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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: Links to Schema posted by grege on November 9, 2002 at 03:19:35:
How's that for an answer?Let's look at the differences here.
If you build the original low TIM amp without the pre-drivers, the bias and output stage will be identical to the AKSA. The front end will have three more transistors.
A single transistor will have less noise than a diff pair will. My VanAlstine MOSFET 120 was a good example of this minimalist design philosophy. It makes the AKSA look complex.
But a dual diff pair will have less noise than a single transistor and is better able to reject power supply noise.
The second stage of voltage gain, sometimes called the Vas, is just as important. The big problem here is that a single ended stage slews faster in one direction than the other, this makes for poor linearity. Most amplifiers use an active current source here and this looks good on paper, but doesn't always sound the best. McIntosh has used a simple resistor here without even a bootstrap capacitor, my MC2120 sounds great. They get around the problems by using a regulated supply for the diff pair and a very high voltage supply with a very large value resistor to go with the single Vas transistor.
If you use a dual diff input you can drive a second Vas transistor and skip the bootstrap cap and not have to worry about fancy supplies.
Using off-the-shelf unmatched transistors and no feedback at all, the Leach topology is capable of about 0.5%THD and 40Khz bandwidth. If you match the transistors you can get that down to 0.05%THD, if you think that matters.
With a modest amount of feedback applied to an already good working design it only gets better.
The added cost; about $0.50, and complexity; three small plastic transistors, are well worth it for the sonics (IMO).
If you use the published board layout you can always add the short circuit protection later if you find you need it.
If you need 500W at 2 ohms for PA all you need to do is add one more pair of outputs and build it as published. I've never heard a better sounding amplifier for PA.
If you think you need more power there is always the Super Leach.
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Follow Ups
- Yes-No-Maybe - djk 19:47:08 11/09/02 (3)
- Re: Yes-No-Maybe - weinstro 11:37:10 11/12/02 (2)
- Re: Yes-No-Maybe - djk 01:05:03 11/13/02 (1)
- Re: Yes-No-Maybe - aksa1@optushome.com.au 22:26:15 11/14/02 (0)
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