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Opinion on the Behringer KM1700 Class-H amp
Opinion on the Behringer KM1700 Class-H amp
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Old 17th May 2017, 10:49 PM   #11
johnplayerson is offline johnplayerson  Canada
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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.
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Old 19th May 2017, 05:01 PM   #12
CharlieLaub is offline CharlieLaub  United States
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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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Last edited by CharlieLaub; 19th May 2017 at 05:05 PM.
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Old 19th May 2017, 07:43 PM   #13
johnplayerson is offline johnplayerson  Canada
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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.
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Old 19th May 2017, 08:10 PM   #14
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by johnplayerson View Post
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.
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Old 20th May 2017, 06:25 PM   #15
johnplayerson is offline johnplayerson  Canada
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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.
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Old 29th May 2017, 01:00 PM   #16
MrKlinky is offline MrKlinky  United Kingdom
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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.
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Old 3rd October 2017, 05:49 PM   #17
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by CharlieLaub View Post
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.
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Old 4th October 2017, 07:22 PM   #18
johnplayerson is offline johnplayerson  Canada
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Default 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.
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Old 24th October 2017, 03:21 PM   #19
CharlieLaub is offline CharlieLaub  United States
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If you are thinking of picking up one of these amps there are several available on ebay right now from the manufacturer as refurbished units at a very attractive price...
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Old 26th October 2017, 11:42 PM   #20
CharlieLaub is offline CharlieLaub  United States
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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".
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