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SOHA II Builders Thread - Page 65

post #961 of 1686
Thread Starter 
yzriver, the front end design in this amp cannot accomodate 12ax7s with any modification. The operating point of this tube (and similar ones) requires much higher plate voltages to work properly.

Sorry about that.

OTOH, 12au7s, 6922s, and similar tubes are plentiful and relatively cheap unless you want to find rare NOS ones.

jjazzyj, that looks pretty good so far. And now there are lots of opportunities for your top.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #962 of 1686
Quote:
Originally Posted by jjazzyj View Post
Trying to figure out what to do about the top. I have some hexagon perforated aluminum that I want to use, not sure how to make it look nice though.
Heh, I wonder if its that stuff you can get @ Home Depot... I've a sheet of brass looking stuff w/diamond cut holes in the garage..

You could give wiatrob a PM about where he gets his perf top material that looks like this.
post #963 of 1686
Our Home Depot here has nothing. Can't even find 1" I.D. rubber grommets. I actually can't find them anywhere. There's a metals supply place here that will mill a sheet of hexagon perforated aluminum. That's where I think I'm going to go. 12$ ft2 plus 3$ a cut. Pricey, but I can them to cut the piece I need along with the holes for the tubes for ~$20. I decided to use these 3/16 low voltage staples with #4 1/2 inch black steel screws to create a little ledge for the aluminum top to sit on. Still don't know how I'm going to secure it though.
post #964 of 1686
I already postet this a while ago:

I got some strage hum on my SOHA II.
It's not dependent from the volume - also hums when potentiomer is set to zero.

Sometimes, it gets louder when I put my hands near the board and gets quieter when I move them away.
If I just leave the amp running, it gets louder over maybe a minute, a hiss component joins the hum, hum disappears, hiss too.
The then amp is dead quiet - no hum, nothing.
Input wiring is now shielded - this did not touch the problem.
post #965 of 1686
jjjazzyj-

My perf material is all surplus, however, Online Metal Store | Small Quantity Metal Orders | Metal Cutting, Sales & Shipping | Buy Steel, Aluminum, Copper, Brass, Stainless | Metal Product Guides at OnlineMetals.com has been used by many here - eBay usually has a bunch as well.

PM me if you want a set of grommets.
post #966 of 1686
Quote:
Originally Posted by Sathimas View Post
I already postet this a while ago:

I got some strage hum on my SOHA II.
Those are strange symptoms. Can you post some pictures of the inside of your amp? How is your transformer mounted and wired? Does this happen with different sets of tubes?

Sounds like it might be a magnetics issue. Pics would definitely help...
post #967 of 1686
I'll post pictures later this day.
post #968 of 1686
Quote:
Originally Posted by wiatrob View Post
jjjazzyj-

My perf material is all surplus, however, Online Metal Store | Small Quantity Metal Orders | Metal Cutting, Sales & Shipping | Buy Steel, Aluminum, Copper, Brass, Stainless | Metal Product Guides at OnlineMetals.com has been used by many here - eBay usually has a bunch as well.

PM me if you want a set of grommets.
I bought some hex perf steel locally, spray painted it silver and figured out a quick and dirty way of attaching it. Not 100% happy with the results. But it does look ok from a far. No grommets yet I'll PM you tomorrow.

Pics:





post #969 of 1686
I like the hex, the grommets will clean up the look - although you may need to vinyl due them like CFCubed did on his CTH - Chris, do you have a link to that process?
post #970 of 1686
Thread Starter 
Quote:
Originally Posted by Sathimas View Post
I already postet this a while ago:

I got some strage hum on my SOHA II.
It's not dependent from the volume - also hums when potentiomer is set to zero.

Sometimes, it gets louder when I put my hands near the board and gets quieter when I move them away.
If I just leave the amp running, it gets louder over maybe a minute, a hiss component joins the hum, hum disappears, hiss too.
The then amp is dead quiet - no hum, nothing.
Input wiring is now shielded - this did not touch the problem.
Sathimas, does this problem repeat itself or does it happen just once after power up?

The photos help. Is it correct that you have a metal bottom and that the board star ground is bolted through a standoff to this metal plate? If so, is the plate grounded to the inlet ground?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #971 of 1686
Here is a picture of the inside.
The case is entirely made of wood, so no grounding of the enclosure.



The problem only appears on startup.
Takes maybe 2 or 3 minutes to go away and does not return.

Reminds me of my SOHA I, it has a similar hum at the beginning,
but this disappears after only a couple of seconds.
post #972 of 1686
Thread Starter 
The first thing that I would try is to ground the star ground point on the board to the ground on the IEC inlet.

I guess you've measured all the voltages/currents and they check out?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #973 of 1686
Well ... could you tell me what the star ground point is?

The initial checked showed no problems.
This problem doesn't seem appear everytime, but everytime the last time I switched the amp on.
post #974 of 1686
Thread Starter 
There is a diagram at Cavalli Audio.

Go to the Wiring and Ground section and then to Board Wiring.

In the box at the top follow the link labelled Ground Wiring with no Standoff. Even though you have a standoff, it is not grounded so you'll need to use this grounding scheme.

At some point it might be good to layer the bottom of the box with a thin sheet of copper and to use this as the ground. But let's cross that bridge later if we have to.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #975 of 1686
Thanks for the advice.
I'll do that later this day or tomorrow, I don't have my soldering iron here.
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