Millett "Starving Student" hybrid amp
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DrivenKeys

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I'm sorry that replacing the pot doesn't appear to fix it.

I just reviewed your photos again. Let me ask a question (don't hit me if this was obvious) - are those MOSFETs connected directly to the copper of the heat sink? If so, they are directly shorted to ground. The Drain pin (center pin) is the same as the tab on the MOSFET. The tabs must be insulated from ground.

If they are isolated, then sorry for the suggestion, but I can't see any insulating washers or pads in the photos.
I actually had the same thought when I first looked. I forgot to ask, figured it was just the photo.
 
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bdbell

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We're not actually sure the grounding does much through the power supply. The Cisco power supply may actually be isolated from ground inside its circuitry. It's one of the reasons we theorized that static charges can develop on the RCA jacks (killing some DIY DACs that output directly from a DAC chip). The primary grounding in the SSMH takes place through the casework. Did you scrape the anodizing away around the inside surface of the back plate at the power jack and RCA jacks? The RCA jacks will work better if they are not isolated with insulating washers.

This pic may help:


Note that it's still important to provide a ground between the DC jack and the back plate.

The other possibilities are the tubes and the power supply. If either one are bad, they can cause some bad humming.
Thanks for the quick reply tomb - I connected the other 680uf cap to the DC jack and that also reduced the hum/noise - tried connecting the 220uf caps also but that increased the noise. So I disconnected the 220uf and reconnected them to the PCB ground plane and then put everything back into the enclosure - and all the hum/noise went away! So, at least for my setup connecting the 2 680uf caps to the DC jack was necessary to eliminate all the noise. BTW - my case does not have any anodizing on the front/back plates.

One last question - I am currently using Elna 470uf RE3 caps and Wima 0.22/100v caps for C3/5 - the wima 0.22 caps are quite a bit smaller than the 250v ones - will it make much difference if I switch to Elna 470uf RFS and the 250v Wima caps?
 
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tomb

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Thanks for the quick reply tomb - I connected the other 680uf cap to the DC jack and that also reduced the hum/noise - tried connecting the 220uf caps also but that increased the noise. So I disconnected the 220uf and reconnected them to the PCB ground plane and then put everything back into the enclosure - and all the hum/noise went away! So, at least for my setup connecting the 2 680uf caps to the DC jack was necessary to eliminate all the noise. BTW - my case does not have any anodizing on the front/back plates.

One last question - I am currently using Elna 470uf RE3 caps and Wima 0.22/100v caps for C3/5 - the wima 0.22 caps are quite a bit smaller than the 250v ones - will it make much difference if I switch to Elna 470uf RFS and the 250v Wima caps?
No, it won't make much difference - most likely. The voltage is not important in this case. 48V is as much as the entire circuit will see (with the Cisco power supply) and 100V capacitor ratings are plenty more than that. What's really important, audio-quality wise, is the actual type of Wima film caps. The MKP10 and perhaps the FKP4, are the best. Metalized polypropylene is superior to polyester. Wima makes both kinds and many in-between.
 
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moosefet

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I posted a 12SR7 build I did of this in here a couple years ago (this post) and I just built another one for a friend who wanted one. This time I etched the front with control labels. The silly lizard poking his tongue out is a bit of an inside joke and he's also a big tumbleweed fan who have a song called silver lizard. Here's the process:

etchant mask



etch



filled, sanded, clear coat



some hardware



wired up and finished

 
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DrivenKeys

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I posted a 12SR7 build I did of this in here a couple years ago (this post) and I just built another one for a friend who wanted one. This time I etched the front with control labels. The silly lizard poking his tongue out is a bit of an inside joke and he's also a big tumbleweed fan who have a song called silver lizard. Here's the process:

etchant mask



etch



filled, sanded, clear coat



some hardware



wired up and finished

This is one of my favorites so far. Very nice and clean.
 
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Swashinxzero

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Are people still building these? Ive been looking at diy amps and (not that its a issue at all) the starving student is a pretty old design right? How is the amp details wise with a hd600?
If i understand it correctly the 19j6 tubes are not cheap anymore and im in eu sooo... rip:frowning2:, ive seen people modify the amp to use different tubes, wont this result in not ideal performance due to it being designed for th 19j6's originaly?
If different tubes can work just as fine are there any tubes available in europe anyone would recomend for using in a starving student build?

ps. if im being rude or anything pls let me know... first time posting in the first forum ive ever joined..:D
 
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ThermalAlchemy

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Are people still building these? Ive been looking at diy amps and (not that its a issue at all) the starving student is a pretty old design right? How is the amp details wise with a hd600?
If i understand it correctly the 19j6 tubes are not cheap anymore and im in eu sooo... rip:frowning2:, ive seen people modify the amp to use different tubes, wont this result in not ideal performance due to it being designed for th 19j6's originaly?
If different tubes can work just as fine are there any tubes available in europe anyone would recomend for using in a starving student build?

ps. if im being rude or anything pls let me know... first time posting in the first forum ive ever joined..:D
http://www.diyforums.org/SSMH/SSMHoverview.php

this is the original website for Pete millet For the starving student headphone amp

https://diyaudiostore.com/products/starving-student-ii

This is the new location at do it yourself audio.com website store with the newest version and new tubes

I believe on Pete Millets website he had a alternative tube that was used I believed it was a 12AU very common not expensive at all.
I believe on his personal website you can download the Gerber files or the schematics and build your own board on Proto board or etch your own PCB.
I own and have built the very original with the unobtainable vacuum tubes and it’s an excellent match for the SeenHeiser HD 650 headphones

You can also go to Pete’s Ebay online store look for pmillite and through one of these above sources you could go directly to his.com website to read more
 
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tomb

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Are people still building these? Ive been looking at diy amps and (not that its a issue at all) the starving student is a pretty old design right? How is the amp details wise with a hd600?
If i understand it correctly the 19j6 tubes are not cheap anymore and im in eu sooo... rip:frowning2:, ive seen people modify the amp to use different tubes, wont this result in not ideal performance due to it being designed for th 19j6's originaly?
If different tubes can work just as fine are there any tubes available in europe anyone would recomend for using in a starving student build?

ps. if im being rude or anything pls let me know... first time posting in the first forum ive ever joined..:D
ThermalAlchemy pretty much summed it up above!

However, if you are interested in the original without the 19J6 tubes, the 12AU7 change has been successfully built by many on the forum. I'm pretty certain the 12AU7 version works a bit better than the 19J6 version, simply because the 12AU7 is a much better tube. That schematic, with its very few changes, is documented here: http://diyforums.org/SSMH/SSMHvariants.php. Given the simplicity of the circuit, changing to another tube does not have a bad effect on sound quality. It might be different if the circuit was more complicated and highly optimized for a single tube type. Personally, I'd settle on the 12AU7 and go from there.

Remember that the entire theme of Pete's original design was Starving Student. He chose the 19J6 tube because at the time, it was $2 each (even less if bought in volume). Fortunately or unfortunately - depending on how you look at it - the design became so popular that stocks of 19J6 tubes were bought up everywhere within a year or two. Now, it's become a rare tube. No dealer has them in stock in useful numbers (100 or more) anywhere. So, given the laws of supply and demand, the price went up - so much so that the more expensive (and plentiful) 12AU7 became an economic alternative. Use of the 12AU7 is not all because the 19J6 is scarce/expensive; it's also an inherently better tube, period.

The downside is that you are locked into about $30 for a pair of tubes (or much more, if you want to spend it). That's almost the same price as the entire Bill Of Materials (including the original 19J6 tubes) when Pete first design the amp: $35.80 (minus casework).

That said, Pete's new Starving Student design attempts to hearken back to that original premise, with another type of inexpensive tube. You have lots of choices - all of them good. :)
 
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Swashinxzero

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ThermalAlchemy pretty much summed it up above!

However, if you are interested in the original without the 19J6 tubes, the 12AU7 change has been successfully built by many on the forum. I'm pretty certain the 12AU7 version works a bit better than the 19J6 version, simply because the 12AU7 is a much better tube. That schematic, with its very few changes, is documented here: http://diyforums.org/SSMH/SSMHvariants.php. Given the simplicity of the circuit, changing to another tube does not have a bad effect on sound quality. It might be different if the circuit was more complicated and highly optimized for a single tube type. Personally, I'd settle on the 12AU7 and go from there.

Remember that the entire theme of Pete's original design was Starving Student. He chose the 19J6 tube because at the time, it was $2 each (even less if bought in volume). Fortunately or unfortunately - depending on how you look at it - the design became so popular that stocks of 19J6 tubes were bought up everywhere within a year or two. Now, it's become a rare tube. No dealer has them in stock in useful numbers (100 or more) anywhere. So, given the laws of supply and demand, the price went up - so much so that the more expensive (and plentiful) 12AU7 became an economic alternative. Use of the 12AU7 is not all because the 19J6 is scarce/expensive; it's also an inherently better tube, period.

The downside is that you are locked into about $30 for a pair of tubes (or much more, if you want to spend it). That's almost the same price as the entire Bill Of Materials (including the original 19J6 tubes) when Pete first design the amp: $35.80 (minus casework).

That said, Pete's new Starving Student design attempts to hearken back to that original premise, with another type of inexpensive tube. You have lots of choices - all of them good. :)

Thank you !! both of you!

looks like im prob gonna start planning a SS build around the 12au7 (ECC82 in eu i think ?) tubes. my electrical knowledge is literally rudimentary at best so this is gonna take a while:D

Thanks again!
 
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I know I'm a bit late, but I recently built my first Starving Student with 12SR7 tubes instead of the 19J6. I swapped all the capacitors and resistors according to a schematic I found here. Did a couple modifications (adding a 3.5mm input and changing the Pot to 100k since my 50k was faulty on arrival), shouldn't be the problem though. Anyway, it works, but the bass is non-existent. It's like the volume for frequencies below ~800 Hz Drops linearily. It sounds weird, and kind of cool on some instrumental songs, but obviously not what I was hoping for.
Can post pics if needed.
I'm also very new to audio and DIY, so any help would be appreciated.
 
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Tjj226 Angel

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I know I'm a bit late, but I recently built my first Starving Student with 12SR7 tubes instead of the 19J6. I swapped all the capacitors and resistors according to a schematic I found here. Did a couple modifications (adding a 3.5mm input and changing the Pot to 100k since my 50k was faulty on arrival), shouldn't be the problem though. Anyway, it works, but the bass is non-existent. It's like the volume for frequencies below ~800 Hz Drops linearily. It sounds weird, and kind of cool on some instrumental songs, but obviously not what I was hoping for.
Can post pics if needed.
I'm also very new to audio and DIY, so any help would be appreciated.
We will need a schematic.

Right off the top of my head, I would check the value of your output capacitors. They should be like ~300-400uf. The stock schematic says to use 150uf capacitors, but that will only work with higher impedance headphones.
 
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FIz3r0

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Can't figure out how to post pics right now, linking from imgur gives me an error message. Maybe because I don't have enough posts.
I used Logistics' schematic (only changes being the mods).
The output caps are electrolytic ~400uF ones. Actually, I'm using 3 capacitors wired in parallel for left and right. Don't know if that makes a difference.

Used to have 150 uF, but it didn't change much from what I could hear.

My headphones are 250 Ohm (DT1990s)
 
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Tjj226 Angel

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Can't figure out how to post pics right now, linking from imgur gives me an error message. Maybe because I don't have enough posts.
I used Logistics' schematic (only changes being the mods).
The output caps are electrolytic ~400uF ones. Actually, I'm using 3 capacitors wired in parallel for left and right. Don't know if that makes a difference.

Used to have 150 uF, but it didn't change much from what I could hear.

My headphones are 250 Ohm (DT1990s)
I see lots of potential spots where you could loose high frequency, but not bass.

Best I could recommend is to start measuring each solder point for voltage. Make sure you give the tubes a minute or two to warm up. Also triple check that the voltage from your power supply is 48v.
 
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tomb

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Can't figure out how to post pics right now, linking from imgur gives me an error message. Maybe because I don't have enough posts.
I used Logistics' schematic (only changes being the mods).
The output caps are electrolytic ~400uF ones. Actually, I'm using 3 capacitors wired in parallel for left and right. Don't know if that makes a difference.

Used to have 150 uF, but it didn't change much from what I could hear.

My headphones are 250 Ohm (DT1990s)
The output MOSFETs are capacitively coupled to the tubes. That capacitor is critical for proper bass response. In the 19J6 and 12AU7 version, that capacitor is 0.1uf and 0.22uf, respectively. It could be that the 12SR7 needs a much bigger cap to connect to the MOSFETs. Generally, there's not much of a downside to making it bigger, except for room. Film caps get very big quickly. Maybe you could get your hands on a 1uf film capacitor just to try?

Just curious also - why three electrolytics in parallel for each channel's output capacitor? If they are all 400uf each (should be 470uf?), there is no perceived advantage to that.
 
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