Anthem D2/D2v/AVM50/AVM50v/ARC1 tweaking guide - Page 1119

Well Said by Bob Who

Well Said by Bob Who

Thanks Bob, this is a great thread.

OK, here is a question that has been bugging me for a while regarding HT setups.

Suppose I am using a couple of different amp types with different voltage gains, say a pair of monoblocks for my front L+R and then a 5 channel amp for my center, surrounds and rears. The monoblocks have a voltage gain of 29 and the 5 channel amp has a voltage gain of 26.

Won't there be a volume tracking issue? That is as I turn up the volume won't the L+R volume increase faster than the other speakers?

Is there anything that the D2V can do to compensate for this? Will ARC compensate for this?

I don't think you're looking at voltage gain correctly. The monoblocks would have a power output of 105 watts into an 8 ohm impedance. The 5 channel would have 85 watts. That doesn't mean the monoblocks get to a given volume level "faster". The relative levels are set in the prepro.

When you set the speaker level in the setup this should compensate for the diferent gain. You may have to increase the S and R speakers to reach 75 DB but once set the pre will increase linearly.

This is how I understand it. I am am wrong I am sure someone will correct me

I am in a similar situation and have had no issues with the sound being at the correct volume at all levels.

OK, let me explain my concern in a little more detail. When you turn up the volume on a preamp you are increasing the voltage on the amp input. The amp output then increases according to the amp gain. Now you use the Anthem to set all the speakers at 75db at one particular volume setting they all match at that setting. However if you turn up the volume again, the voltage at the amp input terminals increases across all the amps by some amount. Since some of the amps have different voltage gains, the power output of the amps will increase at different rates for each voltage increment, and thus potentially the speaker output will increase at different rates. You may have a level match at that one volume setting, but nowhere else.

So as rovingtravler says, the level correction actually corrects the preamp gain so that the match is maintained across the whole volume range. That sounds pretty encouraging. Can anyone verify that this is the case?

That's not correct. The rates are not different for each voltage increment. As I said, the different voltage gains simply mean that the amps have different maximum power outputs into a given impedance.

That definition doesn't agree with anything else I have found on the Internet.

http://en.wikipedia.org/wiki/Gain
http://en.wikipedia.org/wiki/Gain#Example
http://www.diracdelta.co.uk/science/...in/source.html
http://www.softwareforeducation.com/...age-GainWS.php

It does not say anywhere in the links you provided that the decibel gain from a given voltage increase depends on how many volts the amplifier is capable of putting out.

If Vout is 5 volts greater than Vin in the below formula, it doesn't magically become 8 volts greater in the monoblocks:



It's the same 5 volt increase, and will result in an identical dB gain.

Yes, if you are at the max output of the amp your gain will not be a constant as you increase the input voltage. However that doesn't affect the definition of voltage gain as being Vout/Vin. This variation in gain with input is what is called clipping. The waveform changes that occur due to the variable gain are the distortion of the signal that occurs at clipping.

Below that max power output the voltage gain should be a constant. An ideal amp would have constant gain over all combinations of input and output voltages. Of course no such thing exists.

In regard to the equation you showed, lets consider 2 amps, Amp1 with a gain of 2, and the Amp2 with a gain of 10. With amp1 if I increase the input voltage (if I am below the max power output) from 1V to 2V the output voltage will increase according to the gain formula

With amp1 if I increase the input voltage (if I am below the max power output) from 1V to 2V the output voltage will increase according to the gain formula.

With amp2 if I increase the input voltage (if I am below the max power output) from 1V to 2V the output voltage will increase according to the gain formula. Since the gain for this amp is higher the voltage increase will be larger.

Plug the numbers in and solve the equations for yourself to see the impact of the different gains on output voltage.

That's exactly my point. Vout/Vin will be the same for all amps below their maximum output, regardless of whether or not the maximum output is the same.

I think you're confused about what the voltage gain spec is for amps. It doesn't mean "the voltage gain for any given voltage input". It means the voltage gain for the amp at the rated voltage input. If that weren't the case, the monoblocks would always put out 29 volts, regardless of what the preamp puts out. In other words, you seem to think Vout is always 29 for the monoblocks in the formula I cited.

Vout/Vin is not the same for all amps below their max output. Look at the gain equation. If Vout/Vin were the same for all amps then every amp would have the same gain. That is clearly not the case.

However Vout/Vin is the same for a given amp over a range of voltage inputs up until the max power has been reached. If it weren't the voltage waveform representing the music would be distorted by the amp.

Since the voltage gain is constant up until max power there is no sense to specify "at max output" because in fact the gain is the same at any output BELOW max output".

I didn't say all amps have the same gain. I said the ratio Vout/Vin would be the same for all amps.

If I input, say, 100 mV to amp A, it will have a certain output voltage (gain). If I input the same voltage to amp B, it may well have a different output voltage (gain). That's what the level adjustments are for in the prepro. It adjusts the voltage the prepro sends to each amp so they output the same decibel level through the speakers. If, however, I increase the voltage output (volume), the Vout/Vin for amp A will be the same as for amp B. So the decibel gain will be the same. You DO have to specify the input voltage for the gain, otherwise you'd be saying that the monoblocks put out 29V even if the prepro is only sending them 50 mv.

So basically you are still saying the gain definition and equation from the several references I provided is wrong?

If the equation isn't wrong the gain is determined by Vout/Vin and nothing else. If Vout/Vin is the same then the gain is the same. You can't have a situation where Vout/Vin are the same and the gain is different with this equation.

Do you have another proposal as to how gain should be calculated? And references to back it up?

If you don't have an alternative I think we have reached an impasse here and I'm going to give up because everything else you are saying is in conflict with the well established definition of voltage gain I provided earlier.

Let me try citing the spec sheet from a Krell amp. It states:

Gain: 25.4 dB
Input sensitivity: 3.04V
Output voltage: 57V RMS

The dB gain is obviously a constant. The voltage gain for a 3.04 volt input is 57/3.04, or 18.75. if you take the log of 18.75 and multiply it by 20, you get 25.46, which agrees with the dB gain. Now obviously, if you only input ONE volt, the amp will put out less voltage (that's what the volume control is for). It should be obvious that the ratio needs to be a constant 18.75 for the gain to be constant. Now let's say that another amp puts out 40V, with an input sensitivity of 2V (voltage gain of 20). Let's further assume the same speakers. Do the math, and the amp has a gain of 26 db. So you decrease the level in the prepro by 0.6 dB to match the Krell. Now the two are matched. The Krell needs 1.07 times as much input voltage as the second amp to match output levels. So if you input 0.5 volt to the second amp, you input 0.535v to the Krell.

Now, if you increase the volume by 10 db, you need to increase the voltage to the second amp by a factor of 3.16. Now it's getting 1.58V. For the Krell, the factor is the same, so it's getting 1.69 volts. Vout/Vin is the same for both amps. So is the multiplication factor for the two amps. Note that I've increased the volume while maintaining the same voltage gain of each of the amps. Perhaps I didn't make myself clear earlier. Vout/Vin isn't the same for all dB increases, but it is the same for the voltage gain for a given amp.

No. Vout is the same, but Vin isn't. Therefore Vout/Vin is different for the two amps.

Sorry, I should have said each amp. Anyway, I think my post answers your original question.

No, you are incorrect, it is linear. This is why you adjust the levels individually that connect to the different amp inputs - so that the outputs track each other. Don't assume there is a one to one correspondence between voltage and power!

Rather than challenge me to a game of 'my internet reference beats your internet reference' just think - if what you said were true, then NO ONE would ever be able to use different amps in a system if they didn't have 'matching voltage gains.' Every time you changed the volume, the relative balance would vary. And I think we all know that just doesn't happen.

What about using speakers of different sensitivities in the system. Does that complicate things a bit in terms of sound volume?

Ben

As long as the amps and speakers are linear in their response, none of these differences in gain or sensitivity make ANY difference in volume balance. You simply adjust the level of input to each amp channel so as to balance the resulting output of each speaker.

If the speakers are balanced at one audio content level they will remain balanced at other content levels because of the linear response on each amp+speaker path. This is not rocket science.

E.g., twice the input to each amp yields twice the output on each speaker regardless of amp gain or speaker sensitivity differences BECAUSE the response is linear. That's what linear means. It's the input levels that are different after you balance the channels, but that difference only has to be set once.

Problems only arise if you mismatch components so that they can't be operated linearly, such as by forcing an amp to clip or a speaker to bottom out or asking an amp to drive a speaker of such low sensitivity that the amp output can't handle the load.

So volume matching is not a problem.

Nevertheless, mixing different components may be undesirable for other reasons, such as timbre mismatches between different speaker designs, or variation in ability to track transients in different amp designs. These can produce a lack of seamless blending in the surround field.
--Bob

Yes, ultimately this was my question - whether the volume matching process adjusts the preamp gain or just the preamp voltage level. I hadn't considered the fact that there are also speakers in the system with their own gains which of course would never work if the level matching system only adjusted the preamp level even if all the amps in the system had the same gain. If the system response (R) is linear (which it has to be) it follows the relation R = gain*input + constant. The preamp level match could work be setting the preamp gain or the constant to get a level match. I'm confident now that it adjusts the preamp gain.

Thanks to all who answered my question. Now all I have to do is wait for my monoblocks to arrive.


Not to mention effects of room location etc. These are non-linear and we are hoping for ARC someday to fix all of them.

No... the gain of an amp is constant for a given load (and if its not clipping) so if Vin changes, them Vo changes as well to keep the gain constant.

Go back and read the grandparent message. There are two different amps involved here.

I've just received my Oppo BDP-95 replacing my BD-83, under video what's the best option for watching Blurays, Source direct or select 1080p or Auto?

I use 1080p or auto. Source direct bypasses all the great features of the 95... if you use that you might as well have stayed with the 83.

I use 1080p so the Anthem does not try to hunt for a certain type of signal and take to long. I then have my DVD video settings for BD 1, DVD 2, Streaming 3, in the Anthem setup

I told my installer about this and he said he had never heard of this glitch... he talked to anthem directly and they basically said that this is an old issue and there is currently no such problem??????

Can anyone confirm this?

Bob where are you!!! LOL

What glitch are you referring to? Here is the advice given by Bob to set the Volume levels.

Prior to running the ARC measurements, there is another step to do to get the test tone volumes correct:

Using your trusty Radio Shack SPL meter (on Slow Response and C weighting), go into Setup / Speaker Calibration and set the volume trim for the Front Left speaker and for the subwoofer both to 0dB. Then turn on Manual in the first line and scroll down to the Noise Level line. Adjust Noise Level until your Front Left speaker is producing roughly 75dB as measured at your dead center listening position (ARC mic position #1 -- SPL meter pointing straight up). Leave the volume trim setting for the Front Left speaker at 0dB, just adjust the Noise Level line.

Now scroll to the subwoofer line. Leave that line at 0dB but adjust the internal volume knob on your subwoofer until it, too measures roughly 75dB at the same listening position. There is no need to be super precise in these adjustment -- a ball park setting is sufficient.

ARC will use the Noise Level setting you have just made to set the volume for its own test sweep tones, and the adjustment you have just made to your subwoofer's volume knob insures that it, too, can be level adjusted properly to match. If you happen to have any other speakers with internally powered amps (i.e., with a volume control on them) do the same for them.

Back out of the Setup menu. Run the ARC application.

John

Cool thanks for that

I would be interested in your comparison between the two units as it relates to sound and picture quality.