Cal Audio Labs DAC

I have just finished auditioning a used California Audio Labs DAC with both my HT receiver (Kenwood 6060) and my two channel receiver (Onkyo 8011). This took a heck of alot longer than I had expected. My HT is housed in a LARGE entertainment unit so changing cables is a bit of work.
My main reason for trying an external DAC was my new facination with Internet Radio. I was pleased with the way it sounded with my two channel, which has one of these running a USB digital out to analog,

http://www.xitel.com/product_phfl.htm

but I knew the Ascend's in my HT were capable of more than I was getting running an optical cable direct to the Kenwood.
In my HT, where the Ascend's reside, I use the dac in my DVD/CD (Toshiba 290) player for two channel by running the analogs to the receiver. When comparing this set-up to the digital out from the Toshiba to the Cal Audio then analog to the receiver, I could not tell a definitive difference in sound. The Toshiba does a nice job and the Cal Audio did also.
When I ran the digital out from the Xitel to the Cal Audio, there was a small but noticeable difference in the sound from Internet Radio. It was my impression that the sound floor had dropped. Everything just seemed a bit clearer. No one aspect seemed to jump out. Just an overall improvement. This is just what I was looking for. Now the bad news.
The Kenwood has a red light that signals clipping. With the Cal Audio engaged, this light would periodcally flash briefly. This does not happen with the dac's in the Toshiba or the Kenwood. There was no clipping apparent when the light would flash nor was it dependent on the volume. The light would flash in the same place on the CD regardless of SPL. There are several possibilities of why this might occur but there is no inexpensive or less time consuming way to find out. I'm choosing to reject the DAC based on this anomaly.
I also tried the Cal Audio in my two channel system but did not hear any improvement over what I already had in place. This is a very nice low buget system (Mission 761 2-way speakers, Toshiba 2710 DVD/CD player with the Onkyo and Xitel).
If not for the clip warning light being activated, I'd have kept the DAC just based on the improvement in Internet Radio. If the Kenwood did not have this "feature," I'd have never known of a potential problem.
Onward and Upward.

David

Interesting. What's the input sensetivity on the analog input on your receiver? What's the spec for the output voltage on the DAC? I guess the DAC could be overloading the receiver on dynamic peaks.

If you've got a decent multimeter, you can measure the DAC's output on passages that you know cause the clipping light to turn on. Many multimeters have the ability to record the highest reading recorded during a test. If you turn that feature on, then start reading voltages while the source plays, you should be able to note the true peak voltage output.

If the peak is below the rated input sensetivity of your receiver's input, I wonder if the clipping light turns on when input voltage is within say 5% of maximum input sensetivity? If the recorded voltage is higher than your receiver's capacity, you could see if there's a way to attenuate the DAC's output.

Quote:

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Originally Posted by jimsiff

Interesting. What's the input sensetivity on the analog input on your receiver? What's the spec for the output voltage on the DAC? I guess the DAC could be overloading the receiver on dynamic peaks.

If you've got a decent multimeter, you can measure the DAC's output on passages that you know cause the clipping light to turn on. Many multimeters have the ability to record the highest reading recorded during a test. If you turn that feature on, then start reading voltages while the source plays, you should be able to note the true peak voltage output.

If the peak is below the rated input sensetivity of your receiver's input, I wonder if the clipping light turns on when input voltage is within say 5% of maximum input sensetivity? If the recorded voltage is higher than your receiver's capacity, you could see if there's a way to attenuate the DAC's output.

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Output voltage on the DAC is 3.5 vrms.
Imput sensetivity on the receiver is 500mV / 47k
I'm guessing this is the digital optical sensetivity. There is no separate listing for analog. I'll see if I can dig this info up at the Kenwood site.

Any help?
Thanks,
David

Actually I was incorrect when I mentioned input sensitivity in my previous post. Input sensitivity is the minimum voltage necessary to properly process and amplifiy the signal. Most receivers don't give a spec for maximum input voltage, but IIRC 3.5-4 volts is pretty hot. Given that the clipping light turns on even at low SPL, it's likely that the preamp input is where the clipping is taking place.

You can get a rough estimate of the maximum input voltage (based on the clipping light) of your receiver by using a source passage that makes the clipping light turn on for just a split second. Once you find a passage that works, replay that passage with the multimeter hooked to the DAC output. The peak voltage seen by the multimeter will be during that short time when the light is on. That should be a rough estimate of the maximum, as long as the clipping light is accurate.

For comparison, you can measure the output voltage of your CD player's DAC during the same passage and compare the peak value. I would guess that the CD player DAC is in the 2+ volt range, most likely below 3 volts.

You'd probably need to use a signal generator and an oscilloscope to accurately gauge when the receiver clips. Without that, or a voltage attenuator built into the DAC, there's really no way that I can think of to accurately gauge what the receiver can handle. Maybe somebody else will know some other way.

"For comparison, you can measure the output voltage of your CD player's DAC during the same passage and compare the peak value. I would guess that the CD player DAC is in the 2+ volt range, most likely below 3 volts. "

Right you are.

I'll forward this thread to the DAC's owner. Thanks for your help, Jim.

David

It's interesting that some DACs, preamps and sources feel the need to run such a hot output. From what I've seen, there really is no need in most cases.

You can get away without using a preamp if the source has a hot enough output. That can be an advantage if the person has a nice power amp but doesn't want to spring for a high dollar preamp.

In the car audio world, 4 volt outputs started to be the rage about 5-6 years ago because the signals can supposedly resist noise interference better. That said, with proper signal cable & power wire routing and system grounding, noise is not going to be an issue whether using a 2 or 4 volt output. Most car audio amps that I've seen attenuate the input if the head unit uses a 4 volt output anyhow. The SPL output isn't going to be any higher using 4 vs. 2 volt outputs. :rolleyes: