The "mod your Zhalou" Thread

[deuginthesky]

Quote:

Originally Posted by schuang /img/forum/go_quote.gif What a sloppy manufacture! I guess they just get whatever they have and put them in. No QA what so ever. BTW, I use Silver-Mica on mine and they seems to do the job. Again, you don't have to replace 4 green caps, but the correct value should be 470pf if you really want to. Yellow caps is the bottle neck for the entire signal chain. Sean

Guess what ?

Values are not what they should be also on the power board. On mine, the two main caps are 3300µF/35V, they should be 4700µF/25V. By luck, I had bought 4700µF/35V caps to replace them

 

[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Ok, I measured the DC voltage with an off multimeter, it's not zeroed. I tried again, and it's only showing a couple of mV on each channel

Since you have a multimeter, measure the DC supply voltage to the zap board. Switch the multimeter to AC and check again how much ripple you have.
BTW, the same experiment you did with the phones connected to the XLR you can repeat with the phones connected to the RCA pins. Check if you hear the same noise this way.

 

[udo]

Quote:

Originally Posted by deuginthesky /img/forum/go_quote.gif Guess what ? Values are not what they should be also on the power board. On mine, the two main caps are 3300µF/35V, they should be 4700µF/25V. By luck, I had bought 4700µF/35V caps to replace them

Hmmm...
Makes me want to check my Zhaolu's again for capacitor values...

 

[SonicDawg]

Quote:

Originally Posted by Ori /img/forum/go_quote.gif Since you have a multimeter, measure the DC supply voltage to the zap board. Switch the multimeter to AC and check again how much ripple you have. BTW, the same experiment you did with the phones connected to the XLR you can repeat with the phones connected to the RCA pins. Check if you hear the same noise this way.

Where do you measure the AC? from ground to +? My multimeter has only 10V and up for AC, which I don't think is appropriate here. And I tried again to connect the RCA directly to the headphones, and the hum is still there, so I don't think the amp's got much to do with it.

I emailed LCaudio about this problem. Hopefully it will be resolved soon.

 

[Crow]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Where do you measure the AC?

Advice... trace the output pins back to their respective components on the power board and measure there. Measuring directly from the pins is dangerous because if your hand slips you will short out the pins and kill your PSU. I had to rebuild my board because of this. You are looking for 25V between the pins (forgot which ones). As for AC ripple, it seems you would need less than 10V scale...

Best of luck

 

[deuginthesky]

Quote:

Originally Posted by udo /img/forum/go_quote.gif Hmmm... Makes me want to check my Zhaolu's again for capacitor values...

Almost all non film caps have uncorrect value regarding what is wriiten on the PCB. At least on mine.

 

[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Where do you measure the AC? from ground to +? My multimeter has only 10V and up for AC, which I don't think is appropriate here.

Try it anyway. If it reads "0.00" then you can cross this "problem". It's a process of elimination...
Quote:

And I tried again to connect the RCA directly to the headphones, and the hum is still there, so I don't think the amp's got much to do with it.

You're right. I'm not familiar with the zap. Is there an option to set the output to RCA only or XLR only?

 

[SonicDawg]

Quote:

Originally Posted by Ori /img/forum/go_quote.gif Try it anyway. If it reads "0.00" then you can cross this "problem". It's a process of elimination... You're right. I'm not familiar with the zap. Is there an option to set the output to RCA only or XLR only?

I can't really use the multimeter for anything less than 10v of AC, because it's an analog one with needle. It's pretty hard to see anything at all...

As for the zapfilter, I do not think there's a way to choose a specific output. Just wire them differently when you do.

 

[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif I can't really use the multimeter for anything less than 10v of AC, because it's an analog one with needle. It's pretty hard to see anything at all...

Wow, you gotta be a museum curator...

You can buy a decent multimeter for $5 in discount stores (I saw one with transistor and cap measuremets too!) or $7.99 and up on the internet... Radio Shack would be probably $15-20. No DIYer should live without one!
Quote:

As for the zapfilter, I do not think there's a way to choose a specific output. Just wire them differently when you do.

Then the next thing to ask is which configuration you have and whether changing to the other would solve the hum issue on the RCA side.

 

[Epicurean]

I recently noticed some hum I hadn't noticed before in my Zapfiltered Zhaolu when running single ended. It was strange though, even the slightest movement/poking of the power cord changed the sound of the hum

I remembered reading a post by amb on headwize that the transformer emits the most radiation where the cables come out so I turned it around towards the front and also tried to get the power wires as far away from the ribbon cable as possible. Problem seems to be fixed and no hum since then unless I crank up the volume to ridiculous levels.

 

[cotdt]

Quote:

Originally Posted by Epicurean /img/forum/go_quote.gif I recently noticed some hum I hadn't noticed before in my Zapfiltered Zhaolu when running single ended. It was strange though, even the slightest movement/poking of the power cord changed the sound of the hum I remembered reading a post by amb on headwize that the transformer emits the most radiation where the cables come out so I turned it around towards the front and also tried to get the power wires as far away from the ribbon cable as possible. Problem seems to be fixed and no hum since then unless I crank up the volume to ridiculous levels.

balanced is the best way to get rid of such hum. single-ended is a lost cause.

 

[SonicDawg]

Seriously, a good design should not require one to to forfeit the entire configuration of his system to accommodate its inherent flaw... I hope LCAudio can really address this issue

 

[udo]

Quote:

Originally Posted by Ori /img/forum/go_quote.gif You're right. I'm not familiar with the zap. Is there an option to set the output to RCA only or XLR only?

Nope. You just use either two or three wires.

 

[SonicDawg]

Just got their reply:

If the two shunt regulators on the Zapfilter board are hot the supply voltages should be absolute without hum. The 56 ohms resistors should be sufficient
If you shortcut both inputs on the Zapfilter board there should be no hum.

What do they mean by "shortcut[ing]" both inputs? Shorting them all together?

 

[udo]

Probably.
I.e.: disconnect the analog signal from the DAC chip (at the zapfilter...) and connect postive and negative inputs to ground for both channels on the Zapfilter.