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Old 25th November 2006, 12:02 PM   #1
Fuling is offline Fuling  Sweden
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Default Baby Zen for biamping

Not that Iīm not busy working on my Xsoz, I felt that I needed a little side project too

I have a pair of bookshelf speakers with TB 3" and Peerless 5-1/4" drivers that sounds quite good, actually so good that they deserve biamping with class A amps.
Nothing too serious though, just a handful of components assembled on veroboards an then mounted on a big heatsink that I have leftover from the Xsoz project.

After searcing this forum I sort of fell for the Baby Zen, a small "inofficial" Zen amp with low power mosfets and lower rail voltage/bias current.
A version with dynamic current source is also floating around somewhere.
On top of all this Iīm curious about cascoded gain stages, Iīve read alot about it but never tried it myself.

After some cut nīpaste engineering I came up with these two circuits, A) for the TB fullrange drivers and B) for the Peerless woofers.
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Old 25th November 2006, 12:03 PM   #2
Fuling is offline Fuling  Sweden
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And B, which didnīt make it in the first post:
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Old 25th November 2006, 09:57 PM   #3
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Of the two, I find "A" more intriguing. I'll bet that with a bit more research, you can convert the CCS into an aleph version complete with sensing resistors. Then the amp can drive harder transients without clipping.

John
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Old 25th November 2006, 10:17 PM   #4
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In circuite A the drain of irf510 is only connected to the gate of
irf530. I don`t think you have any current path with this connection.

Woody
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Old 25th November 2006, 10:28 PM   #5
Fuling is offline Fuling  Sweden
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Circuit A) is cascoded and has a static CCS, B) is not cascoded but has a dynamic, Aleph-type CCS. I guess any combination of cascodes and CCS`s is possible, this is only my attempt to optimize for the different frequency ranges in my biamped system.

Quote:
In circuite A the drain of irf510 is only connected to the gate of irf530. I don`t think you have any current path with this connection.
I donīt quite understand, I look at the schematic and I see a straight line between the drain of the IRF510 and the source of the IRF530. The gate of the `530 is connected to a voltage divider for about 6,5V bias and has, as far as I can see, nothing to do with the drain of the `510.
Just for clarity: IRF510 is the input mosfet and the IRF530 is the cascode transistor which keeps the input transistors drain at a constant 2,5V or so.
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Old 25th November 2006, 11:28 PM   #6
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Hello ,
I think that what means Woody, is that the cascoded IRF 530 , althought is biased,does not see any AC modulated signal to it's gate... just thought , but I'm not sure I really understood cascoded stages anyway...I'm still studying it
Vince
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Old 25th November 2006, 11:54 PM   #7
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Quote:
B) is not cascoded but has a dynamic, Aleph-type CCS.
Ah, yes... there's the little Aleph bugger. Why not run B with the addition of a cascoded topology--sort of like blending the two layouts. BTW, I really like the simple way you executed your design.

John

edit: how come the word bug-ger is censored?

Also, Fuling, can draw your prints a bit larger? I can't make out all the values. I'm saving your drawings anyway.

Thanks.
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Old 26th November 2006, 12:20 AM   #8
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Quote:
how come the word ++++ is censored?
Ask someone from the Commonwealth
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Old 26th November 2006, 01:08 AM   #9
Fuling is offline Fuling  Sweden
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Quote:
althought is biased,does not see any AC modulated signal to it's gate...
A modulated cascode would of course be even better, but since I donīt have a source resistor there is no place to get that modulation signal from. At least not as far as I can see.
A "static" cascode should be a significant improvement over the basic circuit anyway, at least I hope so.

Quote:
Why not run B with the addition of a cascoded topology--sort of like blending the two layouts.
Might be a great idea, but somehow I have this prejudice that the active CCS is inferior to a regular one when it comes to microdynamics and stuff. I might be totally wrong here though!
The reason Iīll use it in the bass amps is that I want to have better current capability to drive the woofers.
This whole reasoning might sound silly considering that weīre talking 5W amps that will drive 3" and 5" speakers, but for me this hobby is all about experimenting and having fun.

When finished I will of course try both topologies with different speakers (including my main speakers, not the tangbands) to find out if one of them is significantly better than the other.

I can draw better schematics tomorrow, I did these ones in a hurry at work.

By the way, Iīve spent a couple of hours doing some metalwork tonight and now the PSU is almost finished and attached to the heatsink. The heatsink has about a million M3 tapped holes so itīs kind of building Lego or something
The Fets and everything else should arrive on Tuesday or Wednesday so this shouldnīt take too long to finish.
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Old 26th November 2006, 01:19 AM   #10
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I see you have 23 VDC supply.

Is this from a 18VAC trafo?
What type of transformer and VA rating?
Maybe you use a 2x18VAC,
with each channel using only one of windings?

Tell a bit more of your idea for the power supply.
This is an important part of any power amplifier,
as you know.

How much is the bias idle current for each baby-zen?
In case you haven't already mentioned.

lineup
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