COAX signal level to high. please help - diyAudio
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Old 21st October 2011, 03:03 PM   #1
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Default COAX signal level to high. please help

Hello all,

I hope you can help me with this problem

My system are this:

Squeezebox 3, Twistedpair Buffalo dac version 1.1 (9008 chip), LC audio zapfilter 2. Onkyo reciever TXpro515

Squeezebox 3 is connected to DAC by COAX.

I have to listening to my system with the digital volume control in Sueezebox set to maximum 75-80% off maximum volume or else I get a very distortioned signal!

The same happen if I connect a DVD player (Denon DV1920) or my Philips flatscreeen the signal is also distorted due to the high COAX level.

How Can I lower the Coax?

Do any off you know of af COAX volumecontrol?

Will it make any difference to connect a CS8420 in input of the dac and then supply the dac with Wordclk, Bitclk, Serieldata?
Maybe the CS8420 will send out the right signal levels to Dac input?

Please help any one.
Kim
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Old 21st October 2011, 03:37 PM   #2
DF96 is offline DF96  England
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The digital signal level on the SPDIF coax and the audio volume level are quite unconnected. I am not familiar with your equipment, but it is possible that the combination of digital filtering and over-compressed digital media result in occasional excursions beyond the hard limits imposed by a DAC. For example, a digital sinc-compensation filter may boost HF signals beyond what the DAC can handle; it assumes that real music, properly recorded, has little energy up there.
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Old 21st October 2011, 05:10 PM   #3
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Hello DF96.

What do you mean by "The digital signal level on the SPDIF coax and the audio volume level are quite unconnected" ??

I think you are right by "over-compressed" digital media, but how Can I make a digital volumecontrol?

Best regards
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Old 21st October 2011, 05:50 PM   #4
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DIGITAL signal has always the same electrical LEVEL. The numbers that are carried by that signal represent the sound and the sound level. When you change the "volume" in the Squeezebox, you are changing the "numbers" carried by the digital signal, you are not changing the level of that signal.

So I bet is not your DIGITAL COAX LEVEL that is wrong, but is something in your Twisted Pair DAC. Connect the Squeezebox staight to the Onkyo Receiver.

Last edited by SoNic_real_one; 21st October 2011 at 05:52 PM.
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Old 21st October 2011, 08:22 PM   #5
DF96 is offline DF96  England
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I thought you already have a digital volume control in the Squeezebox? Anyway, you basically need a chip which can take the data and multiply by a factor, which is what the Squeezebox must be already doing. Varying the factor varies the volume.
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Old 23rd October 2011, 03:43 AM   #6
awpagan is offline awpagan  Australia
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Quote:
Originally Posted by kimschips View Post
Hello all,



Squeezebox 3, Twistedpair Buffalo dac version 1.1 (9008 chip), LC audio zapfilter 2. Onkyo reciever TXpro515

Squeezebox 3 is connected to DAC by COAX.

I have to listening to my system with the digital volume control in Sueezebox set to maximum 75-80% off maximum volume or else I get a very distortioned signal!

The same happen if I connect a DVD player (Denon DV1920) or my Philips flatscreeen the signal is also distorted due to the high COAX level.

How Can I lower the Coax?

Kim
Just another thought

depending on the output current of the 9008, the dac may have a high current output and into the Zapfilter the Zapfilter may be over driving the input of your receiver.
I used 2 pcm1794's dual mono output approx 15mA, the zapfilter can handle it but the output from the zapfilter was too high for the input of standard commercial receivers.
I had to drop the current output of the dac. (or it was easier than modding the zapfilter).

Allan
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Old 23rd October 2011, 01:10 PM   #7
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Thanks guys)

DF96 yes you are right, the reason I am asking are because Im about to build an preamplifier with digital inputs for Squuezeebox, My flatscreen, and a DVD player all connected by COAX.

I have tried with another Dac (EZdac) with PCM 1974 and connected to my Zapfilter 2, everything working fine but not the soundquality from the buffalo dac.

Questen: do any of you know how to modify my Buffalo dac to lower current output and prevent my zapfilter to be overdriven?
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Old 24th October 2011, 08:56 AM   #8
awpagan is offline awpagan  Australia
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The pcm1794 used a resistor on IREF to vary the output current
I do not think the 9008 has a provision for it
Best would be to ask Russ or Brien on tp's forum

Allan
IIRC someone has already tried the sabre dac with the zapfilter
Try search

Another thought
The 9018 has internal digital volume control
Maybe the 9008 does too
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Last edited by awpagan; 24th October 2011 at 09:04 AM.
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Old 5th December 2011, 03:28 PM   #9
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I think there are some chips (like an ASRC chip) that will do digital volume control in the digital domain. many (most?) truncate data so it will sound like the squeezeboxes do. a lot of dacs now will do volume control in them but that is probably not where you want it done.

I still do volume control in the analog domain (ob disc: I design and build them) and I find that after you finally convert digital down to analog via some dac (dac of the month or whatever) that you insert a vol-control *there*, between the dac and the amp. it still, after all these years, is the best place for vol controls, digital or analog. you also know that any source will be analog by the time it hits the amp/preamp stage, so why not just do it there? if you do vol control only in spdif, what happens to any analog source you may (someday) want to play?
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