It's pretty obvious using the Denon 3700 pre-out as a DAC input is not a safe or authorized use of hardware. At minimum, it could void the warranty. More likely it will reverse the polarity, confuse the volume controls and may cause damaged to the unit or the speaker if gain rises too high with this hack. I certainly would not recommend it and I don't think it can be safely advocated.
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Denon owners of receivers with multi channel pre-outs, you'll LOVE this... if it works
- Thread starter mike7877
- Start date
- Status
It's pretty obvious using the Denon 3700 pre-out as a DAC input is not a safe or authorized use of hardware. At minimum, it could void the warranty. More likely it will reverse the polarity, confuse the volume controls and may cause damaged to the unit or the speaker if gain rises too high with this hack. I certainly would not recommend it and I don't think it can be safely advocated.
Weeb Labs
Addicted to Fun and Learning
I may not be RestorerJohn but I can answer this question. If you have a look at the block diagram below, you will see that the pre-outs are connected via mute IC to the inputs of the amplifiers, downstream of the volume control ICs. This is the only means by which pre-outs can be included, without the need for additional DSP.
As a result, the pre-outs will function as inputs without controllable volume, so long as audio is not muted. Both the DAC and NJU outputs are rather high impedance, so damage is not a realistic possibility.
Last edited:
- Thread Starter
- #43
What about Center and Surround (5.1 surround - side, not rear) being the only channels this is possible with? Extra switches there? I know they can all literally be used as something else other than Center and Surround (sids
- Thread Starter
- #44
See post below yours, more will come.
Weeb Labs
Addicted to Fun and Learning
There are many possible reasons and it will depend highly upon the AVR in question. The block diagram in my previous post featured an AVR-2807 and in that specific situation, the MCU may mute one or more outputs in the absence of an active multichannel input stream. As you might imagine, source code for these MCU implementations is not available for us to reference.
Your AVR may be similar in that respect or may include additional muting in line with the pre-outs. The service manual is always helpful.
If you would like to experiment, then I would suggest supplying the unit with a continuous 7.1 stream, reducing the volume to the first increment above mute and then connecting a source to one of the other pre-outs.
Last edited:
- Thread Starter
- #47
Updating first post with pertient info. All work but Speaker posts on either side (The two used for Speaker A and Biamp/Speaker B/Height 2 located on the outside edges. All Inside ones including Centre can be accesed for a total of Seven channnels. The diagram might enlighten why
JSmith
Master Contributor
restorer-john
Grand Contributor
Likely paralleled from the ouptut of the internal preamp as it connects to the internal power amp.
Quite logical it works, but not ideal. We used to feed signals into record outs on amplifiers back in the day when we ran out of inputs. But they were simply passive loop-outs. This is an active stage.
Whatever you drive into those "preamp out" jacks will be pushing a signal also into the output stage of the AVR's internal preamplifier/volume stage which will cause distortion in the source (due to a likely low output impedance) and a likely HF droop in the response. It isn't a good idea, but with a robust source, you may get away with reasonable fidelity. There is also the prospect of damaging the various internal preamp out buffer stages.
Edit: Thanks to @Weeb Labs, the Toshiba volume IC referenced above will have 1-10uF capacitors connected to each output pin and when "on" the output stage of the IC will be at virtual gnd. There will also likely be a resistor on each pre out. So you have a 1st order RC filter which will take out high frequencies. So the OP may think he's getting better bass, but he's really just rolling off the top end....
Last edited:
restorer-john
Grand Contributor
Further to the above post. Here's the breakdown block diagram of the Toshiba IC for each "preamp out" channel.
If you are driving into the IC (as the OP is doing), the "input impedance"* of the preceding volume stage will vary according to the volume setting on the AVR. As he is likely to turn it "right down" to -∞, as I mentioned above, the OUTA will be pulled to virtual/actual GND.
The OP will achieve better performance if he winds the volume control all the way up and ironically, still feeds his inputs in via the outputs. Otherwise he has a variable high filter that is dependant on the volume control of the AVR. All in all, it is a non-ideal, non-HiFi "discovery". Especially when he changes sources at full volume and destroys his hearing, speakers and maybe the AVR.
* what the DAC/source "sees" as it drives into the "pre-amp outs".
If you are driving into the IC (as the OP is doing), the "input impedance"* of the preceding volume stage will vary according to the volume setting on the AVR. As he is likely to turn it "right down" to -∞, as I mentioned above, the OUTA will be pulled to virtual/actual GND.
The OP will achieve better performance if he winds the volume control all the way up and ironically, still feeds his inputs in via the outputs. Otherwise he has a variable high filter that is dependant on the volume control of the AVR. All in all, it is a non-ideal, non-HiFi "discovery". Especially when he changes sources at full volume and destroys his hearing, speakers and maybe the AVR.
* what the DAC/source "sees" as it drives into the "pre-amp outs".
Last edited:
why would anyone in their right mind would do this? sure it may be 'okay' but there are no benefits that i can think off.
if you think the pre-amp of the Denon sucks then the amplifiers suck even more.
if you think the pre-amp of the Denon sucks then the amplifiers suck even more.
Further to the above post. Here's the breakdown block diagram of the Toshiba IC for each "preamp out" channel.
If you are driving into the IC (as the OP is doing), the "input impedance"* of the preceding volume stage will vary according to the volume setting on the AVR. As he is likely to turn it "right down" to -∞, as I mentioned above, the OUTA will be pulled to virtual/actual GND.
The OP will achieve better performance if he winds the volume control all the way up and ironically, still feeds his inputs in via the outputs. Otherwise he has a variable high filter that is dependant on the volume control of the AVR. All in all, it is a non-ideal, non-HiFi "discovery". Especially when he changes sources at full volume and destroys his hearing, speakers and maybe the AVR.
View attachment 160453
* what the DAC/source "sees" as it drives into the "pre-amp outs".
Just curious, why not use the actual volume control IC's datasheet to see the potential effects?
Good thing you clarified this, someone may be led to think the one you posted earlier would be applicable to the 3700 but in reality it may not. I don't think the service manual for the 3700 is available for purchase, but we know the volume control IC is the NJU72343, and the service manuals for the AVR-X3500H, X3600H are available and those would likely have the preamp/DAC block diagrams a lot more similar to that of the 3700 than the 2807.
Another awesome idea would be get 2 Denon 3600h units and connect the pre outs of the first unit to the pre outs of the second unit. The first Denon would function as the preamp/processor and the second Denon would just serve as the multich power amp. This would give you “separates” at a fraction of the cost and would give you the benefits of separate power supplies for the preamp and amp sections. You could even run the second Denon in pure direct mode so it shuts off the display so nobody says hey why do you have two Denon receivers.
How can this not cause the clouds in the sky to separate and reveal a new level of clarity?
How can this not cause the clouds in the sky to separate and reveal a new level of clarity?
This means that Denon's pre-outs are nothing but passive galvanic access points between the preamp and power amp stages, completely unbuffered... Seems like a poor implementation... Such a suggested connection will cause overload on the connected source, as it expect a minimum of 7kOhms impedance, not few hundreds Ohms...
Weeb Labs
Addicted to Fun and Learning
From an implementation perspective, I think it's quite reasonable. Muting the pre-outs in the absence of a multichannel input stream should be sufficient to deter most people from doing this. At that point, you might as well just bodge your own inputs onto the board.
- Thread Starter
- #60
Everybody trying to explain how this is dangerous, you're wrong!
The pre amp has a ~1.2k ohm resistor in front of it -because of this, close to no power goes into the AVR's preamp from the DAC, hence, there is no damage. As long as your preamp can drive the 1.2k ohm resistor without distorting and there's still enough voltage left over to drive the power amps 10k inputs (there will be if your preamp can drive the 1.2k ohms, you're GOLDEN
No distortion? High level?
Means high performance and nothing will break (more than it would using it any other way)
The pre amp has a ~1.2k ohm resistor in front of it -because of this, close to no power goes into the AVR's preamp from the DAC, hence, there is no damage. As long as your preamp can drive the 1.2k ohm resistor without distorting and there's still enough voltage left over to drive the power amps 10k inputs (there will be if your preamp can drive the 1.2k ohms, you're GOLDEN
No distortion? High level?
Means high performance and nothing will break (more than it would using it any other way)
- Status
