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Old 11th July 2005, 07:49 PM   #21
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Hi Hugh,

What an incredible length of time it has taken me to come up with such a simple circuit.

I have run it with a VN66AFD voltage amplifier (10th June page) which simulates with much higher open loop gain and thus extremely low closed loop thd. I did not make direct A-B comparisons, but did not notice any real advantage. However this driver does make the output stage become slightly inductive and increases first cycle distortion, thus I choose to stick with bipolar and be reassured that the transient response is excellent and damping control more phase coherent.

I might look at this further, but then I ask myself if it will be worth it because I now have other more significant problems to solve - like source and speakers.

I think Carlos feels like me here, ie. don't mess with it - it is already good, though any suggestions for improvements or variation will be viewed and/or tested with genuine interest, for this 'Diamond' as Carlos puts it, has only just been uncovered.

Simulation shows that a wide range of bias conditions will still provide good results, but my intuitively chosen values give excellent real life performance. The class-A provides sufficient continuous damping until NFB assistance is provided via the class-AB output stage, and as before I have gone for 2 degree limits for phase accuracy between 20Hz and 20kHz, which is aided by the 600 ohm input.. This gives bass instruments real firmness and voices a detailed delicacy. The AB bias can be backed right off so that the circuit acts more like a 'dumper' instead of a 'helper', but I'm not interested in that.

I also tried theoretically superior balanced inputs, but in real life ( and quite different to simulated results ) this impinged upon amplifier stabilty margin This was not worth the risk.

I tried Susan's zero global feedback transformer/Mosfet arrangement, and it really does reproduce extremely smoothly, but for me the lack of low frequency phase coherence and hf detail put me back to expanding upon JLH class-A basics.


Hi Carlos,

I have never come across anyone who builds and tries as many amplifiers as you, and so quickly too !!!
If you lived near Mauro, all our amplifier problems would soon be sussed out.
I am honoured that you have not yet found reason to write that it is 'already in bits', 'in the bin' or 'got the 12 bore' !

I now see that you bring all wires to the pcb - this might be the cause of your oscillation.
My pcb has only four small transistors.
The VAS transistor is deliberately allowed to warm up on the main heatsink to increase its gain.
I have only five wires going from pcb to heatsink. Two thick for power rails. One thick for output. One thin input to VAS. One thin from bootstrap to positive driver. All are kept spaced appart to prevent any unexpected cross-coupling.



Hi Mauro,

This amplifier (she) does well in the known to be unrealistic simulation tests I proposed, ie. examination of a first suddenly starting forward sinewave cycle at 10kHz; reverse injected damping examination, also a suddenly starting reverse injected 10kHz sinewave.
Thus I expected it to cope well with real audio requirements, and it does.

I do not have a clue whether this circuit will come out well in your tests, but its loudspeaker reproduction is good, so it must have something going for it. At least it is something different to add to our selection.


I am taking a break from all the hypotheticals at the moment, but I noticed that reproduction comments were not related to electrostatic loudspeaker types, where the driving requirements are completely different and driver back-EMFs are not a problem.
Some amplifiers are good with electrostatics but not with dynamic loudspeakers, and vice-versa; so an amplifier that is said to be good, should have the loudspeaker type tabulated too.


Cheers ........... Graham.
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Old 11th July 2005, 08:36 PM   #22
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Graham, I have a schematic over GM.25-8, what became of it? The amp Carlos now has built is very similar.
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Old 11th July 2005, 08:48 PM   #23
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Quote:
Originally posted by Graham Maynard
I now see that you bring all wires to the pcb - this might be the cause of your oscillation.
The design sure looks interesting and getting a pcb may be harder than expected because the circuits are a bit "nested", right? Not from one end to the other. It will be interesting to see where this design take us.
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Old 11th July 2005, 09:09 PM   #24
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Hi peranders,

The 25W-8 was not powerful enough. This is.

It might look a bit nested but as Carlos said it can be opened out to look more conventional.

With all the drivers and power transistors on the heatsink it becomes very easy to wire up.

Cheers ........ Graham.
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Old 11th July 2005, 09:58 PM   #25
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Default I spent a long time twisting wires, my slow speed drill is damaged, was a hand work

Also i had to fix transistos, and in this case, i had to produce some insulations too.

I was very surprised that did not take too much time to finish, adjustment was fast and easy, but some care must be taken related the bias adjustment, as trimpot has not limiting resistor to avoid excess of current. When you advance control too much..current can go to 10 amps fast!... but this can be done without problem, with the inclusion of a single resistor.

I continue to listen at it with pleasure, and now it is plugged in my DVD, Pearl Harbour Movie is shaking all home glasses...this amplifier go to very deep bass reproduction, and quality is very good. When the bomb penetrated the ship floor, crossing many stages and stopping in the ship's kitchen.... you can perceive, with details, the bombs delay helical mechanics spining... all voice wonderfull, but not too much emphasized in "S" letters, also rain is rain, and claps are claps, bells sounds as bells too.

As all of you know, it is hard to perceive clapping different from rain, and without a helping image to inform you, some doubts can ocurr, as very few amplifiers can inform that to your brain....well, having that "resolution", we can say that the amplifier is fine.

Related the amplifiers published, of course related the ones i could have or construct, as i can remember, only Graham 25W, Aksa55, Symassym from MikeB and this one....Oh!, the first JLH design have to be included, naturally.

I have here one class D also...but rain are claps and claps are rain...i could not perceive difference, also Sound stage is negative...all sound appear having no deepth, separation is good and dinamics too.

Tube sound is great, and those i mentioned have some "tube" alike sound.

regards,

Carlos
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Old 12th July 2005, 11:35 AM   #26
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Default I was thinking, how deer him be so good in design?

I have a lot of "brain" friends, also Hugh is competent as Graham is....but once, Hugh accepted that made a small mistake..... well, but Graham!.... everything he design runs well, of course, if you know him, as he dislike Miller capacitors, if something oscilate he will blame wires, batteries, conections, boards and everything but his amplifier..... the trick is to put a Miller capacitor if unit start to oscilate overheating the zobel filter.

He is lovely and Great, but were you find love you find hate!...how can he so good this way?

This time i will get him..... i found some "unstable" schematic to give a 12 bore or 12 gauge, double barrel shot!!!....ahahahaha!

The circuit is hot as a hell...this way i will use small heatsink!
To avoid guys discover that i am "preparing the results" i will put a fan over it.

To the output TIP35 will be used
To drivers will use reasonable pair...not so good 2SB1566 and 2SD2395
To Voltage amplifier, the good 2SC4793 (ahahahha!...low gain!!!)
And to differential..... BC556C and BC547C

The circuit has not Miller compensation capacitor...he is a destructor, and also a wonderfull thing when guys know how to use it, as need special material and deep tuning.... changing from 2 to 2 picofarads, the value, hearing sibilants sounds.... a kick in the bull!

This time i will get you!

Of course joking, but some true is hidden inside everything.

I will construct this one, as the one that openned the thread is already deeply tested and i could not find defects...so..could not give a shot over it!

But i have 26 of Graham's circuits.... at least one!...yeahhhh!...at least one i will SHOT!

regards,

Carlos
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Old 12th July 2005, 11:37 AM   #27
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Default Graham may be smiling...this crazy brazilian...

But this time i will get him!

regards,

Carlos
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Old 12th July 2005, 11:38 AM   #28
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Default This one will be pretty full of holes when i shot it!

Will produce a very interesting effect.

Booooom!

Carlos
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Old 12th July 2005, 11:40 AM   #29
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Default I will prepare the board.

Will work a little.... already had some fun for this morning.

regards,

Carlos
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Old 12th July 2005, 11:58 AM   #30
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Quote:
Originally posted by Graham Maynard
If you lived near Mauro
'Mauro' num pais tropical. (Jorge Ben will kill me)

Mmm, Carlos, shouldnt the heatsink fins point the other way around
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