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Old 12th May 2019, 01:34 AM   #1
onear is offline onear  Australia
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Lightbulb ACA Cascode

Hi all and thanks for being here,

As a first time noob, firstly WOW!! This place rocks. To Nelson P. You are the reason that I'm even thinking about following this path, the inspiration you provide deserves recognition and note!!

Having read much here and at NP's site, And watching the aforementioned on the tube, I have managed to learn enough to be a danger and not enough to truly understand the subtleties inherent in the designs presented. Further delving is hoped to rectify the situation.

So to the question at hand,

I'm thinking of purchasing two (M.Block) ACA (latest iteration) with a mind to running a pair of Tannoy Cheviot speakers. Am I able to cascode such a project? Is such an idea of merit? Can this be done within the chassis supplied? Can balanced and rca be accommodated? Is it worthwhile constructing power supplies to drive the ACA? Can a soft start speaker protection circuit/PCB be accommodated, again within the supplied chassis? Is the ACA the right way to go, or is there a better way? Am I mad?

Whilst thanks is a little previous, Thanks for reading and for any input you might provide!!
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Old 12th May 2019, 03:40 AM   #2
6L6 is offline 6L6  United States
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Quote:
Originally Posted by onear View Post

I'm thinking of purchasing two (M.Block) ACA (latest iteration) with a mind to running a pair of Tannoy Cheviot speakers.
Neat!

Quote:
Am I able to cascode such a project?
...yes? Specifically what are you intending? A little expansion of your intent would be helpful.


Quote:
Is such an idea of merit?
All ideas have merit. Wether it's of enough merit to do something about only you can decide.

Quote:
Can this be done within the chassis supplied?
Maybe? It's not very big, but there is some excess room.


Quote:
Can balanced and rca be accommodated?
Most likely.


Quote:
Is it worthwhile constructing power supplies to drive the ACA?
I'm constantly impressed with the PSUs supplied. Switchers are getting better and better every product cycle.

Quote:
Can a soft start speaker protection circuit/PCB be accommodated, again within the supplied chassis?
Soft Start and speaker protection are not the same thing, and in this example (ACA) not necessary.

Quote:
Is the ACA the right way to go, or is there a better way?
See below

Quote:
Am I mad?
Not at all.

(Or probably better said, "not any more than the rest of us.")







Assuming you want to cascode to get more power, and power being heat (since we're talking about class-A), and this chassis being pretty small, and also the expense of making a bigger PSU, my suggestions are to either 1) build and enjoy the ACA's as designed or 1) skip trying to make the ACA into something different for little advantage and build an Aleph J.
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Old 12th May 2019, 03:58 AM   #3
onear is offline onear  Australia
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Hi 6L6,
Thank you for your informed reply.

The thought behind cascoding is about improving the quality of sound, not power, as the Cheviots are going to do well as is (?) It's about giving the following transistors an easier time with the intent of improving the quality of sound.
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Old 12th May 2019, 04:01 AM   #4
TungstenAudio is online now TungstenAudio  United States
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I'm thinking that the Aleph J may be the closest cousin to a pair of bridged ACAs, being singe-ended class A. The ACA will have a different sonic signature due to its negative H2 (neg polarity 2nd harmonic distortion). The M2 or M2x is a slightly different animal, but sounds wonderful in its own way. A pair of bridged (guessing what is meant by cascode) ACAs with the kit power supplies are pretty easy to assemble, and will give an amazing 3-D soundstage. Compared to building a full dual-mono Aleph J with linear power supplies for each channel, the ACAs are a simpler build. Cost-wise, they are pretty close.

Last edited by TungstenAudio; 12th May 2019 at 04:04 AM.
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Old 12th May 2019, 04:17 AM   #5
onear is offline onear  Australia
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Hi Tungsten,
Thanks for your thoughts, will take the time to read and understand the Alpha J build guides, literature, et 'al.

Have to admit, am nervous of taking it on.
But hey, no way of learning without doing.
Am limited by not having access to scopes, veriac, dummy loads, etc.
Want to be able to do an excellent, not ok, job.

Thanks again.
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Old 12th May 2019, 04:34 AM   #6
6L6 is offline 6L6  United States
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Cascoding allows for higher voltage rails whilst using lower voltage rated transistors. It doesn’t do much else.
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Old 12th May 2019, 06:05 AM   #7
onear is offline onear  Australia
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Hi 6J6,
Ok got it, I had the impression that cascoding had a sonic benefit? Due to reducing the capacticence of the following transistor, have I understood that right?

Thanks again.
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Old 12th May 2019, 08:53 AM   #8
Zen Mod is offline Zen Mod  Serbia
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take a look at Babelfish J , pretty much most straightforward way of making Aleph J

you can make it on veroboard , or even on Store boards with some ingenuity

it'll sound better than ACA with Tannoys ....... fact is that they more prefer 2 dozens of watts than half dozen
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Old 12th May 2019, 10:10 AM   #9
onear is offline onear  Australia
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Hi Zen,
Thank you, I'll go find your recommendation, and endeavour to understand the way to build it.
And yes the Tannoy wattage had raised questions for me, so thanks for touching in that to.
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Old 12th May 2019, 05:13 PM   #10
Nelson Pass is offline Nelson Pass  United States
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ACA Cascode
Also take a look at the F3 ( schematics at Nymeria ) which is a single stage
cascode amplifier that would be similar to the ACA but which lacks the input buffer
because it doesn't need it....

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