[jerb]

Left my millet on for the last two days, first time its been on for that long.
PLugged in th HF-1's and here a "clipping noise" it can be heard distinctly with out music playing and can be heard during music if I listen carefully.

from what Ive found the clipping noise I'm hearing is from something ocilating (sp?) but that seems to happen in op amps and the millet doesnt use those (Buffers?). could my tube Bias drifted due to thermal conditions? I dont have a multimeter handy to check the bias but could that be it?

What else could possibly cause this noise?

also Ive tried unplugging it and letting it cool down, when I plug it back in it still makes the noise. RF? Bias? Occilation?

 

[nikongod]

do you have diferent tubes to try in there?

i think that High-voltage tubes sometimes "crackle" when they go bad.

 

[sbelyo]

I suppose it could be the bias. I once had a tube drift by a few volts over a full day of being on.

Also keep in mind when swapping tubes, that the bias must be reset. Every time I've tried a new set of tubes I needed to re adjust the bias trimpot.

What happened to you meter? I though you had one? (to check the values with)

 

[jerb]

I had one but dad brought it to work... Havent seen it since

its ok, he owes me a FLUKE for xmas now

High voltage tubes may crackle but these are only running at 11V DC, I do have another tube but I'm not sure of its integrity + I cant test the Bias until xmas.

Suppsoe the Bias had drifted, Whould there be any potential of damage toward the headphones plugged in?

 

[Clutz]

Quote:

Originally Posted by jerb I had one but dad brought it to work... Havent seen it since its ok, he owes me a FLUKE for xmas now High voltage tubes may crackle but these are only running at 11V DC, I do have another tube but I'm not sure of its integrity + I cant test the Bias until xmas. Suppsoe the Bias had drifted, Whould there be any potential of damage toward the headphones plugged in?

Here is a thought- but remember, this idea is half baked. We know roughly what voltage we want as the bias. If you know the input voltage, couldn't we think of a way to create a voltage drop using diodes in series? e.g. Connect x diodes in series to create the desired bias. Also connect up an LED. Turn the biasing pot all the way to the minimum for each channel. Connect the diodes+LED thing to the test points and adjust the bias trim pot until the LED lights up. Then repeat for the other channel. It's not perfect, but since all you really need is a particular voltage - you might be able to make yourself a fixed configured yes/no volt meter of sorts.

It probably wouldn't work - but it's a thought.

 

[sbelyo]

Quote:

Originally Posted by jerb I had one but dad brought it to work... Havent seen it since

Doh!
Quote:

Originally Posted by jerb its ok, he owes me a FLUKE for xmas now

Sweet
Quote:

Originally Posted by jerb Suppsoe the Bias had drifted, Whould there be any potential of damage toward the headphones plugged in?

Not to the headphones, but the tube if over biased may shorten it's life. If you are hearing music I think it's somewhat safe. If it's distorted heavily, then maybe I wouldn't leave it on for long periods until you get your meter.

I've got 4 or 5 extra pairs of 12FK6 and 1 or 2 of 12FM6 if you need a set.

 

[sbelyo]

double post

 

[jerb]

Im going to bug dad when he calls later, He's not going to be back frm japan till sunday though

I may be able to snag one from the school, But I gotta dig it out of the closet.

I Guess Ill use my Blueberry amp for the time being.

 

[sbelyo]

Quote:

Originally Posted by jerb Im going to bug dad when he calls later, He's not going to be back frm japan till sunday though

That's cool... I'd ask him to bring back a new laserdisc player and all the blackgates he can carry

 

[jerb]

I had been using my Emotion+ but I switched baack to my millet.

I can hear teh clipping noise as soon as I turn it on. as I kisten to the amp its always present but it fades in and out.

I can hear the clipping regardless of where the pot is turned to, what headphones are used or how loud the music comming in is. I know its the amp because I can hear the clipping when the amp isn't plugged into any source.

I grabbed a DMM from school to test the bias and it reads 11.95 for both tubes.
I tried switching the tubes around and the clipping is now audible in both channels. I have tried replacing the tubes aswell but the clipping does not go away.

I plugged it in and left it going over night, I checked the bias, one is 11.95 and the other tube is 11.93. the tubes are warm but nothing is hot to the touch. I can now hear ocillations every so often, it sounds like clipping but changes in pitch until it reaches a certain point where it resets and does it again.

powersupply is a regulated EPLAC wallwart + tread so I dont think its power noise.

any idea's?

EDIT: I forgot to mention, when I touch the knob on my ALPs blue velvet pot I can hgear a High pitch through the pot, its equal in both channels

 

[n_maher]

Quote:

Originally Posted by jerb EDIT: I forgot to mention, when I touch the knob on my ALPs blue velvet pot I can hgear a High pitch through the pot, its equal in both channels

This is most likely a grounding problem which raises several questions.

1. Is the pot grounded?

2. Are the inputs and outputs isolated?

3. Is the DC jack isolated?

4. When you hear the clipping are you getting any DC voltage at the headphone output?

5. What is the current draw of the amp?

Give us a bit more information and hopefully we can help you sort it out. And as always, pictures are very helpful.

Nate

 

[jerb]

alright, the pot should be grounded as I have soldered the correct pad on the amp. using the DMM as a continuity tester I have continuity between pins 1,2,4,5 on the Alps (looking at the bottom with shaft pointing up, counting left to right the top row has 1-3 and the bottom row has 4-6)

I am using non Isolating inputs but its istalled in a cardboard box for the present so I dont think thats a problem. same for the I do get .75V when I measure from the barrel of the DC jack to GND on the Millet board.

there is no DC voltage on the output of the amp

Im sorry but Im not sure how to calculate current draw, it cant be mmore than .33A, that is all the wallwart will provide. The wallwart is getting quite warm

 

[Blooze]

Quote:

Originally Posted by jerb Im sorry but Im not sure how to calculate current draw, it cant be mmore than .33A, that is all the wallwart will provide. The wallwart is getting quite warm

I'm not for certain, and I"m sure Nate or Drewd will chime in on possible problems, but it could be your wall wart. Seems like I read that around 350mA would be minimum for good operation. Maybe it's not getting the power it needs. I'm only running at 20.8V (24V wall wart through a TREAD), but the wart is rated up to 650mA and I've never had a problem at any volume setting.

 

[jerb]

perhaps I should just buy a new walwart, they're not too expensive (like $20-25 right?)

I'll wait for a reply from nate/drew befor buying something I may not need

 

[Blooze]

Quote:

Originally Posted by jerb perhaps I should just buy a new walwart, they're not too expensive (like $20-25 right?) I'll wait for a reply from nate/drew befor buying something I may not need

I'd definitely wait as I'm just shooting in the dark, but I paid like $10 for mine as the TREAD is doing the regulation of the DC. It seems like someone else was having problems and they were using a wart that possibly wasn't giving enough current to the Millett. You might try measuring what the current draw is to make sure you've got enough to supply the amp. You might also get a quicker response over at the DIYForum website for the Millett.