Choke specs for the Crack

[mcandmar]

Love the double decker layout, very creative.

Jamie here is the idea fully implemented, i have no idea whos crack this is, its one of the many images i have saved from the gallery section before it got wiped out.

[Grainger49]

Geary,

Your Crack is stuffed.  And I don't mean that in an Australian way.

I like your adaptation to mounting all the bulky upgrades too.

[JamieMcC]

Mark thanks the pics posted really helped and saved me from making a newbie error. I had not been following correctly and had just wrongly assumed without looking at the schematic that the 270k ohm resistor which was removed was the regular shaped 1W one and not the 270 ohm 5W cement one which is sort of hidden from view. 

Looking at the schematic the second 5W 270 cement resistor is before the last 220 cap and the 270ohm 1W is after so that make is starting to make sense. If I am indeed following the schematic correctly?  Just want to be absolutely sure as the Crack is my first diy build and have no prior experience in electronics and what I have generally consider to be a black art!

Edit ah ha something be must starting to sink in that 270ohm 1W looks like it might be for draining the caps down as its after everything else?

[galyons]

Looking at the schematic the second 5W 270 cement resistor is before the last 220 cap...

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F5rennYq.jpg&hash=971afbc2f0fa7d155aedea17382c506dfe6f1487)

Cheers,
Geary

[mcandmar]

The 1w is a 270K, thats just a bleeder across the + and - to discharge the caps on power down.  The choke replaces one of the 270ohm 5w resistors. I would have thought the first one which is over the transformer however now that i look at those pics it looks like it is installed in the second position.  I would want a bit of clarification from the BH guys on that one in case it was put there for a reason, perhaps the current or heat dissipation would be too much for the choke in that position.

[JamieMcC]

Mark, Geary, thanks, very helpful and much appreciate your holding my hand. Think I am on the same page now.

I had edited my above post re the bleeder as I actually had an inkling that's what it was for after pondering over the schematic some more.

[JamieMcC]

Just ordered the Triad choke it seemed rude not to after all your help guys 

Cheers

Jamie

[Paul Birkeland]

With a Hammond 193C, you might be OK with just a CRC filter.

[JamieMcC]

Thanks Paul with the Crack is there any particular reason as two why the second resistor is normally replaced by the choke and not the first one?

[Paul Birkeland]

Hmm, I think I remember looking at simulations of replacing either resistor and concluding that it didn't make a whole lot of difference.

[Paul Joppa]

There are two schools of thought:

On the one hand, the choke can pick up magnetic-field hum, typically from the nearby power transformer. So the choke should replace the FIRST resistor, allowing the later RC stage to attenuate any hum that gets into the choke.

On the other hand, the choke provides a higher impedance than a resistor, so if the last (third) capacitor is a high-audio-quality cap then you want it to isolate it as much as possible from the earlier, crappier capacitors in the power supply. So the choke should replace the LAST resistor, and be located and oriented to minimize pickup from any nearby magnetic component.

[JamieMcC]

Thanks wonderful info I feel like I'm getting a bit of education.

Does a choke get hot and need air to circulate round it to cool?

If I mount as in the pic below perhaps I can incorporate some form of shielding from the transformer with the materials used for the offset mounting some metal or composite channel section to create a base and partial sides or cover in copper foil shielding tape.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fbottlehead.com%2Fsmf%2Findex.php%3Faction%3Ddlattach%3Btopic%3D6030.0%3Battach%3D5460%3Bimage&hash=fe9edddb95e10e0d44d3b6c79ddbb26a69214f56)

[Paul Birkeland]

If you figure that the choke dissipates roughly the same heat as the 270 Ohm 5 Watt resistor, consider how much larger the choke is!  Consequently, it will get warm, but not particularly hot. 

I wouldn't shield the transformer or choke unless there is evidence that it is necessary.  For example, if you laid your choke down so that it was oriented identically to the power transformer, you might need to expend that effort. 

[mcandmar]

I tried multiple positions with the 10H chokes i installed into my S.E.X. amp and didn't detect any interference issues.  The two 150H chokes in the quickie were a different story though, they could detect a mains lead the other side of the room!

[JamieMcC]

Ok noted.

My Choke arrived earlier today which I thought was very quick unfortunately they sent me the a Triad C3X 10H 50mA by mistake the good news when I contacted the shop they said they would put a Triad C7X in the post straight away and I could keep the C3X!