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-   -   Star ground w/ Dual capacitor banks (http://www.diyaudio.com/forums/solid-state/41661-star-ground-w-dual-capacitor-banks.html)

Killjoy99 27th September 2004 10:38 PM

Star ground w/ Dual capacitor banks
 
I am building Rod Elliotís P101 and am working on the Power supply first. The schematic uses the ground plate for a single capacitor bank as the point for the star ground; as seen below
http://web.pdx.edu/~bcwood/Star.jpg

The design that I am using has twice the capacitance of the original and uses two separate banks of capacitors; one for each channel. Here is the design I am using.
http://web.pdx.edu/~bcwood/Star2.jpg

My question is: What is the best method of using a star ground in a setup that has two separate capacitor banks. Should I just have two star grounds, one for each channel, or should I try and create a link between the two plates that will act as a single star ground point.

Thanks for the help.

- Brian

cunningham 27th September 2004 10:47 PM

I think that the second example circuit would work better if you used two seperate transformers and bridge rectifiers, then connect the centertap of each transformer together as ground. Less chance for ground loops.

Rudy 27th September 2004 10:55 PM

try using 1 bridge rectifier/channel and use 1 single star ground

option 2 of your drawing is NOT an option

;)

traderbam 27th September 2004 11:14 PM

Quote:

The design that I am using has twice the capacitance of the original and uses two separate banks of capacitors; one for each channel.
I'm not sure what you are trying to achieve in your second diagram. You see I don't think you are really achieving two separate capacitor banks as both are wired in parallel...it isn't much different from simply doubling the number of capacitors in the first diagram. To provide independent regulation for each channel is best achieved with two completely separate supplies if you can afford the cost and space.

AKSA 27th September 2004 11:26 PM

You really need two transformers, two recifier banks, two sets of caps. This gives the least crosstalk and the best possible imaging; viz, true monobloc construction.

You can certainly derate the size of each transformer. You could go from one 425VA trafo to say two 225VA trafos.

The star earths may then be separated; each bank's star earth serving its own channel. However, to some extent potential crosstalk benefits are negated by many sources, which tie the two earths from each channel together. But it does serve to keep large power currents quite separate.

Be careful with too much capacitance. In my experience the increased self-inductance of such large banks can audibly affect sonics, making them leaden and slow. Capacitor quality is crucial; United Chemicon make good quality caps; Fischer Tausch are also good, as are Rifa.

The rectifiers are very important. Use Ultrafast Soft Recovery types at the very least. Shottkys are even better.

Cheers,

Hugh

paulb 27th September 2004 11:27 PM

Quote:

Originally posted by Rudy
option 2 of your drawing is NOT an option

Why not? Electrically it seems ok. Do you mean it's not as effective as separate bridges? (which I would agree with).

By the way, Rod suggested adding a small amount of resistance between the two capacitors to give a bit of a pi filter.

acenovelty 27th September 2004 11:37 PM

Killjoy99,

This link has been posted on the forum in the past:

http://zero-distortion.com/start.htm
scroll down to : Designing your own power supply

Dejan V. Veselinovic details very clearly how to make a clean, strong power supply. There is nothing wrong with the classic power supply as presented by Rod, except for what you will learn from this link.

A star ground means that all ground lines come to a single point.
If you must have two banks of Caps, use separate trannys and rectifiers for them. Now you have a mono-block.:cool:

Killjoy99 28th September 2004 04:18 AM

OK, sorry about that everyone. It seems I should have given a little bit more information. Here is my issue. I have already purchased an 800VA Trafo for the power supply and have about 40 x 4700uF 100V caps. The originally schematic that I started with cannot be posted or talked about on this site because it is private information to those that have purchased PCB's from Rod Elliot. If you have purchased one of his boards you may look in the secure information on his site and view the Power Supply for P101.

My issue is that the proposed supply only has a total of 30,000uf for a stereo amp setup. That is not per rail, it is for the entire amplifier. This seems to me to be very low. I'm not trying to go overboard and put 100,000's of uF. I'm just trying to increase it a little to maybe a total of 50,000uF or 60,000uF

My first plan was to just do what we all do and just add more caps in parallel to the rest. This would work and keep the entire star grounding the same, but would result in a capacitor bank that is in the area of 12-14 inches long.

I than figured that maybe I could just create two smaller banks and put them next to each other to create a capacitor bank that is like 6" x 8". Below is a picture of the first bank that I made experimenting with drilling and such.

http://web.pdx.edu/~bcwood/101cap.jpg

Is there a way that I can use two banks and connect the Ground Plates using another bar of Copper? Than place the star ground in the middle of the connection plate.

http://web.pdx.edu/~bcwood/101cap2.jpg

I'm not trying to make each channel have its own separate capacitors I'm just trying to increase the capacitance and keep the capacitor bank within a small enclosure.

Thanks for the help

- Brian

sajti 28th September 2004 06:52 AM

I think, that this solution is not the best. Put all the capacitors in one line, and use one ground bridge only!

sajti

traderbam 28th September 2004 08:25 AM

Interesting problem.
What I would do is dispense with the metal bars. Even though they are mechanically attractive. Run a separate ground wire from each cap to a central star post (could be a bolt thread). You'll need to do something similar anyhow for the + and - lines.

Quote:

By the way, Rod suggested adding a small amount of resistance between the two capacitors to give a bit of a pi filter.
I don't see any sense in this.


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