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SOHA Wiring question
Jun 2, 2008 at 11:37 AM Post #31 of 44
Well... I guess my problem with the left channel buzz must definitely be from the cheap china-pot...if i turn it to the absolute maximum, then it completely disappears and the channels are more even then too. Probably for now, I'll just set it directly on the board to function without a pot and use the volumer control from the laptop, atleast until I get the AlienDAC, then I'll see if to get an Alps or if to get somekind of stepped attenuator.
Probably I could also get rid of the hum by adding the output resistors, the RP21s are afterall quite low impedance.

If I remove the pot, should I just connect the inputs and outputs with jumper wires, or should I solder a resistor instead between the INs and OUTs? If my port is the problem, then removing the pot should prove it.

Any comments?
 
Jun 5, 2008 at 10:25 PM Post #32 of 44
Finally took the SOHA back home and made some quick tests/measurements, for now it seems to me as a grounding issue.
B+ stable at around 68v, both 40Vs nicely 40.4-40.5v, 3mV DC offsrt in one channel, nearly inexistant in the other one.

I didnt want to start stripping wires for my tests so I just used the DMM as a jumper (ohm meter position). If I connect the pot body to signal ground (input jack), the buzz/hum reduces, the same if I jumper the signal ground to mains ground. Also, if I touch the cables to the pot, the noise increases drastically.
So for tomorrow morning I have planned the following tests:

1-solder a wire to connect pot body and signal ground
2-connect signal and mains ground (after all the problem came when I changed to isolated jacks)
3-if nothing helps, remove pot
4-add 150R resistors to output
5-if pot removal helps..change Pot wires to shielded microphone cable

any other suggestions are welcome
smily_headphones1.gif
 
Jun 6, 2008 at 1:10 AM Post #34 of 44
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
DO NOT REMOVE POT!

Connect pot body to signal ground (find a place on the PCB).
How long are your input wires?


Around 5" (shielded microphone cable)
 
Jun 6, 2008 at 8:13 AM Post #35 of 44
Looks like its fixed now. This is what I did:

1- solder a wire (solid core copper - its what I had in hand) from pot body to Signal ground

2- solder Jack grounds to a wire attached under a screw in the case

after these 2 changes, there was still a very light buzz (you could barely hear it) in the right channel, so I:

3- Added 200R resistors in the output. - Only had 51R and 200Rs. Tried 51R first but 200R seemed better, in lower volumes its dead quiet now and only starts to hiss at 80-90% of the volume. Will try to get form someone a pair of 150R Vishay-Dales there though.

It still wonders me why it need a "goundloop" not to buzz... kind of annoys me that I ordered the insulated jacks from overseas and they were the problem.

For now it sounds ok though, after the AlienDAC is done and connected, probably I should consider an Alps pot or stepped attenuator (any good/cheap choices for these? I saw in DIYfidelity the "DIY versions" for reasonable amount but I would still have to get quality resistors from somewhere)
 
Jun 6, 2008 at 8:29 AM Post #36 of 44
Quote:

Originally Posted by DolbyR /img/forum/go_quote.gif
Looks like its fixed now. This is what I did:

1- solder a wire (solid core copper - its what I had in hand) from pot body to Signal ground

2- solder Jack grounds to a wire attached under a screw in the case

after these 2 changes, there was still a very light buzz (you could barely hear it) in the right channel, so I:

3- Added 200R resistors in the output. - Only had 51R and 200Rs. Tried 51R first but 200R seemed better, in lower volumes its dead quiet now and only starts to hiss at 80-90% of the volume. Will try to get form someone a pair of 150R Vishay-Dales there though.

It still wonders me why it need a "goundloop" not to buzz... kind of annoys me that I ordered the insulated jacks from overseas and they were the problem.

For now it sounds ok though, after the AlienDAC is done and connected, probably I should consider an Alps pot or stepped attenuator (any good/cheap choices for these? I saw in DIYfidelity the "DIY versions" for reasonable amount but I would still have to get quality resistors from somewhere)


At 80%-90% volume on a SOHA, you'll blow your brains out with every headphone imaginable, might as well throw in the 51R, or better yet, get some nice boutique in there (I never liked any resistor personally, but if you must), put something nice, like Holco/PRP, they're super cheap and sound good; you only need 3, it won't break the bank.
 
Jun 6, 2008 at 8:39 AM Post #37 of 44
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
At 80%-90% volume on a SOHA, you'll blow your brains out with every headphone imaginable, might as well throw in the 51R, or better yet, get some nice boutique in there (I never liked any resistor personally, but if you must), put something nice, like Holco/PRP, they're super cheap and sound good; you only need 3, it won't break the bank.


Yes I know, have of my brains are blown out already
biggrin.gif

It wasnt because of the low volume hiss but because of the right channel hum, it is so low though that you cant barely hear it even with the source muted, but though in long term it could damage the headphones.

I'm not a frined of resistors either thats why I didnt have them before, but seems like for now its my only option... Why do you say I need 3?! Arent they just 2 (R6 & R16)?

And from where would I get those resistors? Any ideas? Gets kinda complicated to find that kind of stuff when you're in eastern europe.
 
Jun 27, 2008 at 6:53 AM Post #38 of 44
Well, the original headphone jack got broken on the SOHA (actually just the plastic washer cracked) so I thought it would be better to get the best I can find locally...

I'm going to use IC/Instrument cable to wire it, I got some stereo one but I'm wondering which is best, to use just one run with one conductor per signal and the shield for ground; or 2 runs - conductors for each signal and also for ground and the shield connected only in the amp-end?
 
Jun 27, 2008 at 9:59 AM Post #40 of 44
Quote:

Originally Posted by adamus /img/forum/go_quote.gif
what guage is it? there is very little power through the wire.


Adamus, would you care to elaborate what you mean? I don't see the relevance of the gauge or the power to my question, as in both ways I described, there will be ONLY ONE conductor per signal channel. Just the second one would let me to use the shielding of the cable really as a shield and not as signal ground.
 
Jun 27, 2008 at 10:29 AM Post #41 of 44
sorry mate, i was half asleep and didnt read properly.
Either is fine. Do whichever is easiest to solder.

By the way, we have almost identical setups. IF you havent gone down the jisbos route yet - - - DO IT. night and day.
 
Jun 27, 2008 at 11:24 AM Post #42 of 44
Quote:

Originally Posted by adamus /img/forum/go_quote.gif
sorry mate, i was half asleep and didnt read properly.
Either is fine. Do whichever is easiest to solder.

By the way, we have almost identical setups. IF you havent gone down the jisbos route yet - - - DO IT. night and day.


Yeah, I know, I know, I must get them
smily_headphones1.gif
Though first I must get the AlienDAC finished (been waiting couple of weeks for my package from Jeff already). After that I'm planning on getting a stepped attenuator to replace the cheap china-pot (you would't imagine unleveled the channel are with it - I actually have to use the windows' balance to correct it).
 
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