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New PCB for shoebox size NAC preamp part I

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Unfortunately tant No 305 didn't survive (seems to be the only one not man enough for the task though). I forgot that my tants are only rated at 35V. Good job I have plenty.

I connected up to measure input current as advised. The meter soon read over 11 amps :eek: (ouch) when the tant gave up. I hope it was the death of the tant that caused the large current and not vice versa, otherwise there is obviously a problem somewhere else.
 
oops - sorry to hearabout your slight accident.

Good luck in sorting it all out - if you need any help just post on here.

Remember to check your voltage ratings ;)

Jim.
 
Has anybody experienced odd 'burn in' effects with SMRs?


When I first fitted them, there was 'more' treble.

Tonight, the system sounds dull and muffled.



Thoughts?
 
...and it manages to sound 'tizzy' at the same time.

I get the feeling there is a whole chunk of upper-midrange that is 'recessed'.

Not sure I like the SMRs for coupling duties.
I'll give them a few more days to bed in before I make a decision.

There are many things that they are doing right, but the overall feeling is of 'wrong' at the moment.
Pity though - they promised so much when first fitted :(
 
Well, I think I found the problem - the system was cold :D


Listening from cold was never a problem before - the sound 'changed' a bit as it warmed up, but it was never 'bad'.

SMR's are the pits when cold... not that they ever get warm, but they make the system sound crap while it's warming up.

Sounding pretty good now though.
 
I don't think I've experienced the issue with SMR's sounding 'poor' when cold but I have found that the initial enthusiasm for them when first fitted doesn't always last.

To my ears SMR's are clinical, I don't pretend to be scientific in any way about SMR's but sometimes I like them and sometimes I don't. Perhaps you could try using one for input coupling and an alternate for output coupling. Just my 2p worth.

Nick
 
I've a curious issue with powering the Starfish.

The Starfish is local regged with a single Traco (0, 30V). All works fine when fed 30V from a 'proper' PSU.

I butchered a printer PSU at the weekend which outputs 31V. Feeding this into the Starfish I measure 0,30V after the CLCLC filter but zero output from the regs.

Any ideas? I've not hooked it up to the PA or source at this point.

Nick
 
Hi Nick,


Sounds a bit odd that 2 power supplies which both output nominally 30V are giving different results.

Is the butchered printer psu a 'floating output' and the 'proper' psu output referenced to earth?
This could explain the difference if the CLCLC is wired incorrectly:

Here's a train of thought:
Which particular config are you using?

I'm guessing that it is local-regged asymmetric.
If so, is the CLCLC wired as per section 11.2.1 of the rev0.6 build manual?
Pay particular attention to the lower differential choke which connects the negative output of the SMPS input to the power star ground.

I say this as I am guessing from the symptoms you describe - could be caused by the negative differential choke connecting to the negative local rail instead of the power star ground.
This would be masked if a raw psu with a ground referenced output was used​

of course, i'm probably barking up the wrong tree. or maybe just barking.

Jim
 
I have borrowd a PSU from work. A nice little unit where you can turn up the voltage on a dial. You can also limit the current drawn.

I have replaced the exploded tant and connected up. At 27 - 30V input, the output on each 27R reads 23.7 to 23.8 V. :cool:

Plugging the starfish into integrated amp next.

:D
 
Fantastic:D

Just a quick note to say that the starfish is now connected back into the main system and performing great.

Thanks again Jim.
 
Great stuff! How does it sound?

I was really impressed by the first stage of the Starfish. Adding the local regs has brought about an improvement, however. The bass has more authority for sure. The main difference, though, is that the sound seems more refined.

I have not had the time to listen to much as yet.
 
Hi Jim,
I have just installed a single traco onto the locally regged asymetric Starfish. How many of the C363 to C371 caps need to be in place?

I have only put C363, C366 and C371 in.

The inductors are in together with the two jumpers which allow for the use of a single traco. I am feeding the traco 15V but at C371 I am only measuring about 5V. The voltage at the 27R resistors measures 9V.:confused:

Aidan
 
I have now gone back to my laptop PSU (at 15V) and everything is fine.

I have plugged the Starfish into the HIFI and it's working well.

I will post with a comparison to my DNM 3C in the near future.:)
 
Hi Jim.

Just thought I'd let you know that I finished one version of the Starfish and it's working a treat.

One minor mishap ..... similar to Hacker (Carl) I'd reversed an electrolytic, only the one on mine didn't survive. Magic smoke got out and all that - bollox!
Quickly swopped out the cap and the pre-amp was up and running.

A bit early yet, but I'm very surprised at the level of detail from this little board!

Initially fed it from a Naim CDI (with flea mod), playing into a small set of powered IBM PC speakers (with a little sub) - sweet as a nut.
After a couple of hours (and when I was happy that it wasn't going to eat itself) I hooked it into my main system (CDS3 into SNAXO/Avondale 135's/SBL's) - 'kin hell !

All this with a basic bench supply running at 30V (it's drawing about 0.11A BTW).

DSC01684.jpg


I'll keep you posted and those two Traco's will be in next.

Thanks for all your hard work.

Dave.
 
Hi Jim,
I have just installed a single traco onto the locally regged asymetric Starfish. How many of the C363 to C371 caps need to be in place?

I have only put C363, C366 and C371 in.

The inductors are in together with the two jumpers which allow for the use of a single traco. I am feeding the traco 15V but at C371 I am only measuring about 5V. The voltage at the 27R resistors measures 9V.:confused:

Aidan

Hi Aidan,

Track it through from the output of the Traco onwards:
-Check there is 30V between the + and - outputs of the traco
-Check there is 30V accross C363
-Check there is 30V accross C366
-Check there is 30V accross C371 (apparently not according to your post)

If there is 30V at C366 but not at C371, then I'd like to bet there is an error in the placement of the inductors in the 'differential filter' section of the pcb.
I havent documented this particularly clearly in the build manual (must update that) but:
-There are only two chokes fitted in the 'differential filter' block.
-One choke goes from +in to +out
-One choke goes from -in to 0v out (odd placement)

If looking at the pcb with the writing 'the right way up' then this means the 'odd' choke goes from the bottom-right hole to the middle-left hole.

Good luck. If you need any help give me a shout.

Cheers,

Jim.
 
Hi Jim.

Just thought I'd let you know that I finished one version of the Starfish and it's working a treat.

One minor mishap ..... similar to Hacker (Carl) I'd reversed an electrolytic, only the one on mine didn't survive. Magic smoke got out and all that - bollox!
Quickly swopped out the cap and the pre-amp was up and running.

A bit early yet, but I'm very surprised at the level of detail from this little board!

Initially fed it from a Naim CDI (with flea mod), playing into a small set of powered IBM PC speakers (with a little sub) - sweet as a nut.
After a couple of hours (and when I was happy that it wasn't going to eat itself) I hooked it into my main system (CDS3 into SNAXO/Avondale 135's/SBL's) - 'kin hell !

All this with a basic bench supply running at 30V (it's drawing about 0.11A BTW).

DSC01684.jpg


I'll keep you posted and those two Traco's will be in next.

Thanks for all your hard work.

Dave.



Great stuff. It's quite a slog building up one of these (all those resistors :rolleyes: ) but when it gets plugged in and working :D

Sit back and enjoy for a while.
There is definately 'burn in' with this preamp (I always rubbished this before, but I've heard it with my own ears with starfish)

Just out of interest, what preamp were you running before?

Cheers,

Jim.
 
Thanks for that Jim.

I don't know what went wrong there. I plugged in a different PSU into the trafo and everything measures up fine.
 
Hi Jim.

I currently use a Naim 252 (changed from an 52) and the Starfish certainly doesn't 'disgrace itself' in their company.

I'm curious now what further performance can be made by using the Traco's and extra regs - I intend to build a dedicated
power supply using a Les W transformer, schottky diodes and T-Net cap(s).

In the meantime, I'll let the Starfish 'burn in'.

Watch this space......

Dave.

P.S. Where are all the others?
 
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