Why is the weaker amplifier louder?

[ripmixburn]

I picked up a Rotel RMB-1565 (ICEpower) multi-channel power amplifier to offload the duties from my aging Anthem MRX300 home theatre receiver, which was recently repaired.

I decided to compare the power amplifer sections of both by using the left channel with the Rotel and the right channel with the Anthem. I used the Anthem’s built-in white noise sequence to compare by ear and to my surprise the Anthem was noticeably louder.

The Rotel is rated at:

• 100 W × 5/ch (20–20 kHz, 0.03% THD, 8 ohms)
• 200 W × 5/ch (20–20 kHz, 0.03% THD, 4 ohms)

And the Anthem MRX300 is rated at:

• 60 W × 5/ch (20–20 kHz, 0.1% THD, 8 ohms)

My speakers are 6 ohm rated. The Anthem is not 4-ohm rated but I was told unofficially by support that it can handle a minimum 4-ohm load.

Does this seem strange to anyone? I don't see any kind of gain on the Rotel, nor do I see a way to increase the preamp output on the Rotel (aside from volume or individual channel levels).

Below are the official specifications for each.

 

[Jdunk54nl]

How did you adjust the volume of each? The input sensitivity of the amp is probably messing with the results.

 

[ripmixburn]

How did you adjust the volume of each? The input sensitivity of the amp is probably messing with the results.

It's my first time doing such a thing, so bear with me, but I did not attempt to push them to their loudest, simply used the receiver’s white noise functon to go from right to left. I think you’re probably right about input senstivity, but this is an area I don't quite grasp. I have no idea what the Anthem’s preamplifer is outputting.

 

[Jdunk54nl]

It's my first time doing such a thing, so bear with me, but I did not attempt to push them to their loudest, simply used the receiver’s white noise functon to go from right to left. I think you probably right about input senstivity, but this is an area I don't quite grasp. I have no idea what the Anthem’s preamplifer is outputting.

Yup and that would explain level / volume differences easily.

 

[DVDdoug]

Yeah, sensitivity or gain... It might take 1V in to to get 100 Watts out of one amp, and 2V in to get 100W out of another amp. The gain is unrelated to power.

Except, you do want an amplifier of any power to be able to reach it's full power from a "line level" input so higher power amps often do have more gain. (Line level isn't tightly controlled/defined and some preamps and other equipment has higher output voltage than others.}

 

[spacevector]

I had the Anthem receiver you got and measured ~0.75Vrms on the preout at 0dB volume control and playing a youtube 1kHz test tone.
This one:

Your amp spec is 100W into 8 Ohms and 200W into 4 Ohms - this is output voltage of 28V. The gain spec is 27.1dB which is 22.6X. So to get full power, amp will need 1.24V input.

At 0dB from the Anthem (0.75V), amp output will be 17V = 72W in 4Ohm.

Do you have a multimeter? If not, good purchase to tinker with!

I could certainly be wrong above - the youtube video I chose could be attenuated signal and so on.

 

[raindance]

It's just gain differences. Of course someone will say the louder one is more powerful, but it is not the case.

 

[MakeMineVinyl]

As already stated, the gain of the two amplifiers is likely different.

 

[pozz]

The louder one may be clipping or well into nonlinearity.

Although gain is the more likely culprit.

 

[ripmixburn]

I had the Anthem receiver you got and measured ~0.75Vrms on the preout at 0dB volume control and playing a youtube 1kHz test tone.
This one:

Your amp spec is 100W into 8 Ohms and 200W into 4 Ohms - this is output voltage of 28V. The gain spec is 27.1dB which is 22.6X. So to get full power, amp will need 1.24V input.

At 0dB from the Anthem (0.75V), amp output will be 17V = 72W in 4Ohm.

Do you have a multimeter? If not, good purchase to tinker with!

I could certainly be wrong above - the youtube video I chose could be attenuated signal and so on.

Wow that's some great calculation, thanks! That sounds about right based on my ears.

Any recommendations on a multimeter? I've never bought one. Is Aliexpress a bad idea? I'm not in a hurry.

 

[pjug]

If you email Anthem they can probably tell you what the gain is in the power section. Then you can see if that explains it.

 

[spacevector]

Any recommendations on a multimeter? I've never bought one. Is Aliexpress a bad idea? I'm not in a hurry.

I use a Fluke but those aren't cheap. AliExpress may be OK but I would not use it beyond 40V - so no poking it into the wall outlet. Amazon has many options too - some even Amazon branded models like this one: https://www.amazon.com/AmazonCommercial-Count-Compact-Digital-Multimeter/dp/B07W3BXNMP

 

[Jdunk54nl]

If you have a little extra, one like this is nice.

Hantek 2C42 Handheld Oscilloscope Multimeter 2 in 1 Multifunction Tester 2CH+DMM 40MHz Scope https://smile.amazon.com/dp/B07PWZV4XJ/ref=cm_sw_r_cp_api_glt_fabc_TRHKMZQQK78HK9Z4QNP6?psc=1

 

[ripmixburn]

Currently watching (recommended by an electrician friend) though at 11 years old, things have changed I'm sure. A good intro I'm hoping.

 

[ripmixburn]

I had the Anthem receiver you got and measured ~0.75Vrms on the preout at 0dB volume control and playing a youtube 1kHz test tone.
This one:

Your amp spec is 100W into 8 Ohms and 200W into 4 Ohms - this is output voltage of 28V. The gain spec is 27.1dB which is 22.6X. So to get full power, amp will need 1.24V input.

At 0dB from the Anthem (0.75V), amp output will be 17V = 72W in 4Ohm.

Do you have a multimeter? If not, good purchase to tinker with!

I could certainly be wrong above - the youtube video I chose could be attenuated signal and so on.

UPDATE: I have sold my Rotel, but still have the Anthem. What am I looking for in a stereo power amplifer in terms of specifications? I need something with a lot of gain?

 

[kongwee]

Normally I will base on power consumption, your MRX300 properly have a bit higher power consumption than your RMB-1565. MRX maximum consumption is 500w for 90w output. If transformer is the same for all model, your MRX may give a better current drive than your RMB-1565.

 

[pseudoid]

I don't see any kind of gain on the Rotel,

Extracted from your posted spec sheet.