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Old 3rd May 2012, 09:10 PM   #5081
bcarso is offline bcarso  United States
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Sooner or later 1/f noise will set a limit to signal averaging strategies. But that is usually a long long way down from typical distortions.
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Old 3rd May 2012, 10:47 PM   #5082
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Any of these worth a mention ?

Last edited by nigel pearson; 3rd May 2012 at 10:52 PM.
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Old 4th May 2012, 01:04 AM   #5083
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Originally Posted by simon7000 View Post
I stole the technique from NIST! They used it to measure better than -200 db re 1 V! (100,000 averages.)
I thought I posted that link, they used it to measure the noise on batteries IIRC. In any case the auto-correlation amplifier is an old concept and I still don't see the use of quantifying distortion at these levels.
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Old 4th May 2012, 01:33 AM   #5084
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I'm interested, Ed.
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Old 4th May 2012, 06:12 AM   #5085
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Originally Posted by dvv View Post
Could you give a few examples of what you consider RF transistors suitable for audio power output use? Or did I get something criss-crossed?
Saying RF transistors I mean those bjt with Ft more than 400MHz (I used two kinds, pictures enclosed)
and MOSFETS like those for base stations of mobile networks, I plan to use some MRF, and already used RD100HHF1
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Old 4th May 2012, 06:43 AM   #5086
dvv is offline dvv  Serbia
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Originally Posted by nigel pearson View Post
Ooooooohhhhh, Pivetta! 20,000 Watts!

On a good day, even our own Wayne might be satisfied - for about an hour.
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Old 4th May 2012, 06:56 AM   #5087
dvv is offline dvv  Serbia
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Originally Posted by VladimirK View Post
Saying RF transistors I mean those bjt with Ft more than 400MHz (I used two kinds, pictures enclosed)
and MOSFETS like those for base stations of mobile networks, I plan to use some MRF, and already used RD100HHF1
Wow, when you said RF, you really meant business!

Not to start a blood feud here, but don't you think you're overdoing the wide bandwidth bit?

I mean, I also support a wide bandwidth, especially in open loop mode, but let's keep it reasonable. How much sound improvement can we expect if our OL bandwidth is not say 80 kHz, but is say 500 kHz?

Frankly, I am curious, I never even thought of using true RF transistors as output devices. In addition to that, my own experience has left me very uncertain regarding output device Ft. Specifically, I find that using now rather old Motorola MJ2119x devices, with a nominal Ft given as ">4 MHz", to sound arguably better than more modern, 30+ MHz devices - I get a warmer, more involving sound each and every time. Same thing when I exchange older (vintage) Japanese metal can TO-3 devices with these Motorolas - never once failed to get better sound. Well, "better" as I hear it, but appearently, many of those vintage gear owners as well.

My reasoning is that it's all nice and fine to have wide bandwidth, but on the other hand, the wider you open the window, the more muck and grime is also able to get in.

If your own experience is different, I for one would like to hear about it.
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Old 4th May 2012, 07:31 AM   #5088
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Originally Posted by dvv View Post
My reasoning is that it's all nice and fine to have wide bandwidth, but on the other hand, the wider you open the window, the more muck and grime is also able to get in.

If your own experience is different, I for one would like to hear about it.
I came to using RF transistors at the output during my competition with various tube amps, both DIY (from my experienced in tubes friends) and bought from industry. For having a good reference-competitor, I bought 8000 Euro SE tube 300B amp.
In short, SS SE finally overtaken all tube competitors. This competition was not for profit, but just to proove something to somebody. I speak about quite a serious level of sound quality. But one should forget about achieving such a level, if special tricks in topology, choice of transistors, quality of caps and NFB resistors are not used.
In fact, RF transistors have much smaller Ciss Crss and more flat Crss vs frequency, and by that they are more similar to tubes.

Last edited by VladimirK; 4th May 2012 at 07:43 AM.
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Old 4th May 2012, 09:06 AM   #5089
Jay is offline Jay  Indonesia
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Originally Posted by dvv View Post
Not to start a blood feud here, but don't you think you're overdoing the wide bandwidth bit?
I think the bandwidth it self might not be important. The important thing is what makes it a wide bandwidth one (such as low capacitance) and finally what you can do with device of such parameters in a real circuit.

Of course, most of the time (most systems) a "slow" system sounds more mellow and more listenable. Not many system will be affected by "overdone" system. When there is bottleneck somewhere in the system chain.

This common bottleneck issue can be solved by designing a complete system, from source to speaker. No secondary sub-system should be allowed to increase the frequency of "attenuate-amplify-attenuate-amplify" of the signal.

VladimirK has made an integrated amplifier for example. He has no choice anyway because the amplifier section do not work well alone or with common preamp so integrated approach is a must.

We haven't discussed the other links such as the specs of the DAC chip (if one has NE5534 in the chain, he may miss so many opportunities ), and the speaker sub-system that has so many "non-scientific/voodoo" contents.
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Old 4th May 2012, 09:34 AM   #5090
dvv is offline dvv  Serbia
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@VladimirK

The sheer competitive bet with friends, for say a dinner or something, is the sweetest possible bet. I do know, because every election time, such as now, I bet with my friends on the outcome. They always lose, so I get four or five free dinners. Been like that since the late 90ies.

I figured as much. But my original question still stands - looking the the available bandwidth alone (if that's even possible), what do you gain by extending it over say 10 times the accepted upper limit of hearing, i.e. extending to over say 200 kHz (ref. full power bandwidth into 4 Ohms, at its upper -3 dB point, closed loop)?

I ask about 4 Ohm loads because I don't think there is such a thing as 8 Ohms, not really, although that may work out to be an average impedance, but since I am a fatalist when it comes to loudspeakers as loads, I know there will be dips well below 8 Ohms, very possibly, in fact probably with some wild phase shifts thrown in as a bonus.

@Jay

Agreed, but that was a given. No sense in having a mediocre system powered by an out of this world amplifier. Although, if one is to overdo it anywhere, the power amp would get my vote.

As for the NE op amps, careful there, they a religion in the UK audio business, and those who speak against deities tend to get burned at the stake.

Much like those who think Cordell was off the mark, and Otala was right.
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