AVR using preouts + internal amplification

[flyingflatfour]

Hi everyone,

In the context of using an AV Receiver‘s preouts for the front stage but using internal amplification for the 4 surround channels in a 7.1 configuration, I would like to understand how this mixed setup works to avoid running into a less than optimal situation.

I have indeed recently understood that most AVRs will see their preamp performance degrade significantly past 1.4V due to internal amplification clipping.

I have a Yamaha DSP Z7 (power output was measured at 155 wpc into 8 ohms, 2 ch driven and 225 wpc into 4 ohms, don’t have a 5 ch driven figure) which I would like to use as follows:

- L + R preouts RCAs -> custom balanced cable with pins 1 + 3 terminated to ground on the RCA side -> active tower speakers using XLR connector
- C preout RCA -> balanced or unbalanced cable depending on amp -> mono block amp -> passive center speaker (rated at 8 ohms, 88dB @1W.m ; “recommended power amp 75-300W”)
- SL, SR, SBL, SBR speaker terminals -> 4x passive bookshelf speakers (rated at 8 ohms, 88dB @1W.m ; “recommended power amp 75-300W”)
- LFE preout RCA -> unbalanced cable -> 12” active subwoofer with 400W internal amp.


My concerns are the following:

- the active towers will receive an unbalanced signal from the preamp on their XLR input. The manufacturer says this will work fine as long as pins 1 and 3 are to ground on the RCA side, but will the signal not be 6 dB lower as a result and therefore require the preamp to compensate by adding 6 dB to the L and R channels, potentially reaching clipping sooner than the other channels?

- how can I choose a mono block amp for my center channel in such a way that it can drive the speaker effortlessly but without having the preout clipping?

- how to ensure level matching for all speakers knowing that the range of adjustment is +/- 10 dB on the Z7?


The Z7 may be run in preamp-only mode, but I’m not sure that means it actually physically disconnects the internal amps to avoid the clipping feedback issue.

Any help appreciated

 

[AnalogSteph]

My concerns are the following:

- the active towers will receive an unbalanced signal from the preamp on their XLR input. The manufacturer says this will work fine as long as pins 1 and 3 are to ground on the RCA side, but will the signal not be 6 dB lower as a result and therefore require the preamp to compensate by adding 6 dB to the L and R channels, potentially reaching clipping sooner than the other channels?

No, why? If the preamp outputs 1 Vrms, the balanced input will be seeing 1 Vrms as well.

- how can I choose a mono block amp for my center channel in such a way that it can drive the speaker effortlessly but without having the preout clipping?

It should have about the same gain as the integrated power amps. Maybe a bit more if more powerful. But with the L and R speakers already handled externally, I don't see why you would even need an external power amp for your center, the old DSP-Z7 is no slouch. From German connect magazine review:

Sinusleistung Stereo 8 Ohm - 160,0 W
Sinusleistung Stereo 4 Ohm - 244,0 W
Sinusleistung 5-Kanal 8 Ohm - 115,0 W
Sinusleistung 5-Kanal 4 Ohm - 160,0 W

They've also got a distortion measurement of the preouts:

-60 dB of H2 and -70 dB of H3 at 1 V is serviceable though not very much to write home about. No idea why distortion is relatively high, 1970s integrated amps could already do better than that.
The 90 dB of SNR in ProLogic (down from 100 dB all-analog) isn't exactly super hot either.

- how to ensure level matching for all speakers knowing that the range of adjustment is +/- 10 dB on the Z7?

Since all the rest should be quite similar, you should be able to dial that in via the input sensitivity adjustment on the front speakers.

 

[flyingflatfour]

No, why? If the preamp outputs 1 Vrms, the balanced input will be seeing 1 Vrms as well.

Are you positive? I have read several times there would be a 6 dB loss, but I never found an explanation... This would be the good news, as I just found out that these active speakers have a 1V RMS input sensitivity.

It should have about the same gain as the integrated power amps. Maybe a bit more if more powerful. But with the L and R speakers already handled externally, I don't see why you would even need an external power amp for your center, the old DSP-Z7 is no slouch

.

I know the DSP-Z7 has got some power on tap, but I just want to get the best possible result out of the front scene. Actually I just realised I made a mistake in my opening post: the surround speakers are only 84 dB sensitivity, thus I figured it would be best to have the Z7 take care of those 4 only and externally amplify the front scene.

They've also got a distortion measurement of the preouts:

-60 dB of H2 and -70 dB of H3 at 1 V is serviceable though not very much to write home about. No idea why distortion is relatively high, 1970s integrated amps could already do better than that.
The 90 dB of SNR in ProLogic (down from 100 dB all-analog) isn't exactly super hot either.

Thanks for these measurements. Do they correlate with these ? https://www.audioholics.com/av-receiver-reviews/rx-z7-7.1/rx-z7-measurements
Unfortunately I am not expert enough to be able to compare by myself.

Since all the rest should be quite similar, you should be able to dial that in via the input sensitivity adjustment on the front speakers.

They don’t have such an adjustment but I just figured out they have a 1V input sensitivity which I guess is good news?

 

[flyingflatfour]

I would still like to understand how to choose a power amplifier for my center channel based on it’s sensitivity (88 dB @ 1W.m)? How much power should it have? I guess it depends on the distance from the listening position?

 

[Matias]

A balanced signal uses both the + and - signals, if you ground one of them and use only the other, than yes, the signal will be half as loud (-6dB). But I would not worry about this: if front L+R are not loud enough, just make the other channels lower. Overall volume should be OK.

All level adjustments can be done on the AVR. I have this too in a Marantz SR7005 driving small surround coax speakers directly and pre-outs to a preamp => amp => passive speakers and sub out to active subwoofer.

Preamp is set to a specific volume (I set it every time, but could also use its "HT bypass", I just don't want to maximize its volume). After all set, by ear (lazy, as I could use a noise meter) I set all levels to sound roughly the same.

 

[Lattiboy]

I went through this for a long time and tried out three different 3 channel power amps (Parasound, Sony ES, and 3x Marantz mono amps). None of them were quite powerful enough for my taste in absurdly hard to drive speakers, so I ended up getting a powerful two channel and having my HT receiver drive the center. I’ve done this with the Denon 3500 and 3600 as well as the Marantz SR6012.

Audyssey did all the channel balancing for me and the setup works incredibly well. Now, I can’t speak to your center channel or your listening levels, but with many AVRs offering 200w when driving a single channel, the need for an expensive 3 channel amp is lowered IMO.

 

[iggymasu]

I went through this for a long time and tried out three different 3 channel power amps (Parasound, Sony ES, and 3x Marantz mono amps). None of them were quite powerful enough for my taste in absurdly hard to drive speakers, so I ended up getting a powerful two channel and having my HT receiver drive the center. I’ve done this with the Denon 3500 and 3600 as well as the Marantz SR6012.

Audyssey did all the channel balancing for me and the setup works incredibly well. Now, I can’t speak to your center channel or your listening levels, but with many AVRs offering 200w when driving a single channel, the need for an expensive 3 channel amp is lowered IMO.

What setup are you running now?

 

[flyingflatfour]

A balanced signal uses both the + and - signals, if you ground one of them and use only the other, than yes, the signal will be half as loud (-6dB). But I would not worry about this: if front L+R are not loud enough, just make the other channels lower. Overall volume should be OK.

All level adjustments can be done on the AVR. I have this too in a Marantz SR7005 driving small surround coax speakers directly and pre-outs to a preamp => amp => passive speakers and sub out to active subwoofer.

Preamp is set to a specific volume (I set it every time, but could also use its "HT bypass", I just don't want to maximize its volume). After all set, by ear (lazy, as I could use a noise meter) I set all levels to sound roughly the same.

Thanks for the confirmation.

You are right, you can just lower the other speakers, but in the end of the day you want to calibrate everything (or the AVR will do it automatically for you) to 75 dB(C) @ -30 dBFS at the listening position, and all speakers should be able to push out 105 dB(C) peak SPL...

 

[Lattiboy]

What setup are you running now?

3600H + M-504. I use the 3600 for just the center speaker and it works great. Center is Boston Acoustics VR-12, mains are Infinity Renaissance 80s.... hence they need for external 2ch power amp.

 

[flyingflatfour]

I went through this for a long time and tried out three different 3 channel power amps (Parasound, Sony ES, and 3x Marantz mono amps). None of them were quite powerful enough for my taste in absurdly hard to drive speakers, so I ended up getting a powerful two channel and having my HT receiver drive the center. I’ve done this with the Denon 3500 and 3600 as well as the Marantz SR6012.

Audyssey did all the channel balancing for me and the setup works incredibly well. Now, I can’t speak to your center channel or your listening levels, but with many AVRs offering 200w when driving a single channel, the need for an expensive 3 channel amp is lowered IMO.

it’s probably a good idea, except you may not be giving your center channel the best performance in terms of SINAD despite it probably being the most critical channel in a home-theatre.

I’d rather use a mono amp for the center and use the internal amps for the surrounds. In my case the L and R are active speakers.

 

[Lattiboy]

it’s probably a good idea, except you may not be giving your center channel the best performance in terms of SINAD despite it probably being the most critical channel in a home-theatre.

I’d rather use a mono amp for the center and use the internal amps for the surrounds. In my case the L and R are active speakers.

I kinda doubt any normal external power amp is going to meaningfully outperform the 3600. According to tests here the 3700H does an honest 160w with quite low SINAD when driving just one channel.

 

[flyingflatfour]

88 dB is indeed quite good in absolute terms, so I think you have a point and your setup must sure work great. Don’t get me wrong, the 3600H is a fantastic product as was proved by measurements. In the future I will probably move to Denon when I want to experience 3D Audio.

 

[flyingflatfour]

BTW how does one edit one’s post? I’ve made a mistake in my opening post: the surround bookshelves are 84 dB @ 1W.m sensitivity.

 

[flyingflatfour]

I found another spec for my active towers: max SPL = 112 dB. My guess is this means it will measure 112 dB SPL @ 1m with an input of 1V RMS which is the specified input sensitivity.

I am wondering which signal is used to measure this spec? Which weighing was used? If it’s a 1 kHz tone then I guess I cannot correlate it with the required 105 dB(C) peak SPL at the listening position, since calibration to -30 dBFS / 75 db(C) is done using a limited bandwith Pink Noise?

 

[valerianf]

Another possible configuration is that the AVR is powering the tower speakers using bi-amp amplification.
It can also power the center channel directly.
The pre-out are used for all the other channels.
It is my configuration at home with 5 internal power amps used.

 

[flyingflatfour]

Another possible configuration is that the AVR is powering the tower speakers using bi-amp amplification.
It can also power the center channel directly.
The pre-out are used for all the other channels.
It is my configuration at home with 5 internal power amps used.

Yes but in my case the towers are actives.

We still have not been able to predict what external amp power is required to drive a 88 dB sensitivity center speaker. It will be 2m away from the listening position. The only thing I could figure is the amp input sensitivity: maximum 1.4V RMS to avoid the AVR internal amp clipping. How does one calculate the required power output and how can we predict level matching with the other speakers connected to the AVR which is limited to a +-10 dB adjustment range... We have also confirmed a 6 dB drop to the front active towers because of the unbalanced connection from the AVR.

 

[valerianf]

My center speaker is a Jamo A804 3 ways 6 Ohms 87dB sensitivity.
For now its configuration is in 'small' but before it was in 'large'.
My Yamaha A-700 never had any difficulty to drive this center channel and the two tower speakers.
The tower speakers are at 0dB when the central channel is at +1.5dB.
I do not see why in your case the Yamaha Z7 would not be able to drive only the center channel.
The Z7 is a powerful amplifier.

How low is the minimum impedance of this center channel speaker?
Is the Z7 getting hot or clipping?

 

[flyingflatfour]

My center speaker is a Jamo A804 3 ways 6 Ohms 87dB sensitivity.
For now its configuration is in 'small' but before it was in 'large'.
My Yamaha A-700 never had any difficulty to drive this center channel and the two tower speakers.
The tower speakers are at 0dB when the central channel is at +1.5dB.
I do not see why in your case the Yamaha Z7 would not be able to drive only the center channel.
The Z7 is a powerful amplifier.

How low is the minimum impedance of this center channel speaker?
Is the Z7 getting hot or clipping?

Sorry but you need to start reading what I wrote: I will use the Z7 to amplify 4 surround bookshelves and my challenge is to find an external amp capable of driving a 88 dB sensitivity center speaker to reference level at 2m distance whilst ensuring I can level match with active towers that will receive a 6 dB down unbalanced signal from the preout which probably clips at 1.4V.

Reference level is defined as 105 dB(C) peak SPL at the listening position.

 

[valerianf]

Sure, you are choosing the architecture that you want.
The Z7 has 7 amplifier channels and you are using only 4 of them for the surround bookshelves.
One other internal amplifier channel could be use for the center I guess.

I have found only a test at Audioholic about the RX-Z7 pre-out:
"The RX-Z7 was able to output 1.9Vrms at < 0.1% THD + N with the max limit of 3.3Vrms before turning off."
It should not bring any issue.
Up to you for to you for the amp.

 

[flyingflatfour]

I keep on reading and educating myself to try to understand.

I found online calculators to determine how much power your amp needs to be based on speaker sensitivity, distance to the listening position, SPL required...

I learned that SPL decreases by 6 dB when you double the distance in an open space. But a room has reflections and adds gain, so some calculators will use a 3 dB rule instead. In my case the room will be substantially treated, so I guess I should use 6 dB to be on the safe side.

Using the following calculator http://www.acousticfrontiers.com/2013322spl-calculator/ I found the following results:

Center speaker: 8 ohms, 88 dB @ 2m from MLP: 102 W RMS / 204 W peak required
Surround speakers: 8 ohms, 84 dB @ 1,5m from MLP: 146 W RMS / 292 W peak required

The difference between RMS and peak is explained in the link. Since all amplifier specs are listed as RMS, this is the value to be considered.

Following these lab measurements https://www.connect.de/testbericht/yamaha-dsp-z-7-316308-6475.html that were posted by AnalogSteph above, the 5 channels driven 8 ohm sinewave figure is 115 W RMS, falling short to meet the spec for my intended usage of the internal amps for the 4 surround speakers. There is also a “music figure” given which is higher but I have no idea what that means.

However, since I will be using bass management for the surrounds, and since I keep reading that the bass uses a lot of power, I understand that the actual power demand will be much less than 146 W per channel. Does this mean that the effective speaker efficiency increases if it is crossed-over at say 80 Hz with a subwoofer??

Having a closer look at Audioholics measurements https://www.audioholics.com/av-receiver-reviews/rx-z7-7.1/rx-z7-measurements I see for the preamp section a very low -109 dBV harmonic product @ 1 V RMS output.

The L and R speakers are active and spec a 1 V input sensitivity with a balanced input. Since they will be fed with an unbalanced signal, am I right to conclude that they can reach max rated output at just 0.5 V RMS if they receive an unbalanced signal???

For the C speaker, am I right to conclude that an amplifier with an input sensitivity of 1-1.4V and rated power output of around 150 W is plenty enough to do the job?

By the way, what happens if I pick let’s say a 300 W amp with a 2V input sensitivity? Would I get 150W with a 1V input signal?

Furthermore, how does the preout signal level in V RMS correlate with the volume scale In dBFS? For instance if I reach reference level of 85 dBC at the listening position with one of my active speakers with just 0.5 V RMS of preout, and if 0 dBFS is 1.4 V RMS, can I calculate the delta in dBFS? This would enable me to predict if I can fall within the adjustment scale of +/- 10 dB for speaker level matching provided by the Z7.