View Full Version : high current receivers on 15 or 20 amp circuits

bjornb17

06-03-2005, 04:47 PM

I have a question thats been bothing me for a while......

how can these "high current" receivers draw 25,40,60,75,etc... amps when circuits in the home are rated at 15-20 amps?

Smokey

06-04-2005, 09:50 AM

how can these "high current" receivers draw 25,40,60,75,etc... amps when circuits in the home are rated at 15-20 amps?

Where have you seen such a Receiver?

The most powerful Receiver I've seen was 2,000 watts Carver which roughly equal between 10-15 amp.

Remember that Watts specification for a receivers does not readily equal [real] amp drawn (I*squared x R=Watt). The mentioned watts is "apparent" watts which is somewhat higher than real watts.

bjornb17

06-04-2005, 04:41 PM

how can these AVERTISED "high current" receivers draw 25,40,60,75,etc... amps when circuits in the home are rated at 15-20 amps?

for example, my HK AVR130 says its 25 amps, but i highly doubt that, since i would have tripped the circuit breaker in my room. where do they pull that number from?

Smokey

06-04-2005, 07:11 PM

for example, my HK AVR130 says its 25 amps, but i highly doubt that, since i would have tripped the circuit breaker in my room. where do they pull that number from?

Where on the amp does it exactly saying 25 amp?

I looked at power specification for HK AVR130 and Total Power Output is 225 Watt (45 Watt per Ch.). So drawn amp is way much less than 25 amp.

Glen B

06-04-2005, 08:34 PM

You are all confused about what this spec means. The 25 amps quoted for the HK AVR130 is the current delivery of the amp's output stage (and power supply) into a speaker load. This is different from the power consumption of the amp from the wall. The total power consumption of the AVR130 is listed in the specs as 540 watts. That information should also appear on the rear panel of the amp. This total power consumption is what you use to determine the unit's current draw from the AC receptacle. Watts = Current x Voltage. Conversely, Amps = Watts / Voltage. In this case, 540W / 120V = 4.5A. The AVR130 draws 4.5 amps from the wall, not 25 amps.

Smokey

06-04-2005, 08:54 PM

The 25 amps quoted for the HK AVR130 is the current delivery of the amp's output stage (and power supply) into a speaker load.

That somehow don't sound right either.

Calculating watts, 25 amp into 8 ohm speaker load equal 5000 watts. Is that even possible :)

Glen B

06-04-2005, 09:15 PM

That somehow don't sound right either.

Calculating watts, 25 amp into 8 ohm speaker load equal 5000 watts. Is that even possible :)

Not right ? And pray tell what voltage did you use in your calculation to arrive at 5,000 watts ?

Smokey

06-04-2005, 09:25 PM

Not right ? And pray tell what voltage did you use in your calculation to arrive at 5,000 watts ?

I used the fomula (Amp *squared* x R = Watt).

So (25 x 25 x 8 ohm = 5 k watts) :)

bjornb17

06-04-2005, 09:27 PM

cooool i have a 5 kW receiver!

j/k

Glen B

06-04-2005, 09:44 PM

I used the fomula (Amp *squared* x R = Watt).

So (25 x 25 x 8 ohm = 5 k watts) :)

The 25A spec is high instantaneous current. You are assuming the load is 8 ohms. The manufacturer does not specify the load impedance, therefore it is unknown. It could very likely be 1 ohm. These high current specs quoted by manufactures are often into very low impedances to demonstrate that the amp will deliver good output into difficult speaker loads. Assuming the load is 1 ohm, 25 x 25 x 1 = 625W. An instantaneous (read dynamic) power output of 625 watts is realistic.

Kursun

06-05-2005, 08:25 AM

I have a question thats been bothing me for a while......

how can these "high current" receivers draw 25,40,60,75,etc... amps when circuits in the home are rated at 15-20 amps?High current receivers do not draw 25-70 Amps. That current can be supplied at the speaker outputs, at a much lower voltage than wall line voltage.

100Volts at 10 Amperes produces the same power as 10Volts at 100 Amperes. There is a step down transformer inside the receiver producing a lower voltage and higher current for the power supply.

bjornb17

06-05-2005, 02:14 PM

ah okay :)

but whats the benefit of high current receiver?

Glen B

06-05-2005, 04:07 PM

ah okay :)

but whats the benefit of high current receiver?

Although a speaker may be rated at a nominal 8 ohms for example, that impedance can dip to as low as 2 or 3 ohms at certain frequencies. While not all speakers may behave in this way, there are many that do. More often than not, these speakers also have low sensitivity, requiring a lot of power to achieve realistic sound levels. The lower impedance puts an increased demand on the amplifier or receiver to deliver more current. If the amplifier or receiver cannot deliver that current, it will sound strained, congested, thin and a whole bunch of other adjectives. It can also overheat and shutdown when driven hard under these circumstances. An amp or receiver that is designed to deliver high current into low impedances will be able to drive difficult speaker loads without any problem.

bjornb17

06-05-2005, 04:40 PM

even though the receiver is rated at 8 ohms, would it have trouble driving 4 ohm speakers?

Glen B

06-05-2005, 04:52 PM

even though the receiver is rated at 8 ohms, would it have trouble driving 4 ohm speakers?

It all depends on the receiver and speaker. You could safely get away with it as long as you aren't driving the receiver too hard.

Smokey

06-05-2005, 06:22 PM

The 25A spec is high instantaneous current.

You are probably right. But it might be less confusing if higher instanious current are stated in term of Dynamic Headroom or output power rather than current. Some people might interpret it as 25 amp drawn from AC by the amp :)

bjornb17

06-05-2005, 06:27 PM

You are probably right. But it might be less confusing if higher instanious current are stated in term of Dynamic Headroom or output power rather than current. Some people might interpret it as 25 amp drawn from AC by the amp :)

like i did :)

Smokey

06-05-2005, 06:37 PM

like i did :)

Then I hope you had a Fire Extinguisher close by :D

bjornb17

06-05-2005, 08:14 PM

Then I hope you had a Fire Extinguisher close by :D

no, i prefer water to put out those high-current fires.

maddgoo1

07-03-2005, 06:58 PM

I was curious in a similar way to find out what the amp draw was for a Yamaha HTR 5790 (110w x 7) and Adcom GFA 555 (200w x 2) which are the two amps I activate simultaneously. Accessories are delayed via an ADCOM ACE515. The amps were measured at a 10 amp spike (at start up) and immediately dropped back to 2 amps...there wasn't much change from 2 amps with the music playing. Seems as if the power drain is only at startup, and well below the 15 amp circuit rating.

Geoffcin

07-03-2005, 07:39 PM

I was curious in a similar way to find out what the amp draw was for a Yamaha HTR 5790 (110w x 7) and Adcom GFA 555 (200w x 2) which are the two amps I activate simultaneously. Accessories are delayed via an ADCOM ACE515. The amps were measured at a 10 amp spike (at start up) and immediately dropped back to 2 amps...there wasn't much change from 2 amps with the music playing. Seems as if the power drain is only at startup, and well below the 15 amp circuit rating.

The amp or receiver will draw a lot of current on startup to charge up the filter capacitors.

Your Adcom should have some mighty big ones too. Amps are rated as to how much current they can swing using a sine wave into a resistive load. 200 watts/channel on an eight Ohm load equates to 40 volts RMS , but the Adcom might swing greater than +/-60v during a transient, while the receiver might only do 25v. This extra current is available when a sudden transient calls for a large output. The lower powered receiver, while not actually driven into clipping, just can't slew the large current, and hence whatever transient your trying to reproduce, whether a drum strike,( or a gun shot in HT), will not have the impact of what it should have been.

You probably already know this, but I would NOT recommend getting close to the terminals of these big caps when they are charged. Amps have killed people, even ones that were shut off.

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