Yamaha DSP-E800 External Decoder Subwoofer Gain - diyAudio
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Old 24th September 2014, 03:46 PM   #1
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Default Yamaha DSP-E800 External Decoder Subwoofer Gain

Non-electronics expert needs some advice.

I own a Yamaha DSP-E800, and am very happy with it. However, it has a problem in the fact it has no gain compensation for the -10db LFE channel level when used with it’s 6-Channel direct analog inputs and an external decoder – the decoder in question being a Panasonic DMP-BDT500 Blu-ray player.

Anyway, I think I may have a simple solution to the problem by using a cermet preset which could be adjusted to limit the level of the Yamaha’s internal decoder’s subwoofer output to a level closer matching the 6-Channel sub input - prior to the input switching between the internal and external decoders and the E800’s main output level control. The problem being I’m not sure what the finer points of the electronics might be – impedance matching, noise, etc.

The part of the circuit I’m looking at is on the INPUT (1) board here:

Click the image to open in full size.

The cermet would be inserted between the junction of R452 (47k) / C431 (10uf/25v), the E line (ground), and the wiper to pin 26 of IC402 (LC78213 Analog Function Switch).
It’s somewhat fortunate that there’s a convenient removable short wire link (J453, if you have the service manual) on the circuit board linking that particular cap/resistor junction and pin 26 on IC402, and also allows an easy connection to ground – so the problem of mounting a cermet preset on the board shouldn’t be too much of a problem.

So the questions would be: does anybody see any major problems with the idea, what value cermet would be most appropriate given the drop in gain required – or, more importantly, is there a better way to accomplish the same thing?

Thanks for any help offered.
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