advertisement


New PCB for shoebox size NAC preamp part I

Status
Not open for further replies.
IMG_4933.jpg


Had a couple of hours spare to play yesterday and shoehorned a few more bits in, now, I left the Noble pot legs full length, reason being to keep the pcb low, as anticipating super-regs will be installed sideways and need the height, that of course is a very long way off, just a simple assymetric for me at the mo ;) imagine fourteen of the things stacked side by side :eek: there will be just enough height and room to spare for VBEs, the selector shaft etc as well.

Transistors and links to go, maybe this weekend, hopefully.

Edit: I should say, the long term plan is to stick with assymetric for a few months then staight to symetrical with traco and local monolithic regs and stay there for a few months and only then ponder the full horror of super-regged audio overload!
 
Jim, this is going to be a superb preamp.

Yes I found the cause of the distortion. A tant! There was no way of telling visually.It was easy to place the fault in the filter section of one side and then I had to start replacing components. Anyway all's well now: in fact this is a bit of an understatement.

I have just plugged the starfish into the place of a DNM 3C, feeding a DNM PA1 into Living Voice Avatars. It sounds fantastic! WOW WOW WOW

All I have at the moment is the basic stage of the starfish. I will probably leave it a week or so before adding local regs.

Thankyou so much
 
Wow! Goodness! Glad to hear you got it working :)

I'm pleased to get feedback about comparisons with other preamps.
...Especially in this case as it was so positive ( flattery will get you everywhere :D )

(Wow - I compare well against a DNM ? Scary ! Maybe I should have been an audio designer.)

I'd suggest leaving it alone for a few weeks to 'settle'.
My first StarFish changed quite a lot as it 'ran in' - they 'mature' a bit.

Happy listening :)

Jim.
 
Yes I'm not ready to compare the starfish to the DNM yet. But my flabber is well and truly ghasted. I didn't think the first build would get close. There are one or two things to iron out though.

There's a little mains hum. It's quiet and you can't hear it unless you turn the volume right up (ie when nothing is playing). Maybe this is because of an earth loop with the PA1, I don't know. I'm using a SPS power supply for the Starfish.

I also need a better vol pot. Audiocom sell the one I have for £27: I bought it from Audiocom's ebay outlet for about £7. There's a touch of crackling, and it's also 250K impedance. It works well but not perfectly.
 
DSC01430.jpg

Built the asymmetric local regulated starfish a couple of weeks ago and its so good I've just been listening to it and haven't posted since.

Yesterday I fitted these two big babies into it and its even better. They're 3.0uF Multicap RTX's and they're f****ing huge and f***ing expensive but they just draw you even more into the music. Can't wait til they're fully burnt in

Tim
 
I feel a bit guilty seeing your work, I have had to get on with the domestic DIY just as I was about to put the final parts in mine :rolleyes: I might as well go straight to assym regged seeing as you're enjoying it!

Looking good, nice ladder too.

How are you getting on with the SMRs?
 
The SMR's are very detailed but can be a bit brittle. Putting the RTX's on the input to the buffer boards had lessened the brittleness but somehow let more detail through. I'd like to fit them to the input to the gain stages but not sure if there's gonna be space - (I'll try bloody hard to find space tho)
 
Tim,

Glad to hear you got another starfish up-and-running !

I'm still using Tants for coupling in mine.

I have some SMRs, but heard reports of them being somewhat 'harsh' so never got around to fitting them.

Those RTXs look impressive. Can you still get the lid on? ;)

Cheers,

Jim
 
timH said:
Built the asymmetric local regulated starfish a couple of weeks ago and its so good I've just been listening to it and haven't posted since.
Click to expand...

If you think that's good, wait 'til you hear the symmetric version!!

Nice work, Tim :)
 
Hi Jiim

I have been somewhat bogged down of late waiting for the latest round of parts to arrive from RS and Farnell. Anyhows....today they have! Yay! It's really coming together!

All is going very smoothly..... but i do have a few questions for you. :D !

1. RS no longer stock those film 22 pF's for C108 and C208. What alternative capacitor would you suggest now in this location?

2. With your earth regen mod, is it still desirable to have inductor L5 just before the regulator ? Or do we have to eliminate inductor L5 if we want to apply your earth regen thingie?

3. Now that all my inductors are in....the L part is taken care off :) ! But what about all those C's? So to complete your CLCLC filter, what capacitor/s would you suggest to fill up all the capacitors locations around the TRACO and all the inductors?

Many thanks

mark
 
Woohoo! - my last few bits from farnell have now arrived so I can get on and build the the TRACO'd symmetric version :)

It also helps that I've stopped debugging the StarFish. Actually the Starfish was built perfectly, the distortion turned out it to be an issue with the CDP :mad:

Amongst the debug process I went totally film caps in the gain stages and I must say to my ears they are excellent. I used to run my other pre (a modded 92) all with film caps but eventually realised I was missing a bit of magic so I went back to a silmic on the output to spice things up a bit.

I must say the Starfish does not sound 'sterile' or 'grey' with the 10u SMR's in place on the gain stage as the 92 did. I may try changing the buffer stages too , I have both Wima MKS2 10u jobbies and SMR's to try here - I'll use the Wima first as they are a rather fetching pink colour :)

Nick
 
For C108,C208 any film cap in 22pF is suitable - something like RS 113-229
Mica would also work well - try RS 495-666

On the inductors: L5 is on one of the linear local regulators - nothing to do with the Traco.

On the Traco, L15 is the 'common mode filter' and L16 is the 'differential filter'.
For the ground regen mod to work:
- you must fit inductors to the + and - lines of the differential filter.
- you must NOT fit the inductor or make any connection accross the 0 line of the differential filter.


Capacitors for the CLCLC filter. Hmmm, I dunno yet.
I plan to make a properly tuned filter for this once I get my test gear set up again and actually get time to play.
For now, I simply wound a coils around some toroid cores and used 10uF tants for all the C positions. Works fine.

I'll release some 'proper' values once I've sorted the filter out.



Jim.
 
nickcase said:
I must say the Starfish does not sound 'sterile' or 'grey' with the 10u SMR's in place on the gain stage as the 92 did. I may try changing the buffer stages too , I have both Wima MKS2 10u jobbies and SMR's to try here - I'll use the Wima first as they are a rather fetching pink colour :)

Nick
Click to expand...


I changed all my coupling tants for 10u SMRs after reading your post.
Must say I had rather low expectations - I am a disliker of harsh things - but it seems to be working!
First impressions were 'a little odd' but having lived with it for a while, I think they are quite good. Not sure it's 'default spec' but well worth trying.

Jim.
 
I changed all my coupling tants for 10u SMRs
Click to expand...

Did you include the buffer stage too? I haven't actually got around to changing the output caps on the buffer stage yet as I've preferred to get the Starfish loaded up with reg's and traco first.

I not totally convinced with the SMR's as output caps. I like the detail, particularly on percussion however there is some harshness in the upper mids on extended listenings to dance/rock music at high volumes. With acoustic tracks and soft vocals the Starfish is stunning with film caps :D

I've given it a few hours to settle down however I am considering a configuration of using 10u Silmics as output caps and all the rest film. I stuck with this on the 92 for ages and was very happy with the extra sparkle the silmics added. I'll may also try a bypass of the output cap altogether and rely upon the BC128 on the input of the 260z.

Personally I like what film caps do however its about balance for me, I may have to configure one pre-amp for dance/rock with tants/bc128 and another with film caps for acoustic/classical.

Nick
 
It was all the coupling caps - for both buffer and gain stage.

It's early days yet - have only listened to a few records so far.


One possible mod I am considering is a switchable treble cut for the filter stage. Would definitely help with some of the 'nasty' CDs - why do modern mixing people often make such a gash of it?
 
Indeed, one could even imagine an adjustment that changes the amount of treble cut - whoops, I've re-invented the tone control.

Seriously, a limited range, cut only treble control can help make otherwise unbearable recordings usable.

Many recording engineers have serious hearing loss, especially at high frequencies, and I suspect this may be to blame.
 
Jim,
I bought a cheap PSU from e-bay. It's mean't to power a Lexmark printer really. It's rated at 30V on the case but I measure it to be 37V. Do you think that 37V is too much to run the local reg version of the Starfish?
 
it's probably fine - 317's and 1086's are rated upto ~29V potential drop accross them (check the datasheet first) so the absolute limit for input voltage would be ~(+24V +29V) = 53V

Jim.
 
Status
Not open for further replies.


advertisement


Back
Top