In the zone (hacking the Denon AVR1905 to become multi-zone)

Previously, on home improvement: I bought a Denon 1905 7.1 amplifier, to serve surround sound in the living room and stereo music to the kitchen.

To my horror, when I came home and turned it on, it didn’t have “Zone 2”.

WTF?! The product brochures I found on the internet said it has it. The product manual specified clearly how it should be operated. (well,

The remote didn’t have a “Zone 2” option on its mode selector, and the on-screen menu ended at option 24 (the manual I found on the internet says option 25 is “Power Amp Assignment” – that’s the one you use to switch between 7-channels and 5+2 channels). Argh!

The downside of buying an 8-year-old amp is, it lacks internet resources. It took an afternoon of internet searching before I found someone commenting,

“Sorry for flogging a dead horse, but doesn’t the 1905 Singapore version not have the Zone 2 capability? That’s what irritated me because I couldn’t really rely on reviews written by US reviewers. “

Which could either mean Denon models differ between territories, or that some local distributors are re-numbering the models. So I downloaded its service manual and opened it up to compare the board models, and they match: it really is a 1905. That’s frustrating, but also provides a glimmer of hope: Denon already issue 5-10 amplifier models each year, which is a lot. I bet they wouldn’t want to issue 3-4 times that number in models.

So I started reading the service manual thoroughly, and indeed, it has several (territorial) sub-models:

Of course, the CPU and main boards are similar on all sub-models. One of the differences is the analog input board (INPUT-VOL), which seems – in the E3 model – to have additional relay switching the output going towards “surround back”, and twice the volume controlling components:

So the use of the non-US sub-model of the amplifier would not allow me to control volume for Zone2, or the switching of the regular inputs (CD, DVD, AUX) to it. In my application, I want zone2 to be connected to computer audio, so I can have the surround-back bus permanently wired to the PC (by hooking the PC to the pre-amp output jacks which can also be used for input), and control the pre-amplified volume through the PC rather than through the amplifier. I just need to make the amplifier “think” that it is the US model.

As the CPU board is similar between all models, I was looking for a jumper or DIP switch that controls what sub-model it “thinks” it is. I took the amplifier apart and didn’t find such jumper, but did find a caption on the printed circuit board that specifies how the sub-model is determined:

	AREA (57P)	R216	R218
	E3/BKEU	100K	OPEN
	E2/EK	100K	180K
	GUT/G1C/G1K	100K	180K
	N	150K	100K

Well, as they say in the treasure hunting biz, “X marks the spot”… All I need is to find and remove resistor R218. This requires some patience as it requires taking apart all of the boards in the amp (R218 hides on the lower side of the CPU board, which is hardest to reach). But once found, it can easily be taken off with a slight touch of a soldering iron.

Before	After

Putting it all back together and turning the amplifier on, and zone 2 works.

As mentioned before, input and volume selection from the amplifier controls does not have any effect on Zone 2 (while the amplifier lets you select input to be routed to Zone 2, it has no effect; volume control turns off the zone when turned all the way down to zero, and turns on to maximum volume when volume is raised above zero.