Simple Killer Amp - Listening impressions - Page 2 - diyAudio
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Old 1st January 2006, 12:35 AM   #11
lineup is offline lineup  Sweden
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I think inner details are overrated.
The outer details I find more important.
The details between these these two extremes, including lower and upper details,
should always be present, in my opinion.

I prefer a good overall performance, that does not disturb the music I listen to.
Lack of some inner details is no big problem for me.
Especially with more heavy pop music played with electronical instruments.

Think this Killer Amp would be almost perfect for me.
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Old 1st January 2006, 12:45 AM   #12
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Hi Francis,

Had I known you would be running the amp directly from a 10K pot, I would have suggested reducing that 1nF polystyrene input capacitor even as far as 100pF, to restore detail at mid settings where source impedance is as high as 2.5K + the 1k of the input filter. In reality it only needs to be large enough to ensure stage bandwidth for the bootstrapped diff'l stage. It's something Chicco and I discussed at length recently in the SKA thread.

there are those of us that believe there is always something lost, however small, when you use such passive sourcing. But it's sooo convenient with CD source.

I'll have to recommend this in the assembly instructions.

Cheers,
Greg

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Old 1st January 2006, 02:43 AM   #13
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rellum-
), I will increase the bias (have to
mod some resistors that are actually a safety for not overbiasing) and test
class A performance. From what I can hear now, it will be putted in a
cabinet and not dismantled like many others.
---------------------------------------------
this guy has been modifying the circuit without consulting the designer no wonder the performance is varied, take a look what
modification is about to be done next! it is not a simple as that
mate! if youre after top performance

Regards
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Old 1st January 2006, 02:56 AM   #14
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Hubert-
"macro-dynamics"

i dont know, what you mean by that, how is that defined scientificly? please help

thanks
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Old 1st January 2006, 03:01 AM   #15
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Hi Mastertech,

The amp uses open cct sensitive pot biasing and limits the available range deliberately. So, for Class A biasing, lower values of CCS biasing resistors must be used. Francis knew this and was simply commenting that he will need to ascertain the best values so that Class A biasing was at the the top of the available range, with the supply voltages chosen.

He did, in fact, contact me privately over this and, with his extensive practical experience, found quite capable of setting it for his needs with little input from me.

He's simply exploring the design and what it can do. It's his prerogative.

Cheers,
Greg
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Old 1st January 2006, 03:16 AM   #16
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Lineup-
I prefer a good overall performance, that does not disturb the music I listen to.
Lack of some inner details is no big problem for me.
-----------------------------------------------
what constitutes overall performance that doesnot disturb music

"Lack of some inner details is no big problem for me." ? hmm

lack of it is disturbed music...

Reagrds
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Old 1st January 2006, 04:56 AM   #17
lineup is offline lineup  Sweden
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mastertech
it is very few recordings that have inner details
so, this is no problem
as long as all normal details are there

as mastertech pointed out, this is not 100% standard setup
amplifierguru however says he think is no big problem
with rellum version


but here is my general reflection:
----------------------------------
My first reaction also, was that this listening test
was not done with the recommended setup.

An amplifier is a system within itself.
It is designed to work good as system.

Also this is a little system within a working environment.
This is power supply, input source and output load.
It can be more or less tolerant to different environments,
but designer had surely some specific requirements
in mind when making design.
Some important factors are for example
voltage and current capacity of power supply and impedance of load connected.


Listening impressions from this test is not the final word,
even if it can give some little hints and is very interesting.

I am sure will come other verdicts here
with a setup that follows instructions 'in the book'.

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Old 1st January 2006, 05:34 AM   #18
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Quote:
Originally posted by amplifierguru
Hi Mastertech,

The amp uses open cct sensitive pot biasing and limits the available range deliberately. So, for Class A biasing, lower values of CCS biasing resistors must be used. Francis knew this and was simply commenting that he will need to ascertain the best values so that Class A biasing was at the the top of the available range, with the supply voltages chosen.

He did, in fact, contact me privately over this and, with his extensive practical experience, found quite capable of setting it for his needs with little input from me.

He's simply exploring the design and what it can do. It's his prerogative.

Cheers,
Greg
Greg,

Do you think the design will benefit from more class A?

It will be interesting to see if there is any audible
difference.

Cheers,

Terry
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Old 1st January 2006, 06:43 AM   #19
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Hi Terry,

Yes indeed. Francis is quite capable of reconfiguring the amp from one mode to another so his resultant impressions will be interesting.

I, personally, would like to believe there is nothing in it from low bias AB to Class A. Simply because I have tamed all higher HD to well below -90 dB and 2HD/3HD around -86 dB each at 50mA per MOSFET. Reasonable thought would have us believe such levels are inaudible and well masked by low order HD from dynamic loudspeakers which is orders of magnitude higher.

Let's wait and see.

Cheers,
greg
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Old 3rd January 2006, 04:27 PM   #20
rellum is offline rellum  France
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Hello,

Yesterday I've increased Iq to run one channel at 1.4A and replaced input RC
filtering caps with some silver mica 100pf/500V caps. Good overall
stability. No overrun. Exemplary offset stability. To perform
some comparisons, I decided to run one channel AB and the other class A. I
made some mono listening tests yesterday evening with manual swapping. First
impressions : no changes. Tomorrow, I connected my switcher. It's a self
made one with wired remote controled relays. Many contacts are in parralel,
the off contacts feed a dummy load to keep each amp allways loaded and
ground is also switched to avoid ground loops. The only change that I
noticed when swapping is in the bass region. No more
impact but a fuller bass sound, with slightly more energy. I connected my
scope at the inputs of the amps and with the ADD+INVERT mode had a flat line
in the middle. Connecting the probes on the speaker outputs, the flat line
is somewhat modulated but at low frequency only.
The less efficiency of the bootstrap caps at LF gives less open loop gain
and thus, increase the output impedance. It wasn't noticeable on two way
speakers or with a low bass content on my own one.
In class A, higher transconductance of the output mosfets gives some more
gain that allows for that bass extension. Clearly, this amp has nothing to
gain with class A. Energy waste.
The bootstrap caps could be replaced with some biggers and best quality. The
P mosfets could be replaced with some IRFP9140. Sadly, I have only two of
them on hand and they are not easy to provide.
A more clever solution could be to add an error correction circuit. But not
an Hawksford one, output stage has gain here. Why not an opamp based one
wich action could be limited to the low frequency range ? A bass extender
could also do a nice job...

This amp is clearly a HIGH FEEDBACK design, but a clever one.
Won't suit everybody's taste.

To summarize, it combines : low cost, high power if needed, very low
distorsion, good definition and an incredible softness wich allows for long
listening sessions.

Cheers,
Francis
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