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Millett "Starving Student" hybrid amp - Page 434

post #6496 of 6786

Looks like I was a little too optimistic about that buzz/hum, I checked all my soldering, made sure nothing was shorting, checked and rechecked voltages, made sure everything was properly grounded, etc etc. 

 

The buzz/hum is only in the the right ear and is independent of the volume, if I put my headphones on and turn the amp on then as soon as it warms up the buzz shows up, audio plays clearly along with the buzz. Also the buzz never gets louder as the volume is turned up either, likewise for all the way down. It is loud enough that I can't ignore it, it imposes on music.

 

There is a second, more normal volume related hum as the volume gets louder I begin to hear, it goes away if I touch the inner enclosure where there is no paint, is there a more permanent solution to that? The case itself is a ground according to my multimeter.

 

I'm quite proud of how it's turned out, regardless of the problems. If I could get rid of that buzz then I'm home free. The sound on this thing is pretty amazing though, I wasn't sure what to expect, but it's more than just "louder" music, a simple MP3 took on a whole new life.

 

I was going to attach pictures but I keep getting an error message, I'll try again later.

post #6497 of 6786

I had similar problem. I had to ground RCA inputs, Headphone jack and pot directly to the DC jack's ground. Before that I had connected these things to different part of enclosure and it was causing buzzing.

post #6498 of 6786

I believe your grounding scheme is not efficient enough. It's kind of a common problem here, as it's usually a first project for most of us. You have to think of the ground as a return path for different signals, and not as a "neutral" point where everything gets nullified. Ground is nothing more than the opposite of the power rail, after all. A perfectly silent tube amplifier uses a balanced wiring for V+ and Gnd throughout the amplifier, with proper decoupling at each stage.

 

The voltage you get at any single point is in reference to the ground at the other side of this point. If that ground point is noisy, the end result is the same as if your V+ was noisy.

 

Power supply grounds are noisy. Signal grounds are sensitive to noise. Therefore, make sure the power return paths are not going across your signal return paths. 

 

This is why the first recommendation most people have is to tell you to use a Star Ground. Connect all your return paths to a single point. Connect this point to the power input jack using a single wire. Connect the star ground to the chassis at a single point, making sure no current flows trough the enclosure. This is not a car, it's an audio device. The enclosure should be used as nothing more than a shield.

 

I had to rebuild my whole amplifier many times to learn all that. Now it's dead silent.

beerchug.gif

 

ps: You can't upload pictures yet because you don't have enough posts. 

post #6499 of 6786
Quote:
Originally Posted by KimLaroux View Post

I believe your grounding scheme is not efficient enough. It's kind of a common problem here, as it's usually a first project for most of us. You have to think of the ground as a return path for different signals, and not as a "neutral" point where everything gets nullified. Ground is nothing more than the opposite of the power rail, after all. A perfectly silent tube amplifier uses a balanced wiring for V+ and Gnd throughout the amplifier, with proper decoupling at each stage.

 

The voltage you get at any single point is in reference to the ground at the other side of this point. If that ground point is noisy, the end result is the same as if your V+ was noisy.

 

Power supply grounds are noisy. Signal grounds are sensitive to noise. Therefore, make sure the power return paths are not going across your signal return paths. 

 

This is why the first recommendation most people have is to tell you to use a Star Ground. Connect all your return paths to a single point. Connect this point to the power input jack using a single wire. Connect the star ground to the chassis at a single point, making sure no current flows trough the enclosure. This is not a car, it's an audio device. The enclosure should be used as nothing more than a shield.

 

I had to rebuild my whole amplifier many times to learn all that. Now it's dead silent.

beerchug.gif

 

ps: You can't upload pictures yet because you don't have enough posts. 

That's actually very helpful, sadly as you just said, I'd have to rebuild the amp to achieve total silence, as it sits I fixed the nasty buzz in the right ear, and it is dead silent with volume at off, at high level maybe 75% volume I begin hearing an audible but mostly harmless volume hiss along with a very slight oscillating "wom wom wom" but together these sounds are not enough to detract from the music especially not at that level of volume. That's also a reasonable explanation as to why I couldn't post pictures, however I must have reached the threshold because the photo uploader is now appearing for me so here it is:

 

EDIT: the oscillating sound is gone as far as I can tell, dunno why, it's probably explainable but whatever I'm happy.

 

 

 

 

 

 

 


Edited by jarscar - 4/30/13 at 9:07pm
post #6500 of 6786
My amp has quite imbalance channel, it go about 60% on the right and 40% on the left. What can be the source of problem?
post #6501 of 6786
Quote:
Originally Posted by proid View Post

My amp has quite imbalance channel, it go about 60% on the right and 40% on the left. What can be the source of problem?

could be a bad volume pot, how low is it turned when this is happening? regular stereo pots have pretty bad channel matching when turned very low. if it isnt the pot, check and make sure all your resistors are the correct values.

post #6502 of 6786
Quote:
Originally Posted by jarscar View Post

Quote:
Originally Posted by KimLaroux View Post

I believe your grounding scheme is not efficient enough. It's kind of a common problem here, as it's usually a first project for most of us. You have to think of the ground as a return path for different signals, and not as a "neutral" point where everything gets nullified. Ground is nothing more than the opposite of the power rail, after all. A perfectly silent tube amplifier uses a balanced wiring for V+ and Gnd throughout the amplifier, with proper decoupling at each stage.

 

The voltage you get at any single point is in reference to the ground at the other side of this point. If that ground point is noisy, the end result is the same as if your V+ was noisy.

 

Power supply grounds are noisy. Signal grounds are sensitive to noise. Therefore, make sure the power return paths are not going across your signal return paths. 

 

This is why the first recommendation most people have is to tell you to use a Star Ground. Connect all your return paths to a single point. Connect this point to the power input jack using a single wire. Connect the star ground to the chassis at a single point, making sure no current flows trough the enclosure. This is not a car, it's an audio device. The enclosure should be used as nothing more than a shield.

 

I had to rebuild my whole amplifier many times to learn all that. Now it's dead silent.

beerchug.gif

 

ps: You can't upload pictures yet because you don't have enough posts. 

That's actually very helpful, sadly as you just said, I'd have to rebuild the amp to achieve total silence, as it sits I fixed the nasty buzz in the right ear, and it is dead silent with volume at off, at high level maybe 75% volume I begin hearing an audible but mostly harmless volume hiss along with a very slight oscillating "wom wom wom" but together these sounds are not enough to detract from the music especially not at that level of volume. That's also a reasonable explanation as to why I couldn't post pictures, however I must have reached the threshold because the photo uploader is now appearing for me so here it is:

 

EDIT: the oscillating sound is gone as far as I can tell, dunno why, it's probably explainable but whatever I'm happy.

 

 

 

 

 

 

 


Where'd you get that case? It's nifty!

post #6503 of 6786

I got the case at taydaelectronics.com it's a diecast aluminum case, I had to prime and paint it myself but I love the size. I sanded the edge of the bottom plate to give it a brushed finish.

post #6504 of 6786

When I was doing research before I built the amp someone mentioned to ground the first decouple cap directly to DC jacks ground. I built mine with everything going to a star ground (except first decouple cap) and I have zero hiss until way beyond listning levels on the volume knob. The the star ground should only be soldered on to the chassi in one spot, this make the case a faradaycage effectivley. You can see that Pete did so him self if you look at the inside picture.

 

Edit. Kim beat me to the punch. Very nice looking amp you got there!


Edited by Grumus - 5/1/13 at 9:03am
post #6505 of 6786
Quote:
Originally Posted by kchapdaily View Post

could be a bad volume pot, how low is it turned when this is happening? regular stereo pots have pretty bad channel matching when turned very low. if it isnt the pot, check and make sure all your resistors are the correct values.

That's how mine is, at anywhere from 0-30% my right channel is a little bit louder, but if I turn down the source audio and turn up the amp volume the audio levels out and both ears have even sound, it's probably because I spent about 50 cents on the pot :/

post #6506 of 6786
Quote:
Originally Posted by jarscar View Post

Looks like I was a little too optimistic about that buzz/hum, I checked all my soldering, made sure nothing was shorting, checked and rechecked voltages, made sure everything was properly grounded, etc etc. 

 

The buzz/hum is only in the the right ear and is independent of the volume, if I put my headphones on and turn the amp on then as soon as it warms up the buzz shows up, audio plays clearly along with the buzz. Also the buzz never gets louder as the volume is turned up either, likewise for all the way down. It is loud enough that I can't ignore it, it imposes on music.

 

There is a second, more normal volume related hum as the volume gets louder I begin to hear, it goes away if I touch the inner enclosure where there is no paint, is there a more permanent solution to that? The case itself is a ground according to my multimeter.

 

I'm quite proud of how it's turned out, regardless of the problems. If I could get rid of that buzz then I'm home free. The sound on this thing is pretty amazing though, I wasn't sure what to expect, but it's more than just "louder" music, a simple MP3 took on a whole new life.

 

I was going to attach pictures but I keep getting an error message, I'll try again later.

Have you tried swapping the tubes? If the hum 'follows' the tube, then you can be certain it's a defective tube, otherwise, it's definitely a circuit problem.

 

cheers!

post #6507 of 6786
Quote:
Originally Posted by the_equalizer View Post

Have you tried swapping the tubes? If the hum 'follows' the tube, then you can be certain it's a defective tube, otherwise, it's definitely a circuit problem.

cheers!

I actually went back and redid a large portion of the grounding, it reduced the loudness of the hum by about 50% and now I have to have the volume up a little higher before the hum is really apparent, it's probably still not as good as many of the amps built by people here but this has taught me a whole lot. I've already got some ideas for a new and improved amp.
Edited by jarscar - 5/2/13 at 11:08am
post #6508 of 6786

hi i was wondering if anyone had a link to a pcb layout for the 12au7 model. i am was going to try to etch one myself but i have not been able to find a layout to use.

post #6509 of 6786
Well, all I can say is what a learning curve! I have just built my 12au7 version. What great fun! I was thoroughly chuffed when it didn't explode on initial turn on and even happier when it played some sound.

Just one thing though, mine seems to be mono. Is this correct? I have checked the volume pot and checked both channels signals are separate, but yes mono. You can remove either RCA lead and each channel goes out in turn, but I did notice that when re inserting the RCA, when the centre pin touches the inner socket without being fully inserted the channel comes back before both signal and earth are connected. I don't think this is right, I think I have a grounding problem.

If I do this with both channels I get a furious hum in both ears. I'm not sure where to start looking... Any pointers?
post #6510 of 6786

*Edit I just did a quick thread search, tons of heat is apparently normal. I'm seriously giddy over how awesome this thing sounds though.

 

Well I've been using this happily for a while now, sounds awesome. One question though: just how hot is this supposed to get? cause after about an hour of listening it is really hot, like I can only hold my fingers on it for about 7 seconds hot. It's not damaging anything and the performance doesn't degrade but it just seems awfully hot for having an aluminum body and heatsinks, though it would kind of confirm everything I've heard about tubes soaking up energy, I just have zero experience with these things.


Edited by jarscar - 5/7/13 at 9:30pm
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