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Old 16th November 2009, 11:00 PM   #941
AKSA is offline AKSA  Australia
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Sheldon,

That was a rueful observation, I cackled quite a bit at that one, never worked for me either!

John,

If you spend your life stirring, you will never get rid of the smell......!

Hugh
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Old 16th November 2009, 11:56 PM   #942
Bigun is offline Bigun  Canada
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I'm back

Business trips calming down, a bit more of my time back under my control.

Just read the last dozen pages, boy it's a busy thread. A busy thread is a good sign. Better to see some 'lively' discussion than apathy.

However, if I go back to the first post I read "Gareth Ingram (aka Bigun) of Ontario will be directing this thread" and based on where things are I think Hugh should fire me

Actually, I like this committee approach. It's better.

So where are we - it's headed to a SE design. Is it the original schematic modified or did we go all the way to CFP or something ?

Cheers,

Hugh
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Old 17th November 2009, 12:14 AM   #943
MJL21193 is offline MJL21193  Canada
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Aww, you guys are too much like tut-tutting old women!

I'm outta here!


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Old 17th November 2009, 12:18 AM   #944
Bigun is offline Bigun  Canada
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Aww, you guys are too much like tut-tutting old women!

I'm outta here!


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Can't stand the heat ?

Love the bike...looks way more fun than amplifiers !
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Old 17th November 2009, 12:27 AM   #945
keantoken is offline keantoken  United States
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I see nothing wrong in microengineering an audio amp.

It is better to be above reproach then below... As long as we're improving the design, why not let it get better? "I couldn't hear the difference" is a poor excuse for coming up with an inferior design (no offense). This is an AKSA project, anyways. Aren't we aiming for excellence beyond reproach?

- keantoken
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Old 17th November 2009, 01:07 AM   #946
AKSA is offline AKSA  Australia
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Hey John,

If you are very lucky, as your testosterone levels drop, you too will become an old woman!! The alternative, if you think about it, is unthinkable!

Never did understand Hardly Movingsons, not enough power, not even for a feisty old woman.....

Gareth,

You've been re-hired!

Kean,

The idea is to do something which really does sound good. This means, in the absence of anything better to measure by, we go for a single ended design, with all its distorting implications. All my experience of amps leads to this conclusion, and particularly with the intimacy and critical musicality of headphone amps where second best is really not acceptable. We don't need big power, so can accept the limitations of Class A, though a formal heatsink might be needed. The amp is very simple at present, I do have other designs, but I want to keep it simple. Nico's point about cap coupling is probably on the money, as a CFP does have wildly drifting offset control. But there are other options, too, such as a rush with se cfp output into a CCS.

Cheers,

Hugh

PS: My choice, something better...
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Old 17th November 2009, 01:12 AM   #947
keantoken is offline keantoken  United States
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Unfortunately I'm sort of out of place in this thread since I've only listened to what, 3 or 4 crappy stereos in my life, each slightly better than the one before. All of them through the worst speakers imaginable.

So while I can offer some technical knowledge, I'm not so good at the musicality and sound.

- keantoken
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Old 17th November 2009, 01:25 AM   #948
Curly Woods is offline Curly Woods  United States
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Unfortunately I'm sort of out of place in this thread since I've only listened to what, 3 or 4 crappy stereos in my life, each slightly better than the one before. All of them through the worst speakers imaginable.

So while I can offer some technical knowledge, I'm not so good at the musicality and sound.

- keantoken
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Old 17th November 2009, 01:45 AM   #949
Bigun is offline Bigun  Canada
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SE and CFP sounds great. My current DIY amp project is also SE and CFP so now I only have to think about a consistent set of challenges.

The rush front end sounds good too. CFP is not new, but the combination with Rush would be a road less travelled. And KT, you've already championed this structure in another thread with some passion - which in my view bodes well for it's use.

I could be mistaken, but did we drop the line-out connections along the way ? - I hope not, the SE Rush-CFP could make a unique pre-amp option.

With a CCS load on the CFP we have the possibility to keep this simple and I like the implication that there would be a constant current draw on the power supply and I think this would a good thing for overall performance.

I am not at all afraid of an output capacitor, don't have to worry about dc drift or hurting somebody's expensive earphones.

How important is the CCS load for the 'sound' - would the use of a MOSFET be worth considering here so that we can stop worrying about SOA and temperature dependence ?

On another topic, I saw some nice drawings for the front panel. I do like the more symmetric layout with the large control placed in the centre. And I agree 100% with KT, the power switch should go where a drunk listener can find it - perhaps the chasis could be designed to support a pint ?

p.s. I like the Harley... it's the bike that gets the girl.
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Old 17th November 2009, 10:31 AM   #950
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Default Question about constant output current

Thinking about the single ended amp it struck me that if we kept the current through the output transistor constant then it would potentially reduce the distortion. Modelling the circuit (32 ohm load 45ma peak current through it) with an extra current sink which sinks an inverted version of the current through the load in parallel with the CCS reduced the 2nd harmonic from -65 to -80dB and the third from -65 to -106dB in my simulator. These are reasonably large reductions if they could be achieved in practice.

I don't know much about amplifier design (although I have learnt quite a bit from this thread) so my question is are there common circuits that keep the current through the output transistor constant or does the whole idea fall down in practice (simulations cancelling 80% of the current variation in the output transistor gave 2nd and 3rd harmonics of -71 and -98dB respectively so the cancellation needs to be fairly accurate the reap significant rewards).

My sketchy (and possibly flawed) idea for an implementation would be to use a small resistor between the +ve supply and the emitter of the output transistor to monitor the current through it and to somehow regulate the current sink to keep voltage across this resistor constant. If the voltage drop is constant it should not affect the operation of the cfp if the value of the collector resistor of the input transistor is adjusted slightly.

Nico - its great to see you back, I have learnt a lot from your posts

Best wishes

Phil
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