New PCB for shoebox size NAC preamp part I

[nickcase]

Mark, glad you asked the questions about the chokes - thanks for the pictures and explanation Carl - helps a lot.

Winding inductors is not a problem but I do struggle with removing the laquer from the wires in order to make connections. the method I use with my wire (salavaged from scrapped transformers) is to heat the ends of the wire with a blow torch until it blackens and then rub off the residue with sandpaper. fiddly and it's tricky not to bugger up the nice windings when heating and scraping.

Are there any other techniques people use?

Cheers,

Nick

 

[PigletsDad]

I use a scalpel to scrape the lacquer off.

 

[hacker]

Stanley knife, scraping the blade repeatedly while slowly turning the wire so that all the laquer is removed.

 

[Jiiim]

Page 19 of the latest build manual states that it is critical the number and direction of turns is as per the diagrams in order for the common mode choke to function as intended.

Sorry about the slight vagueness in the manual about the chokes - I have not set a particular number of turns to use yet, as I need to get in there with some test gear and properly sort out the CLCLC arrangement so it's tuned for the job.

What is important is that on the common mode choke, the coils have identical number of turns and the direction is per the diagram - Each coil must have X turns in the direction shown.

Your one is probably fine. Bung it in and try it.


Glad to see lots of starfish growing up around the world



Jim.


PS - removing lacquer? I get a dang great blob of solder on the end of the iron and hold the wire in it - the lacquer burns off...

 

[martin clark]

Heathen. A Gentleman instructs his valet to supply suitable wire.

[whereas I have to do it myself - same method as Pigletsdad ]

 

[markzb]

Hi Guys

When i wound my coil....i applied a bit of "5 minute" epoxy to hold the 3 coils in place. Once the glue sets, it's rather easy to scrape the legs as they don't flop about. I used an Opinel knife as i think they are great knives for discerning hobbyists

Jiim... i will order a single traco like yours...try this coil out as is and then scope it. I have a picoscope...so i can easily capture and send some jpeg's of the waveforms that result. Then i will add some more turns and scope it again.

Be in touch soon! Look forward to your test bench coming back to life!

Cheers

mark

 

[new naim boy]

Calling 999

I have just finished soldering the starfish asymetric supply. I connected it to 24V supply and measured 58mA current. I also noticed that the 27R resistors are getting very hot is there something wrong?

Aidan

I shall post pr0n soon

 

[new naim boy]

 

[Jiiim]

Hi,

I havent measured the current on my StarFish, but 58mA sounds about what I would expect.
Having the 27R resistors get 'very hot' does suggest something wrong.
I'll have a closer look at your photo and see if I can spot anything.

Jim.

 

[new naim boy]

I think I have found the problem. One of the trannies (bottom right of picture) was squashed so the legs were touching. I have now separated them and powered up again.

This time there are no hot components. The current drawn is now about 78mA. There's very little voltage across he outputs so fingers crossed for connection to CD player.

Aidan

 

[Jiiim]

Trannies always cause problems - tell 'em to wear clothes appropriate to their gender

 

[new naim boy]

Just connected the starfish to portable CD player and powered computer speakers - WOW

I have done an odd bit of soldering before but this is the first time that I have built something like this. Thanks to all those who have contributed to this project.

Next stage is to put it in a box and connect to a real power amp + speakers.

 

[Jiiim]

WOOHOO! It lives - congratulations !

 

[hacker]

Nice one Another starfish! Just wait until you add local regs etc - it's amazing. Congrats, good work.

 

[Linnik]

Hacker, by all means tell us more how it is amazing?!! Keep our goals and dreams burning!

Oz

 

[new naim boy]

Calling Jim an Carl,

I have just connected the starfish up to an old integrated amp and CD player. I plugged the output of the starfish into a tape input on the integrated.

There's music but with a lot of distortion. There's also some mains hum which I didn't get before because I was using a battery powered walkman.

When I turned the volume on the integrated up to loud there was a very loud high pitched screech.

Do you measure about 100k ohms across input/ground?

Finally would you please check that C108 and C208 are 22pf as described in the BOM - only on my pic the caps seems different to yours Jim.

Aidan

 

[new naim boy]

I decided to change the 47 MMks to silmics. It was difficult to see if there was a decent connection with the MMKs - the legs were so fat. Consequently channel 2 is now working properly.

The hum and screeching has gone.

Channel 1 still a bit distorted, though.

Interestingly it was channel 1 where some of the legs on one trannie were touching when I first connected up.

Aidan

 

[BobMaximus]

The starfish is a pre-amp. So you don't want to feed its output through another pre-amp (ie. the one after the tape input of your integrated). Its output should go directly into a power amp.

The distortion you are getting is probably caused by the voltage you are feeding into the tape input being too high. If this is just for test purposes, then turn down the volume of the starfish so that its gain is close to unity (ie. so it doesn't amplify).

This only tests whether the starfish works. It does not tell you how good it is, because you have to get the integrated's pre-amp out of the equation. Adding the starfish in this way will probably make the integrated sound worse than it did without it.

Andy

 

[new naim boy]

Point taken, but this distortion is pretty gross and in just one channel. When I change channels to the integrated the distortion also changes.

I'll miss out the buffer stage and feed the input directly to the pot to narrow down the problem area.

 

[Jiiim]

if it's just in one channel, dont worry about fiddling with how you connect the starfish to anything after it - you know the problem is on the starfish.
As you have one good channel to compare against, tracking down the fault should not be too dificult.
First check should be visual - check everything you soldered in - it's so easy to make a mistake....