@audiotroy
I'm calling BS. The sound of a tube comes from it's transconductance curve characteristics. Tubes require high voltage because they're very high impedance devices. What you're saying sounds like a lot of sales brochure ad copy pseudo-theory. |
@audiotroy
Sorry, pal, but you're flat out wrong. Only somebody who knows nothing about transistors would say the kinds of things you're saying. The optimum operating voltage for a transistor depends entirely on the characteristics of the transistor and how the circuit loads it. There is no silver bullet in just ramming more voltage through the silicon. You have no business advising people on audio gear, much less selling it. |
@audiotroy
Nope... Not fabbing any dies here, but you kinda learn some of this stuff actually building the circuits and trouble shooting them. I’m certain you’ve never soldered a transistor to a board in your whole life, nor looked at a transistor spec sheet. You speak from pure ignorance and an abject lack of experience. Anybody who’s actually built an amp knows that ramming unnecessarily high voltage through an output stage is plain stupid. It does nothing but limit the bias current, shrink the envelope, and increase distortion.
Take note of how I'm not speculating here. I know what I'm talking about because I've been fiddling with this issue on my modified F5 running hot rails.
@georgehifi
Why do you think BJT’s are good for passing high current? They’re the most prone of all devices to thermal runaway. |
@georgehifi
You talk like only BJT stages do that. MOSFETs have no trouble with that either, and they don't require as much thermal runaway protection.
@audiotroy
More opinion. No facts. Yawn. |
@audiotroy
Measurements are VERY suggestive of how a piece of gear will sound. Measurements are how manufacturers get consistency. Measurements are the best indicator of how one piece of gear will work with another.
If I walked into your shop and you started banging on about the technical merits of high voltage solid state gear, I'd nail you down and expect you to better explain your claim. After all, that's a can of worms you opened. Most salespeople I deal with regardless of product aren't stupid enough to crack open that can of worms because every now and then they run across guys like me. I'm about to buy a new phone. I WILL know more about the phone I buy than the sales guy. Guys around here seem to like giving me jazz about "just" building an amp. I could have built an F6, F4, F3, F2, F1, an Aleph, a SIT, a Burning Amp, some Zen variation, some tube deal, a circlotron, or many others. The decision process took longer than building the thing. I spent a lot of time studying circuits and measurements and evaluating the merits of each given what it needed to drive. In other words, I didn't go listening to mysterious boxes clueless about what was inside or what it did. My interest in this hobby is deeper than that. I must be doing something right because this things sounds better than the majority of stuff folks have tried to sell me on. And I'm sure I've spent a very small fraction of what others have spent to get something similar. |
150 watts isn't exceptional for that amp. It's marginally more than the class A envelope. |
That quote was lifted from the B1 buffer article at passdiy.com. I've toyed with building one. You can buy the PCB and matched FETs for $40 directly from Nelson. There are also a few companies that sell PCBs for stepped attenuators. Just stuff them with resistors. For half the price of the Freya you could build the B1 buffer out. For the price of the Freya you could add relay switched inputs and get the face plate customized.
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Can we clear something up? All passives basically suck. It's unavoidable. Let's not confuse passives with buffers just because the stage isn't making gain. If it's got active devices, it's an active pre-amp.
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@georgehifi
Say WHAT!?!? Where did you get the idea FW amps have no gain? My F5 has about 15.5dB of gain. All but one, the impedance converting F4, have voltage gain.
Real passives expose the source and the amp input stage to the varying impedance of the volume control. You can try to passively remedy that, but the source and amp are always going to see some wandering load or source. Buffering the volume pot or resistor ladder or whatever you like with something like JFETs provides a very high impedance to the pot and a very low impedance to the amp. And there's no reason you can't buffer both sides of the pot. You'll end up with vastly superior performance across the volume range. |
@georgehifi
As far as I know, the active stage I'm using has no gain. The amp section for it has the same input sensitivity as the F5 which is about line level. If it has any gain it's modest at best. Why are you assuming an active stage has gain? What makes you think 25kOhm is a good input impedance for any source? And what makes you think 15.5dB is half if normal? Plenty of medium power amps in the range of the F5 are 15-18dB. |
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@georgehifi
Uh... No... It's a cold, hard fact. Volume pots present a miserable impedance to a source and an amplifier, generally speaking. I could probably feed the F5 with one if I wanted because it's got a 100kOhm input impedance, but if you're dealing with an amp with a more typical 40-50kOhm input, putting a 25kOhm pot in front of it is just plain stupid unless your amp has low enough gain you can run close to wide open. Of course, then you present your source with a feeble impedance then. Sounds very imperfect to me. It's not a solution I'd briefly entertain, much less make my problem. |
@georgehifi
Why do you keep assuming I've used a passive? I never have and I never will. I find it ironic you're sitting there deriding gain in a pre-amp which is almost certainly going to be of a higher quality than gain in a power stage. This is like your silly claims about the superiority if BJT's. It's like you don't have a clue what you're talking about. It hardly matters what the beginning impedance of the pot is because when you open it up it's going to drop massively. Is 2kOhm good for anything? That's the whole problem you can't seem to see. You turn the thing up and now your source is seeing a very meager impedance and your amp is still seeing a relatively steep impedance, the kind you just called "unacceptably high". It all over the map depending on where you put the volume. How are you not seeing that???? |
@georgehifi
I can change the gain of that amp for about $10. No idea why I'd want to since it's all the gain I need. I see you've given up trying to technically justify your silliness. Forgive me if I'm not interested in a volume that doubles as a tone control. |
@georgehifi
Oh? You think 10kOhm is a great impedance for a source to be looking at? If you like nonlinear, volume-dependant sound, have at your passives all you like. Just don't tell me how uncolored they are because that's a demonstrably false statement. |
@georgehifi
Oh.... They're better.... That's why nobody uses them! This from the guy who claims only BJT's can deliver current. Why is a volume that doubles as a tone control better? |
@georgehifi
Pure nonsense. MOSFETs are square law devices less prone to thermal runaway with much high gate impedance. Maybe a single big package can move more, but the penalty for paralleling devices is minor and that's done with BJT's in most practical amplifiers anyways. Glad we're done with this.
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@georgehifi
Na... I'll be done when I decide.
Crack open any of those amps and you'll see significant measures taken in circuitry to discipline the thermal misbehavior of those devices. Maybe I'm just not understanding what you mean as far as "more", but there's plenty of MOSFET amps that will deliver massive current all day long. You make a lot of claims you can't seem to back up and I'm not going to be intimidated by your bold bluster and bullying. |
Kalali, I think your right. He just makes it up. Clearly he's never seen the measurements on a Pass amp or any number of MOSFET amps. He doesn't even know that the limiting factor in an amp doubling it's power isn't even the active devices. |
@georgehifi
Since you're hung up on the doubling power, which you say is impossible, I'll tell you how to do it. Remove the source resistors in the source follower output stage of a MOSFET amp. Guys do that all the time in the DIY world, but you practically never see it in production gear because the line between stable and unstable is pretty fine. You don't really want to try that with BJT's because of their more aggressive thermal runaway characteristics. But, if you use MOSFETs with a big enough heatsink, there's a point of equilibrium and you can build a fairly stable amp. |
@georgehifi
Oh.... We're going to just resort to half-truths and omissions, huh? Just going to ignore the thermal issues, the low base impedance which is a much bigger problem than a little gate capacitance. And how do you make a simpler circuits with devices that basically demand a driver stage? |
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Well lookie there, folks! George and I can agree on something! Class A is the bee's knees! |
