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
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
Never done it, but would like to do my Sony it only has stereo out.
Very very annoying for an expensive piece of kit. 😡
Very very annoying for an expensive piece of kit. 😡
brianuk said:
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.
brianuk said:
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.
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?
Regarding DDTS-100 check out this thread,I trhink that is cheaper then buying new receiver.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=59421&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=59421&highlight=
mik said:
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
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
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
brianuk said:
No, that's TWO of them, each output chip has two feeds, out of phase with each other, as they are bridged amplifiers. There are six amplifier chips in total, one for each speaker.
Im a bit of numpty see 😉
If it is then
From the service manual!.
Is this receiver a 6.1 type?
Have you located where the source of the sub-woofer output is?
In Canada we have a Sony receiver called the STRDG500S which is 6.1 at 100 watts per channel and sells for the equivalent of 240 euros.
It looks like my best bet so far against the Creative DDTS-100.
Have you located where the source of the sub-woofer output is?
In Canada we have a Sony receiver called the STRDG500S which is 6.1 at 100 watts per channel and sells for the equivalent of 240 euros.
It looks like my best bet so far against the Creative DDTS-100.
montreal said:
No, a 5.1 type.
Like all the other channels, it's directly out of an 80 pin SM chip (there are two of them) to the output IC.
Interestingly enough, it's only rated at 100W in the USA and Canada?, elsewhere it's rated at 85W. BTW, the manual is dated Feb 2006.
Nigel Goodwin said:
I realize now that yours is designed to connect to a non-powered subwoofer.
I don't think the 6.1 Canadian model is exactly like your 5.1 model. The box is much larger here. I suspect they use the same power amp chips.
It looks like your power supply is single pole and the use of the bridging is to double the output voltage at the speakers.
On the schematic, the voltage on the chips for the outputs (pins 2 and 17) seems to be at 13,6 volts. That may be a DC bias or the AC rms signal strength when fully driven.
If its a DC bias (typical of unipolar power supplies), do they get rid of this bias voltage with large de-coupling capacitors or do they present the same live 13,6 volts simultaneously on both the plus and minus terminals of each speaker output using a shielded plastic plug? If so, it would be dangerous to let either speaker wire contact ground.
I dont suppose I could be cheeky and ask for a copy of that manual or just a couple of scans 
I want to
I want to
brianuk said:I dont suppose I could be cheeky and ask for a copy of that manual or just a couple of scans
It comes as a PDF as part of Sony Assist, but the PDF's are password protected - with the password hidden inside Assist somewhere (so I don't know what it is).
montreal said:
Yes, that's correct - it's common on many small Sony HT units.
DC, as expected from a bridged amp with a single supply.
They use a stupid two pin plastic plug, that you can't buy anywhere - and buying replacement speaker leads is INCREDIBLY expensive! (about £120 for a set of leads last time I checked!).
Yes, it is 'dangerous' if you short the plugs to chassis, but generally the amp just shuts down in protection mode.
Nigel Goodwin said:
Nigel,
So your power amp is actually a bridge formed by 2 amps driven with inputs that are 180 degrees out of phase to achieve the voltage doubling.
I imagine for this reciever to work correctly, all analog (stereo) inputs must be converted to the digital domain so that the sound processor can apply all the bass management features and surround sound emulation for stereo inputs.
Each analog input might have its own A/D converter followed by a digital switch or there may be an analog switch following all the analog inputs followed by a single A/D converter. In any case, I imagine the sound processor deals with only one source at a time and knows exactly what to do with it.
The net result is that the sound processor must have exactly 6 digital outputs which must each be converted back to analog and then split in two paths so that one path can be inverted to feed the pair of power amps in bridge formation.
How easy is it for you to identify the outputs of the 6 D/A converters? Are they CXD9674 or CXD9675? If so, there are 2 pins per output channel in these D/A converters - one non inverting the other inverting.
montreal said:
As I mentioned previously, all six channels (actually 12 outputs) come directly from two 80 pin SM chips - I presume all the processing and conversion is done in those?. I wouldn't expect the numbers of them to be at all useful, I presume they are custom chips?.
EDIT: I've just been and checked the manual, there are actually THREE 80 pin chips, feeding two output chips each. They are labelled 'Stream Processor' and are CXD9634Q's.
Nigel Goodwin said:
Nigel,
So you have 3 CXD9634Q chips labled Stream Processors where each drives 2 CXD9646Z dual power amplifier chips with 33 ohm resistors in series in each path which connects a Stream Processor chip output to a power amp chip input.
If so, I would assume that each 9634 is for 2 of the 6 audio channels and each 9634 contains at least 2 D/A converters to create the 2 analog channels plus 2 extra inverters to provide an out of phase signal for each bridged pair of power amps.
Any chance of you posting an attachment that shows one of the three 9634 processor chips?
Thanks