NC502MP with Denon 4800h Preout Voltage

[408revo]

Hi all, I'm looking on some advice on my current HT system. I recently bought a 4 way amp with NC502MP modules (prefer not to mention make). This is my first amp and have no experience with amps. I know I should have done more homework prior to selecting one. With all the great reviews, I decided to go with the 502 for my LCR speakers. Not until after I had purchased my amp, I find out that you "need" to match your preout's voltage to your amp. There is so many contradicting information on what the Denon's actual preout voltage is. Many sources say it's 1.2v, other say it can easily achieve 2v. If I understand correctly, with the NC502MP requiring 2.35v at 4 ohms (i have 4 ohm speakers), I'm not able to get the power the amp is rated for. I'm still within the return window and thinking of returning the amp, and getting an amp that is closer to the Denon's preout voltage. My listing distance is about 12' away and listen around -15 to -10 on the receiver's volume. Currently don't have any subs connected so I run my LCRs large. I'm just trying to have headroom so when I connect the additional height speakers.

Question, am I understanding this correctly or am I overthinking it and would be fine keeping the 502? I would hate to find out that I actually have less power than connecting directly to the receiver. Also, I noticed that when I reran Audyssey with the amp connected, my trims were adjusted by about +3.5 dBs. Seems that the receiver had to increase the preout voltage by increasing the trims on the LCR channels?

Apologies in advance if I'm not making sense or asking the wrong questions. Any advice would be greatly appreciated. thanks

 

[antcollinet]

Many sources say it's 1.2v, other say it can easily achieve 2v

Test here was done at 2V so it can do at least that. Difference between 2V and 2.35V is 1.4dB - I wouldn't worry about that. Keep the 502.

 

[jdbob]

I expect something similar when I change my external amplifier configuration from using the Denon X4800H's internal amps for LCR, side surrounds, and 4 heights with a Aiyima A70 for the rear surrounds. The new configuration will be a 3 channel Purifi amp for LCR's and the internal amps for all surrounds and heights. According to Amir's review the internal amps in the Denon have 28.7dB of gain while the Purifi (on high gain) has 25dB. So 3.7dB extra output required, so 3.5dB will be the closest.

I just recently ran a new Dirac calibration when I upgraded my height speakers, so I'll just make the adjustment in the Denon levels page, probably have to adjust the rear surround levels as well.

 

[408revo]

thank you for your replies. This stuff can be really confusing. But looks like I should be ok with the 502.

 

[jdbob]

Think I missed something. Since I need to use the RCA to XLR cable I think I should see a loss of 6dB since the voltage will only swing half as much. Or is it 3dB because we are talking about power on the output of the amplifier, I'm so confused. Also, Amir got the 28.7dB of gain on the Denon by using the analog input, but I wonder if that actually equates to what happens when feeding the Denon's pre-amp output to the input of the power amplifier. I see no reason that they would actually have to be identical. Might be fun to use REW to feed a sine wave in and measure the voltage from the pre-amp output and compare it with the voltage to the speaker.

 

[Redacted]

Is the Denon feeding normal unbalanced line level (RCA) into a balanced XRL-type input on the the new 502 amp?

Without knowing what the new amp is, there's only scope for guessing.. Some amps have selectable input levels for example.

 

[Ruediger]

I highly recommend to do a new calibration / room correction measurement once everything is set up.

I haven't seen these exact numbers when switching from internal amps to external.

 

[jdbob]

Did the test for how much gain the X4800H's internal amplifiers have, pretty close to what Amir came up with. Using REW feeding HDMI into the AVR and setting a 60Hz sine wave to a comfortable level I measured 0.101 V RMS on the preamp output and 2.862 RMS on the speaker output. This comes out to a gain of 29.05dB.

So, the Purifi 1ET6525SA 3 Channel unit from Buckeye has 25dB for the high gain setting, minus the 6dB for single-ended to XLR configuration is 19dB, so 10dB less than the Denon's amplifiers. I normally listen between -25 and -30 on the volume control so should still be plenty of headroom although I will probably have to max out the LCR trims and possibly bump the other channels a bit down to match levels.

 

[408revo]

@jdbob, new to all this but trying to to make sense of your test. If you can help me understand how you only got .101v out the preamp outputs. I thought you should be getting around 2v? Also how does adding the preouts and speaker outputs (.101v+2.862v) equate to 29.05dB?

 

[Chrispy]

Think I missed something. Since I need to use the RCA to XLR cable I think I should see a loss of 6dB since the voltage will only swing half as much. Or is it 3dB because we are talking about power on the output of the amplifier, I'm so confused. Also, Amir got the 28.7dB of gain on the Denon by using the analog input, but I wonder if that actually equates to what happens when feeding the Denon's pre-amp output to the input of the power amplifier. I see no reason that they would actually have to be identical. Might be fun to use REW to feed a sine wave in and measure the voltage from the pre-amp output and compare it with the voltage to the speaker

How do you figure that?

 

[jdbob]

@jdbob, new to all this but trying to to make sense of your test. If you can help me understand how you only got .101v out the preamp outputs. I thought you should be getting around 2v? Also how does adding the preouts and speaker outputs (.101v+2.862v) equate to 29.05dB?

I did say "comfortable level" No need to make it full output level since I just needed the ratio between preamp output and speaker output at the same level.

I used Voltage to dB Calculator with the voltage ratio conversion mode.

 

[jdbob]

How do you figure that?

You need to be more specific about what "that" refers to. Also, did you read my followup posts?

 

[408revo]

I did say "comfortable level" No need to make it full output level since I just needed the ratio between preamp output and speaker output at the same level.

I used Voltage to dB Calculator with the voltage ratio conversion mode.

got it. thank you

 

[Chrispy]

You need to be more specific about what "that" refers to. Also, did you read my followup posts?

That the cable changes gain or voltage.

 

[jdbob]

That the cable changes gain or voltage.

It's not so much that the cable itself is making the change, it's a difference between what the source (like an AVR with a RCA output) and destination (like an amp with a XLR input). The XLR is used for balanced inputs. In addition to the ground there are two signal wires, when one goes positive, the other goes negative. The amp only uses the difference between the two which helps to ignore any noise picked up by the cable. It also means that difference is twice the voltage as just one signal wire. So if one of of signal wires is 1 volt, the other one is minus 1 volt, so 2 volts total difference.

When you drive this with a RCA output signal the center of the RCA connector is connected to the "positive" input on the XLR but since the RCA only has one polarity of signal the "negative" on the XLR is tied to ground. So if the positive signal wire is 1 volt, the negative is stuck at 0 volts. The amp will look at the difference as before, but it can only see 1 volt, not the 2 volts as before. This halving of the signal voltage converts to 6dB less signal.

 

[Chrispy]

It's not so much that the cable itself is making the change, it's a difference between what the source (like an AVR with a RCA output) and destination (like an amp with a XLR input). The XLR is used for balanced inputs. In addition to the ground there are two signal wires, when one goes positive, the other goes negative. The amp only uses the difference between the two which helps to ignore any noise picked up by the cable. It also means that difference is twice the voltage as just one signal wire. So if one of of signal wires is 1 volt, the other one is minus 1 volt, so 2 volts total difference.

When you drive this with a RCA output signal the center of the RCA connector is connected to the "positive" input on the XLR but since the RCA only has one polarity of signal the "negative" on the XLR is tied to ground. So if the positive signal wire is 1 volt, the negative is stuck at 0 volts. The amp will look at the difference as before, but it can only see 1 volt, not the 2 volts as before. This halving of the signal voltage converts to 6dB less signal.

The voltage is what it is and the amp will apply what gain it can/is set to. Your example doesn't apply in this case afaict. The Denon should have no problem with low 2V range in any case.

 

[Trdat]

The Hypex Spec sheet has a section on input sensitivity.

I use the Marantz AV 7005 and according to Amir's measurements of a few of the later versions and if I have understood correctly with the volume towards the top it can output close to 6 volts, if not more.

The NC502 must be taking some peaks of significantly higher than 2 volts.

 

[antcollinet]

Since I need to use the RCA to XLR cable I think I should see a loss of 6dB

There is no loss as such. Whatever voltage the denon pre outs put out, that is what the Amp receives on it's input - whatever type of input that is.

This is multiplied by the gain (25dB) to give the output voltage.

What you are thinking of (I think) is that unbalanced outputs typically put out half the voltage of balanced outputs. Say 2V instead of 4V.

But that is not a loss. It is just a lower output.

2V into the amp with 25dB gain will output 36.5V - enough for 316W into 4 ohms, or half that into 8.

 

[408revo]

There is no loss as such. Whatever voltage the denon pre outs put out, that is what the Amp receives on it's input - whatever type of input that is.

This is multiplied by the gain (25dB) to give the output voltage.

What you are thinking of (I think) is that unbalanced outputs typically put out half the voltage of balanced outputs. Say 2V instead of 4V.

But that is not a loss. It is just a lower output.

2V into the amp with 25dB gain will output 36.5V - enough for 316W into 4 ohms, or half that into 8.

So that I understand, let’s say the Denon had balanced outputs in addition to the rca preouts, those would be putting out 4v? That’s where the 6dB difference would be true?

 

[antcollinet]

So that I understand, let’s say the Denon had balanced outputs in addition to the rca preouts, those would be putting out 4v? That’s where the 6dB difference would be true?

A difference - not a loss. But it also depends on the specific design of the device.