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Old 8th November 2010, 04:19 PM   #1
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Default Help with possible ZAPfilter related problem in Zhaolu DAC

Sorry for the long post but I'm desperately trying to figure out an issue I am having with a Zhaolu DAC I have that has a ZAPfilter installed. The DAC chip is the CS4398 and the receiver is CS8414. I acquired a Zhaolu DAC that had a ZAPfilter MK2 installed by the previous owner and it appears the ZAPfilter was installed quite well (unfortunately I can't seem to get in touch with the previous owner regarding this issue). That said I am not a huge DIY guy but have done a fair share of some parts soldering and cable construction. They installed both single ended and balanced outputs, I use the single ended outputs. They have the outputs from the ZAP analog board wired to the balanced outputs and then the single ended RCA's tap off the of the balanced outputs. I used the DAC in a headphone system only for quite some time but recently brought the DAC into my speaker system and started noticing a vague issue with the DAC that I can't quite figure out.

The ZAPfilter Zhaolu DAC sounds fantastic in my speaker system but it has this issue where when I am listening at a moderate to high volume, and a very dynamic piece in the music happens (typically I hear this with well recorded, midrange heavy female vocals when the vocalist is really pushing the vocal) suddenly the sound will become very strained and somewhat distorted. I fear for the drivers in my speakers so I usually turn it down right away but once this happens the distorted sound doesn't want to disappear - it just kind of hangs on even at lower volumes once the strain/distortion happens once. It's puzzling because I never ever had this problem in my headphone system. I also own a stock Zhaolu DAC and have used it in my speaker system and have no problems at all, it's just the ZAPfilter Zhalou DAC.

I have a combined audio and AV system so my preamp is a Yamaha receiver, amp is a Parasound Model 275 and speakers are Dynaudio Audience 42's. I know the ZAPfilter'd DAC clearly has a little higher voltage output than the stock DAC and I started to wonder if the preamp was being overloaded but it's only slightly louder than the stock unit and I have PLENTY of control on volume, it's not like the DAC is screaming hot with voltage by any means. It's so strange that at one moment the DAC sound gorgeous and then a dynamic passage occurs and the DAC is sent into a strained, slightly distorted quality and doesn't seem to come out of it after that. I'm wondering if it's an installation issue but given my level of knowledge here I wouldn't know what to look for and don't have the understanding. Another thing that crossed my mind is if the Toslink interface on the board is an issue (I use TOSLINK from my source) but it doesn't seem likely, all seems fine there, my suspicion is the ZAPfilter. Again not an expert, any kind of a DC problem here? Any issue with the way he wired the ZAP's analog outputs to the balanced outputs first then the single ended taps off of those??

Is this throwing up any clear flags for anyone? Any help at all would be much appreciated, it's been very frustrating. Thanks.

Last edited by Old School; 8th November 2010 at 04:43 PM.
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Old 8th November 2010, 04:57 PM   #2
kevinkr is offline kevinkr  United States
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Sounds like this might be an issue with the Zapfilter, and I would suggest contacting them.. It might be that the input voltage is a bit too high and driving the Zapfilter hard enough that it doesn't recover gracefully from that first clip. Turning down the volume doesn't affect what is going on in the filter at all. Do you connect the headphones directly or do you have an outboard box?

I sold my Zhaolu a long time ago, and no longer remember all of the details, but I somewhat question the use of a Zapfilter with a voltage output dac such as used in your Zhaolu. You might want to try your dac in another system in order to make sure that it is not circuitry in your receiver input circuitry ahead of the volume control that is getting overloaded. (You can try a set of attenuators between the dac and the receiver as well.)
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Last edited by kevinkr; 8th November 2010 at 05:02 PM.
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Old 8th November 2010, 05:02 PM   #3
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Originally Posted by kevinkr View Post
Sounds like this might be an issue with the Zapfilter, and I would suggest contacting them.. It might be that the input voltage is a bit too high and driving the Zapfilter hard enough that it doesn't recover gracefully from that first clip. Turning down the volume doesn't affect what is going on in the filter at all. Do you connect the headphones directly or do you have an outboard box?

I sold my Zhaolu a long time ago, and no longer remember all of the details, but I question the use of a Zapfilter with a voltage output dac such as used in your Zhaolu.
Thanks, Kevin, I appreciate it. Interesting, I just wish I had full understanidng of that. The high input voltage thingsounds very intriguing it's just a bit beyond my knowledge. Regarding the use of headphones, I when I use headphones with the Zhaolu I use it with a Mapletree Audio Ear+ HD tube headphone amplifier and have no problems at all. It's only in my speaker system where the issue occurs.

When you say "but I question the use of a Zapfilter with a voltage output dac such as used in your Zhaolu" can you elaborate a bit more? Thanks!
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Old 8th November 2010, 05:06 PM   #4
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Originally Posted by kevinkr View Post
You might want to try your dac in another system in order to make sure that it is not circuitry in your receiver input circuitry ahead of the volume control that is getting overloaded. (You can try a set of attenuators between the dac and the receiver as well.)
Missed this after you edited your reply. Interesting, I had a suspicion of this an had thought about getting some attenuators to see if this was the problem.

I do have another receiver I could connect temporarily to see if the problem occurs. Thanks.
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Old 8th November 2010, 11:53 PM   #5
wwenze is offline wwenze  Singapore
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Can you try something unconventional?

Set the source CDP/computer to output at an extremely low volume. Play the dynamic music known to result in the problem. Does the output volume from the DAC suddenly increase by a lot?
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Old 9th November 2010, 03:11 AM   #6
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Can you try something unconventional?

Set the source CDP/computer to output at an extremely low volume. Play the dynamic music known to result in the problem. Does the output volume from the DAC suddenly increase by a lot?
Thanks for the reply. Well, I tried a few things tonight that may shed some light on the problem. First, my main source does not have a volume control and so I can't turn down the volume on the source but I do have another DAC that I own which is a Musiland MD-10 which is known to have a very hot 3V output BUT it also has a digital volume control as well. So I inserted this DAC in place of the ZAP/Zhaolu and kept the volume at max. I immediately heard the same strained/strident/distorted sound I sometimes get with the ZAP/Zhaolu as described in my previous post but even worse. I then turned down the volume really low as you suggested and I can't say I noted the volume got "louder" but I did note the distortion completely went away (it actually started to go away when I turned the volume down about -6dB). Since I know the Musiland DAC has a 3V output I would assume the ZAP/Zhaolu must have a voltage output around 2.5V, maybe a bit higher. I'm starting to think what the problem is, is the preamp in my receiver is getting overloaded which seems odd (but I'm not an expert) and that it's not an issue with the ZAP filter.

Further, another test I did, I tried a digital coaxial connection to the ZAP/Zhaolu DAC from a different source, which is noticeably lower in output level compared to the Toslink, and I did NOT get the distortion whatsoever.

It's becoming quite clear now that the ZAP/Zhaolu has a higher than standard voltage output, with Toslink yielding the highest output, and my preamp doesn't like it. I may try some 6dB in line attenuators to put on my interconnects. I know using a "receiver" as a preamp likely makes people sick but until I get back into a better preamp or integrated amp some day this is my current situation.

If you have any other thoughts on this let me know, thanks!
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