Star ground w/ Dual capacitor banks

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I am building Rod Elliot’s 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
An externally hosted image should be here but it was not working when we last tested it.


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.
An externally hosted image should be here but it was not working when we last tested it.


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
 
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.
 
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
 
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:
 
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.

An externally hosted image should be here but it was not working when we last tested it.


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.

An externally hosted image should be here but it was not working when we last tested it.


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
 
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.

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.
 
traderbam said:
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.

I don't see any sense in this.


This is not a good idea. To avoid the noise You have to separate the wire which goes to the amplifier, from the wire, which goes to the transformer.
I think the copper bar is good idea, but use the capaciotors in one group, and use one metal bar.

sajti
 
Best option is imo two bridges, rectify each winding separately.
The ground is connected to the - of one bridge and the + of the other. That gives you + and - and 0

Each voltageline than gets half of the capacitance.

In this way, the amplifier is not directly connected to the center tap of the transformer. And you only have one transformer, since you've already purchased it.

Check http://zero-distortion.com/start.htm

Marc
 
traderbam said:
Sorry, I don't understand what you mean.


Check out http://www.tnt-audio.com/clinica/ssps2_e.html

There is no direct connection between the middle of the transformer and the ground of the amp.

Two bridges, two cap banks, +/- voltage. Connect left and right channel two one power supply.
If you want the ultimate channel separation, double the transfo's, four bridges, four cap banks.
A little bit more expensive...

Marc
 
Yes, I understand what you are saying, Zeno, about configuring the rectifiers and dual secondaries. But I thought I was talking about something quite separate when suggesting individual ground wires to the star point.

Also, I don't understand what the "noise" related problem is when connecting the transformer centre-tap directly to the star point rather than using dual secondaries and combining +/- rectifier outputs at the star point.
 
There are a couple of sources (Slone, Self) that stongly advise against location the star gound at the PS caps. They clain this is a very noisy point in the circuit and using it as a star point risks creating a path for noise to enter the signal path.

An alternative would be to run suitable wire from the point between the caps to another point 4 or 5 inches away where you locate something such as heavy phenolitic terminal strip (or anything of similar function you find convenient). Then run wires from the power and signal grounds to the same point. This should also be used to connect the star point to earth. The idea, I think, is that the impedance to the earthing point as seen from the PS will always be less than to the PCB gound nets.

I hope I'm explaining this correctly and clearly. If not, I'm sure someone will post a claification.
 
I think I forgot to explain this:

The POINT of the cooper plate that is connected to the chassis is ONLY for the CAP's group.
The Center Tap of the Xformer and all other 'ground' wires, MUST be connected to the chassis in the same point (this is the real star ground).

This is my way to GROUND my amps ;)

Rgds

Pedro Martins
 
There are a couple of sources (Slone, Self) that stongly advise against location the star gound at the PS caps.
That's enough incentive for me to put the star point as close to the psu caps as possible! :cheeky:

I'm not sure what they are talking about. What is absolutely crucial and the whole purpose of a star point is to avoid unwanted common loop currents within the same conductors. So all current flows that must not be shared within a common wire must be connected by separate wire to the star. All voltages are relative. So we simply define the star point to be the reference from which all other voltages are measured, including noise.

If you start fudging this with two star points you are much more likely to introduce unwanted intermodulation noise than reduce it, unless your conductors are at -273C. There is an old thread here somewhere where I explain this in more detail.
 
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