How important is external amp gain?

[AcuDefTechGuy]

So if someone inadvertently turns on the Preamp Mode (not using any external amps), will the AVR output anything to the speakers?

 

[VMPS-TIII]

He did ask about 400 watts into 4 ohms. I calculated 29.13db and rounded up to 30db of gain. (I always round up for requirements. It's a conservative design thing with me.) Since there are several amps out there with a rated gain of 32db, they would probably be the best choices with many AVRs. I'm guessing that's why the amp designers seem to be settling on 32db of gain for single-ended inputs.

I'm smiling... my calculations look correct.

The Purifi 1ET400A based amps have balanced inputs that can be used with a Male XLR to single ended RCA cable for a non-balanced pre-amp.

Power Output Per Channel
2 Ohms - 450 W rms
4 Ohms - 425 W rms
8 Ohms - 227 W rms
The original design configuration is with a 26.5dB gain

Am I correct in thinking the 26.5dB gain is fine with balanced inputs as most can provide a 4v gain vs RCA is limited to 2V gain? So it's only an issue if you try to use the Purifi 1ET400A amp with an AVR with no balanced pre-outs that the 26.5dB gain might be insufficient to fully drive a speaker with an 85dB sensitivity?

Thank you!

 

[VMPS-TIII]

So if someone inadvertently turns on the Preamp Mode (not using any external amps), will the AVR output anything to the speakers?

No sound goes to the speakers while in preamp mode under the situation you outlined.

With the Denon 4700 in Pre-amp mode nothing is sent to the speakers until the external amp(s) are turned on.

 

[AcuDefTechGuy]

No sound goes to the speakers while in preamp mode under the situation you outlined.

With the Denon 4700 in Pre-amp mode nothing is sent to the speakers until the external amp(s) are turned on.

Someone could accidentally turned on the Pre-amp mode and won't hear any sound from their speakers and wonder if their AVR is broken.

 

[Irvrobinson]

The Purifi 1ET400A based amps have balanced inputs that can be used with a Male XLR to single ended RCA cable for a non-balanced pre-amp.

Power Output Per Channel
2 Ohms - 450 W rms
4 Ohms - 425 W rms
8 Ohms - 227 W rms
The original design configuration is with a 26.5dB gain

Am I correct in thinking the 26.5dB gain is fine with balanced inputs as most can provide a 4v gain vs RCA is limited to 2V gain? So it's only an issue if you try to use the Purifi 1ET400A amp with an AVR with no balanced pre-outs that the 26.5dB gain might be insufficient to fully drive a speaker with an 85dB sensitivity?

Thank you!

Your question is confusing me a little, but I think the answer is no. I think you want an amp with a minimum gain of 29db for the single-ended inputs.

 

[VMPS-TIII]

Someone could accidentally turned on the Pre-amp mode and won't hear any sound from their speakers and wonder if their AVR is broken.

It's pretty much impossible to turn pre-amp mode on accidentally. You have to go into amp assign select it then run Audyssey for it to take effect.

 

[PENG]

The Purifi 1ET400A based amps have balanced inputs that can be used with a Male XLR to single ended RCA cable for a non-balanced pre-amp.

If you use such an adapter you will get half the voltage.

Am I correct in thinking the 26.5dB gain is fine with balanced inputs as most can provide a 4v gain vs RCA is limited to 2V gain? So it's only an issue if you try to use the Purifi 1ET400A amp with an AVR with no balanced pre-outs that the 26.5dB gain might be insufficient to fully drive a speaker with an 85dB sensitivity?

You would be correct if the 26.5 dB gain is for balanced output, and the balanced output is rated 4 V. What is need to be sure about is the gain for the unbalanced output, you would want it to be 29 dB for use with a Denon or Marantz AVR, if you want the power amp to output up to 400 W into 8 ohms or 800 W into 4 ohms. For those who only need 200 W into 8 ohms, 400 W into 4 ohms, 26.5 dB would be fine too for unbalanced (RCA) inputs.

 

[VMPS-TIII]

Your question is confusing me a little, but I think the answer is no. I think you want an amp with a minimum gain of 29db for the single-ended inputs.

Sorry, not trying to confuse. The Purifi 1ET400A design has no RCA outs only XLR. The only way you can hook it up to a single-ended receiver would be with an adapter cable of Male XLR to male RCA.

If my reading is correct XLR outputs from the various DACs I have been looking at offer twice the output voltage with XLR outs as with RCA. That leads me to believe the lower amp gain of 26.5dB is fine with XLR inputs but if unbalanced is used the 29dB would be preferable.

 

[PENG]

Sorry, not trying to confuse. The Purifi 1ET400A design has no RCA outs only XLR. The only way you can hook it up to a single-ended receiver would be with an adapter cable of Male XLR to male RCA.

If my reading is correct XLR outputs from the various DACs I have been looking at offer twice the output voltage with XLR outs as with RCA. That leads me to believe the lower amp gain of 26.5dB is fine with XLR inputs but if unbalanced is used the 29dB would be preferable.

Yes, but let's be clear, in your case the Denon AVR does not have XLR input so go with 29 dB. The adapter won't help in terms of voltage.

 

[VMPS-TIII]

You would be correct if the 26.5 dB gain is for balanced output, and the balanced output is rated 4 V. What is need to be sure about is the gain for the unbalanced output, you would want it to be 29 dB for use with a Denon or Marantz AVR, if you want the power amp to output up to 400 W into 8 ohms or 800 W into 4 ohms. For those who only need 200 W into 8 ohms, 400 W into 4 ohms, 26.5 dB would be fine too for unbalanced (RCA) inputs.

The amp design only offers 227W in 8 ohms. It reaches 425W with 4 ohm speakers. It sounds like it would be preferable to use balanced connectors with the Purifi 1ET400A design to enable higher gain and lower noise. Rather than modify the original spec to a higher gain and possibly introduce another stage for noise.

Power Output Per Channel (Purifi 1ET400A design)
2 Ohms - 450 W rms
4 Ohms - 425 W rms
8 Ohms - 227 W rms

 

[AcuDefTechGuy]

It's pretty much impossible to turn pre-amp mode on accidentally. You have to go into amp assign select it then run Audyssey for it to take effect.

Someone could turn on Pre-amp mode when they first bought it. Then return the unit to the store. Then the new buyer (who bought it used) might think it's defective since he hooked his speakers to the AVR and got no sound.

The main question is, why is the Pre-amp Mode even necessary?

Why can't they make the AVR with pre-out 2 Vrms and operate at a cooler temperature?

This reminds of how a Toyota Engine can drive with the full V6 and have excellent fuel economy, but a Honda needs to employ a feature that requires the engine to SHUT DOWN 2 valves to get excellent fuel economy.

 

[Irvrobinson]

Sorry, not trying to confuse. The Purifi 1ET400A design has no RCA outs only XLR. The only way you can hook it up to a single-ended receiver would be with an adapter cable of Male XLR to male RCA.

If my reading is correct XLR outputs from the various DACs I have been looking at offer twice the output voltage with XLR outs as with RCA. That leads me to believe the lower amp gain of 26.5dB is fine with XLR inputs but if unbalanced is used the 29dB would be preferable.

Here's the salient point (sorry, ADTG, your special favorite word was just the most appropriate here), XLR to RCA cables like this one:

Benchmark RCA to XLRM Adapter Cable for Analog Audio - pin 3 to RCA shield

BENCHMARK STUDIO STAGE™ RCA TO XLRM ADAPTER CABLE CABLES ARE SOLD INDIVIDUALLY. Price is for one cable, order 2 for a stereo pair. Hand assembled in the USA with true silver solder Applications This special adapter cable connects unbalanced analog RCA outputs to balanced analog XLR inputs. Use...

benchmarkmedia.com

Are really intended to be used from an XLR output to an RCA input.

What you're proposing to do is the other way around, driving an XLR input with a single-ended output. Correct? I think you're going to end up with at least 3db lower output (to the amp with a balanced input) than you need.

 

[VMPS-TIII]

Someone could turn on Pre-amp mode when they first bought it. Then return the unit to the store. Then the new buyer (who bought it used) might think it's defective since he hooked his speakers to the AVR and got no sound.

Only if he can't read and doesn't setup Audyssey. lol

 

[VMPS-TIII]

Here's the salient point (sorry, ADTG, your special favorite word was just the most appropriate here), XLR to RCA cables like this one:

Benchmark RCA to XLRM Adapter Cable for Analog Audio - pin 3 to RCA shield

BENCHMARK STUDIO STAGE™ RCA TO XLRM ADAPTER CABLE CABLES ARE SOLD INDIVIDUALLY. Price is for one cable, order 2 for a stereo pair. Hand assembled in the USA with true silver solder Applications This special adapter cable connects unbalanced analog RCA outputs to balanced analog XLR inputs. Use...

benchmarkmedia.com

Are really intended to be used from an XLR output to an RCA input.

What you're proposing to do is the other way around, driving an XLR input with a single-ended output. Correct? I think you're going to end up with at least 3db lower output (to the amp with a balanced input) than you need.

@Irvrobinson - I agree. If I drive the Purifi 1ET400A amp from a Denon RCA pre-out to a male XLR input on the amp it should have reduced speaker output as the RCA has 1/2 the voltage of an XLR connection.

Hooking the amp up to a quality DAC with XLR outputs would offer significantly higher gain. Increasing gain from 26.5 to 29dB would help overcome the RCA issue.

 

[PENG]

The amp design only offers 227W in 8 ohms. It reaches 425W with 4 ohm speakers. It sounds like it would be preferable to use balanced connectors with the Purifi 1ET400A design to enable higher gain and lower noise. Rather than modify the original spec to a higher gain and possibly introduce another stage for noise.

Power Output Per Channel (Purifi 1ET400A design)
2 Ohms - 450 W rms
4 Ohms - 425 W rms
8 Ohms - 227 W rms

Yes, you can sort of say that about the Purifi amp you are referring to.. Some power amps have 6 dB lower gain (such as Bryston and Parasound, Yamaha, Marantz's and many more) for XLR inputs such that their gain would typically be 29 dB for RCA and 23 dB for XLR. Some power amps offer the same gain, whether it be 26, 28 or 29 dB. Some, like the Purifi, has XLR inputs only, and the gain, being at 26.5 dB, is actually on the higher side, than others.

Now, on a slightly different topic, the 1ET400A's output specs you listed are based on 1% THD+N. I am not saying 1% THD is audible, but the numbers would be much lower if you based the outputs on say 0.005% THD such as the levels that ASR typically used when measuring the Denon AVRs.

 

[AcuDefTechGuy]

Here's the salient point (sorry, ADTG, your special favorite word was just the most appropriate here)...

How dare you!

Now I'm going to have to use a different favorite word - Nexus = Most Important Point.

Here's the nexus...

 

[slipperybidness]

Sorry, not trying to confuse. The Purifi 1ET400A design has no RCA outs only XLR. The only way you can hook it up to a single-ended receiver would be with an adapter cable of Male XLR to male RCA.

If my reading is correct XLR outputs from the various DACs I have been looking at offer twice the output voltage with XLR outs as with RCA. That leads me to believe the lower amp gain of 26.5dB is fine with XLR inputs but if unbalanced is used the 29dB would be preferable.

Good that you clarified this item! When I was speaking about 29-32dB of gain being a typical range, I was indeed specifically referring to single ended (i.e. RCA) inputs. I assumed single ended b/c that is the default choice for consumer grade gear.

 

[VMPS-TIII]

Yes, you can sort of say that about the Purifi amp you are referring to.. Some power amps have 6 dB lower gain (such as Bryston and Parasound, Yamaha, Marantz's and many more) for XLR inputs such that their gain would typically be 29 dB for RCA and 23 dB for XLR. Some power amps offer the same gain, whether it be 26, 28 or 29 dB. Some, like the Purifi, has XLR inputs only, and the gain, being at 26.5 dB, is actually on the higher side, than others.

Now, on a slightly different topic, the 1ET400A's output specs you listed are based on 1% THD+N. I am not saying 1% THD is audible, but the numbers would be much lower if you based the outputs on say 0.005% THD such as the levels that ASR typically used when measuring the Denon AVRs.

Here is a 257W reading at 4 ohms with THD+N 0.0002%

 

[PENG]

Here is a 257W reading at 4 ohms with THD+N 0.0002%

View attachment 41709

That's good, that ASR actually measure done. You can see that if you accept 0.005%, you will get over 300 W.