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Millett "Starving Student" hybrid amp
Nov 10, 2010 at 12:16 PM Post #5,566 of 7,277
most probably you either short-cut the mosfets or fried them resulting in a complete
open mosfet. You can check if the filaments are still operable by testing the resistance
between the corresponding pins (#3 and #4). For the future tests you can first use
a powerful resistor instead of the tube filament.The working point for mosfet is set
by R2 and R4 resistors so the circuit will not notice the absence of the tubes.
When there is no smoke/sparks
smily_headphones1.gif
and the voltages in the key points seem to be
reasonable then you can try it with the tube.
 
 
Nov 12, 2010 at 2:52 PM Post #5,567 of 7,277
hey thanks for the tip with the resistor,
the mosfet was fried , swapped both and now its back working, tube seems to be ok :)
Don't have any cheap headphones to try right now, so there's something else to do hehe
I forgot to install the socket mounting ring ...
Think it's time declutter some of the wire mess, but not now.. with the amount of beer I already had :)
cheers,
Marcus
 
Nov 13, 2010 at 9:35 PM Post #5,569 of 7,277
OK, I tried to find it with a search, but 350+ pages?  What are the ramifications of changing the heat sink you use?  I know it's supposed to be about sound, not looks, but I want to build a nice wood case for it, something reminiscent of my Yamaha CR-820 or an old Marantz. 
 
Can I use something like this? Do I need two, or can both MOSFETs use one heat sink (is the tab just a heat conductor, or is it electrical ground as well?)
 
http://cgi.ebay.com/Heatsink-CPU-MOSFET-HEAT-SINK-16-FIN-DENSITY-102-x-64-/250541753999?pt=LH_DefaultDomain_0&hash=item3a5573c68f
 
Nov 13, 2010 at 9:52 PM Post #5,570 of 7,277
Both mosfets can share a heatsink
 
this is what I used

 
cheers
FRED
 
Nov 14, 2010 at 12:31 AM Post #5,571 of 7,277
In addition to my previous question (see 2 posts above) what do you guys think of using a potentiometer to adjust gain? And what value potentiometer would be best for this? (I plan on using a blue velvet, since this build is already over budget I'm just going with it.)
 
Nov 17, 2010 at 7:17 PM Post #5,573 of 7,277
Hi yes 12AU7 the original valves are just too hard to find at a sensible price
 
cheers
FRED
 
Nov 17, 2010 at 7:17 PM Post #5,574 of 7,277
Revolink,
 
I've used similar switches to good effect setting up multiple gain choices for single triode sections on guitar amps before. The switch you're looking at has 1/4" solder lugs and is more than stout enough for what you want. It's not a mini switch, though....
As far as using a pot to vary gain, I can't advise as I've not used a full sized pot for such. I'd think the switch would be the easier way to go but I leave the resistor values to you.
 
Legis31
 
Nov 22, 2010 at 7:22 AM Post #5,575 of 7,277
Hy all!
I am wondering how the SS would compare to a bravo v2? Has anyone tried both? I could get them for roughly about the same price. Actually, the materials for the SS would be a bit more expensive than the bravo completely assembled. The headphones to drive are HD580's, and sometimes my HD555's.
My other question would be, that is there a significant difference in sound quality using more expensive parts for the SS? I mean, I can get the R's and C's for 1c each and for 1$each, and that is quite a difference given the total price of the amp, but I don't know whether it's worth it.
 
Nov 23, 2010 at 5:52 AM Post #5,576 of 7,277

 
 
Hi, i just did a draft layout of the p2p circuit for 12AU7 SS. can anyone do a check on this and let me know if i did it correctly? 
 
ignore the placing of the 1/4 jack as it was placed there for easy interpreting of the diagram. 
 
The brown lines are all ground lines. 
 
Thanks in advance! 
 
Nov 24, 2010 at 2:48 PM Post #5,577 of 7,277

 
Quote:
rauschie said:
Hy all!
I am wondering how the SS would compare to a bravo v2? Has anyone tried both? I could get them for roughly about the same price. Actually, the materials for the SS would be a bit more expensive than the bravo completely assembled. The headphones to drive are HD580's, and sometimes my HD555's.
My other question would be, that is there a significant difference in sound quality using more expensive parts for the SS? I mean, I can get the R's and C's for 1c each and for 1$each, and that is quite a difference given the total price of the amp, but I don't know whether it's worth it.
Click to expand...


 
There's kind of a tacit agreement to keep this thread on the technical aspects of the build and not to post listening comparisons in this thread. Maybe someone who hast listened to both amps can send you a PM with his/her impressions.
 
 
Quote:
howc said:
SNIP
 
 
Hi, i just did a draft layout of the p2p circuit for 12AU7 SS. can anyone do a check on this and let me know if i did it correctly? 
 
ignore the placing of the 1/4 jack as it was placed there for easy interpreting of the diagram. 
 
The brown lines are all ground lines. 
 
Thanks in advance! 
Click to expand...



I won't comment on the quality of the layout as my expertise there is null. As to the wiring, the circuit seems to be correct. I'd just do a small change in wiring a jumper for pins 1 and 6 at the tube sockets, as you did for the other pin pairs, instead of independent wires going from each of those pins to the junction of C4/R7 - C2/R1.
 
cheers!
Oscar A. Ross
 
Nov 25, 2010 at 1:41 AM Post #5,580 of 7,277
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