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Old 2nd April 2007, 05:28 PM   #201
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Quote:
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I think with DIY we may realize a better way in this regard. Nelson, thanks for bringing this forward [/B]
Continuing on with that line of thought...
Now we could run a BIG signal from the preamp (front end?), and put the attenuator in the output stage chassis (F4). This would attenuate the noise on the cables as well.
Neat design as usual, Nelson. Thanks for sharing it with us.
Is it bootstrapping that is enabling the nearly rail-to-rail swing?
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Old 2nd April 2007, 05:36 PM   #202
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yes, interesting isn't it?


good thought NS

A unity gain power <amplifier> with a stepped attenuator at the input, preceded by a high voltage non adjustable linestage/ or source......

Thats out of the box



Edit: You could even make it seem conventional so you don't reach for the volume at the amp under the rack or on the floor. You could take a twisted pear Joshua Tree type relay attenuator and put the pot in the linestage chassis, then implement the relays in the <amp>. A simple 3 wire jumper between the two for control.
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Old 2nd April 2007, 06:37 PM   #203
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Quote:
Originally posted by nobody special
Is it bootstrapping that is enabling the nearly rail-to-rail swing?
There isn't any bootstrapping in this version.

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Old 2nd April 2007, 08:02 PM   #204
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Quote:
Originally posted by Nelson Pass


There isn't any bootstrapping in this version.

Mr. Pass,
You're killing me!
Is it the jfet front end? Isn't there usually a need for 3.5V or so more volts swing than the output rail (each rail) to get it to swing all the way?
Very interesting design.

mpmarino,

I'm thinking about building an X front end using a folded cascoded differential pair running on 80V rails to drive a pair of these bridged. Should be very similar to a commercial pp X-amp, I would think. If I remember right, Nelson has said before that the pp X series doesn't use feedback on the output stage.
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Old 2nd April 2007, 08:07 PM   #205
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Jason's post regarding:
Any boards available for this project?
Quote:
Originally posted by jleaman
Has any one got any boards for this amplifier, id like to buy a set to try this amp out, i think i have adequate heat-sinks too.

J'
Has been moved to : WTB: F4 PCB boards

/Hugo
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Old 3rd April 2007, 01:04 AM   #206
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Quote:
Originally posted by nobody special


Is it the jfet front end?

I think that the jfets are doing just one thing--providing high input
impedance. So, I see F4 as one stage 0dB-gain amp. As simple as
it should be . . . I can't read Papa's mind tho . . .



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Old 3rd April 2007, 04:47 AM   #207
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> I think that the jfets are doing just one thing--providing high input impedance.

And also a low output impedance to ensure high bandwidth for the power MOSFET follower.

> So, I see F4 as one stage 0dB-gain amp.

Spot on. But whether it is one stage depends on whether you define a follower as a stage. The JFEts essentially form a complememntary unity-gain impedance converter.


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Old 3rd April 2007, 05:44 AM   #208
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Patrick,


I fully agree with you about your additional views.
By the way, I considered F4 as an amplifier of current gain.


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Old 3rd April 2007, 06:23 AM   #209
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> By the way, I considered F4 as an amplifier of current gain.

I thought about using that term, but then the gain is dependent on output impedance, which is reactive for a power amp. So I thought I stick to using the term Follower.

PS Following Peter Daniel's comment about the F3, I am thinking that I can couple the (digital) source directly to the input of the circuit in post #185, and perform volume control at the 100R 4W resistor before the 3rd stage (shunting it by a 0R1 resistor would give 60dB). I need to get rid of the 2x 39Rs and replace them each with a magnified diode (using e.g. a TL431 or a BC550).




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Old 3rd April 2007, 07:44 AM   #210
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Quote:
Originally posted by steenoe
Hi Tony I am using 2, 300VA trafos with 2x18V secondaries.
The rails run at about 22V DC, but I didnt take an excact reading.
Its all about apples and pears, allright, but I have no doubt, the F4 is the best sounding amp, that I have ever made/heard! My A-X's are about to be under heavy modification The A-X's might be almost as good in the bottom, but the middle and topend register is much better with the F4! When I first sat down and listened, carefully, I first thought: whats that trembling noise?? I then realised it was the drummers slight touches on the brass's!!
Thats how amazing the F4 is! Drop all your other projects, and go straight to the F4! Beleive me, you wont regret it

Steen
well I am ipressed. if there any diferent with proac 2.5(which is verry fuzzy and untransaprent with low resoliution ) i think I find a new competitor to my 4fets xa 20 . we will build we will see. thanks NP as always for sharing circuits for DIY comunity


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