Modded Crack - add bypass cap, choke and Cree diodes

[Paul Joppa]

One of our moderators posted that replacing any one of the existing diodes with just one Cree would do the job. ...

This is not technically true. You can add a Schottky between the bridge of 4 diodes and the first filter cap, and that is widely thought to be effective.

[Doc B.]

Has anyone looked at the effect of this on a scope?

[ALL212]

a year ago...somewhere in there... I bought another Crack and built it stock.  Tried using my o'scope but it was not up to the task.  I don't know the make/model but I didn't see any difference in wave forms.  Now - I might not have been looking in the right place or had the scope on the right settings but I did have fun playing around, just no useable results.

My ears told me something good happened when I put that diode board in with the Cree's on the Crack.

Thanks Paul for the clarification on the right way to add a single Cree.  (I'd best turn my Reduction over and see exactly what I did under there!)

Here's what I did under there...  Solitary cap, red leg to furthest back resistor.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_2923_zpsqe8ffmnm.jpg&hash=102fded2aa8785fb313a26a401b248a4fedd4233)

[Doc B.]

You want to look at the power supply. Right at that first cap would be a good place. Maybe on the heater secondary too. Look for spikes. The UF4007 is an ultrafast recovery diode and should have only a very tiny recovery spike. The Schottky should have none. Will the Schottky remove a spike from another diode? I dunno about that. People have used tube rectifiers after a SS diode because they are slooow and thus filter out the quick spike. They do the same for the musical transients.

[mcandmar]

I cant get my head around that single diode in series, wouldn't it just conduct all the time being forward biased?

[Paul Joppa]

Here is a site with some information on reverse recovery, which applies to non-Schottky diodes:

http://electronics.stackexchange.com/questions/13912/what-is-the-reverse-recovery-time-in-diode

The reverse recovery happens very quickly, which causes noise of a buzzy nature that radiates as radio waves and infects nearby circuits.

Schottky diodes (and vacuum diodes) do not have this mechanism, so they prevent the recovery from happening rapidly when placed in series with a regular junction diode - making the recovery spike insignificant.

[mcandmar]

It was the single schottky diode after a rectifier bridge that i don't understand, how could it possibly make any difference?

W2AEW did a great video demonstrating reverse recovery here, he is worth subscribing to as all his videos are great, though some get into RF voodoo which is over my head.

 

[Jhya]

For anyone curious, I e-mailed Parts Connexion and they told me the PCB for this mod is back in stock!

Google "Discrete Bridge Rectifier PCB - TYPE 2 (TO-220 Radial Style)," and it's the second link.

I ordered mine and will post my impressions once installed. Happy listening and take care!

What is the total cost including shipping and handling for the rectifier PCB? I'm reading from Parts Connexion FAQ that a $5 handling charge will be included if order is less than $25. So the cost of the board will be $1.95 + $5 handling + ~$6 shipping?

[Bacci]

Did I just hear that? Holy mackerel!! 

[ALL212]

You've replaced the stock diodes with the board/Cree's? 

Ya...you probably did just hear (or not hear the noise) that!   

[adydula]

So help me understand this all...is the idea of replacing the diodes a good thing or a not so good thing? Based on some of the comments and concerns that Doc posted I am concerned and a bit confused. I would like to try this but not unless its really been "scoped" out....

Alex

[lthomash]

Alex, I do not believe that using Cree diodes improves the sound in Bottlehead gear, I have a bad habit of using the Cree's in most of my builds because they look "cool" not because they might improve the sound quality.

Lee Hankins

[Bacci]

I just tried them out because they are relatively cheap (like 10$), everyone who tried them was so wild about them and the diode bridge PCB is on promo but more importantly available at the moment at Partsconnexion.

To my ears the Cree SiC Schottky's sound like a nice upgrade both in noise and clarity, but why?
Most seem to think reverse recovery current (or better the lack thereof) is responsible for the goodness (but at "only" 50/60Hz AC... why?), maybe other properties like lower forward voltage drop, ... could be playing a role?
Bear in mind that everyone with one or more Crees already had a choke installed beforehand, which affects pretty much everything in front of the reservoir cap.

[Tom-s]

You want to look at the power supply. Right at that first cap would be a good place. Maybe on the heater secondary too. Look for spikes. The UF4007 is an ultrafast recovery diode and should have only a very tiny recovery spike. The Schottky should have none. Will the Schottky remove a spike from another diode? I dunno about that. People have used tube rectifiers after a SS diode because they are slooow and thus filter out the quick spike. They do the same for the musical transients.

Anyone tried this?

[Doc B.]

Are you asking if anyone has looked for spikes on the heater secondary?