[FallenAngel]

I heard the Mundorf ZN's are very good, but the regular MCap's are not.

 

[makasin]

Which resistor will I need to match the output for a 32ohm can?

 

[a1rocketpilot]

The output resistors aren't really necessary. They were placed there so that the volume could be matched between headphones of various impedances. It is safe to take those out and run the amp apparently and you may have a sonic benefit if you do.

Aditya

 

[tomb]

Be careful with that advice. I once gave it, too. However, the SOHA has a gain of at least 18 - perhaps more, depending on the 12AU7 tube variant. Combined with the Grado's high sensitivity at 32 ohms, it makes the SOHA almost uncontrollable - with all volume adjustment in the first 1/8 turn of the dial. The resistors help to tame that somewhat.

It is true that the sound quality may be better without them, but perhaps not enough of an improvement to warrant the hassle with Grado's - better to put in some Vishay-Dales or other reasonable quality resistor. Even 50ohm phones may have a little bit of this issue. It depends ...

 

[makasin]

could you suggest a value that would be good to use for a grado?
I dont have enough electrical knowledge to figure out what could match a 32ohm at a gain of 18.

With the electronics that I got (Xicon, not the best) will the amp at least be better than my ol creek?
I just looked at my bank statement and im in the negatives because Mouser charged me twice for one order apparently...

 

[tomb]

The original value determined by mains_hum (one of the 3 designers) was 150 ohms, but you aren't bound by this and can experiment. With higher resistances comes more noise, lower resistance results in less volume control. I would consider the 150 ohms an absolute maximum and work back from there. You may find 75 or 50 ohms is enough.

Most likely, you will find the sound of your SOHA compared to the Creek different, not better or worse. Again, the original designers used Xicon caps. The point of my post up there was to identify things that you could do to improve sound without spending an arm and a leg. Ultimately, the SOHA sound is mostly dependent on the tube. The first step would be to change the tube. That said, the JJ 12AU7 is one of the recommended tubes that sound good - hence, my post about other things you might try.

If by some small chance you are disatisfied with the sound, those things are the first thing I'd try to change. You could probably get everything I mentioned for less than $20 shipped from Mouser. (Brown Dog adapter for the OPA551's is $3 + $1.85 shipping from http://www.cimarrontechnology.com) Without the opamps, probably less than $10.

Ultimately, the SOHA should pair very well with a set of Grado's - providing oodles of low-end power and punch, with a mellow smoothing of highs that still provides good detail.

Sounds like you have some stuff to settle with Mouser if they charged you twice for something.

 

[makasin]

yeah its really crap, because it made me overdraw. Im gonna call them foolzors up tomorrow and to see whats up.
Well thanks for the suggestions, Im probably gonna use 100 ohm or 80 or something like that.
Yeah, those characteristics are what I was hoping for. More warmth, deeper low end, with a more laid back high end. I cant wait till all my parts come. Thanks everyone so much for all the help, this forum is the best place in the world, if only it wasnt so indirectly expensive hehe.

 

[tomb]

Good luck.

Let me correct one thing - I forgot this stuff is still at two places - the nice Elna Silmics are at DigiKey; the V-D resistors and Wima MKP box caps are at Mouser. In that case, I would change the caps as the last thing - and we're only really talking about C1, C13, and the box caps around the opamp. Again, you'll probably be fine with what you have.

 

[makasin]

Weird, I just got off the phone with mouser and they said that the additional charge (which doesnt match what they charged me) of 66 bucks is like a reserve or placeholder thing? But why would they reserve 66.00 of my money for no reason? Anyone have this happen to them? They claim itll be gone within 24-48 hours, which is just enough time for my bank to rape me with overage fees. Yay!

 

[makasin]

How do I go about maximizing tube life of my JJ ECC82's? Is it better to keep it on all the time or to turn it off when not in use? Or somewhere in between? How long should I expect this tube to last?,

EDIT:
OK so I got all the parts except for the PCB, and I just looked at the transformer that I got and got slightly confused. Here is a pic of the connection diagram:

My question is, do I just wire the red and blues (both 15v rails) to the board and I am done with the trafo wiring (except for the fuse of course)? I am confused about the "Grounding point Test GND" black line. Do I have to attach that to a ground or is that just for testing purposes only?

Oh and credit goes to digi01 for his wonderful site:
http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.htm

 

[makasin]

What kind of wires should I use for hooking up the transformer and the in/outs?
I have a spool of 18 guage copper from ratshack. Is that sufficient or do I need anything beefier?

 

[mb3k]

18AWG is more than enough (http://www.powerstream.com/Wire_Size.htm)

 

[tomb]

Yes, Mb3k is correct. In fact, most of us use hookup wire of 22 gauge. You'll find that teflon-insulated wire is best. The insulation doesn't melt. Regular PVC-insulated hookup wire, the insulation will start to pull back from the solder joint as you solder, exposing more wire at every joint - a really irritating trait. The teflon stays put and doesn't melt. Navships is an Ebay seller that sells lengths of various teflon-insulated hookup wire for reasonable prices. You can get several colors and shipping for probably less than $20.

The PVC will be OK - just remember to put a piece of heat shrink - longer than you might think - on the wire before soldering.

Of course, your power cord should be a code-rated lamp cord or similar molded plug set.

About the tube in your earlier post - they're pretty much light bulbs, so life and usage is similar, I think. I can't find where I saw some numbers quoted, but I think it's in the few thousand hour range. Higher voltages and biases will tend to shorten tube life, but the SOHA is not really setup to adjust those higher than what's designed. So far, I turn my tube amps on and off like a computer: flip it on about an hour before you're really ready to listen to it - it takes 2-3 hours for the tubes to develop their best sound, anyway. During the day, if you think you will be listening to it sometime in the next couple of hours, then leave it on - don't turn it off. There have been some discussions about leaving tube amps on overnight and/or unattended - but I wouldn't do that. If you go to bed or leave the house, turn it off. There's too much heat going on to leave one unattended for long.

The "Test Ground" on the board is because there are various definitions of Ground with the SOHA - yes, it's a test reference point. You should also note that Digi provided two signal ground points - only one is ever used with headphones (unless you get into "magnum" balanced amps).

 

[makasin]

What are the risks of fire or some awful thing happening. Im just worried my noobness might result in something going wrong with my soldering job and like set my house on fire or something. LOL it sounds a little crazy but im just curious. Has anyone had any problems with overheating/failing of components?
It looks like its not the case since all the parts are rated higher than what is actually going to be flowing through them.

 

[tomb]

Your noobness may be dangerous around the transformer, its primaries, and the wall outlet. Be sure you fully understand what you're doing there. Messing with line voltage always has the potential of fire or electrocution.

The amp itself is fairly tame. The highest voltage is the B+ at about 60-70V, enough for a sting, perhaps, but way below the lethal voltages of classic tube amps. Tubes get hot, though, so that's the reason for the recommendation about not leaving one unattended for extended periods.