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Digital to Analog audio converter problems!

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Dennis47

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Post Sat Oct 28, 2017 11:38 am

Digital to Analog audio converter problems!

Has anyone experienced problems with a DAC audio adaptor for a TV?

I recently purchased a new RCA TV and found it needed a digital to analog audio converter adaptor
to interface with my Carver audio system which consists of a HR-752 receiver, TFM-15 amplifier
(connected to HR-752 with a Z-1 coupler), SD/A 490t CD and a TDR-2400 dual cassette deck. HR-752
powers Polk Monitor 10s and a Polk SW6 Monitor series 2 Sub. TFM-15 powers Polk Monitor 7s (rear)
and Polk Monitor 4s (side).

I purchased, admittedly without appropriate amount of research, a FiiO Taishan Coaxial/Optical to R/L Audio
Converter. It is connected to TV with coaxial, to receiver with RCAs and powered by USB port on TV.

Immediately after connection I noticed a 50% drop in output volume (according to my equalizer)...then noticed
a buzz thru speakers when Hologram control was engaged, so disengaged it. After a few days of listening the left
channel in both receiver and TFM-15 began to intermittently drop-out. If I raised the volume level the left
channel would again appear normal for a short time. This went on for several more days and then the TFM-15
stopped producing sound and the HR-752 still lost the left channel intermittently even when the TV/audio adaptor
were not engaged.... #-o #-o #-o

I found if I powered-off the HR-752 unplugged it then plugged and powered it on again the left channel sound returns!

The TFM-15 has stopped producing sound altogether (this may be just coincidence as the amp is 25 years old), but
all of it started after introducing the audio converter.

I'm thinking an incompatible audio converter is the problem.

Any ideas on what could be causing these problems and/or how to solve them?
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radioeng2

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Post Sat Oct 28, 2017 12:33 pm

Re: Digital to Analog audio converter problems!

I would lay any blame on the DAC at all.

Sounds like lower voltage output but otherwise very much sounds like units that need serviced.

Good luck.

Mark
I was there "At the Fest!" Hope you were too!
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Dennis47

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Post Sat Oct 28, 2017 4:50 pm

Re: Digital to Analog audio converter problems!

Thanks for the response radioeng2.
I trust your opinion after the advice you gave me for the repair of my SD/A 490t.

I did take the TFM-15 amp to the shop earlier today for a diagnosis and refurb.
However, I'm still confused about the HR-752 as I've been running it for the past
two days without the TV connected and have had none of the problems mentioned
above. I've tested it with tuner and CD. I do plan on taking it in for a diagnosis.

This afternoon I tried reconnecting the TV and all problems were evident as soon
as DAC was connected. As I understand it the DAC basically just passes a signal....
so how can it be affecting the receiver? If not, why the problems with just the TV
and not the tuner and CD?

Also, is there a better DAC to be had...one which will produce a stronger audio
signal or is the siganl strength dictated by the TV electronics?
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Robert R

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Post Sat Oct 28, 2017 5:43 pm

Re: Digital to Analog audio converter problems!

I just run about a 20' audio cable from the TV's output (stereo mini jack) to my AUX inputs (RCAs). Works great. Only problem is that there is virtually nothing on TV worth watching...

RobertR
"You know what folks? I'm happy."
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Robert R

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Post Sat Oct 28, 2017 6:44 pm

Re: Digital to Analog audio converter problems!

Your DAC could be delivering a shitload of high-frequency garbage.
RR
"You know what folks? I'm happy."
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jjptkd

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Post Sun Oct 29, 2017 8:16 am

Re: Digital to Analog audio converter problems!

Since you have two new items in the mix its likely one of those is defective I'd think. Its possible there is an issue with the output on the TV or the DAC could be bad.

If you're going to go the DAC route I'd recommend spending a few more bucks on something decent. I've used and liked the PS Audio DAC III which can be found used for around $300. Benchmark makes a good DAC their basic DAC1 can be found for $400-$500.

Of course you probably should check the TV for any additional audio outputs as Robert suggested if you want to keep things simple and costs down, 3.5mm to RCA cables can be found on ebay for $5 shipped I believe if you don't have one already.
Oppo Sonica DAC / Pre
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Dennis47

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Post Mon Oct 30, 2017 5:33 am

Re: Digital to Analog audio converter problems!

jjptkd.....

It also occurred to me that the TV, DAC or even the coaxial connector could be
a possible source of the problem.

Do you experience any loss of signal strength with the PS Audio DAC III? I'm thinking
for $300 bucks it should do some magic. I wasn't expecting a $300/$400 expenditure
as my TV didn't cost much more than that. It's my low budget system. I will,
however do some research on the DACs you mention. Is a loss of signal strength a
phenomena inherent with using a DAC?

Unfortunately the only audio out (TV mode) available is the coaxial connection
that I'm now using.
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Robert R

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Post Mon Oct 30, 2017 6:04 am

Re: Digital to Analog audio converter problems!

Don't ignore what Radioengineer said - you could have a couple of problems there.
An o'scope would reveal a lot about that DAC output.
I can't imagine that a DAC would be so lacking in gain - one should expect it to at least be unity, if it's working right.


RR
"You know what folks? I'm happy."
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radioeng2

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Post Mon Oct 30, 2017 9:24 am

Re: Digital to Analog audio converter problems!

I saw mention of optical in the original post and mentally jumped to isolation being present. But after reading more closely, I'm thinking it's likely for the Omni-present, typical cable ground loop. It's so typical to have problems with the ground potential being different and a buzz resulting. And depending on the DAC internal build, it might cause some weird issue.

But don't start with assuming the erotic/exotic. This sounds to me like the DAC could have just simply lower gain and there probably is a ground loop.

First off, audio out level should be listed on a DAC usually. Look and see if it's listed. If you have hum, do you have some automatic level adjust present in something and its holding level down due to the hum maybe? And also it should be mentioned how often people misinterpret louder levels as a good thing or lower levels (within reason) as bad. A particularly econo DAC might simply have a limited voltage supply and simply design a lower output than another company that more correctly used a higher voltage, at greater expense, and has more output. So look at any figures given on specs and see if anything lends a clue.

It's easy to take a couple negatives and tie them together and come up with a problem being greater than it is. Not saying that's the case here, just cautioning I see it all the time. Sometimes stepping back a bit and looking at each thing separately can yield a different look at the problems and ways to get it working.

I'd suggest looking at investigating any potential ground loop before going further. Also, maybe try using the DAC in separate duty for a minute and see if it works any differently just being used on a CD player for instance.

Post back any more clues....

Mark
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Magnaryder

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Post Mon Oct 30, 2017 10:14 pm

Re: Digital to Analog audio converter problems!

I had a shitty little optical DAC($19) on my tv until I bought Yggdrasil. It operated fine. Test the input you’re using by running another device on your input. Then run another optical device into the DAC. Same for the wires simple deduction will identify your problem.

ray

BTW, Schiit builds a $99 DAC
Magnaryder

Its going to be used equipment when I sell it, so it may as well be used equipment when I buy it.

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Dennis47

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Post Tue Oct 31, 2017 1:52 am

Re: Digital to Analog audio converter problems!

Robert R...Thanks for your response.
I'm thinking the same thing...so I'll be eliminating the source of the problem one component at a time.

radioeng2
DAC specifications:
Fiio Tasidhan Model No. D03K
Power supply 1.5V
Output amplitude 1.5V (0db Fs)
Frequency Response 20Hz-20KHz
Signal to Noise Ratio >95db
Crosstalk >85db
Total Harmonic Distortion <0.008

TV has no published specs for audio output.

I dismantled the system completely and started adding back just the HR-752 receiver, a pair of speakers,
and the TV with DAC. I switch the power chords from the TV and receiver, which were plugged into seperate
outlets, to a common ground power bar and the buzz with the Hologram mode has disappeared. Still don't
understand how/why only the Hologram mode was effected.

I am. however, still encountering the left channel signal drop-out. I tried reversing the L/R RCAs (from DAC
to receiver) and still get drop-out in the left channel so I think there is a problem with the HR-752, but it is
triggered by something on the TV/DAC end as it does not occur when TV/DAC are not connected and tuner
is the signal source..... ](*,) ](*,) ](*,)

magnaryder
I think you hit the nail on the head..."shitty little DAC".
I'm using the DAC in coax mode (not optical) just for the audio signal.
Time to replace the DAC with something decent before I cause any further damage.
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radioeng2

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Post Tue Oct 31, 2017 10:17 am

Re: Digital to Analog audio converter problems!

Those are almost a "universal" DAC. As in they are sold under all kinds of product names. Cheap, generic, etc. But I still think just replacing it your likely to still have issue with the audio interruption. I'm not seeing likelihood the DAC's the problem. Instinct more than anything. Could be a defect I suppose...but testing it otherwise should help answer that question real quick.

This is the modern world we live in. Perfect digital everywhere (and getting better each day). Just gotta get it to work and decode and keep the updates loaded and figure out why the blankity blank thing.... :rolleyes:

Mark
I was there "At the Fest!" Hope you were too!
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Magnaryder

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Post Tue Oct 31, 2017 1:20 pm

Re: Digital to Analog audio converter problems!

To field test the dac plug a cd player into it and see if the same situation occurs.

ray
Magnaryder

Its going to be used equipment when I sell it, so it may as well be used equipment when I buy it.

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Dennis47

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Location: Indiana

Post Tue Oct 31, 2017 4:21 pm

Re: Digital to Analog audio converter problems!

magnaryder,

I connected the SD/A 490t to directly to the DAC and did an A/B comparison between
the DAC and HR-750 receiver (CD direct). First, no left channel drop-out. Second, only
about a 10% signal strength reduction. Third, about a 15%-20% reduction in signal
dynamics. Still a substantial improvement in performance.

So I guess radioeng2 was right. Seems the problem(s) is with the TV audio output.
I tried contacting RCA.com to see if there is a design flaw or if there is a problem
particular to my TV. Seems RCA.com is having problems with their Service Warrant
Provider performing warranty work at present. Rats!
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jjptkd

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Post Tue Oct 31, 2017 5:10 pm

Re: Digital to Analog audio converter problems!

What model tv do you have?
Oppo Sonica DAC / Pre
Sunfire 300x2
Klipsch Cherry RF-5's w/ RC-7 Horn & Crossover
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