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Old 29th October 2004, 08:16 AM   #41
janusz is offline janusz  Australia
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Default amp under development

Hi Quazi,

I should have somewhere an article written in mid or later 1990s on quasi complementary amp design. It was in Electronics World. If you would like to get it send me email and I'll scan it and send to you as an attachement to the reply.

I have one quick question for you - where one could buy good quality toroidal transformers (quiet enough to be used in audio) for power amplifiers nowadays? I need 625V 2x40V toroids and these are not typical for the main suppliers such as Altronics, Jaycar, Wiltronics etc. I had a nice supplier of custom made toroids in Adelaide but I am afraid his business went down. The only one I know is Harbuch. Are toroids from Harbuch good enough?

When it comes to components I mentioned these are not so esoteric and usually cheaper than standard quality parts in Australia. The only drawback is that shipment costs are relatively high but with a larger order still it is often cheaper.



Cheers,
Janusz
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Old 29th October 2004, 10:31 AM   #42
quasi is offline quasi  Australia
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Default Hayayayay...amp_man_1 and janusz;

Hey it's Quasi not Qauzi !!!! sheeeesh.


Thanks amp_man_1; Yep thanks for the info and Iget everything except ...Umm....I still don't get it regarding the positive rail drive (it's ok....I'm not that smart). Without the collector of Q7 tied to the +70 volt rail how can it deliver sufficient voltage to the positive rail FETS if the collector is tied only to the 60 volt rail. This means that Q7 can only deliver a max of 60 volts relative to gnd to the gate of the FETS. Problem is, the drain near clipping is almost at 60 volts with repsect to gnd and then the gate needs to be around 67 volts (with load connected) to achieve a 7 volt drive between the gate and source.

Ok...or are you saying that it receives the extra voltage through the base emitter junction of Q7 straight from the Q4? In this case Q7 is basically a diode so do I need Q7 at all?

Or are you saying that I should not worry about the assymetric clipping because the whole thing isn't linear here anyway.

Please try and explain it one more time ...just the relationship of the voltages from Q4 to Q7 and the gates of the FETS. Sorry but I really want to understand this.

Cheers
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Old 29th October 2004, 11:36 AM   #43
quasi is offline quasi  Australia
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Default Hey Janusz

What a coincidence. I currently run 2x Harbuch 625va torroids in my PA amp. These are 60 0 60. I've had these for 10+ years and they seem good in every way.

But you know what? A friend of mine bought an old variac with 3 1kva torroids in it from a metal recyclers. Pulled one apart and indulated the winding (now a primary) then overwound the secondaries. Total price including (secondary windings) about $20 Aus. each with excellent results.

Yes please, I would like to see that article on the quasi amp. Email on the way.

Cheers
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Old 29th October 2004, 12:05 PM   #44
AKSA is offline AKSA  Australia
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Hi Janusz,

For my Australian AKSA customers, I use and recommend highly the Harbuch transformers made under licence from Antrim of Northern Ireland by Peter Buchtmann in Hornsby.

They are better made than even the ILP which used to be sold here years ago from Britain.

Cheers,

Hugh
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Old 29th October 2004, 03:48 PM   #45
AndrewT is offline AndrewT  Scotland
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Hi Quasi,
You are right, the driver needs a higher voltage than the Fet output. Again you are right with the latest schematic, the quasi output Fet must share the -Vrail with the driver. You could add a regulated negative rail to the pre driver stages but you would not gain much by raising its voltage. I asked in another thread about the distortion advantage to swinging the VAS stage over a shorter range between the supply rails but got no response. Your layout gives a higher +Vpk than -Vpk but quasi topology forces this on you.
regards Andrew T.
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Old 29th October 2004, 04:02 PM   #46
Eva is offline Eva  Spain
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I suggest bootstrapping to lift the voltage amplifier supply up to 15V above the power supply rail. This grants symmetric clipping
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Old 30th October 2004, 11:30 AM   #47
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Arrow Commentable thoughts

ok ...ok......Quasi not Quazi

U r rite in this respect, but There must be a phenomena for Asymmetric Clipping occuring at output.
Secondly In full drive conditions The symmetry must be maintained at any cost or u wont hear at output what u have fed at input. There is also a margin of preclipping which also insures that the mosfets aren't subjected to full saturation.

Regards
Workhorse Technologies.
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Old 31st October 2004, 02:38 AM   #48
quasi is offline quasi  Australia
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Default Final Version (I hope)

amp_man_1

On the contrary you have contributed to the final design.

I note your point about the requirement for symetrical rails for the input and driver stages and this is reflected in the final design

Check it out.
Attached Files
File Type: pdf schematic design_ n-mos3.pdf (31.3 KB, 2701 views)
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Old 2nd November 2004, 12:12 AM   #49
janusz is offline janusz  Australia
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Default Antrim toroids

Thanks Aksa and Quasi

for the info on Antrim toroids.

I made an enquiry with HARBUCH asking if their toroids were good for audio PS and Peter replied that they do not guarantee acoustical silence and that I might need a special design. So I told him that in that case I would take one toroid first and if I am happy with it I'd order another one and asked him how should I pay for the order and since then he got quiet!!! I asked him again and ... silence. Is that guy over sensitive or what? Looks that he is not much interested in selling his toroids to every one. What should I do - especially now that you recommend Antrim toroids as really good ones.

Janusz
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Old 2nd November 2004, 07:43 AM   #50
AKSA is offline AKSA  Australia
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Janusz,

You have just discovered that many component manufacturers are unwilling to deal with audiophiles because they ask too many questions, take up a lot of time, buy tiny numbers, and generally make unreasonable demands.

Peter is in fact an honest man, but he is not noted for his refined customer skills. I know where he is coming from; he doesn't care to whom he sells his products but he won't be involved in a design discussion because his time is valuable.

His are the best made toroids in Australia in my opinion. You really can't go wrong.

Cheers,

Hugh
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