Will my 1V pre-out be able to harness all of Hypex power amp's power?

[Symphoniac]

Hello all, I would like to use a Hypex (or Purifi) based power amp such as the Apollon Hypex NCx500 ST NCOREx Stereo Amplifier (https://apollonaudio.com/product/hypex-ncx500-ncorex-st-stereo-amplifier/) connected to the pre-out of my Yamaha RN800A which outputs at 1 Volt. I've read in numerous places that 1V is not sufficient to fully harness the max wattage of some power amps, in this case 380W at 8ohm and 600W at 4ohm. I tried to read up on the various technical reasons this might be and it's hurting my brain, so was hoping someone could explain it like I'm 5. Thanks!

 

[617]

An amplifier makes the output signal louder in proportion to the loudness of the input signal. Some amplifiers will produce their full output with a small (1V) signal. Some expect a larger 2-4V signal to run at full loudness. Professional audio equipment like mixers tend to output a beefier signal than an AVR (or cd player, or tape deck, or phono preamp) and so professional amplifiers 'expect' this input level, and won't run at full tilt with a 1V signal. Conversely, a consumer type amplifier may be overdriven if you plug it into a professional device, unless you have some way of lowering the volume on that device.

You need to contact Apollon or whoever to ask what the input sensitivity of their amp is. It may be adjustable, since although these amps may use hypex modules, they often have a separate sort of pre-amplifier which may be of their design. This smaller amplification stage may expect a 1v signal, or a 2.83v signal, or whatever. Another manufacturer using the same module may have a different input sensitivity. In any case, it is best to ask.

Just email and ask 'My AVR outputs a 1V signal - will this be sufficient for full output levels' or something like that.

 

[Blumlein 88]

It is about gain. Your amp will amplify the input voltage, and the resulting output voltage across the load determines power output. Skipping some stuff, to get 380 watts at 8 ohms requires the amplifier output a signal of 55 volts. So you need to boost the input from 1 volt to 55 volts. This would be 35 db of gain. That amp has variable gain settings, but the highest one is 29 db. So you would be 6 db short of max power, and that would equate to 1/4th the power. You need 2 volts in to get 55 volts out at full power at the max Hypex gain of 29 db.

One moment, please...

 

[Symphoniac]

It is about gain. Your amp will amplify the input voltage, and the resulting output voltage across the load determines power output. Skipping some stuff, to get 380 watts at 8 ohms requires the amplifier output a signal of 55 volts. So you need to boost the input from 1 volt to 55 volts. This would be 35 db of gain. That amp has variable gain settings, but the highest one is 29 db. So you would be 6 db short of max power, and that would equate to 1/4th the power. You need 2 volts in to get 55 volts out at full power at the max Hypex gain of 29 db.

One moment, please...

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Thanks for the thorough explanation! Does this then imply that the maximum wattage I get with my 1V pre-out is roughly 3/4 x 380W = 285W? Since that extra 100W is wasted, then does it make sense to limit my purchase to power amps that are rated around 285W (assuming they support 29db gain)? Also, I assume there is no headroom at this 285W figure, meaning that really I should get something rated much lower, 200W, to allow for dynamic range?

 

[sam_adams]

From the available Ncore spec sheet:

 

[Blumlein 88]

Thanks for the thorough explanation! Does this then imply that the maximum wattage I get with my 1V pre-out is roughly 3/4 x 380W = 285W? Since that extra 100W is wasted, then does it make sense to limit my purchase to power amps that are rated around 285W (assuming they support 29db gain)? Also, I assume there is no headroom at this 285W figure, meaning that really I should get something rated much lower, 200W, to allow for dynamic range?

Not quite. When I said 1/4th the power, that is what the resulting output would be. About 95 watts. As to what amps you look at it isn't so much limiting power output, you first need to determine how much output your speakers need and then match that to something that will put out that much with a 1 volt input. For instance if you speakers only needed 100 watts or less, the amp you listed is fine, and will never be stressed yet you have all the power your speakers need. 1 volt out is on the low side of things and you don't see lots of amps with more than 29 db of gain. So the 1 volt of your pre out is going to be a limiting factor, but not necessarily an impossible one.

So first question, how much power do you need? Work from there.

 

[Symphoniac]

Not quite. When I said 1/4th the power, that is what the resulting output would be. About 95 watts. As to what amps you look at it isn't so much limiting power output, you first need to determine how much output your speakers need and then match that to something that will put out that much with a 1 volt input. For instance if you speakers only needed 100 watts or less, the amp you listed is fine, and will never be stressed yet you have all the power your speakers need. 1 volt out is on the low side of things and you don't see lots of amps with more than 29 db of gain. So the 1 volt of your pre out is going to be a limiting factor, but not necessarily an impossible one.

So first question, how much power do you need? Work from there.

Ok i think I follow, so basically sqrt(95*8)/29 = .95 or approx 1v. If this math is correct, it seems i am unlikely to get more than 100w at 8ohm with any external power amp, so might as well just stick to using my integrated, which already puts out 100w at 8ohms.

 

[Blumlein 88]

Ok i think I follow, so basically sqrt(95*8)/29 = .95 or approx 1v.

Yeah, close enough.

 

[Symphoniac]

Quick update... I saw that Audioholics bench tested the RN1000a, whose internals should be very similar to my RN800a, and I was pleasantly surprised to see the pre-out was measured at at greater than 3V despite its nominal 1V rating (same rating as RN800a). Graph below is from Audioholics, and you can also see that you get a little extra power by enabling pure-direct. Assuming this test result applies to RN800a (might be a big assumption), can I now assume I'll get full power from the Apollon or any similar power amp that requires less than 4V of input power?

 

[Blumlein 88]

Get a multimeter. Measure a 400 hz sine wave at the preamp output jacks. You will know the output without relying on specs. If it is 3 volts, then you are good to go.

 

[Symphoniac]

Get a multimeter. Measure a 400 hz sine wave at the preamp output jacks. You will know the output without relying on specs. If it is 3 volts, then you are good to go.

Would something like this work? Thanks for the suggestion, I had no idea this was something I could measure without expensive equipmen!

 

[Sokel]

Would something like this work? Thanks for the suggestion, I had no idea this was something I could measure without expensive equipmen!

Yes,it should work,best use a 100Hz signal.
Do you know how to measure or you need a mini guide?

 

[Symphoniac]

Yes,it should work,best use a 100Hz signal.
Do you know how to measure or you need a mini guide?

I'm totally ignorant, so any links to newbie guide would be great, thanks!

 

[JeremyFife]

The power amplifier(s) you mention are good. Your Yamaha is pretty decent too.

Get an amp, try it out. Worst case, you need another upgrade but I'd be really surprised if it doesn't sound good, and loud.

 

[Sokel]

I'm totally ignorant, so any links to newbie guide would be great, thanks!

Ok,first disconnect everything from your amp,speakers,subs,etc.
Find a stereo 100Hz 0dbFS test signal and have it ready for playback
Put your DMM's dial to the 200V range on the right (where it shows the alternative sign)

Now comes the tricky part as you must not short the probes under any condition.
Find a sacrificial,old RCA cable (one will do,you don't need stereo) cut the one plug and expose the two wires inside.
Make sure they don't touch each other.Plug the other end to one of the preout
Put each DMM's probe to each wire (don't short them!) ,playback the file and read the reading at full output.
Repeat with the other channel.
Keep the duration of playback as short as possible,a 4-5 sec file is enough.

 

[Ron Texas]

There's nothing wrong with your RN800A. Save your money.

 

[Symphoniac]

Ok,first disconnect everything from your amp,speakers,subs,etc.
Find a stereo 100Hz 0dbFS test signal and have it ready for playback
Put your DMM's dial to the 200V range on the right (where it shows the alternative sign)

Now comes the tricky part as you must not short the probes under any condition.
Find a sacrificial,old RCA cable (one will do,you don't need stereo) cut the one plug and expose the two wires inside.
Make sure they don't touch each other.Plug the other end to one of the preout
Put each DMM's probe to each wire (don't short them!) ,playback the file and read the reading at full output.
Repeat with the other channel.
Keep the duration of playback as short as possible,a 4-5 sec file is enough.

I really appreciate you writing this up yourself! (I thought you might just supply a link)

Now I just need to order a multimeter... not that anyone is holding their breaths, but I will report back here on what I find/measure just to close the loop.

 

[Blumlein 88]

Would something like this work? Thanks for the suggestion, I had no idea this was something I could measure without expensive equipmen!

I would say no or iffy on that meter. The lowest AC voltage scale is 200 volts. It supposedly will measure to the nearest .1 volts, but that low on the scale the accuracy is iffy. You'll be measuring somewhere around 1 volt perhaps on a 200 volt scale. It is digital and no problem to read, but that reading may not be highly accurate. Sorry to complicate matters.

 

[Blumlein 88]

Amazon.com

This meter might be more suitable. It claims to have plenty of low voltage accuracy for your purposes. About $10 more.

 

[Symphoniac]

Ok,first disconnect everything from your amp,speakers,subs,etc.
Find a stereo 100Hz 0dbFS test signal and have it ready for playback
Put your DMM's dial to the 200V range on the right (where it shows the alternative sign)

Now comes the tricky part as you must not short the probes under any condition.
Find a sacrificial,old RCA cable (one will do,you don't need stereo) cut the one plug and expose the two wires inside.
Make sure they don't touch each other.Plug the other end to one of the preout
Put each DMM's probe to each wire (don't short them!) ,playback the file and read the reading at full output.
Repeat with the other channel.
Keep the duration of playback as short as possible,a 4-5 sec file is enough.

Multimeter delivery is on-route, and in the meantime, I got an RCA cable stripped and ready, and am now trying to generate a test signal in REW so I can save it to a wav file on my network attached storage for playback.

Can someone please confirm if the following settings are correct? I set it to 100Hz and 0dbFS, but not sure if the other parameters are correct. For example, should I uncheck the default 'Add dither'? Also, next to dbFS, there is a text box where you can change what appears to be a voltage value. Should I leave this as is (1V)? Lastly, does the channel, L, R, mono, matter? Thanks all!