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Old 26th November 2008, 04:00 PM   #11
SY is offline SY  United States
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A CCS diff amp is an excellent way to go SE to PP. I know that it violates his philosophy, but I'd sure want to put grid-stoppers in.

Understand that this circuit will not be good for all loudspeakers because of the low damping factor. I'd guess that it would pair best either with sealed boxes with lowish QTc or as a treble amp in a biamp setup.
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Old 26th November 2008, 05:27 PM   #12
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Quote:
Originally posted by SY
Understand that this circuit will not be good for all loudspeakers because of the low damping factor. I'd guess that it would pair best either with sealed boxes with lowish QTc or as a treble amp in a biamp setup.
Or almost all the diy designs in the FR forum, on the frugal-horn site, and many on the p10-hifi site.

dave
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Old 26th November 2008, 05:49 PM   #13
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A tried and proven performer is my PP-1C design. The two tricks are the use of a cascode gain/driver stage, which really does improve the sonics over any non cascode topology - and the odd layout around the cathodes of the output tubes.

This makes the amp into a quasi differential amp, with all those advantages, but also allows some peak currents to flow on loud passages, while a full differential design is only pure Class A1.

Will work fine with the iron and chassis you have.

The schematic is at:

http://www.vacuumstate.com/index.tpl...737.7121998302

Scroll down to the bottom of that page, past all the interesting preamp designs.

Regards, Allen (Vacuum State)
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Old 26th November 2008, 05:54 PM   #14
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Take a look on my website for the ST-70 driver circuit listed there, works great with triode connected EL34 and uses a single ECC83 and two ECC82 for a stereo amplifier. It's quite an old design and bears more than a passing resemblance to the Mullard 5-20 circuit. It can be adapted to cathode biased EL34 without difficulty..

Link here: http://www.kta-hifi.net/projects/amp...0amp/st70.html

Design works just fine with point to point wiring - you do not have to make a pcb.

I sold something like 100 kits before I discontinued the business and many people have also made their own clones based on the information here..
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Old 26th November 2008, 06:12 PM   #15
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Quote:
Originally posted by planet10


Or almost all the diy designs in the FR forum, on the frugal-horn site, and many on the p10-hifi site.

dave
Planet10: I'm not sure I got your point.......the design pairs good with these or doesn't have enough damping for these?....


Quote:
Originally posted by Allen Wright
A tried and proven performer is my PP-1C design. The two tricks are the use of a cascode gain/driver stage, which really does improve the sonics over any non cascode topology - and the odd layout around the cathodes of the output tubes.

This makes the amp into a quasi differential amp, with all those advantages, but also allows some peak currents to flow on loud passages, while a full differential design is only pure Class A1.

Will work fine with the iron and chassis you have.

The schematic is at:

http://www.vacuumstate.com/index.tpl...737.7121998302

Scroll down to the bottom of that page, past all the interesting preamp designs.

Regards, Allen (Vacuum State)

Allen: I actually have your PP-1C schematic on my desk...I have a note scribbled on it that it's around 8W class A, is that correct? (I have no idea where that came from..)
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Old 26th November 2008, 07:24 PM   #16
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BW, you asked:

>I have a note scribbled on it that it's around 8W class A, is that correct? (I have no idea where that came from..)<

I seem to remember 10-12 watts, but it's 10 years since I built one.

It was intended as a very low priced kit for Malaysian DIYers through our Malaysian agent, but doing it again I would certainly up the B+ voltages to +400, but no other changes.

If you wanted to do it right, then use a choke input filter, as we use in our PP-2C design, and all our commercial products.

Regards, Allen (Vacuum State)
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Old 26th November 2008, 07:35 PM   #17
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Why use cascodes as drivers?

They suffer from pronounced odd order distortion. It will also be added to the PP output stage that also suffer from the same. Sounds nice in guitaramps but not elsewhere.
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Old 26th November 2008, 08:15 PM   #18
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I've seen the measurements of Allen's cascodes (and my own and Joe Curcio's). Distortion is quite low and quite low order. So they can be designed properly, though I'll grant that I've sure seen a lot of bad ones. The big issue with them is the lack of power supply rejection, but that's not too big a hurdle for power amp input stages.
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Old 26th November 2008, 09:05 PM   #19
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Sy,
It is easy to see by using FFT that cascoded are a lot worse than the same config´d triode. As for Mr. Wrights I did a sim where the FFT was just like his measured. I also did the same with Eriks(Audion, AI etc.) in post 5 and those had a much nicer overtone spectra. This is in theory, if it is the same when you listen to them I can´t say.

I have listened to Curcios (remember this circuit was done in the 70´s) as I did a ST-70 rebuild and I was not impressed. As I said earlier, I love them in my guitaramps TULP-circuit where their overtone spectra come in handy!.

So when you can do something that eventually is better with the KISS principle: Do it!
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Old 26th November 2008, 09:43 PM   #20
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Lars asks: >Why use cascodes as drivers?<

Because they sound GREAT!

If you look at the distortion curves published with my amp's schematic, you will not see any great amount of odd order distortion. In fact in our preamps, without a following zero NFB power stage to add significant distortion, the cascode stage normally has distortions lower than 0.005%, also without any NFB!

They just have to be designed right, using the correct tube run at the correct currents and voltages, and that means hi gM tubes at high currents.

Regards, Allen (Vacuum State)
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