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Millett "Starving Student" hybrid amp - Page 43

post #631 of 6522
7/15/08 at 4:29pm
No - the fet washers - I have the metal one attached to the top of the screw instead of the plastic one. I will be back tonight and will try and mess around with it. I also plan to nix the copper plate to figure out the issue.

Thanks guys!
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post #632 of 6522
7/15/08 at 5:00pm
Before making wholesale changes like the removal of the copper plate you might want to undertake some simple troubleshooting. Otherwise you're fighting a fire by burning down the house first.
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post #633 of 6522
7/15/08 at 6:14pm
I was going to connect all the grounds together because I know that something is getting grounded that shouldn't and it will result in a better sounding amp in the end (with a cleaner ground line). I need to fix other things, granted. We will see if those other things fix it - and then the tweeking will begin. Besides, I have some parts around and wanted to see the results of a bit of tweeking (within all ranges given).

But, I need to get it up and working first. The tubes are not getting power ATM and nothing seems broken. I will be working on this from 7:30 til about 10PM tonight - I will update then!

I do really love building stuff and it gives you the greatest feeling in the end.
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post #634 of 6522
7/15/08 at 7:51pm
Assuming you've rechecked your layout against the schematic I'll say the following - before any of us give any more advice we need some information:

Step 1: Check the wallwart. Report the results of measuring the unloaded voltage. If you blew the wallwart no amount of troubleshooting of the amp is going to make a bit of difference.

Step 2: Check the power supply jack wiring. Measure and report the voltage at the dc inlet. If power isn't making it inside the chassis clearly that's problem #1 to solve.

Step 3: Report the results of measuring voltage across C1.

Then we can go forward.

However, if you insist on ripping the whole thing apart I'm going to throw my hands up in defeat. There's nothing wrong with the ground plane approach and assuming it's done correctly I'd question whether or not you'll get a "better sounding amp" using a star ground. I can guarantee that Pete's amp sounds better than mine and he used the copper plane.
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post #635 of 6522
7/15/08 at 10:07pm
Quote:
Originally Posted by n_maher View Post
There's nothing wrong with the ground plane approach and assuming it's done correctly I'd question whether or not you'll get a "better sounding amp" using a star ground.
I suggested a star ground because there were wires everywhere. I figured it would make -=Germania=- think about layout a little more, and it would make things easier to look at. But, either method is probably fine in this case.
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post #636 of 6522
7/15/08 at 10:26pm
This may be a silly question. I was wondering if you can use the case itself as a heatsink instead of the 2 black ones that most people are using for this build. I have a 2-3mm thick aluminum top I am going to use for the case and wondered if I could get away with using it directly as the heatsink.
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post #637 of 6522
7/15/08 at 11:02pm
Quote:
Originally Posted by m0b1liz3 View Post
This may be a silly question. I was wondering if you can use the case itself as a heatsink instead of the 2 black ones that most people are using for this build. I have a 2-3mm thick aluminum top I am going to use for the case and wondered if I could get away with using it directly as the heatsink.
That's sort of hard to say with any certainty and at a minimum it would be safe to say that the case would get very hot. I wouldn't do it without some additional heat sinking or heat management.
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post #638 of 6522
7/15/08 at 11:06pm
Quote:
Originally Posted by dsavitsk View Post
I suggested a star ground because there were wires everywhere. I figured it would make -=Germania=- think about layout a little more, and it would make things easier to look at. But, either method is probably fine in this case.
Agreed, it's not bad advice, but I think she's got a mountain to climb before she worries about the wires running everywhere. In theory (at least in my brain) the ground plane allows for a simpler layout and therefor one that should be easier to trouble shoot. Of course, it has its share of challenges, but a star ground would as well and would require that she rewire a large portion of the amp.
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post #639 of 6522
7/15/08 at 11:09pm
I just finished my build and I'm having a few issues.

Upon initial power up, both tubes glowed, but audio only came through the left channel. All I could hear from the right was humming. In the process of testing voltages to try to narrow down the source of the problem, I accidently shorted my circuit somewhere.

Now, nothing but humming comes out of both channels, and I no longer get 48V in. I tested the wall wart and it outputs 48V with no load. Only one of the tubes attempts to fire up, and it just pulses. The input voltage oscillates at the same frequency from 0 to approximately 10V. Any suggestions on how to figure out what I broke? Ha
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post #640 of 6522
7/15/08 at 11:33pm
Oh yeah, I swapped out the tubes with another set and nothing changed.
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post #641 of 6522
7/16/08 at 12:44am
Quote:
Originally Posted by shortkidsrus View Post
I just finished my build and I'm having a few issues.

Upon initial power up, both tubes glowed, but audio only came through the left channel. All I could hear from the right was humming. In the process of testing voltages to try to narrow down the source of the problem, I accidently shorted my circuit somewhere.

Now, nothing but humming comes out of both channels, and I no longer get 48V in. I tested the wall wart and it outputs 48V with no load. Only one of the tubes attempts to fire up, and it just pulses. The input voltage oscillates at the same frequency from 0 to approximately 10V. Any suggestions on how to figure out what I broke? Ha
I haven't built one of these, but at first glance, I would disconnect the PSU and with your meter on ohms, check the power input to ground. If it is pulling the input power down to 0V, I would suspect a short or component fried to a short? Q1 is a possibility.
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post #642 of 6522
7/16/08 at 2:03am
Yeah I was thinking that I had cooked one or both of the FETs.

I checked the power input to ground and it is not shorted.

The symptoms have changed a bit:
-Left channel tube lights up just fine
-Input voltage is a steady 48V
-Right channel tube remains dark, but voltage is zero across all right channel components except FET drain, which is 48V

Is there a way to test a FET without switching it out?
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post #643 of 6522
7/16/08 at 8:22am
Quote:
Originally Posted by shortkidsrus View Post
Yeah I was thinking that I had cooked one or both of the FETs.

I checked the power input to ground and it is not shorted.

The symptoms have changed a bit:
-Left channel tube lights up just fine
-Input voltage is a steady 48V
-Right channel tube remains dark, but voltage is zero across all right channel components except FET drain, which is 48V

Is there a way to test a FET without switching it out?
Testing a MosFet, Testing
The handheld simple test with a DMM seems to work pretty well when I've done it, but you'll need to remove the MOSFET, first. Note that use of a solder-sucker is contraindicated according to that article.
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post #644 of 6522
7/16/08 at 11:52pm
I am a supreme idiot!

I seriously wired the pins on the socket in reverse!
It was a relatively simple fix and this thing has some of the lowest hum I have ever heard in a tube amp.

I also got the HD580's in today and they sounded aweful with my solid state....They sound great, even stock, with this amp.
Sennheisers and tubes have always made a great mix! Thanks Pete for a great amp.

One thing is that I barely turn the pot at all and its loud. I think that you could power some low wattage speakers off of this thing easily.
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post #645 of 6522
7/16/08 at 11:55pm
BTW - sounds great with all of my headphones.

The SS is more analytical - but the tube sounds better.
Yeah, I am drinking a beer to celebrate now. My tubes have a golden glow which looks awesome reflecting off of the gold surface.
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