin up. There are two fans, but the noise is much less objectionable compared to the EP2500 I had. This was from about 3 feet away in a quiet room. It's similar to a noisy desktop computer fan. I think that slowing the fans and/or replacing them with "quiet" fans the noise will practically disappear, although it still will not be "silent".