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Millett "Starving Student" hybrid amp - Page 44

post #646 of 6566
7/17/08 at 12:48am
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post #647 of 6566
7/17/08 at 6:15am
Quote:
Originally Posted by -=Germania=- View Post
I am a supreme idiot!

I seriously wired the pins on the socket in reverse!
Yep - it's worth paying attention to the responses

Quote:
Originally Posted by n_maher View Post
snip

Also, I'd swear from looking at those pictures that you have the headphone jack wired wrong. Again, it's a little hard to see in the blurry pics but I just compared it to one of my amps that's sitting here and it sure doesn't look right.

snip
Quote:
Originally Posted by Postal_Blue View Post
X2 That was my first thought. Looks like you wired the switched side of the jack thus breaking the circuit when you plug the headphones in.
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post #648 of 6566
7/17/08 at 8:35am

Grounding question

I've finally got all the parts together and will start my Starving Student in a day or two. As a total newbie, I suspect I'll be posting a fair few questions here over the coming days

First off - I don't intend to go the "ground plate" way. I'm using a metal case and think I'll wire the grounds back to a tag. Do I have to isolate ALL the input and output sockets from the chasis? The rca input sockets and power jack have chasis-insulating washers, but the 6.35mm output jack and 3.5mm input jack don't. Am I going to get ground-loop hum if these components are grounded by the chasis AND wired to ground?
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post #649 of 6566
7/17/08 at 8:52am
here is the latest on mine... It sounds really good.




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post #650 of 6566
7/17/08 at 9:06am
Quote:
Originally Posted by -=Germania=- View Post
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.
You shouldn't be getting any hum. Was the headphone jack the only issue? It would be good if you could share your trouble shooting experience so that if someone else has a similar issue the potential fix is already here in the thread.

Quote:
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.
The gain is very high compared to other headphone amps but as previously discussed this amp's power into 8ohm would probably not be sufficient to drive even efficient speakers. Unless you're talking tiny desktop computer types.
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post #651 of 6566
7/17/08 at 9:20am
Pretty cool, Vixr! I like the Lansing case - we don't see many of those around here. That may change soon, I hope, but it's not a topic for this thread.
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post #652 of 6566
7/17/08 at 10:11am
thanks Tom, This was a really cool learning project for me...P2P is not nearly as hard as I once thought. I had most of the parts and getting the tubes was easy too.
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post #653 of 6566
7/17/08 at 11:03am
^ The noise floor is virtually non-existant....but I can hear a bit of it. I have to admit that its is noisier with even relatively clean sources.

I was able to fix the problem by simply going over data sheets again and realized that I had wired the tube socket in reverse and it was grounding out the tube.

I have to admit that having the ground starred did help me trace things better and figure out the issue. Once that happened, it was darn simple to fix.

I should also mention that I just used some cheap hook-up wire like the kind that you can get at radio shack (stranded) and it worked just fine. I can imagine that this amp might scale well with upgrades on the capacitors (I used 220's on mine - Nicho) in terms of quality and then using better hookup wire (minimizing the length of the tinned copper components). Now that I have one built, I am almost thinking of doing a balanced version!

I have to say that these sound really great. Also, where have you gotten your tubes that glow purple and gold. Mine is a nice gold color, but I might want to try a few different tube brands and see difference.


About using as an amp for speakers. I would say that anything that can be powered by the S.E.X. Bottlehead Amp would run just fine off of this amp. Also, mini monitors or computer monitors would sound really great with this small amp. I have some around somewhere, I will test and get back.
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post #654 of 6566
7/17/08 at 11:24am
Quote:
Originally Posted by -=Germania=- View Post
^ The noise floor is virtually non-existant....but I can hear a bit of it. I have to admit that its is noisier with even relatively clean sources.
It has some noise floor sure, but if you're hearing humming, buzzing or otherwise there's an issue that is not intrinsic to the design. More than likely it's with the grounding but impossible to say for sure not knowing what type of noise you're talking about.

Quote:
I was able to fix the problem by simply going over data sheets again and realized that I had wired the tube socket in reverse and it was grounding out the tube.
Glad you got it working. A small hint for others: some, but not all tube sockets have their pins numbered on the bottom.


Quote:
About using as an amp for speakers. I would say that anything that can be powered by the S.E.X. Bottlehead Amp would run just fine off of this amp.
Say what? The Bottlehead is a trafo-coupled design and capable of about 2W output into 8ohms in stock form. The SSMH puts about 1/2W into 100ohms and .25W into 32ohms so you can see where this is going when you move to an 8ohm load. And there are other factors that make this a pretty poor (if not awful) speaker amp, the first of which is the cap coupled output stage. But as you've demonstrated you don't have much use for my advice so I'll just stop.
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post #655 of 6566
7/17/08 at 11:50am
^ I only say that because I hooked up some cheap bookshelfs to it and they did fine powering it.

It would likely be fine for those computer speakers if you don't want to have two amps (use a switched jack for output to some speaker posts). However many of those computer speakers have a mini input, so there would likely be no need.

I trust your opinion more than my own, but I am just going by experience.

I have yet to hook these up to a set of really nice speakers, but it could make a really good desktop solution to have a switched system and are using those speakers I was talking about (maybe like the ones Travegan sells?).
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post #656 of 6566
7/17/08 at 12:28pm
Quote:
Originally Posted by -=Germania=- View Post
^ I only say that because I hooked up some cheap bookshelfs to it and they did fine powering it.
Define "fine". Made noise, sure, but with those 220uF output coupling caps you said you used you have a -3db point nearing 100Hz (assuming 8ohm speakers). That's pretty non-ideal and if they're closer to four you can double that rolloff point. You'd need to triple the cap value to get a more acceptable number and then you're probably going to start having issues with on/off thump if you don't already. And odds are the amp was clipping even if you weren't hearing it.

Quote:
I have yet to hook these up to a set of really nice speakers,
I would suggest never doing that.
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post #657 of 6566
7/17/08 at 12:52pm
Nate, I used the 220uF caps because I had em laying around. I haven't noticed any problem driving my HD-600s...are the 220uF caps too small?
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post #658 of 6566
7/17/08 at 1:15pm
Quote:
Originally Posted by vixr View Post
Nate, I used the 220uF caps because I had em laying around. I haven't noticed any problem driving my HD-600s...are the 220uF caps too small?
Not for headphones... for 4-8 ohm speakers they are unless you hate bass...

-3dB point:

1/(2 * Pi * R * C) where C is in farads
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post #659 of 6566
7/17/08 at 1:17pm
Quote:
Originally Posted by vixr View Post
Nate, I used the 220uF caps because I had em laying around. I haven't noticed any problem driving my HD-600s...are the 220uF caps too small?
For your Senns and even Grados, they're just fine.

The equation for the cutoff frequency of a high pass filter (which is what the cap coupled output forms with your headphones) is 1 / [2 * pi * R * C] where R is the impedance of your headphone and C is the value of the cap used in Farrads (note that 1uF = 1 x 10^-6F)

In your example R = 300 and C = 220 x 10^-6 so we get a -3db point of 2.41Hz which I think is plenty low.

[edit]Pars is clearly faster, but I provide better examples.
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post #660 of 6566
7/17/08 at 1:44pm
Quote:
Originally Posted by -=Germania=- View Post

I trust your opinion more than my own, but I am just going by experience.
Please, please, please, please...get a clue. They're all over the place, jumping up and down, waving their hands, making incredibly patient efforts to be polite and helpful.
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