Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Millett "Starving Student" hybrid amp
New Posts  All Forums:Forum Nav:

Millett "Starving Student" hybrid amp - Page 452

post #6766 of 6806

just got back from measuring, the resistance on the 2k ohm scale is (.02, .002, no reading) and (.019, .002, no reading) for each tab, going from left to right looking at it from the powerswitch side.

post #6767 of 6806
Quote:
Originally Posted by AHorseNamedJeff View Post
 

just got back from measuring, the resistance on the 2k ohm scale is (.02, .002, no reading) and (.019, .002, no reading) for each tab, going from left to right looking at it from the powerswitch side.

 

I think we need to clarify here the difference between the tab and the pins.

 

 

The tab and middle pin are internally connected. That's why you're supposed to electrically insulate the tab from the heat sinks.

 

On this amp, the drain/tab/middle pin is connected directly to the 48 V supply. If your heat sinks are grounded and the tab touches them, you're shorting your PSU. That would explain why nothing works.

 

And well, if you're getting 2 ohms between the middle pin and the copper plate, which I assume is ground, you've pretty much confirmed a short.

post #6768 of 6806

Good clarification, Kim.  I also agree with your assessment - pretty much suspected that this was the case. ;)

post #6769 of 6806
Quote:
Originally Posted by KimLaroux View Post

Quote:
Originally Posted by AHorseNamedJeff View Post

 
just got back from measuring, the resistance on the 2k ohm scale is (.02, .002, no reading) and (.019, .002, no reading) for each tab, going from left to right looking at it from the powerswitch side.

I think we need to clarify here the difference between the tab and the pins.




The tab and middle pin are internally connected. That's why you're supposed to electrically insulate the tab from the heat sinks.

On this amp, the drain/tab/middle pin is connected directly to the 48 V supply. If your heat sinks are grounded and the tab touches them, you're shorting your PSU. That would explain why nothing works.

And well, if you're getting 2 ohms between the middle pin and the copper plate, which I assume is ground, you've pretty much confirmed a short.
okay I'll look into that when I get home from school. Pete also PMd me about the FETs being wired wrong.

Edit, yeah I looked at the pictures and I got the red and green wires backwards...
Edited by AHorseNamedJeff - 5/27/14 at 7:36am
post #6770 of 6806

alright got the wries all fixed and yep the tabs ARENT insulated form the heatsinks, how should I mount the MOSFETS but still keeping them insulated?

post #6771 of 6806
Quote:
Originally Posted by AHorseNamedJeff View Post
 

alright got the wries all fixed and yep the tabs ARENT insulated form the heatsinks, how should I mount the MOSFETS but still keeping them insulated?


You need a heat sink insulator:

http://www.diyforums.org/SSMH/SSMHheatsink.php

 

EDIT: (middle diagram)


Edited by tomb - 5/31/14 at 5:43pm
post #6772 of 6806
Quote:
Originally Posted by AHorseNamedJeff View Post


I used the heater kit that's listed in the BOM sheet and installed it correctly (I think)

 

 

Quote:
Originally Posted by AHorseNamedJeff View Post
 

alright got the wries all fixed and yep the tabs ARENT insulated form the heatsinks, how should I mount the MOSFETS but still keeping them insulated?

 

The BOM lists a kit from beezar, but the website does not seem to be selling any kit with a shoulder washer anymore... 

 

 

A shoulder washer is a piece of plastic the insulates the tab from touching the screw and washer.

 

 

 

You also need an insulating pad behind the transistor, which you seem to have in the pictures.

post #6773 of 6806
Quote:
Originally Posted by KimLaroux View Post
 
Quote:
Originally Posted by AHorseNamedJeff View Post


I used the heater kit that's listed in the BOM sheet and installed it correctly (I think)

 

 

Quote:
Originally Posted by AHorseNamedJeff View Post
 

alright got the wries all fixed and yep the tabs ARENT insulated form the heatsinks, how should I mount the MOSFETS but still keeping them insulated?

 

The BOM lists a kit from beezar, but the website does not seem to be selling any kit with a shoulder washer anymore... 

 

 

A shoulder washer is a piece of plastic the insulates the tab from touching the screw and washer.

 

 

 

You also need an insulating pad behind the transistor, which you seem to have in the pictures.

 

I only referenced that page because it has this:

heatsinkmtg.gif

 

Which is also similar to this on the MiniMAX site:

heatsinkmtg.gif 

heatsinkmtgparts.gif

However, I don't think anyone implied that he was using a BOM from Beezar/DIYForums.org.  He built a p2p version with a copper plate.  That pretty much indicates the original Pete Millett version and BOM, I would think.  You are correct to point out the shoulder washer - that could indeed be causing the problem.  However, those heat sink pads (if that's what they are) look like they could be copper film and might be quite conductive.

 

In any event, I'll change the stock on the shoulder-washer heat sink kits on Beezar tomorrow - just have to make some more of them up - but he can get them almost anywhere, I also wasn't suggesting that he should order them from me.;);)

post #6774 of 6806

Oh right, you just made me realize the BOM I have is the one you made for the complete kits you used to sell. Is there even a BOM from Millett? I've never seen one. Really curious now which BOM he's referring to.

post #6775 of 6806
Well, if Pete's BOM reference is not in the very first post of this thread, then it's definitely on his website -pmillett.com.
post #6776 of 6806

Yep its on the webpage for the amp..

 

Good news everybody! IT WORRRRKS.

 

One of the gentlemen at the recent meet fixed it, turns out the only problem was the FETs were shorting because they weren't insulated on their mounting!

 

This amp is wonderful sounding! lush and warm with plenty of impact in the bass! loving it with Pink Floyd right now on their Division Bell album.

post #6777 of 6806

Just an FYI, but I came across a relatively decent supply of 19J6's.  I'm going to test them all out and depending on how many of them are good, I will offer SSMH PCB kits again.  This is just in the beginning stages, but I wondered if there was still interest in using the 19J6 tubes and doing an all-up kit again with custom-machined case.  If I can get all the rest of the parts, it would be exactly as originally offered and still described here:

 

http://www.diyforums.org/SSMH

 

I think the last time the kits were sold at $120.  That may have to go up some, but we'll see.  It will probably be for full kits, only, because of the up-front investment I'd have to make.  If the tubes test out OK, perhaps 30-40 kits, just to be safe and leave enough tubes for replacing ones that end up microphonic.

post #6778 of 6806

I'd be interested in bringing this project back from the dead.

post #6779 of 6806

I've built a few of the kits and they're superb.

 

I'd definitely buy another one.

post #6780 of 6806

I have a strange issue

When I'm using my Senn HD600 I don't receive any humm, But when I connect my new NAD viso HP50 I receive an annoying humm in my right ear. Not audiable when playing music but very annoying during silence. It isn't affected by the volumeknob

The HD600 has an impendace of 300ohm and the NAD has a impedance of 25 ohm. Could this cause this rather high pitched hum? And does somebody knows if it's caused by something in particular (already swapped tubes, problem remains right)

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Millett "Starving Student" hybrid amp