Millett "Starving Student" hybrid amp
post-6814800
Post #5,386 of 7,249

Fred_fred2004

Member of the Trade: Fred_fred2004 (Ebay Store)
Joined
Sep 13, 2008
Messages
952
Reaction score
28
Joined
Sep 13, 2008
Posts
952
Likes
28
I'm too impatient, I just wack in some cheap headphones and listen

 
     Share This Post       
post-6815828
Post #5,387 of 7,249

ArtemF

New Head-Fier
Joined
May 30, 2010
Messages
25
Reaction score
0
Joined
May 30, 2010
Posts
25
Likes
0
in principle, nothing bad should happen given that you've put the output caps. To be on a safe side
you can start from the output: measure the DC voltage on the output jack. If there's no DC component,
switch to AC measurement mode and check if the amp doesn't generate by itself when the volume knob
is in the left (=min) position. If there's no AC component, you can plug (cheap) headphones and give it a try.
 
If it doesn't work, check the voltages in key points of the circuit and start investigating the problem.
 
     Share This Post       
post-6815889
Post #5,388 of 7,249

revolink24

Headphoneus Supremus
Joined
Jan 12, 2008
Messages
2,881
Reaction score
40
Joined
Jan 12, 2008
Posts
2,881
Likes
40
A couple of questions. Would 63V 220uF Nichicon Electrolytic caps (Mouser number 647-UHE1J221MPD work for C1, C3, C5, and C6? And is there a decent alternative (or maybe Im missing it) to C7/C8 on Mouser?
 
     Share This Post       
post-6815943
Post #5,389 of 7,249

baka1969

Chaser of Ghosts
Joined
Sep 20, 2008
Messages
3,440
Reaction score
73
Joined
Sep 20, 2008
Posts
3,440
Likes
73
Quote:
Originally Posted by the_equalizer  


" The output stage has enough muscle, so I think it'd do perfectly with the 8 ohms cans. Though the lowest impedance I've tried with the amp has been some 16 ohm earbuds; it had no problems with them.
cheers!"

Thanks! :)
 
     Share This Post       
post-6815949
Post #5,390 of 7,249

FallenAngel

Headphoneus Supremus
Joined
Mar 7, 2006
Messages
9,624
Reaction score
64
Location
Toronto
Joined
Mar 7, 2006
Location
Toronto
Posts
9,624
Likes
64
C1 and C6, I'd use considerably higher than 220uF, maybe even 1000uF.  For C3 and C5, I would really recommend 470uF Muse ES, not HE.
 
Quote:
A couple of questions. Would 63V 220uF Nichicon Electrolytic caps (Mouser number 647-UHE1J221MPD work for C1, C3, C5, and C6? And is there a decent alternative (or maybe Im missing it) to C7/C8 on Mouser?


 
     Share This Post       
post-6816448
Post #5,391 of 7,249

revolink24

Headphoneus Supremus
Joined
Jan 12, 2008
Messages
2,881
Reaction score
40
Joined
Jan 12, 2008
Posts
2,881
Likes
40
Thanks for the response. What thermal material do you use for the MOSFETs (if any)? Also, does anyone know of a DPDT switch that could be used as a gain switch?
 
Also, these would be correct for C7/C8, correct? http://www.mouser.com/ProductDetail/Nichicon/UES1C221MPM/?qs=kArNe9LFxXkkfHBfMYU2Pw%3d%3d
 
More edit: What do you think of this DPDT switch for a gain selector? http://www.mouser.com/ProductDetail/Mountain-Switch/108-1MD2T2B3M1QE-EVX/?qs=sGAEpiMZZMvudeGI7i40XJQ7caDfyBlLkZYiLn5EiQs=
 
As far as I know it would go each RCA to 2 and 65, and then 50k resistors or so at 1 and 4 and 100k at 3 and 6. (if you look at the data sheet on Mouser)
 
I suppose this NKK would be higher quality, but any DPDT ON (ON) toggle should work, correct? http://www.mouser.com/ProductDetail/NKK-Switches/S335T-RO/?qs=V2oqQAr0jIiS08sISfWzXQ%3d%3d
 
The only difference I can see between the two is 2A vs 15A, but there shouldn't be more than 2A on R16/R17, should there?
 
     Share This Post       
post-6817800
Post #5,392 of 7,249

the_equalizer

1000+ Head-Fier
Joined
Jul 5, 2009
Messages
1,138
Reaction score
68
Joined
Jul 5, 2009
Posts
1,138
Likes
68

 
Quote:
I'm too impatient, I just wack in some cheap headphones and listen


That's definitely an option  :)
 
Quote:
Hello!
 
I'm now finished with my build, the tubes are glowing, but I still haven't put my heaphones on it: I found a really nice post from the_equalizer about testing your amp, so It doesn't destroy your whole setup

 
Here it is: http://www.head-fi.org/forum/thread/319231/millett-starving-student-hybrid-amp/3870#post_6032606
 
I've got some questions about it, more precisely about the different voltage test:
- How do you measure the voltage at the tube filaments
- How do you measure the voltage in the Output Jack? Do you plug in a Mini to Mini, and measure at the other side?
- How do you measure the voltage in the Jack Plug?
 
Thank you very much, I'll post some pics!
 
Antoine

 
- Measure  from ground to the tube's pin 3 or 4 (the one that is NOT grounded, naturally)
- Measure from the ground lug to the the left, then the right lug (be sure to measure with the volume at min, and at mid or max)
- Measure from the ground lug to the 'hot' lug.
 
As always, measuring a 'live' circuit requires care and a steady hand so as not to short out things.
 
As someone else posted, the risk of DC at the output jack is minimal, due to the capacitors. Still, you could get a defective cap or have some serious miswiring that puts DC at the output, so it's still a good idea to measure and then use some cheapos for the first listen.
 
cheers!
 
     Share This Post       
post-6817808
Post #5,393 of 7,249

the_equalizer

1000+ Head-Fier
Joined
Jul 5, 2009
Messages
1,138
Reaction score
68
Joined
Jul 5, 2009
Posts
1,138
Likes
68


Quote:
Curious, does anyone know how this would pair with the DT990/600?  I'm considering trying to build one as a relatively cheap summer project to burn time and get an intro to amps as well.  Other option I've been looking into is the CK2III.

The highest impedance cans I've tried with my SSMH have been Sennheiser HD-600's and I found the volume output by the amp more than enough to drive those cans to nice volume levels.
 
Still, I've never heard 600 ohm Beyers so it could be different. Anyway, you can easily build a 12AU7 version and, if you find the volume insufficient, just swap the tubes for 12AX7's (drop-in replacement no rewiring needed at all) which have noticeably more gain (I have tried them in my SSMH).
 
cheers!
 
     Share This Post       
post-6818824
Post #5,394 of 7,249

ArtemF

New Head-Fier
Joined
May 30, 2010
Messages
25
Reaction score
0
Joined
May 30, 2010
Posts
25
Likes
0
2 revolink24:
 
thermal material is __necessary__ to insulate your mosfets from the ground.
Otherwise you'll have to insulate the radiators that might be tricky.
Check the list of items provided by Peter Millet on the first page.
I recall there were two mounting sets that included thin insulating pads.
 
     Share This Post       
post-6818842
Post #5,395 of 7,249

revolink24

Headphoneus Supremus
Joined
Jan 12, 2008
Messages
2,881
Reaction score
40
Joined
Jan 12, 2008
Posts
2,881
Likes
40
Well some insulator is necessary, although whether these MOSFETs need thermal conductive material seems to be up for debate. But Beezar is still selling the mounting kits! Yay TomB! I totally didn't realize that.
 
     Share This Post       
post-6842511
Post #5,396 of 7,249

Beftus

100+ Head-Fier
Joined
Feb 14, 2010
Messages
188
Reaction score
11
Joined
Feb 14, 2010
Posts
188
Likes
11


Quote:
As someone else posted, the risk of DC at the output jack is minimal, due to the capacitors. Still, you could get a defective cap or have some serious miswiring that puts DC at the output

If you forget to add the 2K resistors right at the output (R6,R12) you get ~12.5 volt DC at the output. Been there, done that...
 
     Share This Post       
post-6843175
Post #5,397 of 7,249

the_equalizer

1000+ Head-Fier
Joined
Jul 5, 2009
Messages
1,138
Reaction score
68
Joined
Jul 5, 2009
Posts
1,138
Likes
68


Quote:
If you forget to add the 2K resistors right at the output (R6,R12) you get ~12.5 volt DC at the output. Been there, done that...

Yeah. That would qualify as a serious miswiring !    So how is your SSMH doing Beftus? Tried different tubes? Has it burned-in nicely?
 
cheers!
 
     Share This Post       
post-6843268
Post #5,398 of 7,249

Ikarios

1000+ Head-Fier
Joined
May 23, 2006
Messages
1,408
Reaction score
17
Joined
May 23, 2006
Posts
1,408
Likes
17
two quick questions - if I'm using a gain switch to switch between 50K and 150K ohm resistors (using a 50K ohm pot), is it better to put the resistors on the input of the gain switch (i.e. split the line from the input and connect the resistor leads to the poles of the switch) or is it better to connect the input to the main pole of the switch and connect the resistors to the switching poles (i.e. split the resistors at the "pot side")?
also, what do I do about input ground in this situation? Do I need to connect it to the switch? In other words, can I use a DPDT switch for gain or do I have to use a 3PDT? I was planning on using a DPDT but I seem to have confused myself with all this wiring and switches (currently have five planned...
)
 
     Share This Post       
post-6843517
Post #5,399 of 7,249

the_equalizer

1000+ Head-Fier
Joined
Jul 5, 2009
Messages
1,138
Reaction score
68
Joined
Jul 5, 2009
Posts
1,138
Likes
68
I'm not sure about the first question. That is, I'm not sure if one way is better than the other. Maybe some others might chime in, or you can simply do both and see which one works better.
 
About the ground switching, no, you do not need to switch ground lines, as ground is a common reference point to all lines; a DPDT switch should do nicely.
 
cheers!
 
     Share This Post       
post-6843570
Post #5,400 of 7,249

Beftus

100+ Head-Fier
Joined
Feb 14, 2010
Messages
188
Reaction score
11
Joined
Feb 14, 2010
Posts
188
Likes
11
Quote:
 
 
Originally Posted by the_equalizer /img/forum/go_quote.gif

Yeah. That would qualify as a serious miswiring !    So how is your SSMH doing Beftus? Tried different tubes? Has it burned-in nicely?
 

It's burned in very, very nice. Haven't tried other tubes as it sounds so schweet already!
I have a second SSMH still in parts (gonna use Elna caps), waiting to be built into a functioning amp. Haven't gotten around to building it yet, I just came back from my holiday in France. Will report back here with the results of the second build.
 
     Share This Post       

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top