[ltmon]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Pin 2 is connected to the tab internally. This is the drain which is connected to B+. The chassis should be grounded. So, if the tab is touching the chassis, then this would short B+ to ground.

Thanks, see my above edit for more info.

Have I likely damaged the transistors with this mistake?

L.

 

[dsavitsk]

Only one way to find out.

 

[n_maher]

Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif Can I wire the film cap bypass by just soldering like this? Also, I hope I have the positive and negative sides matched up (WIMAs weren't marked).

You can certainly wire the Wima's like that and they aren't marked because they don't have a polarity.

 

[Nonchalance]

Lol I feel stupid, made same mistake again, haha. Schematics led me to believe they had polarity.

I'm done for now until I can get a ground plate drilled. I'll post finished pics when I'm done

 

[PJPro]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif I think your tubes are remarkably well matched. Amplification factor is ~13.5 on one, and ~13.4 on the other -- no way you can hear that difference. If anything, it looks like the pot is a little out of balance, though really only a little. You can try to correct it by making one of the input resistors slightly larger than the other -- put a 1M rheostat in parallel with R17 and adjust it until the voltage on the outputs match . Then measure across R17 and replace the resistor and a pot with a resistor of the new value. (You could also do a 100K rheostat in series with the input to R16, adjust that, and replace R16 with the value of the resistor + rheostat.) Or you can replace the pot. But, all in all, it really looks pretty good.

OK. Thanks.

 

[Nonchalance]

I plan on screwing the strips onto a copper plate and connecting all the ground connections to one of the lugs on the terminal strip. But I'm actually a bit confused. The lugs don't seem to be connected on the outside. So are they connected somewhere inside or do I have to manually bridge each lug on the strip?

I'm using the Keystone strips

 

[tomb]

Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif I plan on screwing the strips onto a copper plate and connecting all the ground connections to one of the lugs on the terminal strip. But I'm actually a bit confused. The lugs don't seem to be connected on the outside. So are they connected somewhere inside or do I have to manually bridge each lug on the strip? I'm using the Keystone strips

According to that data sheet, it's Figure 13. That one has a single lug that's attached to the mounting lug. So, you'll need to bridge all ground connections to that lug.

 

[ltmon]

Quote:

Originally Posted by ltmon /img/forum/go_quote.gif Thanks, see my above edit for more info. Have I likely damaged the transistors with this mistake? L.

I've fixed this. I'm still not sure what was going wrong, but after I while I gave up and wholesale replaced the transistor mounting kits with some mica ones I had lying around and it was fine... no shorts found, and lights on in the pretty glass things!

Unfortunately when I went to measure DC offset I have found another problem. The right channel is measuring about 2V DC when power is applied, with no source connected and volume at a minimum. This is measured against the ground level of the chassis.

At that level, I'm afraid to plug in headphones to find out what it sounds like.

Any idea what would cause such a measurement?

Thanks again,

L.

 

[n_maher]

L.

Something very strange is going on indeed since it should essentially be impossible for you to see DC offset on the output, that's the whole reason the output coupling caps are there. Have you double checked your wiring vs. the schematic?

 

[tomb]

I agree with Nate - you've got something else going on.

While that may the true issue with those MOSFETs, let me emphasize a warning that was clearly described in the SSMH PCB Build Thread: Don't torque down to exhaustion on the Bergquist pads in the heat sink mounting kits. The metal tabs on the MOSFETs will cut right through the pads and then into whatever metal is on the heat sink/case underneath, too. It sort of ruins the whole purpose when that happens.

Firm and tight is just right.

 

[ltmon]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Firm and tight is just right.

I was only firm and tight, but, due to my inaccurate casework, on a slight angle. I think the edge of the MOSFET must have bitten down first, and the rest is history.

I will see if I can check the output caps, as I'm pretty sure I heated one of them more than I intended whilst soldering. I wouldn't have thought enough to turn it to mush, but you never know...

Thanks for the answers.

L.

 

[ltmon]

I cleaned up and then reflowed C5 and R12 (which looked a bit dodgy) and the offset dropped down to < 10mv on both sides.

Sounds really good now, thanks all for the help.

 

[n_maher]

Quote:

Originally Posted by ltmon /img/forum/go_quote.gif I cleaned up and then reflowed C5 and R12 (which looked a bit dodgy) and the offset dropped down to < 10mv on both sides. Sounds really good now, thanks all for the help.

That may very well be below the threshold of your DMM depending on how good it is. Glad to hear that it was a seemingly easy fix.

 

[cwboomer]

I downloaded this and thought this would save me from my own ignorance.

I thought I'd post and show it.

Anywho. It looks to me like this diagram has the ground wires from the RCA jacks going to the "ground" of the pot, versus to the chassis. It also looks like the tubes are being bridged between 3 places 1-2, 3-4, & 5-6. Is that correct or am I reading that wrong? I can't tell from the pictures of other wirings that I've seen. Lastly, my silliest question of all. Which lead is which on the headphone jack? I couldn't find a wiring diagram for it. (I can figure out ground). Thanks for you patience with my point-to-point, non-schematical ignorance.

Admitting dumbness,
dan
Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif Did anyone here follow the wiring diagram posted here a while back? It's probably neater than anything I can come up with, but does it work?

 

[Nonchalance]

The grounds of the RCA jacks are connected to the pot grounds then to the actual grounding material on the diagram.

Apparently 3-4 are NOT bridged. 1-2 and 5-6 are though.

For the jack, the tip of the jack is left, middle is right, and back part is ground. See Wikipedia's article..

I ended up not looking at the diagram, more fun to figure stuff out on your own, I'll let you know if it blows up on me