[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Overall, I think the amp (Darkvoice 336i) is very sensitive

Not much info on it, but it's likely that the input is DC-coupled and the amp is high-gain with little or no feedback. This can result in more sensitivity to DC offset or hum from the source.
Quote:

Btw, I found that with the original 100ohm and the 56ohm resistors, I get hum AND statics/pop and clicks. With the radioshack 47ohm ones I only get hum and free of statics

You may be picking up a local radio station. The RS could be more inductive wire-wound type...

 

[SonicDawg]

Ori, what do you think of doing a XLR to RCA connection, from the Zapfilter to Darkvoice, to eliminate the noise?

 

[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Ori, what do you think of doing a XLR to RCA connection, from the Zapfilter to Darkvoice, to eliminate the noise?

That won't work well. Since the amp is single-ended stereo, the grounds of the two channels are shared, which means that you cannot use the nagative polarity of the balanced outputs as the RCA ground.
Check inside the amp to see if there is a blocking cap between the RCA HOT pin and the tube's grid. If not, then I'd try a small cap externally (you can use alligator clips to route the signal temporarily) and verify if that's the source of the hum. If you're OK with a soldering iron then install these inside the amp. You can always reverse that "mod".

 

[cotdt]

As an alternative to the Zapfilter, what do you guys think of this tube/mosfet hybrid analog stage?

http://www.welbornelabs.com/hyb.htm

 

[SonicDawg]

Quote:

Originally Posted by Ori /img/forum/go_quote.gif That won't work well. Since the amp is single-ended stereo, the grounds of the two channels are shared, which means that you cannot use the nagative polarity of the balanced outputs as the RCA ground. Check inside the amp to see if there is a blocking cap between the RCA HOT pin and the tube's grid. If not, then I'd try a small cap externally (you can use alligator clips to route the signal temporarily) and verify if that's the source of the hum. If you're OK with a soldering iron then install these inside the amp. You can always reverse that "mod".

From this picture, it seems that the amp has a blocking cap:

As for adding caps to the signal, what uf caps are a good choice?

 

[looser101]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif From this picture, it seems that the amp has a blocking cap: SNIP As for adding caps to the signal, what uf caps are a good choice?

No blocking cap that I can see. Checking the schematic that I have it also doesn't show a blocking cap. And the pot is 100k. So .47uF - 1uF is more than enough.

~Renato

 

[looser101]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif As an alternative to the Zapfilter, what do you guys think of this tube/mosfet hybrid analog stage? http://www.welbornelabs.com/hyb.htm

I've looked at it several times. And THIS ONE too. Try it and let us know.

~R~

 

[Ori]

Quote:

Originally Posted by looser101 /img/forum/go_quote.gif No blocking cap that I can see. Checking the schematic that I have it also doesn't show a blocking cap. And the pot is 100k. So .47uF - 1uF is more than enough.

That value is very conservative, Renato. I'd say 0.1uF or even 0.05uF would be just fine. The grid should be close to ground potential, so a low voltage cap is fine. I'd look for a copper foil type but good results can be had from cheaper Sprague "orange drops".

 

[High-Q]

Quote:

Originally Posted by High-Q /img/forum/go_quote.gif Thanks for confirming that the psu is faulty Renato, I'll send it back tomorrow.

I got the zapfilter back two days ago with a new powersupply. After installing I didn't have any problems. Everything is up and running. Thanks a lot for all your help guys!!

 

[SonicDawg]

High-Q, did you contact partsconnexion or LCaudio directly? I am thinking that my PSU could be faulty...

 

[SonicDawg]

Is a dc offset from + to ground of 50mv good?

I just measured both channels and found them to be pretty consistent.

nvm: stupid meter was not zeroed...

Anyway, I am really done with this hum witchhunt now. Maybe I should just start building the current buffer stage and forget about this silly hum

 

[Ori]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Is a dc offset from + to ground of 50mv good?

Not good.

There is definitely a problem with your zap or installation.

 

[deuginthesky]

On my D2.5a, the green 0,1µF film caps (EDIT: on the analog stage) seem to be Vishay MKT1826, they are written 100 1826 then under is written 0044. On the top you can read "ero".

So there are two brands of film caps on the board: Vishay and Wima.

 

[SonicDawg]

Quote:

Originally Posted by Ori /img/forum/go_quote.gif Not good. There is definitely a problem with your zap or installation.

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. So I don't think DC offset is the problem here.

Btw, I tried taking every component out of the case, and laid them as far apart from each other as possible, grounding the case, and hooking up the zap PSU directly from Zhaolu power input, nothing avails! Still the same hum, all the time

I really don't want to go balance for the sake of a silly hum, not to mention all the time and money spent acquiring different tubes for my amp, which I love greatly. Do you guys think replacing the PSU caps will help?

 

[High-Q]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif High-Q, did you contact partsconnexion or LCaudio directly? I am thinking that my PSU could be faulty...

I emailed LC-audio about my problem and sent the complete package back with a description of the problem and a request to test the kit. They emailed me back within a couple of days that they had sent me back the zapfilter with a new powersupply. Only took a week in total with eastern in between.