Choke specs for the Crack

[TravAndAlex]

I went with a non-standard mounting location for my choke since I decided on a couple diminutive Panasonic film caps for the output.  Allowed the choke to mount on one side (a bit further from the transformer) and the film caps to mount on the other side.  Almost looks like it was meant to be that way.   

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2F24d31bt.jpg&hash=bb3455a310e3e089f16a4696aa3033a7039554c2)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi66.tinypic.com%2F2rx75t2.jpg&hash=19d34ee8bc171ce35b6995935893021b96dd83be)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2F259cym9.jpg&hash=49e568209e43d9fe28599d9c5a4641b67df92ee0)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2Fww0zet.jpg&hash=ba4f744e8573eef97788f211d8e0eaa9d25ae2c7)
 

[i luvmusic 2]

Either 270 Ohm resistor can be replaced by the choke.

-PB

I actually like the choke it did make the background quieter,What do you think of replacing both 270R 5W resistors with a choke(The issue is where to put the second choke but it's ok i will try to find a place for it by moving stuff around)?Thanks You for your reply!

[Paul Birkeland]

Some have just made a deeper base to allow room for the second choke.

You could also look for a choke with ~550 Ohms of DCR and more than 10H and just use a CRC power supply. The Hammond 158L may be a good choice.  I would parallel the two 220uF caps on the IEC side terminal strip together after the choke.

(Note that I haven't tried this, so YMMV)

[i luvmusic 2]

Some have just made a deeper base to allow room for the second choke.

You could also look for a choke with ~550 Ohms of DCR and more than 10H and just use a CRC power supply. The Hammond 158L may be a good choice.  I would parallel the two 220uF caps on the IEC side terminal strip together after the choke.

(Note that I haven't tried this, so YMMV)

I maybe able to put the second Choke on the Pot side,I don't want to do a circuit changed just incase i need to do some trouble shooting in the future at least i know that what i did is changed components.Thanks again!

[Tom-s]

Don't know if it's worth it. Didn't really hear much of a change with the second choke. Tested with and without.
Just left it in nevertheless.

(https://ep1.pinkbike.org/p5pb13669239/p5pb13669239.jpg)

[i luvmusic 2]

Thanks for the info,Another question do i need to ground the Choke chassis?Thanks!

[Paul Joppa]

Yes, all the iron should be grounded to the chassis plate, for safety reasons. It's good practice to insulate the iron from the plate so it can be grounded to a single point, preferably near to where the power is grounded.

The reason is to minimize the leakage currents in the chassis plate, and keep them well away from the audio circuitry.This reduces a potential source of hum.

[i luvmusic 2]

Yes, all the iron should be grounded to the chassis plate, for safety reasons. It's good practice to insulate the iron from the plate so it can be grounded to a single point, preferably near to where the power is grounded.

The reason is to minimize the leakage currents in the chassis plate, and keep them well away from the audio circuitry.This reduces a potential source of hum.

THANK YOU!

[larcenasb]

Wow, this thread is loaded with great information! Thank you Paul J. and Paul B. for being so open in the forums, providing to-the-point, no-nonsense, clear information and advice to all of us. I've become a fan of both of your scientific and kind responses, and this makes me even more proud to be an owner of the Crack.

Paul J., I posted a question to you in the Crack thread at Head-Fi, but it's more sensible to reach out to you here. You've said, "I would never use less power supply capacitance (last cap) than in the output cap, and I'd prefer at least twice that - if it were my amp." Currently, I'm using three 68uF Audyn Q4 caps (2 outputs, 1 last PS), could you please explain what the difference instead would be if I used two 47uF outputs and a 100uf PS cap? Which would fare better in terms of bass roll off, the three higher capacitance 68uF caps, or two 47uF outputs and the doubled 100uF PS cap? My cans are 600ohm AKG K240 Sextetts, and I do have the C-7X choke installed. Thanks so much and take care!

[Paul Joppa]

I don't follow the HeadFi forum - PB is the headphone guy. Hopefully he will post based on his much greater experience. I'll just give the theoretical argument:

The issue is that the PSU cap and output cap are effectively in series in the current loop; if they are both 100uF then the effective output capacitance is 50uF. Not an issue with 600-ohm phones. At 160 ohms, there would be a bass rolloff at 20Hz - lower than that and you would likely hear a loss in the deep bass.

[larcenasb]

Is there an equation to calculate this? So, right now my effective output capacitance is 34uF from my 68uF caps, with bass roll off at 8hz using my K240. What if I increased the PS cap to 100uF but use 47uF caps for outputs? How much will the effective capacitance decrease in this case? Or does it stay the same as the output when the PS cap doubles the output?

And in that case, if using a PS cap that triples the outputs' capacitance, does the effective capacitance double the outputs (220uF last PS cap + 47uF outputs = around 100uF effective capacitance)?

Thanks so much for your response and your time. Take care!

[diynewbie]

Please correct if I have this wrong.  Still trying to figure this stuff out.

The -3dB roll off frequency is calculated by 1/(2*pi*R*C).

In this case, R is the impedance of the headphones in ohms and C is the effective capacitance of the last PS cap and the output cap in farads (not micro farads).

The effective capacitance of capacitors in series is calculated by 1/(1/C1 + 1/C2 +…).

[Paul Birkeland]

Which K240 headphones do you have?  They have come in several flavors with different impedances.

Another issue that's worth considering is that when you start shrinking the last PSU cap in the Crack, you will let more power supply noise through,which is very undesirable.

[larcenasb]

Hi Paul B.

I have the K240 Sextetts, 600 ohms.

Also, in the PSU, along with the last 68uF film cap and C-7X choke, I'm using 470uF electrolytics for PS caps 1 and 2. I'm happy to say, the background is dead silent even with the volume maxed out.

I'm just trying to decide if I should raise the last PS cap to 100uF and use two 47uF output caps. Considering my choke, 470uF PS caps, 68uF last PS cap, 68uF output caps, and 600-ohm headphones -- bass doesn't roll off till 8hz -- is there any other reason to have a last PS cap that doubles the outputs besides the bass roll off? What would you do if it were your amp and using 600-ohm cans?

Thanks so much!

[Paul Birkeland]

I'd use the 470uF->choke->470uF in parallel with whatever film caps you have, then use 47uF or 68uF caps on the outputs.  The extra R-C power supply node shouldn't be necessary with the rest of the changes.