Low-cost center channel output??

[Xulonn]

I am considering the possibility of adding a center channel to enhance dialog intelligibility with video, but don't have a component with an AV processor - and will not be adding rear speakers which would be 6 inches behind my head in my really small room. Raspberry Pi's only handle 2-channel, so HiFiBerry and their competitors will not be offering a multichannel option. And I am not interested in replacing my HTPC with a cheap Android media box.

I can think of the two possibilities below. Comments on specific experience with 3.0 channel A/V would be especially appreciated.

My Topping DX7s DAC has balanced and RCA out - apparently separately buffered, and o.k. to use both at the same time. The balanced out goes to my stereo power amp. Could I use a good RCA Y-cable designed for a subwoofer - feeding a mono amp with a volume control to drive a center channel? I am aware that there might be level-matching issues, but I would just set the center channel volume to my liking.

Another optiou would be to get a HDMI extractor/DAC like the one below ($56). Then I could pass the HDMI signal from my HTPC to my TV through the extractor, extract and convert the audio channels, and use only the center channel RCA out. If it is a half-way decent DAC, I wouldn't worry about sound quality, because I would still listen to music only in stereo. (I could even drop-ship it to Amir so he could test the L/R channels.)

 

[Doodski]

I am considering the possibility of adding a center channel to enhance dialog intelligibility with video, but don't have a component with an AV processor - and will not be adding rear speakers which would be 6 inches behind my head in my really small room. Raspberry Pi's only handle 2-channel, so HiFiBerry and their competitors will not be offering a multichannel option. And I am not interested in replacing my HTPC with a cheap Android media box.

I can think of the two possibilities below. Comments on specific experience with 3.0 channel A/V would be especially appreciated.

My Topping DX7s DAC has balanced and RCA out - apparently separately buffered, and o.k. to use both at the same time. The balanced out goes to my stereo power amp. Could I use a good RCA Y-cable designed for a subwoofer - feeding a mono amp with a volume control to drive a center channel? I am aware that there might be level-matching issues, but I would just set the center channel volume to my liking.

View attachment 56833

Another optiou would be to get a HDMI extractor/DAC like the one below ($56). Then I could pass the HDMI signal from my HTPC to my TV through the extractor, extract and convert the audio channels, and use only the center channel RCA out. If it is a half-way decent DAC, I wouldn't worry about sound quality, because I would still listen to music only in stereo. (I could even drop-ship it to Amir so he could test the L/R channels.)

View attachment 56834

You want to connect the left and right outputs into one RCA and use that for center? Like a reverse Y-cable setup.

 

[Xulonn]

You want to connect the left and right outputs into one RCA and use that for center? Like a reverse Y-cable setup.

Apparently that is what those subwoofer Y-cables are for, so I was curious if he same goes for a center channel. However, I have seen advice that recommends a 100Ω resistor somewhere in the path to combine L+R stereo into monaural.

 

[Doodski]

Apparently that is what those subwoofer Y-cables are for, so I was curious if he same goes for a center channel. However, I have seen advice that recommends a 100Ω resistor somewhere in the path to combine L+R stereo into monaural.

In my experience I've never combined the left and right stereo output channels into one common connection for the purpose of "summing" them into quasi mono. I suppose one could use a resister(s) but it really depends on the output circuitry of the component you are taking the stereo signals from. The signal might be DC voltage isolated through capacitors at the stereo output. My advice would be to use a separate unit and derive the center channel from it.

 

[andreasmaaan]

Hey there @Xulonn,

In terms of option one, you need more than just a Y-cable for the two channels to sum correctly, although not much more. Basically, all you need to do is build a simple circuit involving a couple of resistors. I'm no expert on these circuits, but from what I understand, this simple implementation (stolen from the old Rane website) will do the job:

In terms of option two, what I'd be worried about would be two different DACs processing the signal (one for the L and R channels and the other for the C channel). These DACs are likely to have different latencies from each other. Humans are very sensitive to interchannel delays, hence my concern regarding this approach.

 

[Doodski]

The stereo summing circuit you propose would work if the 475Ohm resisters are a good value to limit any current in circuit and would rely on DC blocking capacitors in the source DAC signal path. There will be some issue large or small with levels because the circuit is not a summing circuit but relies on algebraic processes to determine the level of the "quasi mono" output. Voices will be at louder levels sometimes and at reduced levels at other times. That may make it sound off and be annoying at times. Otherwise it'll probably work. Take your chances though.

 

[Doodski]

If there are no DC blocking capacitors in the source DAC stereo output circuit or if you just want to be sure. Put small 10V or 16V ~370 micro Farad capacitor in series with the 475Ohm resisters to block any DC voltage that may be present in the DAC. By the time you order in the parts, assemble them, get a soldering iron, get solder and a small box to make the cable you might be better off just buying something that has a mono output for the center channel amp.

 

[Xulonn]

Thanks guys. Thy Y-cable route sounds too complicated to do correctly.

So if I do add a center channel, I think I will go with the 5.1 A/V HDMI audio extractor DAC. Then I can use the $60 Douk/Nobsound MC-103 Pro XLR switch box that Amir tested and recommended in January.

I can connect the Topping DX7s to the Douk switcher with normal XLR cables, and connect the L/R from the 5.1 HDMI Extractor/DAC to it with RCA>XLR converter cables. When I want to watch a video, I can simply switch the source going to my 2-channel Classé power amp. The center channel line out can go via RCA to a separate monoblock amp with volume control, and I will just turn it on when I need it.

Problem solved!

 

[andreasmaaan]

Thanks guys. Thy Y-cable route sounds too complicated to do correctly.

So if I do add a center channel, I think I will go with the 5.1 A/V HDMI audio extractor DAC. Then I can use the $60 Douk/Nobsound MC-103 Pro XLR switch box that Amir tested and recommended in January.

I can connect the Topping DX7s to the Douk switcher with normal XLR cables, and connect the L/R from the 5.1 HDMI Extractor/DAC to it with RCA>XLR converter cables. When I want to watch a video, I can simply switch the source going to my 2-channel Classé power amp. The center channel line out can go via RCA to a separate monoblock amp with volume control, and I will just turn it on when I need it.

Problem solved!

Just to clarify @Xulonn because I'm not sure I understood correctly: when you're watching stuff, will you have different DACs for the L/R channels and the C channel?

If so, I'd advise against this for the reason I mentioned above.

 

[Xulonn]

when you're watching stuff, will you have different DACs for the L/R channels and the C channel?

Absolutely not. As I said before, the switch box is for switching the L/R main channels (stereo amp and speakers) back and forth between the two DACs, with the center channel amp and speaker totally independent. The center channel amp would be switched on and volume adjusted only when watching video. Dialog is more important to me than bangs, crashes and special effects with subterranean bass, so I want a center speaker to improve dialog intelligibility.

My LibreElec Intel NUC HTPC is connected to a Topping via USB for music playback, but it is also connected via HDMI to my Samsung 40 LCD TV for both audio (which is then turned off) and video. When watching video, the USB source for music will be switched off and the HDMI Extractor/DAC switched in. All channels will be "extracted" from the HDMI cable, L/R will now feed the main stereo amp, and the center sound track will go to a separate mono amp (not a lot of choices for mono amps with a volume control, but I like the one below - a subwoofer amp with full range mode) and the center speaker. The center channel will be turned off when listening to stereo music via USB.

The reason I want to send the HDMI extractor DAC to Amir is to see how well HDMI digital audio compares to Toslink optical, s/pdif coaxial or USB digital audio. Bits are bits tells us that the quality should theoretically be the same as USB, Toslink, or coax digital, but Amir has demonstrated that flawed hardware/software implementations can turn good bits into bad sound.

 

[andreasmaaan]

Absolutely not. As I said before, the switch box is for switching the L/R main channels (stereo amp and speakers) back and forth between the two DACs, with the center channel amp and speaker totally independent. The center channel amp would be switched on and volume adjusted only when watching video. Dialog is more important to me than bangs, crashes and special effects with subterranean bass, so I want a center speaker to improve dialog intelligibility.

My LibreElec Intel NUC HTPC is connected to a Topping via USB for music playback, but it is also connected via HDMI to my Samsung 40 LCD TV for both audio (which is then turned off) and video. When watching video, the USB source for music will be switched off and the HDMI Extractor/DAC switched in. All channels will be "extracted" from the HDMI cable, L/R will now feed the main stereo amp, and the center sound track will go to a separate mono amp (not a lot of choices for mono amps with a volume control, but I like the one below - a subwoofer amp with full range mode) and the center speaker. The center channel will be turned off when listening to stereo music via USB.

The reason I want to send the HDMI extractor DAC to Amir is to see how well HDMI digital audio compares to Toslink optical, s/pdif coaxial or USB digital audio. Bits are bits tells us that the quality should theoretically be the same as USB, Toslink, or coax digital, but Amir has demonstrated that flawed hardware/software implementations can turn good bits into bad sound.

Perfect! Thanks for clarifying.

 

[Prana Ferox]

If your source is an HTPC in the first place, does the sound card / motherboard have 5.1 analog out? Many do. It may take some trickery to output HDMI and analog at the same time.

 

[Xulonn]

Perfect! Thanks for clarifying.

De nada! I just inserted the picture of the amp that I forgot. I need to get and learn how to use a diagramming app that - would make such explanations much easier.

Although there were some dedicated center-channel "add-on" mono amps with volume controls available 10-20 years age from companies like AudioSource, that tiny market segment has disappeared.

However there are a couple of ChiFi Class-D subwoofer amps available with selectable full-frequency mode that bypasses the low-pass crossover and should be perfect for my needs. Otherwise, I would probably have use a basic monoblock and an outboard attenuator.

 

[Xulonn]

If your source is an HTPC in the first place, does the sound card / motherboard have 5.1 analog out? Many do. It may take some trickery to output HDMI and analog at the same time.

I dual boot my older Intel NUC5PCYB (Celeron N3050 CPU) to either LibreElec (Kodi) or Daphile (Logitec Media Server). NUC's use laptop processors and don't have expansion slots - but otherwise are great as HTPC's - especially the new NUCs with more CPU power, more memory, and more GPU power. On my older NUC, the analog output sucks and is only a 3.5mm 2-channel.

So for my music playback system, I use USB out to a Topping DX7s DAC, and feed the video out to my Samsung 40" 1080p LCD-TV via HDMI. Everything worked perfectly from the day I first set it up - without any tweaking. HDMI and USB work fine simultaneously - and both can carry a 5.1 digital data signal. I connect to an Ethernet switch for either high-speed internet or my Synology NAS where I store my A/V files.

My music system has only 2-channel DAC, but it is one of the best available. And a center channel requires a 5.1 decoder. I was looking for the easiest way to simply add a proper center channel to my current configuration. What I've ended up considering at this point in time is about $200 total for a 5.1 HDMI>RCA decoder, a Nobsound/Douk 3-in, 1-out line-level switch, and a mono amplifier with a volume control. (I may add digital side DSP unit from miniDSP for the music playback side, but there is no easy way to add it to the audio in video mode. As long as I have limited bass and no horrible bass issues, I am good for now.)

I thought about replacing my 2-channel Topping DX7s DAC with a good 5.2 channel DAC that had USB input, but could not find one that I liked. I spent hours searching the internet, and the only such DACs that I could find were the mediocre-performing Creative Labs unit that Amir Tested, and the Mocha X-3B which is at 10 years old. I would not consider either on for my main music system, so the "switch-over" to a separate HDMI Extractor/DAC still seems to be the best solution for me.

Always more fun ahead in this hobby. I could just give up and get a 5.1 A/V receiver, but what fun would that be? Besides, in addition to not performing very well in Amir's testing, they all seem to come loaded with proprietary digital features that I don't want or need. And they take away all of the fun - and challenges - of trying to build a system with just the features you want, while giving you few, if any, options to play with the system configuration.

 

[Doodski]

View attachment 56926

I dual boot my older Intel NUC5PCYB (Celeron N3050 CPU) to either LibreElec (Kodi) or Daphile (Logitec Media Server). NUC's use laptop processors and don't have expansion slots - but otherwise are great as HTPC's - especially the new NUCs with more CPU power, more memory, and more GPU power. On my older NUC, the analog output sucks and is only a 3.5mm 2-channel.

So for my music playback system, I use USB out to a Topping DX7s DAC, and feed the video out to my Samsung 40" 1080p LCD-TV via HDMI. Everything worked perfectly from the day I first set it up - without any tweaking. HDMI and USB work fine simultaneously - and both can carry a 5.1 digital data signal. I connect to an Ethernet switch for either high-speed internet or my Synology NAS where I store my A/V files.

My music system has only 2-channel DAC, but it is one of the best available. And a center channel requires a 5.1 decoder. I was looking for the easiest way to simply add a proper center channel to my current configuration. What I've ended up considering at this point in time is about $200 total for a 5.1 HDMI>RCA decoder, a Nobsound/Douk 3-in, 1-out line-level switch, and a mono amplifier with a volume control. (I may add digital side DSP unit from miniDSP for the music playback side, but there is no easy way to add it to the audio in video mode. As long as I have limited bass and no horrible bass issues, I am good for now.)

I thought about replacing my 2-channel Topping DX7s DAC with a good 5.2 channel DAC that had USB input, but could not find one that I liked. I spent hours searching the internet, and the only such DACs that I could find were the mediocre-performing Creative Labs unit that Amir Tested, and the Mocha X-3B which is at 10 years old. I would not consider either on for my main music system, so the "switch-over" to a separate HDMI Extractor/DAC still seems to be the best solution for me.

Always more fun ahead in this hobby. I could just give up and get a 5.1 A/V receiver, but what fun would that be? Besides, in addition to not performing very well in Amir's testing, they all seem to come loaded with proprietary digital features that I don't want or need. And they take away all of the fun - and challenges - of trying to build a system with just the features you want, while giving you few, if any, options to play with the system configuration.

Keeping your audio system integrity intact while adding the center channel is obviously your goal. I think you've achieved that so far.

 

[Soniclife]

I've been wondering the same thing, and not found a nice solution I'm OK with so will follow how this goes.

One question, if you use the simple HDMI > 5.1 analogue what happens to the rear surrounds and .1 that you will not be using? Do you not really need a 5.1 to 3.0 mixdown control?

 

[nm4711]

As already mentioned, going with an y-cable would probably not give the desired results.

Does the HDMI>RCA decoder really decodes surround sound formats or is it a multichannel DAC? If it is only a DAC, it can only work if your Windows(?) LibreElec decodes the multichannel sound and passes the channels in PCM format to the decoder. The decoding with Windows Linux could be a problem. But I'am not sure about it.

I thought about replacing my 2-channel Topping DX7s DAC with a good 5.2 channel DAC that had USB input, but could not find one that I liked. I spent hours searching the internet, and the only such DACs that I could find were the mediocre-performing Creative Labs unit that Amir Tested, and the Mocha X-3B which is at 10 years old. I would not consider either on for my main music system, so the "switch-over" to a separate HDMI Extractor/DAC still seems to be the best solution for me.

There are good multichannel DACs, but those don't decode surround sound either.

Always more fun ahead in this hobby. I could just give up and get a 5.1 A/V receiver, but what fun would that be? Besides, in addition to not performing very well in Amir's testing, they all seem to come loaded with proprietary digital features that I don't want or need. And they take away all of the fun - and challenges - of trying to build a system with just the features you want, while giving you few, if any, options to play with the system configuration.

I fully understand that. If I want to add a center to my system, I probably have to go this way, because I just use a cheap FireTV stick for playback and so I would need the AVR for decoding. But I wouldn't need the Amps of the AVR, nor would I use it for music playback.

 

[nm4711]

I've been wondering the same thing, and not found a nice solution I'm OK with so will follow how this goes.

One question, if you use the simple HDMI > 5.1 analogue what happens to the rear surrounds and .1 that you will not be using? Do you not really need a 5.1 to 3.0 mixdown control?

If the box decodes the Surround Sound format you probably need this. If the PC does it you could configure it to 3.0, I guess.

 

[Soniclife]

If the PC does it you could configure it to 3.0, I guess.

I would expect it's possible to get windows to do this in the sound card driver by telling it which speakers are in use. Then the OP could use a USB sound-card with 5.1 out. No use for me as I want to keep the PC out of video playback.

 

[Xulonn]

Keeping your audio system integrity intact while adding the center channel is obviously your goal. I think you've achieved that so far.

Indeed, Dood. I think my plan will work - I may use my stimulus check to buy the speakers and electronics. Amir already tested the switch box and liked well enough for use with his testing of other gear. I may buy the HDMI 5.1 Decoder and amplifier soon and have them drop-shipped to Amir for testing. I don't expect them to measure as SOTA, and they are not as important to me as my music system. But I do hope that they are decent and have low noise levels.