[bperboy]

So, I was thinking about my Millett today, and I was wondering what those little caps do on the BJT position for the MOSFET edition. I've been running it however long without them, should I add them in?

 

[ericj]

They give that FET gate capacitance equal to it's mate.

 

[bperboy]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif They give that FET gate capacitance equal to it's mate.

Ehh? So I should get a few of those?

 

[IcantHearU]

Just a quickie - aren't the recommended heatsinks generally the anodized aluminum type and therefore they really don't conduct from either the transistors or the regulator - so, aside from being cautious, there really is no 'need' for the insulating mounting kits?
I ask becasuse I've been guilty of touching the heatsinks on two different MOSFETS/etc.(on my M^3) on numerous occasions with no ill effect, whereas if the heatsinks were electrically tied to the transistor, there would exist the possibility of creating a bridge and therefore a short?
Thanks

 

[ericj]

Quote:

Originally Posted by bperboy /img/forum/go_quote.gif Ehh? So I should get a few of those?

Not sayin you don't know this, but, i'm sure some others don't, so, here's a basic overview.

People sometimes overlook the way that most discrete components exhibit some electrical characteristics other than their primary characteristic.

Thus, resistors generally exhibit some inductance, capacitors have an equivalent resistance, inductors exhibit some ohmic resistance, and nearly everyone agrees that many capacitors exhibit some tiny amount of inductance. But there's at least one guy who insists that capacitors can't have inductance.

Inherent in the construction of FETs is some capacitance on the gate.

irfz24 and irfz34 are complementary but one has more gate capacitance than the other. Adding that capacitor makes their performance more similar.

 

[tomb]

Quote:

Originally Posted by ericj They give that <MOS>FET gate capacitance equal to it's mate.

Quote:

Originally Posted by bperboy /img/forum/go_quote.gif Ehh? So I should get a few of those?

Amb says without them, it results in an assymmetric wave of the signal from the N-channel MOSFETs. I'm not exactly sure what effects you may hear from that that, if anything, but it probably wouldn't test well.

 

[tomb]

Quote:

Originally Posted by IcantHearU /img/forum/go_quote.gif Just a quickie - aren't the recommended heatsinks generally the anodized aluminum type and therefore they really don't conduct from either the transistors or the regulator - so, aside from being cautious, there really is no 'need' for the insulating mounting kits? I ask becasuse I've been guilty of touching the heatsinks on two different MOSFETS/etc.(on my M^3) on numerous occasions with no ill effect, whereas if the heatsinks were electrically tied to the transistor, there would exist the possibility of creating a bridge and therefore a short? Thanks

I assure you I'm not trying to be flippant about it, but heat shrink vs. exposed leads is "cautious," too. You're technically correct, but it's a small scratch away from disaster without the insulator kits - something as simple as too tight with the nut and lock washer, for instance.

 

[amphead]

Quote:

Originally Posted by IcantHearU /img/forum/go_quote.gif Just a quickie - aren't the recommended heatsinks generally the anodized aluminum type and therefore they really don't conduct from either the transistors or the regulator - so, aside from being cautious, there really is no 'need' for the insulating mounting kits? I ask becasuse I've been guilty of touching the heatsinks on two different MOSFETS/etc.(on my M^3) on numerous occasions with no ill effect, whereas if the heatsinks were electrically tied to the transistor, there would exist the possibility of creating a bridge and therefore a short? Thanks

Steve, its just not worth the risk, as Tom said. You will be better off with the "insurance policy". Also,it's time to thank you again for those boutique DBs.

 

[TzeYang]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif So if you wan't to drive your headphones harder, bias the output lower?

my understanding is that it depends on the load you're driving and the voltage level you're listening at.

Just bias it higher so it has a larger headroom and not easily drop out of class A.

 

[tomb]

Quote:

Originally Posted by TzeYang /img/forum/go_quote.gif my understanding is that it depends on the load you're driving and the voltage level you're listening at. Just bias it higher so it has a larger headroom and not easily drop out of class A.

I think amphead's smiley-wink got lost in the translation. I looked hard at that comment and decided he wasn't asking/looking for a correction.

 

[thunder]

For any 1st time builders I've found what looks like a really good priced soldering station that comes with a bonus deal multi-meter if purchase is over 50.00 us$ >http://www.circuitspecialists.com/prod.itml/icOid/7307 This seems like good priced way to get started ! If anyone has had experience with this Co and or its products please let me know. Thanks

 

[ruZZ.il]

although if 'harder' means to be 'pushing to the limits of loudness without concern of maximum quality', whilst trying not to overheat/burn out the transistors.. then I'd guess bias lower, yes. but you may as well build a different type of amp then or, I may be wrong..

 

[eddiewalker]

It was a close call after I got everything set up and biased, then couldn't get any sound output. Luckily all it took to make my new Max live was to reorient one of the diodes in the muting circuit.

Thanks to everyone involved. I'm enjoying this thing so much I'm going to have a hard time turning it off to figure out casing.

 

[ruZZ.il]

congrats!

glad you got it figured out.
specs?

 

[amphead]

My guess, is that biasing the DBs at a lower voltage produces more boom with less clarity, maybe more harmonic distortion. The available voltage swing would be less, as TzeYang says about the headroom. This results in clipping of the signal if driven harder, with the extra current pumping the headphones drivers. Usually not what you would want. Thus biasing the DBs higher, resulting in less current flow, but without harmonic distortion induced by clipping of the signal? Thoughts?