[sphinxllama]

@headphonejunkie

thanks a lot for your quick answer!

Does the wiring has to look like that:

EDIT: To SAFE my pride I have to delete this

Used the mouser IEC power entry module with fuse holder Partnumber:693-6200.4315

EDIT: FallenAngel Thanks for your answer I think it is to late and I did not think...

 

[FallenAngel]

Definitely not! Good thing you're safe

Don't connect the red and black wires to house ground, just connect them together and isolate them from everything else. I would suggest a good mechanical connection, some solder and electrical tape over it.

EDIT: Connect the top pin to the case for safety and make sure your input / output jacks are isolated from the case.

 

[regal]

Quote:

Originally Posted by sphinxllama /img/forum/go_quote.gif @headphonejunkie thanks a lot for your quick answer! Does the wiring has to look like that: EDIT: To SAFE my pride I have to delete this Used the mouser IEC power entry module with fuse holder Partnumber:693-6200.4315 EDIT: FallenAngel Thanks for your answer I think it is to late and I did not think...

You must have a short

 

[sphinxllama]

Hello,

thanks to everybody I finally finished my SOHA.
It works now fine, but there is only one thing I am not pleased with. When I connect my mp3-player and do not play music and just touch the volume nob and turn it louder I get a rush in my headphones. Is it a ground problem? Where could it be?

greets

EDIT: even when I came to close to the tube I can hear some rush. Is that normal?

 

[Yen]

Quote:

Originally Posted by sphinxllama /img/forum/go_quote.gif When I connect my mp3-player and do not play music and just touch the volume nob and turn it louder I get a rush in my headphones. Is it a ground problem? Where could it be?

If you are using a blue alps (or a copy), ground the pot by screwing the ground wire to one of the screws of the pot's casing... That could help.

 

[sphinxllama]

@Yen
Thanks for your answer. Yes it is an AlpsPot I think a RK27. So I should wire from the potground on the pcb to a screw on the pot?
But what confuses me is that when I come to close to the tube there is a rush too.

 

[tomb]

Quote:

Originally Posted by sphinxllama /img/forum/go_quote.gif @Yen Thanks for your answer. Yes it is an AlpsPot I think a RK27. So I should wire from the potground on the pcb to a screw on the pot? But what confuses me is that when I come to close to the tube there is a rush too.

Tangent's photo of grounding the RK27 pot (on the PPA):

There are actually four input pads next to the pot on the SOHA. Only one Ground is needed; use the other one to wire to a screw on the RK27 as shown in the photo above.

As for your hand, it's hard to tell. You may have a shielding issue with the tube. There is a small ground pad near pin 1 on the tube. That is sometimes used for a small snubber cap, but I haven't heard of anyone using it. Get the pot grounded first. If you still have noise issues with your hand and the tube, you might try that pad.

 

[sphinxllama]

And again thanks for your help

Sometimes a picture is worth more than a thousand words. especially in my case

 

[sphinxllama]

O.K. I used some spare time and did that job. It worked. Now the rush, when touching the pot is gone! Thanks to Yen and tomb

The problem with the tube is not gone so. I took some pictures maybe the problem can be seen easier.





Can not see a groundpad on that tube?

 

[achina]

Have you checked out this thread?

http://www.head-fi.org/forums/showthread.php?t=228976

It may be a grounding problem. Looks like you don't have it in a case yet though.

 

[tomb]

Sphinxllama,

The tube "ground" is actually an internal shield. As mentioned, it's usually decoupled from Ground with a small snubber cap jumpered from pin1 to that extra pad shown in the photo:

As I also said - I haven't seen one yet where this is necessary, though.

Achina has a good point with his post. Did you by chance connect house ground (the third prong on a house wall outlet) to the SOHA board? The Ground on the SOHA board is for the center tap from the transformer, only. If you have tied it into house ground, you'll get a huge hum and noise. The only thing that should be connected to the SOHA "Ground" pad is the center or combined tap from the xfmr.

If that's not it, you may have a bad tube - perhaps one overly sensitive to RF noise.

Those are my guesses, anyway.

 

[Yen]

Quote:

Originally Posted by sphinxllama /img/forum/go_quote.gif The problem with the tube is not gone so. I took some pictures maybe the problem can be seen easier.

It is the tube catching some interference from other electronic devices. Especially if you are using it near a PC it will catch even more.

I have also noticed, when I removed the output resistors (R6/16), that rushes are heard more often. Try casing your amp in a metallic case (which you have done already) and try some 50-100ohm quality (holco, kiwame etc. if you have $) resistors and rushes will dissapear or be less frequent and at lower volume.

 

[headphonejunkie]

I noticed your transformer wires are not twisted. I twisted mine. I am not sure if this will make a difference though.

 

[sphinxllama]

@tomb
I soldered a wire from pin1 to that pad but it got even worse. the rush was there even without comeing to close to the tube. and music only played on one side. now I desoldered everything and it only rushes when I come to close to the tube about 5mm.

@yen
the amp stands away from any big electronical gear like tv or pc. so I think that point I can skip.
the output resistors I have exchanged with jumpers. the soha kit came with vishay dale resistors I think with a value of 150Ohms. so I did not use them because somewhere I read that resistors in that place will cause a loose in soundquality. and with beyerdynamic DT880 250Ohm impedance headphones the volume is not to loud when turned a little from zero position so both sides of the headphone are powered.

@headphonejunkie
thanks, will try this option tomorrow an will post if it had some effect on the rush.

the rush is not that bad, it can hardly be heard when music is playing and only if I come to close to the tube. but other than that it has no effect on the quality. it is just strange phenomenon to me.

After a long day I will now enjoy the SOHA

P.S. can not stop saying thanks for all your great and tireless helping

 

[headphonejunkie]

Twisting the wires help them avoid any electrical interference from each other and should help them not give off any EMF to other components;hopefully.