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New PCB for shoebox size NAC preamp part II

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DSCF1341.jpg
 
I've been trawling this thread, the build manual and latest BOM.

I'm confused about details of the windings for the differential and common mode filters for the tracoed symmetric Starfish, as there are several contradictory stories.

Do I need 2 or 3 windings on the common filter?

And how many turns on both Common and Differential filters?

Thanks for any advice - it's all finished apart from these and the NERT.

Andrew H.
 
Jiim posted the following somewhere up above, hope it helps:

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 across the 0 line of the differential filter.

And here's what I ended up with:

...I've just done exactly the same and here's what I ended up with:
  • 1 Traco - from what I'm reading there's little or no benefit to going to two since the VBE additions are no longer considered necessary.
  • Common Mode Filter - 3 windings of 14 turns each.
  • Differential Filter - 2 (across + & - rails) individual windings of 19 turns each - no connection across the "C" pads
  • C363-365 - 10uF tants - to be replaced by 47pF ceramics.
  • C366-8, 10uF tants - to be replaced by 3.3uF Wima MKS2s
  • C370,371 - 47uF electrolytics - though I don't think they're really needed at all.
  • C369, 1000uF electrolytic
  • R1 - 10K resistor to the LED
  • I'm still working on the NERT, but I believe it connects across the + & - power out pads and the either the Power Ground or differential mode center pad - they are the same (I think)
http://i26.photobucket.com/albums/c114/neiljadman/Starfish/PowerSupplyFilters.jpg

I used 20 GA enammel coated wire on the windings but may try something finer to get more windings on.

I too would love to have some confirmation that I did it right before I power up!
And the NERT dropped in nicely!
 
Thanks Neil. I was confused by the latest BOM which seemed to be saying 2 windings for the symmetric version. I probably just misunderstood it. Anyway. have implemented as you suggest.
 
Has anyone done a comparison - with and without Traco/nert?

Am i right in thinking Mr Tibbs removed the Traco from his 102 because he wasn't 100% happy with the results?
 
Thanks Neil and Jiiiim - Another Fish lives!

It made a few funny burbles when I first powered it up but now seems OK. No idea what it sounds like yet - still on the test system.
 
I do seem to have an ongoing problem with my newly completed tracoed symmetrical fish.

The symptom is that on a cold start, I have maybe 30 secs of hum from both channels. This hum gradually breaks down into an intermittent noise like big single motorbike, then suddenly stops, followed by dead silence wen music isn't playing - no hum, very low hiss even on full gain.

If I let it warm up for 20 mins or so, there is a very short period of burbling on switch on - maybe 2 secs or so, then dead silence again.

What sort of things should I be looking for?
 
First thing I'd check is the raw voltage rails - accessable via "positive power out", "Power ground" and "Negative power out" all in the middle of the board.
They should be around +/-15V - if they are taking a while to come up that would do it. If so, the problem is in the traco, chokes or nert.

If thats all ok, then move on to the outputs of the local regulators. All should be approx + or - 12V. Again they should come up straight away.

If all the power supplies are behaving, then the problem lies somewhere in the audio circuits.
 
I don't get +- 15v, so givem I don't have a NERT yet, and the Traco measures +-15 at the output pins, I guess its the chokes.

Jiim, can you confirm winding details? I currently have 2 at 22 coils for the differentials, and 3 windings of 11 (all I can fit on the core) for the common. Is the third winding on the common needed?? The latest BOM makes me think it might not be.
 
Aha!

If you are not using the NERT, you must have 3 chokes in each filter position.
Fit another 22uH choke in the differential filter.


The latest BOM has the NERT built into it and has the filter coils configured appropriately.

Without the NERT, all the filter coils must be fitted.

Let us know how you get on.

Cheers,

Jim
 
Now I understand! Thought the NERT was optional and just one more potential point of failure, so should get it going in basic form first. Neil, thanks for the NERT offer. I do think I should try to build one first as part of my education, but will pm you on your kind offer if I don't have any luck.

And even in its misbehaving form, it is sounding pretty good, remarkably.
 
I've added the other coil, and now get +-15 at the test points, and silence, once the Traco has powered up. It does seem to take quite a while to do this though - maybe 20 secs or so. Is this a normal length of time to get up to voltage or have I messed the Traco itself up as well??
 
Good stuff - glad to hear it's working.

Just back from hols, hence tardiness of reply.

How does it sound?

Cheers - jim
 
Hi Jiiim.

In non NERTED form, sounded pretty good in my test system, though didn't try it in main system as I wanted to get the NERT sorted.

NERT is now in, but running very hot - too hot to touch, so need to investigate a bit before I can report back on sound..
 
Andrew,

Are you using one or two TRACOs? Using two in my Starfish caused the NERT to overheat, esp the PNP transistor. With only one TRACO the NERT was pretty cool.

Check the resistor values and the NERT wiring.
 
Yeah, using 2x +/-12V Tracos here. I'm using Jim's revised NERT specs, and it just runs warm. Mind you, I'm using DH44H11/DH45H11 transistors bolted to a heatsink...
 
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