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New PCB for shoebox size NAC preamp part I

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You can get rid of most of them, but not in a Naim style (single rail) circuit.

I think any practical system will have some somewhere; either in the signal path, or equivalently, forming part of a servo circuit.

But I don't see why you can't get down to having just one in the path.
 
Thing is, don't want to be the first to try it, :D which is beside the point as mine's yet to be built, I've a sneaking suspicion Jim or Carl are giving it a go anyway or if not why not?

Suspense...
 
about component selection for feedback.

I have 1K RC55Y resistors and MMK's which will be used in the feedback loop but I only have 10K RC55Y's left.

If I use these 10K's for R134/R234 instead of 12K what will be the result?

To my humble reasoning this will provide more signal to a negative feedback loop and result in slightly smaller gain ... or am I full of it?

Nick
 
nickcase said:
about component selection for feedback.

I have 1K RC55Y resistors and MMK's which will be used in the feedback loop but I only have 10K RC55Y's left.

If I use these 10K's for R134/R234 instead of 12K what will be the result?

To my humble reasoning this will provide more signal to a negative feedback loop and result in slightly smaller gain ... or am I full of it?

Nick
Click to expand...

Nick, I've got 11K8 and 12K1 RC55Ys at home - I'll call you.
 
Thanks PD - thought as much.

BTW - how much does x12 equate to in dB?

I'll call you.
Click to expand...

Thanks Carl - cheers for your help with the vol and balance rig for the remote project too :D
 
markt said:
Thing is, don't want to be the first to try it, :D which is beside the point as mine's yet to be built, I've a sneaking suspicion Jim or Carl are giving it a go anyway or if not why not?

Suspense...
Click to expand...


I'm still using tants for coupling.
I'm not convinced they are in any way a limiting factor.

I've tried various different caps here over the years - It's a great way of changing the sound of your system, but not improving it.

If your aim is to truely remove all capacitive coupling from your system, then StarFish isnt going to do it for you : StarFish is built upon the fact that I really rather like what the naim circuits do and I wanted to get the best out of them.
It is possible to re-design the circuit to remove the capacitive coupling, but the topology changes to such an extent that it really isnt the same circuit any more.

It's not all doom-and-gloom though - I dont like to blow my own trumpet, but StarFish is the best preamp I have heard as yet.
I believe there is more to come from it by selection of components and configuration - so get building :D I want your comments on what works and what doesnt...


Jim.
 
Jim,

Really, you've got to give Wima MKS2 a little try, doubled (or tripled) up, very transparent without f*^"ing the music up, I haven't got on with tants so far but another shot won't hurt, maybe the tants I've had so far were a little to high on the rating, cheapest variety, those red Panasonics might be different, a comparison won't hurt.

BTW 0.6w resistors for the circuit can be had in a 0.25w size package via MFS25 Phillips, cheap at Rapid who also have a line of precision resisors from BC/Phillips (TCO 15ppm 0.4w) at around 15 pence each, just not for the feedback though, airy but slow, everywhere else just fine.
 
Oh I get it - so using this:

0cebf8abae5f07a048cc247a351cb8af.png


I can calculate any ratio I like :)

Thanks Martin
 
Jim,

In the Starfish schematic the buffers first positive divider is down as 330k while the original circuit is 270k, have I read it right?
 
Hi Jiim

Thanks for the latest build manual. I am getting off my behind now and am starting to build the beast and she is certainly looking good! I do have a few questions for you! Hope you could assist...oh...its going to be a traco'ed symetrical local regulated version.

1. I would like to use 25V 56 uF SP Oscons for the caps after each regulator as opposed to the Stargets you recommend in the BOM. Any objections? In the past lots of good things were said about these Oscons which is why i am keen to opt for these.

2. What would your preference be for the traco's given the choice? Install just one or two in series? Carl had some problems before with his going poof? Any suggestions what to do here?

3. Is the 27R resistor the best approach for all the "L's" after each local reg? Is an off the shelf inductor available or should we "roll" our own? A while ago, there was a photo of your Starfish with some vertical inductors...and now the build manual shows the use of 27R. Basicaly, what would be the best thing to put in here Jiim? I want to fit and forget ;) Hee hee

Here is a shot of the transistors and tantalums. I personally opted for BC128 as the coupling caps.

starfish2.jpg


Cheers

mark
 
2. What would your preference be for the traco's given the choice? Install just one or two in series? Carl had some problems before with his going poof? Any suggestions what to do here?

3. Is the 27R resistor the best approach for all the "L's" after each local reg? Is an off the shelf inductor available or should we "roll" our own? A while ago, there was a photo of your Starfish with some vertical inductors...and now the build manual shows the use of 27R. Basicaly, what would be the best thing to put in here Jiim?
Click to expand...

These questions are of interest to me too. I noted the previous use of commercial L's too and wondered about the reason for change.

I am also considering options for powering the beast.

Ideally I would like to use a laptop PSU which has two rails 18V and 36V since I can re-task my 'big' PSU. I am concerned about using SMPS to power the Traco (also SMPS) and was considering using a fet VBE in the following manner:

Laptop PSU (36V) >> VBE (fet based dropping 6V) >> Starfish with Traco >> Starfish passive CLCLC filter

This would hopefully clean up some of the crud from the laptop psu before the starfish. I noted also that Carl started off using VBE after his traco's but has since switched to the CLCLC passive filter and the mysterious 'ov regen thingy'. Was this an improvement Carl? What did the output look like on the scope?

My other alternative is use the headamp PSU (75VA, shottky, 4800uF, ALWSR) which supplies a single 24V rail straight into the Starfish and the digital circuits of the 92.

I could just try out both but as I'd rather not have to butcher my 92 and headamp psu to find out. Thoughts welcome.

Nick
 
The laptop psu should work fine, it's definitely worth a try (pics on using a cap multiplier to clean up these here). I think I'd rather do that than share a single reg between the audio and switching sides.
 
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