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Millett "Starving Student" hybrid amp - Page 425

post #6361 of 6779
Would anyone give me an estimate on how much a pre-assembled would cost, and if anyone would be interested in selling one to me?
post #6362 of 6779
The cost of parts for a regular Millett is somewhere in the neighborhood of $100-$200. Not sure about the starving student, but the regular Millett is pretty straight forward on strip board.
post #6363 of 6779
The cost of parts for a regular Millett is somewhere in the neighborhood of $100-$200. Not sure about the starving student, but the regular Millett is pretty straight forward on strip board.
post #6364 of 6779

Hey everyone,

Thanks for all of the input into building this amp.  It sounds great!  I have a few questions about some minor issues I am having:

 

1)  If one of the RCA inputs are unplugged I get one of the headphone channels spike to max volume....when both are plugged in, everything is fine.  Could this be due to the fact that I grounded my headphone jack to one of the RCA inputs?  I did this as I was having a loud hum/buzz when it was grounded to my ground plate.  I am not sure why.

 

2)  I have a hum when I touch my volume knob (I already tried to ground the POT without success as someone stated in the past posts).

 

3)  When the POT is turned up to MAX volume, I have a constant buzz (is this what is referred to as the ceiling max?).  When it is at a normal volume I hear no buzz at all and everything is crystal clear.

 

4)  Just an FYI, when this amp is plugged into a DAC (from my computer) I can hear noise that is related to my hard drives (reading and writing data), keyboard, mouse movements, etc.  I am assuming this is due to Electrical Interference or RFI the tubes are picking up.  Anyway to fix this?

 

5)  A question about grounding.....At first I was not thinking and just following the schematic.  I grounded the POT, RCA inputs, and Headphone amp as seperate lines all connecting to a single point on the grounding plate.  I had a TERRIBLE loud buzzing to the point I thought it was going to blow my headphone speakers.  After walking away and thinking about it, I realized I needed to run the ground from the RCA inputs to the ground terminals on the POT.  I also grounded my headphone socket to one the RCA input.  I then ran one single ground from this "circuit" to a single point on the ground plate.  Is this correct?

 

Thanks! 

 

 

 

 

 

 

 

Dustin


Edited by dustinsterk - 1/28/13 at 8:39am
post #6365 of 6779
Quote:
Originally Posted by scootsit View Post

The cost of parts for a regular Millett is somewhere in the neighborhood of $100-$200. Not sure about the starving student, but the regular Millett is pretty straight forward on strip board.

When I built my SSMH the total parts cost was around $100 including case, tubes and everything. I added a GrubDAC to that, which was another $20-30 or so. I built mine point to point, it wasn't really that hard after I got all the parts mapped out and rechecked the schematic for the zillionth time. There's a million P2P builds and pictures in this thread for reference, and there was some work with a stripboard layout at some point, which there was a separate thread for.

post #6366 of 6779
Quote:
Originally Posted by Ikarios View Post

Quote:
Originally Posted by scootsit View Post

The cost of parts for a regular Millett is somewhere in the neighborhood of $100-$200. Not sure about the starving student, but the regular Millett is pretty straight forward on strip board.

When I built my SSMH the total parts cost was around $100 including case, tubes and everything. I added a GrubDAC to that, which was another $20-30 or so. I built mine point to point, it wasn't really that hard after I got all the parts mapped out and rechecked the schematic for the zillionth time. There's a million P2P builds and pictures in this thread for reference, and there was some work with a stripboard layout at some point, which there was a separate thread for.


I think my price had a skeletonDAC, too, an E12 muting circuit, and a PS. That all was close to $150 ish

 

That's unbuilt, of course. Though, building it isn't as hard as you might think. I could really help you with that. I laid it out on stripboard in DIY creator and would be happy to share the board layouts. If you wanted it custom built, I'd bet you'd pay closer to $200 or $250. If you were buying someone's used amp, it would probably be closer to or less than parts cost.


Edited by scootsit - 1/28/13 at 12:15pm
post #6367 of 6779
Quote:
Originally Posted by dustinsterk View Post

Hey everyone,

Thanks for all of the input into building this amp.  It sounds great!  I have a few questions about some minor issues I am having:

 

1)  If one of the RCA inputs are unplugged I get one of the headphone channels spike to max volume....when both are plugged in, everything is fine.  Could this be due to the fact that I grounded my headphone jack to one of the RCA inputs?  I did this as I was having a loud hum/buzz when it was grounded to my ground plate.  I am not sure why.

 

Does it do this regardless of which RCA is unplugged, or is it the same for both? If it's only for one, I'm guessing you have one of the RCA not grounded properly.

 

Quote:

2)  I have a hum when I touch my volume knob (I already tried to ground the POT without success as someone stated in the past posts).

 

If you used an off-board PSU, it's probably not earthed. In this case, you don't even have a ground to ground it to. Connecting the pot's shaft to 0 V may help, or it may make it worse. I'm clueless how one should go about fixing this... anyone else got experience with this?

 

Maybe you should start by verifying, using a DMM, that the pot's shaft is indeed grounded.

 

Quote:

3)  When the POT is turned up to MAX volume, I have a constant buzz (is this what is referred to as the ceiling max?).  When it is at a normal volume I hear no buzz at all and everything is crystal clear.

 

Any amplifier will output some audible noise when the volume is maxed. It's normal, and not really a problem. If you listen to music at this volume, you have more serious problems to take care of. wink.gif

 

Quote:

4)  Just an FYI, when this amp is plugged into a DAC (from my computer) I can hear noise that is related to my hard drives (reading and writing data), keyboard, mouse movements, etc.  I am assuming this is due to Electrical Interference or RFI the tubes are picking up.  Anyway to fix this?

 

By "DAC from my computer", do you mean that you're using your sound card's audio out? If yes, then it's normal. The inside of a PC is drowned with all sort of RFI and EMI. If your sound card is not shielded, as most cheap cards are, then its audio signal gets polluted with all this junk.

 

Quote:

 

5)  A question about grounding.....At first I was not thinking and just following the schematic.  I grounded the POT, RCA inputs, and Headphone amp as seperate lines all connecting to a single point on the grounding plate.  I had a TERRIBLE loud buzzing to the point I thought it was going to blow my headphone speakers.  After walking away and thinking about it, I realized I needed to run the ground from the RCA inputs to the ground terminals on the POT.  I also grounded my headphone socket to one the RCA input.  I then ran one single ground from this "circuit" to a single point on the ground plate.  Is this correct?

 

It depends on your religion. There is no consensus on how one should wire grounds inside an audio device. Just look at the mess created by ground loops in commercial products... it's endless.

 

You're the only person able to answer this question. Did changing the ground scheme improve on the buzz? The level of the buzzing is your only gauge telling you if one scheme is better than the other.

 

As for the discussion on the cost, should I start counting how much mine cost? I lost count at around 500, but I'll do the math again if anyone cares. rolleyes.gif Though honestly, I think I'll sleep better if I don't know.

post #6368 of 6779
Quote:
Originally Posted by KimLaroux View Post

 

Does it do this regardless of which RCA is unplugged, or is it the same for both? If it's only for one, I'm guessing you have one of the RCA not grounded properly.

 

 

If you used an off-board PSU, it's probably not earthed. In this case, you don't even have a ground to ground it to. Connecting the pot's shaft to 0 V may help, or it may make it worse. I'm clueless how one should go about fixing this... anyone else got experience with this?

 

Maybe you should start by verifying, using a DMM, that the pot's shaft is indeed grounded.

 

 

Any amplifier will output some audible noise when the volume is maxed. It's normal, and not really a problem. If you listen to music at this volume, you have more serious problems to take care of. wink.gif

 

 

By "DAC from my computer", do you mean that you're using your sound card's audio out? If yes, then it's normal. The inside of a PC is drowned with all sort of RFI and EMI. If your sound card is not shielded, as most cheap cards are, then its audio signal gets polluted with all this junk.

 

 

It depends on your religion. There is no consensus on how one should wire grounds inside an audio device. Just look at the mess created by ground loops in commercial products... it's endless.

 

You're the only person able to answer this question. Did changing the ground scheme improve on the buzz? The level of the buzzing is your only gauge telling you if one scheme is better than the other.

 

As for the discussion on the cost, should I start counting how much mine cost? I lost count at around 500, but I'll do the math again if anyone cares. rolleyes.gif Though honestly, I think I'll sleep better if I don't know.

 

Hello KimLaroux,

Thanks for the response.

 

The loudness only happens when one of the channels is unplugged....I will double check the grounds, etc.  Thanks for the suggestion!

 

In regards to the max volume, I am not listening to it that loud, trust me this thing cranks.  I just noticed that you can start to hear that hum as you get closer and closer to the max volume....I was just making sure that was "normal".  :)

 

By "DAC from my computer"...I am referring to a DAC (the Schiit Modi) that I have attached via USB cable.  The funny part is when I connect the same RCA cables (from the DAC) to another amp I dot NOT hear any computer noise.  It is only when it is connected to this amp.  That is why I am wondering if the tubes could be picking up the noise.

 

Thanks for the feedback on the grounding....I was unsure if there was a "proper" way to do it.  I think I have found the best way for this amp considering the case I used.

 

Thanks again!

 

--Dustin

post #6369 of 6779


Finished the Starving Student chassis today

Unfortunately, I am solder-challenged. I've soldered past projects but I mostly ended up with bad joints, perhaps I can blame my cheap soldering iron. In other words, this is currently a paper weight. Lame-sauce :/

If someone lives close to Houston and can help solder the components, then please contact me!

This is the original millet schematic based on 19J6 tubes
Edited by ahshan06 - 1/29/13 at 4:49pm
post #6370 of 6779

Pimpest switch ever.

post #6371 of 6779

Just an FYI, if anyone needs the Cisco power supply for this project, I have about 100-125 of them.  I would sell them for $10 if you are interested.  Just send me a PM.

 

They are Cisco part number:  34-1977-03       48V, .38A

 

Thanks,

Dustin

post #6372 of 6779
Hi everyone, just bought a built SSMH from a friend, but one of the channel (left to be precise) doesn't sound correctly. It crackles and sounds very low, almost no sound at all. What could possibly be the problem? I suspect one of the caps is broken, but no idea which one. Any help? smily_headphones1.gif
post #6373 of 6779
Quote:
Originally Posted by cpdelc View Post

Hi everyone, just bought a built SSMH from a friend, but one of the channel (left to be precise) doesn't sound correctly. It crackles and sounds very low, almost no sound at all. What could possibly be the problem? I suspect one of the caps is broken, but no idea which one. Any help? smily_headphones1.gif

Could be a bad tube, have you switched them to see if the problem follows the tube?

post #6374 of 6779
Quote:
Originally Posted by cpdelc View Post

Hi everyone, just bought a built SSMH from a friend, but one of the channel (left to be precise) doesn't sound correctly. It crackles and sounds very low, almost no sound at all. What could possibly be the problem? I suspect one of the caps is broken, but no idea which one. Any help? smily_headphones1.gif

Right, it's fairly easy to work along the signal path in this amp. There is of course a risk of shock when working on a live amp, so all the usual caveats... I'm not responsible for any harm you may do to yourself or if you set fire to your house... but honestly it's not a very dangerous amp (I did get a decent belt off one of the my big decoupling caps a while ago whilst trying to discharge it).

 

Carefully power up the amp with case open and the innards accessible.

 

First of all, stupid question do both the heaters light up?

 

When following these instructions if any step doesn't read like it should report it here so we can try and work out the problems.

 

Now let's check the power supply path. With your DMM on VDC you should see 48V at the power input to the amp and going to pin 2 of each mosfet. You should also have a CRC pi filter with about 45-47V on the other side of the 2k resistor. Then check the voltage at the top of R1 and R7, they should be the the same as the voltage you measured after the pi filter. After this measure the voltage on the tube cathodes (pins 3 and 8 on 12a_7s and pin 7 on 19J6s) it should read around 2V from memory, but the most important thing is that both tubes read the same.

You can also check the heater voltage now (between pins 4 and 5 on a 12a_7 or pins 3 and 4 on a 19J6), it should read either around 13V or 19V.

 

Now for a signal path check:

 

I recommend connecting a cheap source that you're not fussed about and then play some music or test tones at a decent volume from your source (test tones are best due to them being constant power). Set your DMM to AC 20V or similar then measure the power on both RCA input jacks (or just both channels of whatever input jack type you're using). Left and right should have the same voltage, if not you're problem is before the amp, if its the same move down the signal wires to the pot. I turn the pot to about 50% and then measure the voltage on the wiper (with the source still playing). Once again the left and right channels should measure the same (I recommend turning the pot half way because they are rather imbalanced in the first 10-20%). 

 

Now you want to measure the AC voltage on the tubes plates (pins 1 and 6 on 12a_7 builds pins 1 and 2 on 19J6  builds) you should now see your amplified voltage and it should be very similar across both channels (allow a bit for valve differences). If it is the same continue this process if not go the note a. Next I would ask you to measure the AC voltage on the other side of the coupling capacitors C2 and C4, it should be the same as on the other side. Now, set your DMM to DC 20V and measure the voltage at the mosfet gates (in the same place as you took your last AC measurement). Once again they should be the same and about 16-17V for 12a_7s and 24V for 19J6s. If this is the case then switch back to AC and measure the output of the mosfet, where it connects to coupling capacitors C3 and C5. Once again report any difference you find here. If everything is still the same then check the voltage on the other side of these capacitors. If you still haven't found your problem then I would say to check your headphone jack for damage, beyond that I'd be at a loss.

 

note a: So if your not getting the same voltage out of your tubes then check the plate voltage (same place as the AC signal but in DC this time) it should read around 24V for both channels. If it's not an issue and your tube heaters are correctly powered then I'd reckon that your left channel tube is damaged. To test this swap the left and right tubes around, the faulty channel should now have switch over (only swap tubes with the amp powered down!)

 

Good luck with your debugging,

Chris

post #6375 of 6779
I'm just casing up my MSSH which I've built to drive my DT880 600ohms. I was wondering if there's anything I should do to optimise it for high impedance phones.
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