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Old 15th June 2009, 03:57 AM   #21
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Quote:
Originally posted by coloradosound
I ... but am still left with 6 amps that could do nothing
more than drive 8 ohm loads! These Acoustats go down
to 1-2 ohms at some of the lower freqs! I thinks that if
I could use single driver boards to run all devices in parallel
it would do what I want much better and maybe going
all out and coscoding the outputs with some large MOSFET'S
ot BJT's and maybe even regulating the output stage as well!
I believe that the only way to drive 1-2 Omhs speakers with an amp with SIT transistors in output stage is to use output transformer. If not, one must get out from the linear (desirable) operation region of a SIT transistor.
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Old 15th June 2009, 08:58 PM   #22
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It's really my experience that if you have such a low impedance load,
complementary source-follower output stages are the easiest way
to go.

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Old 16th June 2009, 04:08 AM   #23
fff0 is offline fff0  Singapore
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For example, F2?
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Old 16th June 2009, 07:41 AM   #24
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Speaking about Single-Ended amps most of us would link this approach to non-low-impedance speakers. On the other hand, many of us will say that such speakers are usually not champions in bass reproduction. So, typical conclusion is that SE amps are for jazz and light music, not for rock or classics.
With my Paradigm Studio 100 v4 it would be better not to deal with SE. Nevertheless, as a stubborn child I try to adjust the SE Zen9 to difficult load. Why? Because I like Zen9 or FirstWatt F3 sound, and many others like it as well. For instance, LM3886 also sounds not bad, but it is not my preference.
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Old 16th June 2009, 10:12 AM   #25
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For those who think about more power from Zen9, I would propose to look at avionics LDMOS transistors manufactured by NXP (Philips).
They are 700W, 0,15deg/w, 75V, 45A, 9S, low parasitic capacitances (their usual application - 1 GHz amplifier).
But, be prepared for very high price. Datasheets are enclosed.
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Old 16th June 2009, 10:54 AM   #26
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Maybe even better will be 110V LDMOS transistors
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Old 16th June 2009, 06:31 PM   #27
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Quote:
Originally posted by fff0
For example, F2?
More like an F4 with a front end for voltage gain. You might want
to look at the A75 as an appropriate example.

I haven't done anything like this in quite some time because it hasn't
fit the First Watt agenda, but there's nothing particularly difficult
about it.

SE designs are possible, but realistically you will put much more work
into them to get the high current that is easily obtained from push-
pull followers.

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Old 17th June 2009, 04:13 AM   #28
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Nelson of course is absolutely right, for providing enough punch at low frequencies the push-pull follower is an easiest way. Many people built and reported impressions about A75, for instance, Peter Daniel. But in general, for everyday listening, he prefers Aleph. Squeezing out enough bass from SE amp is time consuming and relatively expensive, but it is a price of preserving sweet middles and tops. Possible alternative to high-power SE is bi-amplification, but one can encounter unexpected difficulties on this way also. Did anybody test bi-amplification with A75 and FirstWatt F3 ?
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Old 23rd June 2009, 04:23 AM   #29
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Speaking about mechanical design of class A power amps I would like to vote in favour of monoblocks with external power supply. This idea is supported, in particular, by listenable positive effect of exsessive power transformers, and by possibility of using the same power supply for different amps. In my case I use the same power supply for both Zen9 (shown in post #4) and Zen4 (picture below).
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Old 23rd June 2009, 08:06 PM   #30
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It gets my vote - particularly suitable for DIY.

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