# Adding a Power Amp to bi-amp from a Denon 3805



## Malice (May 1, 2006)

Hi all,

When I first got my 3805 together with my B&W 604s3 speakers, I used the Audioholics suggested workaround to get my Denon to bi-amp the front speakers. I was impressed with the difference.

Then last year I purchased another pair of B&W 602s3 for a 7.1 set up, and hence I needed to un bi-amp the 3805. TBH I have found the 7.1 set up to be significantly better for sound stage image steering than the 5.1. So I kept with the 7.1 set up.

Now I want to bi-amp the fronts again by using a separate power amplifier.

In the "old" days Denon produced the POA-T10 as an external amp for the AVC-10SE (I think that's the model) to get 7.1 amplification instead of the 5.1. These are like hens teeth to get hold of, and expensive. 

Question: What technical features or specifications will I need to purchase in order to ensure my 3805 and a new external power amp are matched as closely as possible?

Obviously watts per channel is a good starter, but I imagine details like signal to noise ratio, input sensitivity of the power amp, output voltage of the Denon etc, will all have a bearing on the matching of a power amp to the Denon.

As an indication of tech specs, this is my Denon's details:

• Analog
Input sensitivity / input impedance: 200 mV / 47 kΩ/kohms
Frequency response: 10 Hz ~ 100 kHz: +0, –3 dB (DIRECT mode)
S/N: 102 dB (DIRECT mode)
Distortion: 0.005% (20 Hz ~ 20 kHz) (DIRECT mode)
Rated output: 1.2 V
• Digital
D/A output: Rated output — 2 V (at 0 dB playback)
Total harmonic distortion — 0.008% (1 kHz, at 0 dB)
S/N ratio — 102 dB
Dynamic range — 96 dB
Digital input: Format — Digital audio interface
• Phono equalizer (PHONO input — REC OUT)
Input sensitivity: 2.5 mV
RIAA deviation: ±1 dB (20 Hz to 20 kHz)
Signal-to-noise ratio: 74 dB (A weighting, with 5 mV input)
Rated output / Maximum output: 150 mV / 8 V
Distortion factor: 0.03% (1 kHz, 3 V)


Your invaluable help will be greatly appreciated!

Bob


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## F1 fan (Jul 6, 2006)

Most importantly the input sensitivity of the separate amp must be the same as that of the Denons Amplifier section.Some amps have built attenuation controls which allow you match levels.


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## Malice (May 1, 2006)

What I am not 100% sure about is the output sensitivity/spec of the Denon's pre-outs. The spec above is not clear to me.

EDIT:

I cannot even fathom out whether a 3805 pre-out feeding another 3805 will provide the same match as I cannot reconcile the analogue input sensitivity of 200mv with any of the stated output figures!!


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## F1 fan (Jul 6, 2006)

The analog specs you listed are for the inputs only and not the pre out.The pre out level is dependant on volume control setting and it should be more than enough to drive a separate amp to it's full output.
Edit. Although its not clear what output the 1.2 V is refering to.What is Direct mode?I assume it bypasses all EQ ,processing etc?


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## Malice (May 1, 2006)

"more than enough" doesn't mean that much does it when I have seen the spec on another multi-channel amp (same rated watts per channel) where the analogue input sensitivity was 150mv and signal / noise ratio was 96db? The Denon's is 200mv and 102db. So for the same signal thrown at these, isn't it the case that the output will be different for any given input voltage? It's not a case of driving an amp to its maximum output is it? Dunno?!!!


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## F1 fan (Jul 6, 2006)

Those specs you are stating for the analog preamp input not the power amp input. (They are completely different things) Power amp input sensitivities are generally in the 750 mv to 1 v range with an input impedance of 50 -100 k.


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## brucek (Apr 11, 2006)

> Your invaluable help will be greatly appreciated!


My advice (for what it's worth). Your biggest bang for the buck improvement would come from adding a single, good quality stereo external power amplifier to drive your mains. You could bi-wire them if you wanted. 

This would reduce the strain on the Denons power supply for the remaining speakers in HT mode and it would really improve your two channel.

Trying to match different amplifier manufacturers products is tough enough when bi-amping a speaker, but to attempt an internal receiver amplifer and an external amplifier of another manufacturer would produce unpredictable results.

You would need an amplifier that produced the same gain as your receivers amplifer and also one that had an input sensitivity that matched to produce full rated output. Your preamps max output (full volume) is 1.2 volts RMS, so when do you want the external amplifer to reach its full rated output? Who knows, because you don't have those figures for the internal amps in the receiver. The overall response of the mains speaker would be altered...

Passive bi-amping when both amps share the same supply is regarded as a zero sum result (i.e. bi-amping with a receiver using a single supply). The same change in sound in that case can be obtained from passive bi-wiring.

Just some ideas anyway....

brucek


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## Malice (May 1, 2006)

F1 fan said:


> Those specs you are stating for the analog preamp input not the power amp input. (They are completely different things) Power amp input sensitivities are generally in the 750 mv to 1 v range with an input impedance of 50 -100 k.


I knew this would be a learning experience! Thanks.


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## Malice (May 1, 2006)

brucek;
Although I understand some of the reason why passive bi-amping may prove to have little or no benefit, in my experience the bi-amping I had experimented with worked really well. I was very impressed with my results.



> ...good quality stereo external power amplifier to drive your mains


Or perhaps a reasonable stereo amp to drive the surround backs, whose performance will be less demanding and perhaps may be easier to integrate with the fronts rather than having a stereo drive the front pair with the Denon driving the Center. The rear soundstage steering may be a little compromised, but perhaps rather that than the front/back soundstage with different amplification between the front pair and the other 5 speakers.

Thanks for the input. There is much to consider.


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## Malice (May 1, 2006)

F1 fan said:


> Edit. Although its not clear what output the 1.2 V is refering to.What is Direct mode?I assume it bypasses all EQ ,processing etc?


I missed this question...

Yes you are correct, mostly. Pure Direct has no bass management at all but you can choose whether you want to apply any EQ or not in this mode. All video circuits are turned off to help with the purity of the processed signals.


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## brucek (Apr 11, 2006)

> Or perhaps a reasonable stereo amp to drive the surround backs, whose performance will be less demanding and perhaps may be easier to integrate with the fronts rather than having a stereo drive the front pair with the Denon driving the Center.


Yep, you could get a relatively inexpensive amplifier for this duty, as long as the back channels are directed to a line-level output at the rear of the receiver. This would maintain the front main and center being driven by the Denon and free's up those back channel amps so you could bi-amp your mains...

brucek


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## Malice (May 1, 2006)

Now here's a bit of lateral thinking re the pre-out and analogue input sensitivities. "Normal" power amps have analogue inputs and no digital processing, whereas I was thinking about perhaps getting an older 5.1 AV receiver (say a Sony ES series @ 120W) and using the digital (optical) for connection.

I think the Denon has optical pass-through on Opt3 and Opt4, but the manual and resources on the web are somewhat ambiguous re Denons implementation of "Digital output". That being the case I think I could connect my DVD to Opt3 and then the Opt 3 optical out to the external amplifier if it has digital processing.

This way there I would imagine there would be minimal mismatching of sensitivities on the amps in question.

Does anyone have any opinions on this assumption?

EDIT:

Just thought why this may not work.... there will not be a volume correlation between one amp and another.


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## Malice (May 1, 2006)

brucek said:


> Yep, you could get a relatively inexpensive amplifier for this duty, as long as the back channels are directed to a line-level output at the rear of the receiver.
> brucek


Yeah, the Denon has pre-outs for all the channels, including the rear surrounds.

Just out of interest, how would one go about calibrating the level of the external amp when it has its own volume control? What would the process be of at least getting the same SPLs from all the speakers for the same input (say test tone off the Avia test disc)?


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## brucek (Apr 11, 2006)

> but the manual and resources on the web are somewhat ambiguous re Denons implementation of "Digital output"


The only function of a digital output on a receiver or processor is for digital dubbing using a CD or MD recorder. It's analogous to an analog tape loop, only in digital.



> Just out of interest, how would one go about calibrating the level of the external amp when it has its own volume control?


Set the back channels speaker setup trim to the same level you used when you used an internal amp (as a start) and adjust the input level control of the amplifier to match the level in the speaker setup pink noise. If you think the input control of the amp is down too far, increase the receiver trim on the back channels until its reasonable. It's a trade off between the input sensitivity of the amplifier to produce a full power output and noise from the receiver.

brucek


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## F1 fan (Jul 6, 2006)

Ok had to leave for the day so missed a lot of this discussion.If you really want to bi-amp I would advise going the power amp route instead of using another AVR as it would be a complete waste of features.You could probably get the power amp to work fine in the bi-amp mode but if the 1.2 volt spec is the max out voltage from the front ch pre outs that is on the low side.Therefore you would have to pay particular attention to the input sensitivty of the amp.Your idea of using an amp to drive the surrounds might be the best one or atleast easiest to implement.


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## Malice (May 1, 2006)

There is an opportunity to buy a old S/H Sony amp, and at around $100 cannot be too bad for a 120W per channel (fronts) amplifier, not least of which is that it is Sony "ES" standard. 

What I am not clear about is how this amp would handle either a fixed or variable line-in, and whether which would work better given that the amp would have its own independent volume control.


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## brucek (Apr 11, 2006)

Well, it has a 5.1 input that you would use. You're paying for a lot of stuff you don't need since it's an integrated amp. Why not get a simple stereo power amplifier?

brucek


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## basementjack (Sep 18, 2006)

I have some Sony 55ES 2 channel amps and I don't think the amp is anywhere near whats in the denon 3805.

I think the logical steps for you would be:
1) enjoy what you have, cost = $0
2) add an external 5 or 7 channel amp, cost = $900-1500
3) upgrade to a new Receiver, cost = $1800+

When I was looking for a new setup, I brought home a Denon 3805, and side by sided it with a rotel preamp, and thier 5x120 power amp.
Since rotel's preamp is more expensive than the denon, one configuration I played with was using the denon as a preamp, to the rotel 5ch amp.
I was really surprised that doing so didn't really sound any different (to my ears) - indicating to me that the Denon 3805's amp is pretty close in sonic character to the Rotel 1075 amp.
I also tried both the 3805 and the Rotel preamp paired up with 3 of the sony 55es amps I have, and was dissapointed with the results.

So my summary is, the 3805's amps are better than older sony ES amps.
- the 3805's amps sound similar to the $995 rotel 5ch amp.
- in a typcial setup, I didn't see much advantage of the spearate amp, but I have a small room and different speakers...
- in your setup, the rotel amp might be a consideration- you could use 4 of the 5 channels to biamp the fronts, and the 5th channel for the center.

while I haven't heard one, I suspect the 4000 series denon might be a tad better than the 3805 you have now - so it might make sense to upgrade the receiver to a newer one.


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## Guest (Aug 7, 2007)

ah I have a Denon 3805, I am buying a Emotiva amp alothough not quite sure if I am getting the MPS and buying modules for it gradually or the two channel amp and buying 4 of them. But will be using the Denon as a pre/pro for a while.


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