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SOHA II Builders Thread - Page 6

post #76 of 1669
Thread Starter 
That's great grendel. The amp should be silent.

On the holes, did you use the hole sizes shown on the diagrams on the website? If so, I should make them bigger. If you did use this hole size perhaps you can tell me, when you're through, what a good hole size is.

If anyone else has a suggestion for the right hole size please let me know and I'll change the drawings.
post #77 of 1669
grendel - is your pcb in the 2nd slot or 3rd slot? I'm wondering cause I need the board in the second slot in order to squeeze in my pot of choice. On the other hand I want to have enough tube sticking out so I can grab onto it to roll tubes.

Any word on the group buy and cases?
post #78 of 1669
Runeight, the top panel drawings on your web page give a 404 error when you try to access them, so I used the board drawing to locate the holes for the tubes. I made 1" holes with a chassis punch and put in plastic snap in bushings. I am going to enlarge the holes and use bushings with a 1" ID.

Rds, I am using the third slot. There is not a huge amount of tube to hold on to. I use a piece of rubber to get a grip on the exposed glass. If you will use the second slot it will be harder. Maybe a short piece of 3/4" ID gum rubber hose would work well to grip the tubes?
post #79 of 1669
Thread Starter 
Sorry about that. I guess I forgot to test those links. They are available now.
post #80 of 1669
Thread Starter 
grendel I meant to ask if you have any further listening impressions?
post #81 of 1669
So I finally had a chance to build the the HV PSU. The amp still sounds wonderful, but I'm still also getting a little bit of hiss/hum with closed headphones and no music playing. The transformer is in another box so the noise is definitely from the amp.

I also noticed that the left tubes is microphonic and it's very strange. I touch the left tube - there's some serious noise in the left headphone. I touch the right tube, there noise in the left headphones again.

When I follow the setup instructions everything looks good up until measuring between TBL and TB+L (or TBR and TB+R) - both values are around 15V, not 19V.

EDIT: Just changed tubes, TBL to TB+L is now 20V and TBR to TB+R is 17V. Noise seems to have gone down a little bit as well. I'll see if I have any others as well.
EDIT2: Changed from GE 5963 to GE 6680 tubes. Noise is less again, plus tubes not microphonic. Still a little hiss/hum though. voltages are 22V TBL->TB+L and 18 TBR->TB+R. Strange pattern that the left one is ALWAYS higher, no matter the tubes.
post #82 of 1669
Thread Starter 
FallenAngel, the variations between tubes are normal. This is because you're measuring the difference between the B+ and the right triode. The plate voltage on the right triode varies according to how well the two triodes are matched. So, don't worry about this. You could, however, double check the tail current for both tubes just to have it the same amount.

It's hard to diagnose the noise. I guess the obvious questions:

1. Is the star ground connected to a metal ground point?
2. Do the tube sockets have dirty contacts?
3. Are all the solder joints on the board clean.
4. Is the pot grounded?
post #83 of 1669
Quote:
Originally Posted by Uncle Bob View Post
...
PS. my pcb arrived today
How is your build going?
post #84 of 1669
Quote:
Originally Posted by runeight View Post
FallenAngel, the variations between tubes are normal. This is because you're measuring the difference between the B+ and the right triode. The plate voltage on the right triode varies according to how well the two triodes are matched. So, don't worry about this. You could, however, double check the tail current for both tubes just to have it the same amount.

It's hard to diagnose the noise. I guess the obvious questions:

1. Is the star ground connected to a metal ground point?
2. Do the tube sockets have dirty contacts?
3. Are all the solder joints on the board clean.
4. Is the pot grounded?
Thanks for the info. The tail current is set to 2mA on both (400mV).

You're going to laugh at the 4 answer
1) Not yet
2) Should be clean
3) Not yet
4) Yep

I'm also using unshielded signal wiring spliced, stripped and twisted together to a pair of "testing" RCA jacks.

I'm guessing these are all likely culprits and I'll make everything nice and pretty tonight and post results again.
post #85 of 1669
Quote:
Originally Posted by Ferrari View Post
How is your build going?
It's progressing, pretty much all of the passives are mounted and I'm hoping to get a few hours work on the board this weekend.

GeWa has been pretty quiet, wonder how he's getting along?
post #86 of 1669
I have had a chance to listen to my SOHA II for a few days now. I must preface my comments by stating that I am not a "golden eared" audiophile and can only compare this amp to my SSMH with my Alien DAC with Blackgate output caps and SR80s (recabled because one of my cats chewed up the cord).
Given that, I can say that this amp is a big step up from the SSMH. On "funk is its own reward" by Stanly Clarke, the base line at first seems a bit stronger on the SSMH, but with the SOHA II the bass is tighter, deeper and there is a slight vibrato that is not audible with the SSMH. After comparing, the SSMH is slightly loose in comparison.
On the California Guitar Trio's "Yamanashi Blues" off "an opening act: live with King Crimson" the sense of the hall around the musicians is more spacious with the SOHA II. The SSMH seems boxed in in comparison.
This amp also is much less forgiving of poorly mastered or compressed material. Some of the music on my computer is in FLAC, now I will need to re-rip the rest.
It is obvious this amp is better than the equipment I now have to use with it, but I have started saving for a pair of HD 600's, and will build a Gamma 1 DAC once boards are available.
post #87 of 1669
I agree with everyone's comments about the SSMH, so far. I would add that it's expected, because the design goals were different and the prices for building are quite different.
post #88 of 1669
Just cased the the first of the two prototypes I have been playing with. The noise has dropped considerably (and I really mean considerably); but it's still there, and quite noticeable with no music playing using closed Denon D5000 headphones. Even with my RS-1, I can't hear it, but with those damn 25-ohm Denons, the noise is there.



runeight - now the 4 answers are Yes, clean, clean and yes.
post #89 of 1669
Thread Starter 
what kind of noise is it? hum? buzz? static? white noise?
post #90 of 1669
Quote:
GeWa has been pretty quiet, wonder how he's getting along?
I'm kinda busy with work lately. I wont go into detail because you will declare me insane! As far as the SOHAII, I'm a little over half way with populating the board. Still haven't figured out yet what I'm gonna use for C2L/R. I want to use a polypropylene cap here, but the ones I have are a little to big.



Regards
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