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Millett "Starving Student" hybrid amp - Page 5

post #61 of 6522
4/24/08 at 10:00am
48VDC is what you want.
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post #62 of 6522
4/24/08 at 2:22pm
Quote:
Originally Posted by pmillett View Post
Have you ever actually killed a pair of headphones? It's pretty hard to do.

I've done a lot of very bad things to many pairs, and so far only fried one pair of Grados.

I can say for certain that they won't stand 300VDC.

Pete
So the e22 circut isnt needed?
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post #63 of 6522
4/24/08 at 3:02pm
Quote:
Originally Posted by malldian View Post
So the e22 circut isnt needed?
Kind of goes against the idea of "super cheap" amp to spend almost the same amount of e12

It's still not recommended to send large amounts of DC to your headphones, even for a short amount of time. It might not "burn" them, but it definitely isn't anything that would be good. I've blown a couple of KSC75 while testing, it's not particularly easy, they don't like 12V DC sent through them for a second during startup, but they absolutely hate getting it for 30 seconds. That's how I burned one of the drivers.

You can always add on a time delay as per the scraped down version of e12 used by the Millet MAX, that only costs a couple of dollars, I built one for my integrated amp, mostly for peace of mind.
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post #64 of 6522
4/24/08 at 3:51pm

Balanced Diet for Starving Students

For those of you looking for a more balanced diet, here is a balanced version of the starving student. This is totally untested, and is just a suggestion of where to start if you are so inclined.



It adds a small input transformer ($10 each, available from http://www.edcorusa.com/products/tra...sm15k-15k.html) and does away with the output caps (note that you may need a small trimmer in line with one of the heaters to eliminate DC offset --- depends how consistent these tubes are). It also draws double the current, which means you'll either need two of the recommended Cisco power supplies (dual mono) or you'll need a beefier supply. The cathode bias resistor value is half to maintain the same bias on the tube, but otherwise parts values don't change much.

Also, please note that the output sits up about 19V above ground, so the output cannot be referenced to ground, and it will not play well as a preamp without taking some precautions.
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post #65 of 6522
4/24/08 at 4:00pm
Quote:
Originally Posted by FallenAngel View Post
You can always add on a time delay as per the scraped down version of e12 used by the Millet MAX, that only costs a couple of dollars, I built one for my integrated amp, mostly for peace of mind.

Is there some kind of schematic available for just that part of the circuit?
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post #66 of 6522
4/24/08 at 4:21pm
Quote:
Originally Posted by J.D.N View Post
Is there some kind of schematic available for just that part of the circuit?
Of course, check out the e12 Delay under the Tweak section of the Millet MAX site

Millett Hybrid MAX e12 Delay

Total cost is about $4
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post #67 of 6522
4/24/08 at 6:20pm
Quote:
Originally Posted by FallenAngel View Post
Of course, check out the e12 Delay under the Tweak section of the Millet MAX site

Millett Hybrid MAX e12 Delay

Total cost is about $4
$3.50 of that $4 is for the dadgum relay.

EDIT: There's still a power supply issue - somebody's got to burn off 24V(!) somewhere or change a lot of that circuit. I already offered an opinion on using it, though, so I won't repeat it.
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post #68 of 6522
4/24/08 at 7:23pm
Quote:
Originally Posted by tomb View Post
$3.50 of that $4 is for the dadgum relay.

EDIT: There's still a power supply issue - somebody's got to burn off 24V(!) somewhere or change a lot of that circuit. I already offered an opinion on using it, though, so I won't repeat it.
Come on, a master tinkerer like you can find a way around it

Damn, LM317 is out of the question because it only handles up to 37V, but an LM317HV can do up to 57V - how about we use that to drop 12V, then we use a cheapie LM317T to drop another 12V and we have our 24V e12 PSU costing about $3

Shouldn't be a big problem without overheating, the e12 eats basically no current, TO220 regulators shouldn't get too hot.
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post #69 of 6522
4/24/08 at 10:16pm
Yes, well - maybe. The thing is, Colin's implemenation of the circuit is already regulated from 24-27VDC down to 10-12VDC. That burned enough Watts at the current use of the relay (16.7ma) that he had to substitute the TO-220 BD-139 instead of a TO-92. With the Starving Student we'd need to go a total about three times that heat dissipation.

However, there are 48V Omron relays in the very same series - that might be the answer.

I wonder if Pete or Nate could actually measure the voltage spike from turn-on to cap charge/MOSFET bias. That might calm some concerns.
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post #70 of 6522
4/24/08 at 11:08pm
.
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post #71 of 6522
4/24/08 at 11:24pm
Quote:
Originally Posted by bhjazz View Post
Regarding the Cisco power supply: specs on it look like 48V @ 0.38A. Should that PS be difficult to source (well, just in case...) would a 48V supply be okay @ 1A? 2A?

And, just to be sure: the Cisco is an AC/DC supply, is that correct? Pete's webpage describes the tubes as running on 19VDC.

Thanks!
I think that those amperages will be find, the amp will only use/take what it needs.
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post #72 of 6522
4/25/08 at 12:04am
Quote:
Originally Posted by dsavitsk View Post
For those of you looking for a more balanced diet, here is a balanced version of the starving student. This is totally untested, and is just a suggestion of where to start if you are so inclined.
You read my mind! I was thinking 'starving student under $100 balanced amp' and boom...here's a starting design.

This place rocks! Thanks dsavitsk!
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post #73 of 6522
4/25/08 at 12:19am
Well jazz, if you're not too starving Pete and I have been working on something a little bigger for the past couple of months.
It's not a hybrid, in fact it's all tubes and it's not for the feint of heart or wallet.

Anyone who wants to see or listen to it should swing by CanJam table 13. I'll be publishing the design when I get back and can polish the documents.
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post #74 of 6522
4/25/08 at 12:44am
Ouch! I'd be shouting SWEET, but alas, I won't be able to make the cross-coutry trek to Florida. Damn. Damn. Damn. I suppose I should complete the basic premise of this one plus the other few I've started so I can clear my plate for your all tube surprise. Cool.
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post #75 of 6522
4/25/08 at 12:59am
Quote:
Originally Posted by n_maher View Post
Well jazz, if you're not too starving Pete and I have been working on something a little bigger for the past couple of months.
It's not a hybrid, in fact it's all tubes and it's not for the feint of heart or wallet.

Anyone who wants to see or listen to it should swing by CanJam table 13. I'll be publishing the design when I get back and can polish the documents.
Now that this is the second bombshell in less then two weeks, CanJam sounds like its going to be the blast.
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