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Air guitar Pre

Hi Graham,
and my my, I might have seen that schematic before, heh. It is indeed very nice and does make the standard naim circuit seem wooly by comparison. found it a bit 'clean' at times but on a split rail, it probably would be something else again and sling in Mr Tibbs' tracos to clean up the ground.... This could be awesome (Well you will know exactly how much so already).
The devil is in the details as ever and now have a bag of questions:
Tried this with the fet? Subjective experiences?
You use no caps at all for powerrail decoupling with superregs- how come? soinic impressions? did you try decoupling rail to rail as well as both rails to earth?
Care to outline the raw psu? How many windings? standard 2 x split rails or maybe 4 windings feeding 2 x +/- rails?
You used some clc filtering iirc?
Double superregs in series also iirc? What were your subjective impressions going from 1 to 2 as didn't do it for me at all.
Keen to hear more and sounds like you've put in some serious experimental hours- good stuff
cheers
Ced
 
laverda said:
Sorry, S-man, I'm not the one who can answer these questions, (I'm as thick as shit) I just build and listen......If its better I keep it, if not, it goes in the bin.

You seem to have the 'know how' with how these things work.......I'm always willing to give a new idea a try......I dont analize (thats for the Gods) they do that very well here. I thank them one and all.

Graham
Click to expand...

Thanks for your honesty, Graham.

Can anyone else provide an explanation for the tweaks in this circuit? It seems strange that whoever added the clever bits missed the opportunity to take out C3.
 
ced

fets? not yet but am thinking along those lines........I've got all the speed (sonic) I think I need for now but then again......

I tried rail decoupling (only to grd) but made no significant difference either way.........a friend (thanks Rob) tried it and worked a treat. I cant work out why mine does'nt see it. Not worried though.......been like it for 8 months now.......and no signs of any probs.

Raw PSU ....ah now then............

two secondaries 600va at the mo, 4 soon though (phased) onto full wave bridges using Philips BYV27-150 or 200's (these have just doubled in price BTW) so that each rail has its own winding. Smoothing is via serised 5.600uf x3 (Avondale cap 6 type) with 10uH air chokes between. Caps are snubbed (0.1uf film and 1r) bridges have a 2.2k accross the output stops em rattling (seems to work) dont know how ar why..........some one might enlighten me.

So this raw smoothed power is then fed to 4 sregs 2 x + and 2 x - 30v out the out then goes to another 4 these are set to 22v out and then on to the last 4 set at 14v. I did find that in this series config the regs need more headroom than the 4v recomended by the great ALW (less than 6v headroom and the first one starts to loos it at about 1k) Each reg has an LCR 13 turns of 0.8 lachqured with 1R on its power in. Though a 1R works quite well on its own.

So whats all this PSU bollocks about..............

low level information retreaval...........atmosphere, each time you add a sreg there's a level of refinement added to the presentation 'space', 'air' depth and speed, this speed (leading edge) has a lot to do with how the Naim sound 'works' IMO, its exciting too listen too.....but in a standard Naim system after a while it gets on your tits IMHO. This is down to the Naim regs.....LT317T's they are very basic.....all be it selected. IIRC two thirds of these regs are rejected by Naim during their selection/testing prosess. They need to speak to some one......about that

I have tried to retain the 'leading edge' (the Naim sound) bit but now its refined and smooth. I can listen for hours with out getting tired of it and with amazing levels of detail with all the spine tingling atmosphere, that music to my ears.

Graham
 
S-Man said:
Thanks for your honesty, Graham.

Can anyone else provide an explanation for the tweaks in this circuit? It seems strange that whoever added the clever bits missed the opportunity to take out C3.
Click to expand...

S-Man ..if you (or anyone else) thinks its worth a tweek just post it here and we'll give it a go.

You comments previously removal of C3 works on CAD..........how it would sound?, we will see (hear).

Graham
 
To give credit where it's due, the modifications shown are based on two inputs: -

1. The dual-rail implementation (my idea, with input and experience from CED and Laverda)

2. The bootstrapping (courtesy of Walt Jung)

The changes increase the open loop gain of the stage (through bootstrapping) and the component value changes are there to keep the quiescent bias conditions the same. The great thing about this is the circuit remains almost unchanged topologically, with no more complexity.

You can't remove C3, the circuit isn't thermally stable enough to support it's removal. Try a monte-carlo or thermal sweep in CAD then look at the output before the coupling cap.

The logical extension of the above mods was a FET input, but I've not (yet) had any significant benefits from that, but the donor preamp wasn't ideal at the time.

Andy.
 
I notice that Laverda commented that decoupling the output of a superreg makes no audible difference - this not surprising, as the output impedance of a superreg (microohms) is waaaaay lower than the esr of even a classy capacitor (few milliohms at best), let alone the total impedance of the capacitor at any relevant frequency (ohms?).

Throwing decoupling capacitors at a superreg is just a waste of money and board space.
 
I notice that Laverda commented that decoupling the output of a superreg makes no audible difference - this not surprising, as the output impedance of a superreg (microohms) is waaaaay lower than the esr of even a classy capacitor (few milliohms at best), let alone the total impedance of the capacitor at any relevant frequency (ohms?).

Throwing decoupling capacitors at a superreg is just a waste of money and board space.
Click to expand...

I'll add a couple of caveats to that, if I may ;)

There are always good arguments for local decoupling (i.e. remote from the regulator) if the trace inductances become significant to the circuit being powered. The super reg is doing nothing useful at higher frequencies, so local decoupling needs to take over, if the circuit requires it.

This is a better solution (practically) than remote sensing, which whilst good on paper brings with it complexities (in terms of potential stability issues) and rarely seems to bring anything sonically :)

Also, it shouldn't be overlooked that the super-reg's characteristics are altered by the output capacitor, since this is the dominant pole in setting the open loop bandwidth, changes here do have audible effects on the regulator itself.

Andy.
 
Graham,

So in summary... You have one transformer (soon to be two transformers) currently with 600va secondaries with +/- ~38-40v raw bridged / smoothed then into 3 super regs in series x2 for one for each channel (I assume). ie 6 + super regs and 6 - super regs. Each SR with a 8v step down. 30>22>14.
 
Andrew L Weekes said:
To give credit where it's due, the modifications shown are based on two inputs: -

1. The dual-rail implementation (my idea, with input and experience from CED and Laverda)

2. The bootstrapping (courtesy of Walt Jung)

The changes increase the open loop gain of the stage (through bootstrapping) and the component value changes are there to keep the quiescent bias conditions the same. The great thing about this is the circuit remains almost unchanged topologically, with no more complexity.

You can't remove C3, the circuit isn't thermally stable enough to support it's removal. Try a monte-carlo or thermal sweep in CAD then look at the output before the coupling cap.

The logical extension of the above mods was a FET input, but I've not (yet) had any significant benefits from that, but the donor preamp wasn't ideal at the time.

Andy.
Click to expand...




The cat has been liberated!

I hope you didn't mind me re-posting your diagram Andy, I thought that there would be a reference to it sooner or later, it seemed a shame to not point it out in light of the potential air guitar order, and, well, it's got a future hasn't it?!
 
Just to move the group buy on a bit, I think I'll do a poll on a seperate thread to see whether pfm-ers want a standard Air Guitar board, updated board (may take a long time) or any other option. I'll wait a little while for any suggestions. If the demand for standard boards reaches the 40+ mark, I'll probably start going ahead.
 
Good idea.

Has anyone tried these split rail gain stages along with Time Align?

<ducks for cover>

Happy to wait for a re-jigged Air Guitar.
 
The link Andy put in that thread to a diagram on his ALW Audio website doesn't work...


Andy, has it been removed?

Jo
 
Andrew L Weekes said:
You can't remove C3, the circuit isn't thermally stable enough to support it's removal. Try a monte-carlo or thermal sweep in CAD then look at the output before the coupling cap.
QUOTE]

If you replace R3 with 680K//560K, then short C3 - the output varies from -0.7V to + 1.2V over the range 0 degC to 100 degC. The circuit is unlikely to see this in practice, so this looks OK to me.
Click to expand...
 
The circuit is unlikely to see this in practice, so this looks OK to me.
Click to expand...

Try it out and see!

This is a difficult one, there's no advantage whatsoever to feeding LF signals into a power amp or speaker setup that it's incapable of handling, or that generates more problems than it cures, but this is balanced against an understandable desire to remove a horrible electrolytic capacitor from a very sensitive location.

Like a lot of this stuff, it's suck it and see, but make sure you keep an eye on the DC bias changes as you run it, and ensure they don't give rise to problems.

I've not analysed this in any detail, it's more a gut feel.

Andy.
 
Further to the comment above, the biggest problem in my view with removing the cap, having thought about it further, is the total lack of repeatability.

The transistor hFE's will vary dramatically and the DCOP will be uncontrolled, over a 10-40 deg C sweep I'm seeing larger voltage shifts than you, but the point is you are relying on a transistor parameter that is essentialy uncontrolled and shouldn't be relied upon.

Yes you can tweak for an individual case, but with any DC gain in the circuit (as you will have with the 47u removed) you are trying to stabilise each circuit on a case-by-case basis and if you ever need to change a device, you've got to do it all again.

This might be OK for a DIY circuit, but it wouldn't be my choice.

I think the Naim circuit is great, but it has limits. Maybe if we want to remove all of these limitations, we should start elsewhere?

Andy.
 
Andrew L Weekes said:
I think the Naim circuit is great, but it has . Maybe if we want to remove all of these , we should start elsewhere?

Andy.
Click to expand...

I too like this Naim circuit or rather the sound it produces, I have thrown lots of PSU at it and it does it for me, big time...........if it has limits lets 'do' a proper one.............or are you just teasing Mr Weekes.

TIA and quivering with antisipation....

Gra
 
I think the Naim circuit is great, but it has limits. Maybe if we want to remove all of these limitations, we should start elsewhere?
Click to expand...

Yes, time for a clean sheet.

Mr Tibbs

EDIT: Hot off the press... PD has delivered?
 
If we/you/us build it .................


They will cum....................


The work bench is clear, iron is hot, flux at the ready............

don't tell me, its an opamp.

Graham
 
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