Replacing power supply resistors with chokes

[debk]

It looks like there is a space just to the left of the power transformer (looking from the top) it may just fit.

Deb

[Paully]

Forgive me if this is a really silly question but I am curious.  When talking about shielded wires the ones we use for building from bottlehead seem to have an inner foil.  If I wrap the wires of the choke in aluminum tin foil and then put shrink unsulation over it to make sure it can't short anything out, am I providing extra protection from hum pick-up?

[Beefy]

Forgive me if this is a really silly question but I am curious.  When talking about shielded wires the ones we use for building from bottlehead seem to have an inner foil.  If I wrap the wires of the choke in aluminum tin foil and then put shrink unsulation over it to make sure it can't short anything out, am I providing extra protection from hum pick-up?

No. Aluminium provides virtually no protection against magnetic fields.

[Paully]

Oh well, thanks for the response!

[Paully]

I don't know.  12-24" maybe?

[debk]

I put a Triad C-7X choke into my Eros.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2FP1000344-2.jpg&hash=47ff975ce1ee5df69981c198117076d71db8b222)

Fairly easy to do, just had to drill two holes, remove the resistor and solder in the two leads.  I also ran a ground wire from a solder lug I placed on one of the screws to the star ground lug on the power tranfo.

It did make a large difference in the sound.  It sounds "brighter" and maybe more detailed now.  I originally had a rear firing super tweeter on top of the speakers to add "a little twinkle to the high end".  After the choke was installed I disconnected the super tweeters, it was just to bright.  I may try and add a L-pad to the super tweeters to tone them down a bit, or play with the capacitor connected to them.

No problem with any 60Hz hum being picked up.

First impression is that I like the way it sounds with the choke.

Debra

[Paul Joppa]

Cool! Thanks for documenting this; we all learn when one person experiments. The beauty of community....

[Grainger49]

Debra,

Does the plate still fit within the base with the choke mounted there?  It looks awfully close to the edge.

[debk]

Yes the plate still fits on the base.  The perspective in the photo makes it look like it hangs over the edge.

I could have mounted it a little closer to the PCB.   I had to sand down the inside of the wood case a couple of mm.  Forgot to take into account the lip the top plate sits on. 

Debra

[Grainger49]

Thanks.  I own a rotary rasp that makes quick work of nibbling out wood.  I'll take it to Paul's house.

[debk]

I just used a Dremel tool.  It took only a few seconds to sand the area down

Debra

[Doc B.]

Hey Deb, do you have a scope? Your description of the sound makes me curious to see if maybe the choke is picking up some high frequency interference that makes the sound seem brighter. Might be interesting to look at the noise floor and see if there are any really high frequency spikes riding on it, like maybe up in the MHz range.

[debk]

Sorry, I don't have a scope.  probably should look into getting one

Deb

[debk]

Actually I do kind of have a scope.  It is the DPScope, a USB scope that goes out to about 1MHz.  I have not used it in a few years and forgot about it.

I used it connected to one of the outputs with no input into the Eros

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros4.gif&hash=1d022918a3695c5de5ef3a46985e76d7f96f8d75)

Since we were looking for possible high frequency spikes, I set the scope to do a FFT

40Hz/div Shows a 60Hz spike
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros1.gif&hash=7d251a01c6e07d0e1904d0adc6446746a79baefa)

20KHz/div
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi566.photobucket.com%2Falbums%2Fss102%2Frktdoc%2FEros%2Feros3.gif&hash=2c2c3376955f457beb6aadaeae54c6718cbd0335)

Don't know if this data is meaningful or not, or if I even made the measurements properly.
Probably should get a real scope with a higher bandwidth.

Debra

[Grainger49]

Debra,

1M Hz bandwidth is enough to tell if you have any oscillations.  And the software is more versatile than my Tek digital storage scope.  Your FFT shows no high frequency noise.  I am surprised that the FFT shows such high 60 Hz component, but that is the advantage of it versus the scope trace itself.