[loki993]

Im just not sure a Cmoy would satisfy my needs. Maybe a Mini3, but I really wanted to try tubes. I will build one of these eventually. 
 
 
How is this with DT-770 Pro 80s? Anyone know? Would the optional mods make it better with them or worse?

 

[akiroz]

Interesting design, as i am a student myself (high school no less), i've always thought valves costs at least $10USD ea.
I currently specialize in designing descrete solid-state amps and always wanted to try the "sound of tubes".
just a quick question: is the tubes' heating element acting as the output resistor?, will that induce thermal noise?

 

[Starfire]

Quote:

Im just not sure a Cmoy would satisfy my needs. Maybe a Mini3, but I really wanted to try tubes. I will build one of these eventually. 
 
 
How is this with DT-770 Pro 80s? Anyone know? Would the optional mods make it better with them or worse?

The only parts I would leave out on any build would be the 50K resistors off the pot, they have no effect on the quality of the sound, just the level.  On something like an 80ohm headphone I'd keep them too.  All the other "optional" parts are there to improve sound.  I typically increase the value of the electrolytic capacitors on my builds for better filtering of power noise and a bit of an increase in bass response, but be sure to use decent capacitors such as the Nichicon Muze series.
 

 

[bengoshi2000]

All the parts are in... build thread to follow soon...

 

[Starfire]

Cool I'll follow along!

 

[scottwhat12]

Hey all!
I really want to build a starving student, have just started electronics and i have built a cmoy and some other small things with pcb kits. Im just having trouble trying to understand how to ground? on the schematic it shows what needs grounds but where do i connect them to, just the chassis? any helps appreciated. 
Thanks

 

[tomb]

Quote:

Hey all!
I really want to build a starving student, have just started electronics and i have built a cmoy and some other small things with pcb kits. Im just having trouble trying to understand how to ground? on the schematic it shows what needs grounds but where do i connect them to, just the chassis? any helps appreciated. 
Thanks

You can do that, assuming the chassis is metal and you make certain that the ground connections are good, electrically speaking.  Many cases that are sold and used for DIY are anodized and you need to be sure that you scrape the anodizing off where you make the ground connections.
 
OTOH, if you use a non-metal case, then look at Pete Millett's first couple of posts that started this thread.  He used a copper plate (available for purchase from Mouser) and grounded everything to that.
 
 

 

[Oeufdepoire]

I have a few (maybe silly) questions. I didn't search through the 400+ pages of this thread for the answers. Here they are :
 
Why are there two RCA plugs for the signal input ? Why no "standard" female jack ?
Would I be able to use the amp with my Sansa Clip+ as the source ?
Would this amp be usable with my Grado SR80i's ?
 
Thank you

 

[bengoshi2000]

In case anyone is interested, I've started a build thread...
 
http://www.head-fi.org/t/597166/another-millett-starving-student-build#post_8165147

 

[the_equalizer]

1.- Input connector(s) can be whichever you wish. RCA jacks are actually the standard but if you wish to use a female phone jack instead you can.
 
2.- Certainly
 
3.- Yes
 
cheers!
 
Quote:

I have a few (maybe silly) questions. I didn't search through the 400+ pages of this thread for the answers. Here they are :
 
Why are there two RCA plugs for the signal input ? Why no "standard" female jack ?
Would I be able to use the amp with my Sansa Clip+ as the source ?
Would this amp be usable with my Grado SR80i's ?
 
Thank you

 

 

[bengoshi2000]

Ok, my first (hopefully only) screw-up so far.  I thought I had ordered a stereo 50k pot with integrated switch... turns out it's mono (i.e. only one pot, not two).  Since I don't want to order another pot from Mouser and wait for it to ship, I found that RatShack has a stereo volume pot, but it's 100k (vs. the 50k spec'd on the BOM).  Could I use the 100k RatShack pot and leave out the 50k pots (R16/17)?   

 

[Starfire]

Yeah it'll work in pinch.

 

[bengoshi2000]

Let the troubleshooting begin...
 
So this weekend I got the ssmh wired up (with the exception of the rca inputs, volume control and the headphone jack).  Before getting things settled into the case, I decided to do a quick and dirty test by hooking it up to the power supply to see if anything would smoke.  Well, nothing smoked... but not much of anything else happened either.  I expected to get some sort of glow at the heaters.  No dice.
 
I got out my MM and took some measurements.
 
Cisco PS:  48v
 
Tube Pin #4 (L and R):  12.5v  
I'm getting zilch on all other pins.  For 2 and 7 I'm assuming that's ok with no input, and since 5 is the ground I wasn't expecting anything there either.  But I thought I'd get some reading on pins 1 and 6...
 
I slid the tubes a wee bit out of their sockets and took readings at the pins (thinking maybe a bad socket) but got the same results.
 
Q1 and Q2:  D = 48v, G = 12.5v, S = 12.5v
 
Any ideas??
 
Note:  I had to do some adaptation at R2/8.  I left the 390k resistor out of my purchase list.  A friend gave me a some 120k and 270k resistors.  I wired those in series and used them in place of the 390k resistors.  I have no idea what wattage they are (though the size makes me think 1/4 watt) and they are carbon film (the rest of the resistors are metal film).
 
EDIT #1 2/28/12:
I've been doing some vigorous reading in this gargantuan thread and I came across a post by Dsavitsk that indicates the FET's should be reading:
 
Pin 1 (gate) - 4v-5v above heater
Pin 3 (source) - 12.5v (feeding the heater, tube pin 4).
 
It wasn't stated specifically in the post, but since the drain connects straight to the power source the 48v reading I noted would be correct.  And my reading on the source of 12.5v. is also correct.  Error must be in R13, R1/7, C2/4, R4/10, R2/8 or the associated wiring/solder joints.
 
The way I constructed my perfboard/p2p wiring, I worked each junction of the left and right sides at the same time (and they are mirror images of each other on the board).  So if I made one error on the right side, I probably duplicated the error on the left. 
 
Sorry to put down my thought process here in this post, but maybe another electronics newbie like me will find it helpful...
 
EDIT #2 2/28/12:
More troubleshooting done...
 
The R13 side of R1/7 reads 42.5v, the Tube #1 pin side of R1/7 reads 0.
The R13 side of R2/8 also reads 42.5v.
The junctions at R2 and R4 (and R8 and R10) read 11.5v.
The Tube #6 pin sides of C2 and C4 are also 0.
 
I was thinking that my R1 and R7 resistors were bad... I pulled R7 and it tested out to a perfect 33k.  
 
The fact that I'm getting 0v on the tube side of R1 and R7 makes me think they are shorting straight to ground... I just can't figure out where/how.
 

 

[bengoshi2000]

Day 3 of trying to work this out and I've gotten nowhere.  The problem seems to be somewhere around R1/7 and C2/4.  I'm desperately in need of some assistance...

 

[bengoshi2000]

Okay... my 2nd Dip$h*t moment:  Both tubes wired backwards.  I had assumed that tube pinouts were drawn as if one was looking down from the top of the tube (as opposed to looking at the tube from the bottom).  Rank newbie mistake...
 
I did a rewire and the heaters began to glow as expected.
 
Now I've got to figure out why I'm getting 100+ volts at the gates of both 'FETs...  (don't worry, once I read that voltage I shut it down... the 'fets only saw that voltage for 20 seconds or so).
 
FETs were reading 48v and 12.5v on the drain and the source, respectively...