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Millett "Starving Student" hybrid amp - Page 8

post #106 of 6522
5/2/08 at 4:52pm
Quote:
Originally Posted by Gross View Post
Vacuumtubes.net is half the price of tubedepot.com. oh well.
Nice! I'd never heard of them before. I've had good luck ordering form tubedepot as well (understanding, of course, that they are out now...heh...don'tcha wonder what they think when they get runs on tubes like this all at once from us DIY monkeys...haha...)
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post #107 of 6522
5/2/08 at 4:58pm
I ordered my tubes from RadioDaze.com and received my order very quickly. I placed the order on Wed, it shipped on Thurs (from NY), and I received it in Calif. on Monday.

Excellent service!

Scott
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post #108 of 6522
5/2/08 at 6:11pm
Quote:
Originally Posted by srserl View Post
I ordered my tubes from RadioDaze.com and received my order very quickly. I placed the order on Wed, it shipped on Thurs (from NY), and I received it in Calif. on Monday.

Excellent service!

Scott
Ditto on that!
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post #109 of 6522
5/3/08 at 5:01am
I've read all 8 pages of the thread and I'm not understanding; Is it that if you accidentally leave your headphones plugged in and you turn off the amp, it could potentially damage them?
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post #110 of 6522
5/3/08 at 12:40pm
Quote:
Originally Posted by John E Woven View Post
I've read all 8 pages of the thread and I'm not understanding; Is it that if you accidentally leave your headphones plugged in and you turn off the amp, it could potentially damage them?
And what part of the following you don't understand?

Quote:
Originally Posted by pmillett View Post
Pretty much all single-ended amps with an output cap have a bit of a turn-on thump... but since the bias on the FET comes up somewhat slowly (2k resistor and 150uF) it's not too bad. Audible but not enough to damage anything.
The strength of the turn-on thump is proportional to the size of the output capacitor. With the 150uF specified in the Pete's schematic, the dangers of damaging the headphones are really virtually zero. You can calculate the energies involved, if you are so inclined, and see for yourself. If your phones are low impedance, you might want to increase the output capacitor for deeper bass response. That's OK too, as long as you don't get crazy about it. Putting there 22000uF is not advisable.

Of course, there is no such thing as 100% guaranty and it is your responsibility what you do with your headphones. That is the reason, why responsible people provide careful statements (note the explicit mention of 150uF in the quote above). Especially since this is DIY and DIYers are known to tinker with "approved" designs, often without really understanding them.

Quote:
Originally Posted by pmillett View Post
I have yet to fry any headphones this way, but I can't gurantee there aren't some particulary sensitive headphones that wouldn't like it.
BTW, if you buy a commercial amp, would you first measure its turn on/off transient behavior, or would you just trust the designer/manufacturer? Maybe you shouldn't since there are designs out there that are potentially more dangerous to your phones than this AC coupled "Starving Student".
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post #111 of 6522
5/5/08 at 11:41pm
hey nate what are those little tiny whiskey barrel shaped resistors you used?

Also, anyone know if the all parts are available at digikey (well just those listed as coming from Mouser on the bom)? I usually prefer mouser for their site's "project manager", but I was gonna try to use Panny FMs rather than Nichicons for the electrolytics
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post #112 of 6522
5/5/08 at 11:59pm
Quote:
Originally Posted by pinkfloyd4ever View Post
hey nate what are those little tiny whiskey barrel shaped resistors you used?

Also, anyone know if the all parts are available at digikey (well just those listed as coming from Mouser on the bom)? I usually prefer mouser for their site's "project manager", but I was gonna try to use Panny FMs rather than Nichicons for the electrolytics
FYI - 50V is as high as Panny FM's go. You'll have to use FC's if you want Panasonic.
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post #113 of 6522
5/6/08 at 12:08am
I'm pretty sure that I stuck darn close to the BOM that Pete posted and I don't have access to the parts that I ordered right now. I'll try to double check and post back in a day or so.
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post #114 of 6522
5/6/08 at 12:22am
a couple more BOM Qs...

the film caps apparently are obsolete?

the link for the heatsinks goes to some that are 1.5" tall, but the notes say they should be 2". It looks to me like pete and nate both used the 1.5 inchers, or am I mistaken? And what's the N at the end of the part number mean, besides an extra dollar?

What's the advantage to using that big piece of pcb material for a ground plane? Could you just ground everything to the case if you're using a metal one, or would that be susceptible to interference? What exactly did you do, nate?
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post #115 of 6522
5/6/08 at 9:32am
Quote:
Originally Posted by pinkfloyd4ever View Post
a couple more BOM Qs...
the film caps apparently are obsolete?
It's possible, look and see if it's just an ROHS thing, perhaps an alternate part is already listed. I'll have a look later.

Quote:
the link for the heatsinks goes to some that are 1.5" tall, but the notes say they should be 2". It looks to me like pete and nate both used the 1.5 inchers, or am I mistaken? And what's the N at the end of the part number mean, besides an extra dollar?
Without looking no idea what the N means. And yes, I'm using the 1-1/2 tall version and things seem fine. I'll try and ask Pete if they should have been 2".

Quote:
What's the advantage to using that big piece of pcb material for a ground plane? Could you just ground everything to the case if you're using a metal one, or would that be susceptible to interference? What exactly did you do, nate?
I wouldn't use the chassis as the ground plane, I think it'll open up the possibility of noise. I used a terminal strip at the rear of the amp as a star ground which I then tied to the chassis in one location. Using the PCB material just means less wiring, but more drilling.
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post #116 of 6522
5/6/08 at 1:20pm
Quote:
Originally Posted by holland View Post
My point with the Jameco switcher is that it is awfully expensive for what it is.

You could get a toroid that puts out 1A or more @ 48V and build your own with cheap regulation for about that much and get more current to boot. You can cheap out on the filter caps for some higher ripple or use a whole bunch of small caps in parallel.

If using the LM317 is too hard or costly, you can use the LM7824 and LM7924 and don't use the ground but the + and - rails for the entire 48V differential. A rectifier can be made from 4 diodes and some small caps.

Another note, Jameco has a 24V AC parallel 0.8A split-bobbin for $4. In series it will put out 48VCT AC @ 0.4A.
The wallwart case is a couple of dollars. Add a fuse, wiring, diodes, caps, LM7824 and LM7924 and you'll have a bare bones linear DC supply for less than the Jameco switcher.

Just something else to think about, instead of jumping straight to a $30 PS.

be carefull with not overdoing the capcitance as some regulators are not stable with very large capacitor banks even though they are thought to be (one of those never verified asumptions). EG the 317T has had simulations run on it showing problems >1000uF capacitance.
Second the thoughts on using a lienar regulator though, they are almost always much lower nosie than switchers.
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post #117 of 6522
5/6/08 at 2:58pm
Quote:
Originally Posted by kipman725 View Post
be carefull with not overdoing the capcitance as some regulators are not stable with very large capacitor banks even though they are thought to be (one of those never verified asumptions). EG the 317T has had simulations run on it showing problems >1000uF capacitance.
Second the thoughts on using a lienar regulator though, they are almost always much lower nosie than switchers.
Are you sure that's with a LM317? This is well-documented with LDO's, but not the LM317, AFAIK. The LM317 isn't really an LDO.

For instance, Tangent's well-established, quiet and stable STEPS PS (LM317-based) uses a bank total of 4000uf after the rectifiers.
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post #118 of 6522
5/6/08 at 3:35pm
Guys, all this discussion surrounding LM317's is making me nervous. Isn't Vout on the LM317 limited to 37V therefore rendering it worthless with regards to this amp?
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post #119 of 6522
5/6/08 at 3:51pm
.
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post #120 of 6522
5/6/08 at 4:00pm
Quote:
Originally Posted by n_maher View Post
Guys, all this discussion surrounding LM317's is making me nervous. Isn't Vout on the LM317 limited to 37V therefore rendering it worthless with regards to this amp?
Good point - it looks to me the differential has to remain between 3V and 40V, so I think you're right: 37V limit.

I assume all this discussion means the power supplies have dried up on ebay? That would still be the preferrable source.
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