adding pre-outs to an inexpensive HT receiver.

[montreal]

Hello,

Up until now, I never needed a home theatre receiver since my Sony DVD player had a built-in Dolby decoder and Bass Management features.

Recently I purchased a cable STB for my HDTV. Unfortunately this cable box (Scientific Atlanta 8300HD) only provides a SPDIF output for the Dolby Digital 5.1 content arriving via the cable.

I have looked around for a standalone Dolby decoder and the only one I have come across is the Creative DDTS-100. This unit does not have the Bass Management features that I need (my 15" main speakers double for my missing sub-woofer), and Creative is not publishing any audio specs for this product. I have no way of knowing if the sound quality of the Creative DDTS-100 is similar to an FM radio or something better.

All the computer based soundcards that I have investigated do not have built-in Dolby AC3 decoding chips, these cards merely re-route SPDIF from a DVD player onward towards a HT receiver.

This leaves me with the option of buying an inexpensive HT receiver for the sole purpose of attaching my 6 power amps to the built-in Dolby decoder inside the receiver.

Most high end HT receivers offer pre-out sockets so that you can bypass the receiver's multi-channel power amps in case you want to use your own separate standalone power amps.

If I was going to tear into a cheap HT receiver, my hope would be that I could easily identify the analog wires going to the input of each of the receiver's power amps.

Has anyone attempted to pull apart an inexpensive HT receiver?

Thanks

[brianuk]

Never done it, but would like to do my Sony it only has stereo out.

Very very annoying for an expensive piece of kit.

[montreal]

Originally posted by brianuk
Never done it, but would like to do my Sony it only has stereo out.

I have never taken the cover off a HT receiver nor seen a schematic diagram of one to know if the 5 or more power amps are modular and completely analog.

Have the manufactures come up with a new type of inexpensive mass produced power amplifier module that is driven with a digital signal as opposed to an analog signal?

If so, it may be impossible to tap into an analog source for each channel within such a HT receiver.

[Nigel Goodwin]

Originally posted by brianuk
Never done it, but would like to do my Sony it only has stereo out.

What model is your Sony?, I'll look in the manual at work tomorrow.

Generally there are seperate audio feeds to the seperate power amplifiers, so it should be easily possible.

[montreal]

If the power amps are separate and we can tap their inputs, would it also make sense to remove the power amp modules or at least disconnect the power supply feeds to them so we don't keep this chassis running warm day in and day out for no reason?

[brianuk]

DAV S500, i think

[mik]

Regarding DDTS-100 check out this thread,I trhink that is cheaper then buying new receiver.
The Quest for the holy DIY Decoder

[montreal]

Originally posted by mik
Regarding DDTS-100 check out this thread,I think that is cheaper then buying new receiver.
The Quest for the holy DIY Decoder

Thanks for your suggestion.

I was following this thread last year.

I have written to Creative several times asking them if their DDTS-100 decoder includes Bass Management. It does not. I need Bass management in order to instruct the decoder that my audio system has no sub-woofer.

I have 3 front speakers and two rear speakers. All my 3 front speakers are 15 inch co-axial so I have avoided purchasing a sub-woofer.


Fortunately for me, the DDTS-100 does not have a hi-pass filter on all the 5 channels. I would not want to limit the bass energy going to all 5 loudspeakers since all my loudspeakers are full range co-axial.

Perhaps I do not completely understand the way Dolby Digital 5.1 is encoded and decoded. I am assuming that whenever there is audio content coming out of the sub-woofer channel of the decoder, this content was specifically encoded to be on the sub-woofer channel and does not appear simultaneously on any of the other 5 channels.

Since I don't have a sub-woofer connected to the sub-woofer channel of the decoder, I would need to redirect the output of the sub-woofer channel of the DDTS-100 back into the 2 front left and right speakers, so that any audio content on the sub-woofer channel would not be lost.

Otherwise the DDTS-100 would be for me a low cost alternative to buying a HT receiver for the sole purpose of obtaining a Dolby 5.1 decoder.

What remains a mystery to me is how much quality there is in the opamps that are used inside the DDTS-100.

Most of the soundcards made by Creative that go inside computers have impressive audio specifications.

Does anyone know if the analog electronics inside the DDTS-100 are as good?

Thanks

[Nigel Goodwin]

OK, I've checked the HCD-S500 manual, here's a clip of a couple of the output stages, the inputs are on pins 8 and 11 (presumably out of phase for bridging), and come directly from 80 pin SM chips, via 33 ohm resistors.

[brianuk]

Hi Nigel,

Are you saying that that is four of the 6 analogues at line level before the Power amps?

Im a bit of numpty see

If it is then how on earth did you get this information ?!

Was going to sell it for pennies but if I could get 6 outputs it may be a totally different story, I'd probably use the rear power amps and line out the rest. Then merge the four out into two fronts that can handle the bass, easily.

Thanks,
Brian