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Old 27th June 2010, 08:19 AM   #101
AKSA is offline AKSA  Australia
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Hi KT,

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What is this MAC thing? Sounds interesting!
This is the Melbourne Audio Club, of around 115 members, founded in 1974 IIRC, where I often debut my new amps. I've been a member and office bearer for years. Nice guys, but like all two channel clubs over the years the membership is predominantly older, rather than younger...

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There's so much information flowing like plasma from the bowels of the internet and there's just no way I can keep track of it all. Paul Bysouth keeps sending me things to read! AARRGH!!!
I'm not sure you mean 'plasma', a more earthy description might be in order....
Paul sends me lots of stuff too, Anthony, it's a shame we can't all meet, he is a very clever, highly creative man with a brilliant maths mind - a fully degreed, well experienced EE with an abiding interest in audio.

I'm presently (trying) to lay out a very complex amp of his design - Paul is a devotee of the Alison circuits you have put forward here.

It seems you are making a difference, KT, and remember, don't complain about the pace of the internet, how do you think the old codgers feel, guys like me and Paul??

Hugh
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Old 27th June 2010, 05:17 PM   #102
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I made a difference? To whom?

BTW, I sent you an Email.

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Old 1st July 2010, 10:15 AM   #103
glennb is offline glennb  Australia
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Originally Posted by AKSA View Post
...You are right, CRC supplies. I do it to quarantine the rectifier charge pulses from the speaker earth return currents. This reduces intermodulation; I can clearly hear an improvement. It also looks very cool, and means you can buy more caps of less size.
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Hugh
Yes, this keeps the high current charging and switching pulses in the transformer - rectifier - capacitor loop, away from any audio circuitry. Although, EM radiation can still occur into nearby circuitry. The R and 2nd C act as a low pass filter that takes some of the sharp triangular corners off the waveform from the 1st C. The result is more sinsusoid shaped ripple on the 2nd C and lower peak ripple current. I reckon the R should be in the range 0.22 - 1 Ohm for a power amp and the 2nd C should be at least double the 1st C. Higher R values give lower ripple, but they also waste energy and lower the maximum continuous output power of the amplifier. The 2nd C should also be bypassed with lower value film capacitor(s) or a RC snubber fitted.

The R can also be an L for greater reduction in ripple and higher order harmonics, but to have much effect on the 100 (or 120) Hz ripple, it needs to be at least 2mH - 10mH, or even higher. A low DCR aircore inductor in this range is quite bulky for a typical amplifier and may actually radiate or pick up EM energy (a bad thing). I have been doing some experiments with powdered iron toroid inductors and they are reasonably small, have low DCR, can take the current without heating up, and have basically zero EM radiation and pick up.
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Old 1st July 2010, 10:42 AM   #104
AndrewT is offline AndrewT  Scotland
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your rCrC PSU is good.
I agree the philosophy of making the middle r quite small and also the ratio of 1:2 for first stage C:second stage C.

The advantage offered by replacing the middle r with a small inductor is the extra attenuation given to HF products results from the fast switching of half wave cycles. a few tens of microHenries will do. Try 30 turns (three layers of 10T) of 1mm wire wound around 12mm core giving ~13uH.
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Old 7th July 2010, 06:10 AM   #105
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Originally Posted by keantoken View Post
I made a difference? To whom?

BTW, I sent you an Email.

- keantoken
Hi Kean, Well you told me how to work LTSpice and get sensible distortion plots for one!

thanks!!
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Old 7th July 2010, 11:28 AM   #106
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You're welcome, Pip.

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Old 7th July 2010, 03:09 PM   #107
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Hello keantoken

I agree with audiopip, your LTSpice thread are a must, I learn a lot with your help an the help of other ones in that thread.

And I should say that all you new amps ideas are bringing new blood in the forum.

Bye

Gaetan
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Old 8th July 2010, 01:27 AM   #108
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Yeah, we have to encourage these young guys, particularly when they know more than the old guys
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Old 8th July 2010, 02:15 AM   #109
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Well Kenpeter, Ikoflexer, Bigun, Ostripper and myself tend to cooperate, all of us have our own projects going for the moment and we dip in and out of each other's work. I actually don't look around the forums much, so no doubt I've missed some things.

I wouldn't say I know more than the old guys... I might seem knowledgeable because I've soaked up a lot from the discussions here, but I haven't been able to apply most of it to practical application. So my skill or lack thereof is "awaiting approval".

Thanks for the encouragement,
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