Dual choke on crack

[Tom-s]

For the power supply i'm planning on replacing both 270 Ohm resistors with Triad C-7X choke's.
But because of the limited space i'm thinking of placing both of them next to the transformer hosing on top of base plate.
Would this be a problem? This way i'd have more space for caps and diode upgrades on the power supply.
How dangerous is it to have these on top?
They would sit very close to the on/off switch.
Could any others show pictures of how you implemented 2 chokes in the crack?

 

[Paul Birkeland]

I don't believe that they will physically fit.

If you can get them to fit, be sure to use a rubber grommet where the wires pass through the chassis plate.

 

[Tom-s]

Thank you for the reply PB.

I'm just about sure the two of them won't fit under the hood. Surely not leaving enough space for caps and other upgrades on de PS. Although i've read that with 2 chokes i could get away with smaller caps. Any recommendations on these sizes?*

Edit*: Also saw another reply where one of you guys stated it to be best that the last film cap is about the size or bigger than the output caps.

That's why i thought about placing them on top of crack. But then you have electrical parts open to the exterior.
What is the danger in having these on top? Is there constantly 250V+ 90mA open to the touch?
On S.E.X. there's chokes on top. Why aren't these a potential voltage hazard?

 

[Tom-s]

That would be a bit drastic.
It's more easy to build a new wooden case that gives more space under the hood while using the same alloy base plate.
I didn't think of the magnetic interference with those 2 chokes.
I was planning on mounting them on top of crack in the same manner as done on the S.E.X. kits.
Why isn't this a problem on S.E.X.?
Only detail on crack is that because of the on/off switch they'd be both mounted a bit more to the front.

(Sorry if i ask novice questions, but like a lot of guys on here, it all started with the crack )

 

[Natural Sound]

If it were me I'd wire them off to the side and listen test to see if it was worth the effort of physically mounting them. There may or may not be that much sonic gain in adding the chokes.

There just isn't a lot of room to work with in the Crack kit. The Crack-a-two-a solves that issue.

Keep us posted.

 

[lth1]

I believe that you are wasting your time and money, but I respect that it is your time and money to waste.  I do not believe that the second choke has any sonic benefit (I have already tried this).  But, this is coming from one who is always trying to improve the sound by throwing money at a project, but for me it is personally rewarding (I enjoy throwing away my children's inheritance). 

Putting money into better (i.e. usually more expensive) output caps is the more logical and productive approach.  Like a lot of the individuals on this Forum I am sure that I would have saved a lot of money by originally purchasing the Mainline, but the Mainline and Crack-a-two-a were not in production when I purchased my first Crack, and I do enjoy the OTL sound.  ;D

 

[Tom-s]

This was the reply i was looking for. Someone who actually tried it.
I know there's not much to gain with the second choke. I've read that with a second choke it to be possible to lower the capacitance of the PS caps even more than with just one choke.
So via this route i hoped to get more sonic gain from a better film cap (with or without bypass) on the last PS cap and have more room to fit better (bigger/better electrolytic, or small film caps) for the other PS caps.

Anyone else who tried 2 chokes?

Could someone please measure the Triad C-7x choke for me? I found a few measurements on the Triad website but i don't have the exact width of the silver center and the extension of the coil to each side of this silver part. Thanks in advance. With these i'd know if it actually fits. The space to mount them between PT and edge is only 38mm's and then there's the heat shrink tube that goes over it for safety and electrical insulation from the PT.

Thanks guys for all the feedback! It really helps a lot.
And about the money eating and time wasting thing that gives you joy. That's what i'd call a good hobby!

Oh and Lee; your builds are awesome! Love the woodwork!

 

[richmi]

Hello,

I think it might be possible to fit two Triad C-7x chokes under the Crack chassis. One would be located in the back of the Crack where a lot of builders put it. The other one could be mounted on nylon standoffs above (as seen when the Crack is turned upside-down) the headphone jack. This way, both chokes would be turned 90º relative to each other. You would only have to twist the chokes wires together and solder them at the proper terminals. And then, you have to run a wire from the choke's case to the safety ground tab near the power entry module.

Perhaps that would be locating it too close to the small tube and it could interfere with it, I do not know.

(Standoffs here if you have problems finding some: http://www.ebay.ca/itm/10x-Nylon-Standoff-Spacer-M4-Female-x-M4-Female-25mm-/251232421895?hash=item3a7e9e8807:g:ElgAAMXQySpRJPOH

This seller has screws too.)

Bypassing the last capacitor in the power supply with a good film cap made a noticeable difference at a smaller cost than that of a 220uf 250 volt cap if you really run out of space.

Here is a photo of my Crack with a few changes, notably the addition of a choke and two large film output capacitors so you get an idea of how much room is left.

Richard

 

[Paul Joppa]

The C7-X is about 1.75 inches wide - the core is a 1.0" stack, with 0.375" bobbin flanges each side.

 

[Tom-s]

Thanks for all the replies. For placing a pair of them inside the crack. I might place one above the Cree diodes board and the other on the back like others do.

So top mount would be impossible. Because of the 38mm that's needed and they measure 38mm (1.5") by themselves for the part that needs to go on the alloy plate without the protective heat shrink sleeve.

 

[BNAL]

I installed 2 chokes in my Crack. It was tight, but fit.

 

[Tom-s]

And? Did it make an audible difference, the second choke?
No magnetic interference with this setup?

Two chokes should be oriented at 90 degrees from each other because of the magnetic field they radiate. 

Meaning that one should be in the horizontal plane and the other in the vertical plane?
Both in the vertical plane with a 90 degree angle between them wouldn't help?
So my other placement, mentioned above, is incorrect?

 

[BNAL]

It did not cause noise in the circuit and do not think that there was a sonic benefit. The one choke and especially the film bypass cap on the last electrolytic improved the sound IMO. 

 

[Paul Birkeland]

You could also get a Crack-a-two-a instead.  It's power supply will outperform any modifications that can be done to a stock Crack.

 

[Tom-s]

Thanks for the reply.
So,  this about concludes putting multiple chokes in or on crack. It's just too much for the small amp and gives no sonic benefit.
Will go with just one choke, cree diodes rectifier and possibly an 220uf 250v Ansar film cap.

 

[JamieMcC]

With a single choke you should be able to use 50-100uf for the last cap in the power supply and still achieve a massive improvement in ripple. If using two chokes the last cap potentially running a psu simulation shows (if I have configured it properly *doubtful*) then 5uf would achieve similar results in reduction of ripple to a single choke and a 100uf cap. What effect sonically this would have I don't have a clue perhaps PJ or PB might comment.

I have used 100uf film cap with a single choke and I couldn't really make out much different between using it and a 200uf film cap that I tried later. You will need to look closely at the dimensions of a 200uf film cap as they are big you will run out of ground clearance very quickly I ended up building a slightly larger enclosure.

Some pics here of the install here

http://bottlehead.com/smf/index.php?topic=5284.msg50967#msg50967

 

[Paul Joppa]

AS I have said before (though not recently) the last PSU cap is in seroes with the output cap and the power tube - that make up the signal current loop. Thus the effective output capacitance is the series impedance of the output - for example, if both caps are 100uF then the headphone sees a net 50uF. Not a problem for 300-ohm phones. but noticeable bass loss for 30-ohm phones.

 

[Paul Joppa]

I should have mentioned that the CrackaTwoa has a shunt regulator in place of the last PSU cap, so only one cap is in the signal current loop.

 

[Tom-s]

Thanks you for the replies. I found that with some dremel work. It would be possible to top mount a pair (could save 2-3mm on each side of each choke). Will do a temporary setup first. And if i like the sound, the look and if there's no magnetic interference i make it permanent. (For now i'm waiting on the parts to arrive).
This leaves me with much more space under the hood.

Of the guys with 2 chokes. It didn't influence the sound in any negative way?

Still in doubt about that magnetic interference Grainger mentioned earlier.

 

[Paul Joppa]

If the chokes are mounted as on the SEX amp, they will be in a null from the power transformer field and there should be no magnetic interference. Make sure they are centered fore-and-aft; even 1/4 inch makes an easily measured difference.

Feed the leads through a rubber grommet-lined hole between choke and power transformer, that way they are pretty inaccessible, improving the safety. There's not much room for that hole, so measure carefully!