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[Quoting xelion]

Ahh, mb3k's tutorial is exactly what I needed. Answered several of my questions.

and gewa, is that a picture of my transformer? It doesn't look the same...(sorry if that is a stupid question)edit: yeah so I looked at it some more and it made sense. Just one question, what is L and N?

Okay, only questions now: The small pot, yeah, still not sure which direction to orient it. Tomb said that the side with the screw goes towards the diagram on the silk screen, but the screw is on the side, it doesn't face that direction. So yeah.

And the transformer fuse stuff. I'm going to look for the data sheet, but then I'm just a little confused on how exactly to wire it. Hopefully I'll figure it out when I read the data sheet.

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I think what I had said was that you needed to purchase the Bourns-style 3299W pot trimmer - those have the inline leads, and the adjustment screw is on top. You probably need to buy the right ones. Trying to adjust the bias points with a screwdriver from the side for the rest of the life of your SOHA is not a good idea. I haven't looked at the cap positions vs. the trimmers lately, but a side adjustment screw may be impossible to use, not just "difficult."

Also, sorry for the bashing, but please let me emphasize something else. Even if you don't touch any of the power components, which would preclude endangering your health, incorrect power wiring will still smoke your amp - very quickly. NEC wire-sizing and breaker standards are meant to protect the wires in the walls of your house. The device you plug into the wall out in the open does not have those same standards or protection. It can flame very easily if things are messed up. So, please be careful. You might want to have a little fire extinguisher handy.

Greg: I think dBel was talking about me with bashing - he said you got it right!

I haven't had any shorting problems on my Milletts with the Intersils - as long as the output resistors are in there. Seeing as how I haven't finished the enclosures yet, the board is not that stabe. So, I sometimes take a second or two forcing the plug into the socket while holding the board with the other hand. That's plenty of time for shorts to occur, but no death to the Intersil's. I don't think I would worry about converting to XLR.

And yeah, electricity = bad, I know. I have to learn about it some how. Why don't you stop telling me how dangerous it is(I already know) I'm going to build the amp anyways, so you might as well help me out.

Seems to be very comprehensive, starting from history of discovering electricy, theory about electrons, covering electron tubes and explaining how operation amplifiers works. I found it very useful when wanted to truly understand what's going in even the simplest amplifier. A bit hard reading though...

Best regards,
Jari

The only question I have now is what do I hook all the ground wires to? I'm using a plastic enclosure.

And to test the amp, what order would I do that exactly? Apply power, watch to see if it explodes (with some protection) and then test what points exactly?

Oh, also, where can I hook a switch and power led in? Can I do that straight from the AC1/2? Or would that be too many volts? I didn't see a specific spot for them on the board, so just looking for some help.

Thanks,
xelion.

edit: kay so I read the guide for the SOHA on these forums and found this:

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[Quote]

Wire everything up but don’t put the tube/opamp in yet. Measure the voltages at the B+, V+, V-, and heater. They should be >80V, +12V, -12V, and -12.6V respectively. If they are not then there is a problem that must be fixed before inserting either the tube or the opamp.

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Where would those be? Do I just measure the spots with the labels on the board? And what is heater?

Also, this may sound entirely stupid, but I measure with the multimeter from ground to the test point, right? Put one lead on ground, and the other on the test point?

again thanks for the help.

[Edited by xelion on 12-02-2006 at 10:46 AM.]

for the mains switch, put it between the mains input and the transfo, preferably a dual pole switch (that cut off the Live AND neutral). Even in this case, ALWAYS plug off from the wall before working on the amp (you are NEVER sure).

For the LED, you have a position just under the tube socket. Adjust brightness and voltage limit for the LED you use with the RLED value (play around 2kOhms for bright blue led). If you don't like to put led under the tube, or have no room enough, just solder two small wires in place of the led, and put the led where you want it to be.

For the testing point question, yes, just stick to the labelled point (in square box, +60V, +40V, +40V, +12V, -12V, -12.6V). On that point, I think I remember a long discussion: without opamp in place (the 8 legs component that goes between D1 D2 D5 D6, and don't solder it directly, solder first a so called DIP-8 socket adaptator) the +12V -12V could read very different than anounced, and that's normal, but I don't remember the figures, maybe someone else can help on this. For the two +40V, this is the point where you have to read +40V AFTER you adjusted the variable resistor to achieve this ok? So the first time you test there, it can be very different than that. And here also, I'm not sure if you'll read something interesting/intelligent/relevant without a tube installed in its socket. Anybody wants to comment on this?

And of course, yes, all these voltage are to be understood 'between the tested point and the ground'. the ground is simply the 0V point of the amp, all voltages are relative to this, and your music is a voltage swinging around the ground.

And just to go further, basically, a tube works like this:
- A filament, or heater heats (obviously) itself, or a special metal, that emits free electrons. For that, the heater requires voltage, Usually, tubes require 12.6 or 6.3 volts, and eat more or less Ampers (be sure in the SOHA to put a good heatsink on the LM337, for the guys works a lot and heats up too).
- Now, if one puts a difference of potential, naming a voltage between this source of electrons, and a plate, the electrons will flow from the source to the plate, that's what's called B+, it's the working tension of the tube. Here we are in very low working voltage, usually, tubes work around 250V. Some tubes are specifically made to work with low working tension, like the one used in the Millet Hybrid (12FK9, 12FM6, 12AE6A...).
- and all this marvelous electronic device would not do a lot if, between the source and the receiving plate, a modulating net was not in the path. this grille affects the electric field, and modulates the flux of electrons. The variations induced by the signal (your source music) to the grille, modulates the flowing electrons that arrive to the plate, and this amplifies the signal.

Now, in the SOHA, the tube amplifies voltage, but does not deliver enough ampers (current) to drive properly headphones, hence the opamp, that follows (does not modify) the voltage, but delivers more ampers to the headphones.

Now one of the characteristics of tubes is that they emits continuous current, and your headphones will surely not like this, so you have to cut continuous current, but let alternative current pass, and that's the business of C2 C14. After that, the opamp beef up the current, and up up and away to your ears!

This is very rough, and someone more precise can explain better than I , but so, you have the big picture.

Keep going, slowly, read a lot!

All the best

OK, whew!!! I found out what was wrong... When I soldered the central pins in place, I soldered from the silkscreened side. The V+ pin needed to be soldered from the bottom of the board too... It works fine now!!! Yay!!! It sounds awesome. DC offset is now .00 mA in left channel and .02 mA in the right.

[Edited by vixr on 12-02-2006 at 08:12 PM.]

Just one question, on the led, I have one under the tube, but I was wondering if I could put another one on the front of my amp?

I guess there isn't much need for that, but meh.

Also, the cord I was planning on using doesn't have an earth ground, should I scrap that plug and find one that does?

[Edited by vixr on 12-03-2006 at 08:09 AM.]

Xelion: I think it's a very good habit to always ground the electronic you do if allowed by the schematic, just to be sure. It's a supplementary protection. for the LED, you can simply pick up current from the LED under the tube, and airwire the second led from it. Now, if you use the same leds, you'll draw twice current, and it will modify the leds light intensity. Maybe you will need to change the RLED value to something else (I never know in which way, lower, higher, don't ask me, I always try).

continue posting picture of your board, we can so check easier if all seems ok.

All the best,

Quick rundown first:
-12.6V (-13.2V)
+/-12.0V (+/-12.0)
+60V (+79.5V)
+40V (+79.5V)

Notice those last two readings. This is with a completed amp. Tube, opamp, and pot are all installed....as is everything else.

The problem right now is that the trimmers aren't making any adjustment to the 40V values.
Also, even with a measured -13.2V on the heater, I'm not glowing.
I'm fairly green when it comes to tubes, but would this make sense if the heater isn't working?
I measured directly across the heater on the tube and it's reading 14 ohms. Don't know the spec of the tube, but this sounds like it could be a correct value.

Not certain if this could have anything to do with it, but the LED isn't lighting. It's possible I guess that I got backwards. Even if I have the LED in correctly, why wouldn't it be glowing? There's a measured -13.2V present.

I've double checked everything and even went back and read this and the other 36 page thread.

[Edited by ck42 on 12-03-2006 at 02:48 PM.]

I don't believe there's any explanation for what you measure and the actions you note - unless the tube is not conducting.

I pulled the tube out just enough to get the meter probes on the tube's pins. I verified connections all the way to pins 4+5 on the tube....so the connections are there all the way to the physical pins on the tube. Still no go. So close...yet so far.

Chance I got a bad tube?? Does ~14 ohms across the heater pins sound right? How likely would it be for the heater resistance to be correct and still not work?

I just measured the tube I have (ECC82 from JJ) and I get a reading of 12,4 Ohm across pins 4 and 5.

Regards

....NOW...I seem to have lost my -12.6V line

Pulled the tube to take a measurement again and powered it up....now the LED is lighting LOL!

Getting -3.0V now with the tube removed...no idea if that's anywhere near the expected value w/o the tube.

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[Quoting runeight]

ck42 make sure that your grids are grounded when you make these measurements or they will not be accurate.

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..hmmm. Do I need to manually ground the grids?

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[Quoting runeight]

If you don't have a volume control attached to the amp, then you should manually ground the grids. Or you can just attach a 1M resistor from the grids to ground permanently.

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Volume pot is attached. Entire amp is built and wired up.