[shake]

Quote:

Yes, that is the right idea. As wakibaki also suggested, if you are using a shielded cable for your input,
it can ground at the amplifier instead of at the power supply.

The inputs are going to be RCA jacks.  What do you mean by ground at the amplifier?  Ground to case at the input jacks or somewhere in the amplifier circuit?  The case is going to be grounded by the output/input jacks and I don't know if Alps pots ground the case as well.
Quote:

a single "star gnd" is usually "too simple" to be "the best" - I use a hierarchy - gnds may be dirty/noisy or clean - to varying degrees
 
the power supply xfmr CT/rectifier/reservoir caps have the largest current spikes, they should be a separate "star", then a branch from there goes to the "clean gnd" "star" point, the Vreg reference terminals can be "between" the two, "Kelvin Sensing" actually runs these to the clean gnd
 
my output connector star drawing, shown in the 1st post can be about as good as it gets if you only have one channel - or go "dual mono" = two completely separate amps, power supplies, separate R,L connector headphone gnd pins, "balanced" headphone connector
 
if you have only a single dual polarity supply, and/or use the shared common R,L gnd TRS connector you have to compromise from that ideal
 
I think a good compromise is to use the TRS common gnd as the "clean gnd star point"
 
when everything can't be at the same point you can sometimes get near the same effect by making the resistance between them low with gnd planes on a PCB or heavy Cu buss - Cu Roof Flashing is the most easily available Cu sheet stock

So the transformer/rectifier/regulators/caps are their own  ground, and I have a wire from there going to the TRS ground of the output jack where all other grounds go?

 

[wakibaki]

The inputs are going to be RCA jacks.  What do you mean by ground at the amplifier?  Ground to case at the input jacks or somewhere in the amplifier circuit?  The case is going to be grounded by the output/input jacks and I don't know if Alps pots ground the case as well.

 
Sorry, this seems to have given rise to some confusion. It's not a straightforward issue and it's difficult to strike a balance between making a workable, straightforward recommendation and overwhelming a beginner with a mass of choices which he may not initially fully understand.
 
It's common where a large case with possibly a number of well-spaced boards is employed to bring the signal from the input to the amplifier(s) using (a) screened cable(s). In this case there arises the question of where to connect the screen. Obviously the incoming signal ground must connect to the screen at the jack end via the jack. The jack itself may be insulated from the case or may not be. The choice of whether it is or not hangs on the type and complexity of the grounding topology ultimately adopted. The other end of the screen should connect to the star point. If quiet and noisy star points are employed then this end of the screen should connect to the quiet star point. In this case the quiet star point will typically be the output ground, and the case will also connect to the output ground. This makes the screened cable redundant to a degree, if the input connector is not insulated from the case. Most people, however, prefer not to have signals carried in the case
 
The scheme I described is taken from Douglas Self's Audio Power Amplifier Design Handbook, and I recommend it to you above the complications involved in a dirty/quiet topology for an early build. Note that the output connectors are insulated from the case. Separate outputs with their own ground returns are preferred for a stereo amplifier as a few inches of wire sharing ground at the output terminals will probably dominate crosstalk performance, but crosstalk rarely becomes objectionable, as the preponderance of 3-wire headphones indicates.
 
Pots don't normally connect to ground unless one of the terminals is explicitly connected by the designer, although in some cases the hardware (case) may be connected to ground.
 
w

 

[shake]

Ah ok.  Screened cable = shielded cable.
 
I just check out the spec sheet of the RCA input jacks I'm going to use, and it looks like they can be installed to be grounded to the case or isolated from it with the supplied washers.  So if I isolate them from the case, I connect the input ground/'negative' terminal close to the output ground?
 
Quote:

Obviously the incoming signal ground must connect to the screen at the jack end via the jack................ The other end of the screen should connect to the star point.

Which end is which?

Quote:

in some cases the hardware (case) may be connected to ground.

That's what I'm trying to find out.
I'm using ALPS rk27 pots, which have ground terminals.  Do I just not hook the ground pins up to anything and have the input ground going straight to the output ground?
 
The output jack I'm using is this. 
 
 
Quote:

Yes, that would turn it into a center tap transformer.
 
You could also wire the secondaries independently like
in this schematic:
 

 
X1 and X2 would connect to the secondaries of the transformer.
X1-1 = Green
X1-2 = Red
X2-1 = Brown
X2-2 = Blue

This is an example of a star topology for the power section?  So all I would have to do is add another rectifier and not turn the transformer into a center tap one.

 

[jcx]

if the TRS gnd connector gets too crowded then you can use another "clean star" "point" instead with heavy wire to the TRS gnd - a PCB gnd plane is one possibility
 
from a hum/safety gnd loop issue the better construction is "double insulated, reinforced insulation" pwr xmfr, 2 wire pwr cord and floating the case
 
but there are construction requirements to meet the safety standards so may not be a good 1st line power hobby project choice - already done for you in most "wall warts"

 

[shake]

Quote:

if the TRS gnd connector gets too crowded then you can use another "clean star" "point" instead with heavy wire to the TRS gnd - a PCB gnd plane is one possibility
 
from a hum/safety gnd loop issue the better construction is "double insulated, reinforced insulation" pwr xmfr, 2 wire pwr cord and floating the case
 
but there are construction requirements to meet the safety standards so may not be a good 1st line power hobby project choice - already done for you in most "wall warts"

I might solder a small copper sheet to the ground pin.
 
Well, the spec sheet says that the transformer is insulated, and I don't know what else I can do for that.
I'm going to wrap the ground pin on the power jack with heat shrink wrap.  I chose the 3 pin connector because of the higher availability  of the cables.
By floating the case, do you mean make sure it's not touching anything else?  I'm planning on setting it right by my DAC, which I think may be earth grounded.

 

[jcx]

when you build your own line powered supply you are stepping into some technical/regulatory complexity
 
some line transformer manufacturers are scary - don't clearly state safety standards that their product meets - "International/Universal" transformers with "double insulation", speced as passing 4 kV HiPot are considered safe to use without safety gnding the circuit output, case - can use 2 wire power cord (USA)
 
without the special construction, any transformer (legally) sold for line power connection should be safe with the secondary/case connected to the 3rd prong safety gnd of the outlet
 
but you can get hum from too much gnd leakage current from other devices, or inductive coupling - safety gnd isn't always quiet, worst is when separate branch circuits are used in outlets on different walls of the same room
 
for a headphone setup it is often easy to just power everything, source, DAC, Disc Player, Computer from the same outlet with a power strip - then the gnd noise should be much less
 
 
 
while separating the power xfmr CT/diode/cap current pulses in a "dirty star" with a single branch to the "clean star" is useful - the details of the "clean star" are much less important with headphone sized currents and wire of reasonable size for easy handling

 

[shake]

Thanks jcx, I'm understanding it better now.
 
The spec sheet for the transformer lists those safety standards, so I should be good on that.
 
You're just saying that I could do  it either way (earth ground or not), but earth grounding may introduce a lot of noise.

 

[wakibaki]

Quote:

Ah ok.  Screened cable = shielded cable.
 
I just check out the spec sheet of the RCA input jacks I'm going to use, and it looks like they can be installed to be grounded to the case or isolated from it with the supplied washers.  So if I isolate them from the case, I connect the input ground/'negative' terminal close to the output ground?
 
Which end is which?

That's what I'm trying to find out.
 
I'm using ALPS rk27 pots, which have ground terminals.  Do I just not hook the ground pins up to anything and have the input ground going straight to the output ground?

 
Right, the screened cable I was envisioning was a single core with the screen carrying ground. Things get a bit complicated in a stereo system. The problem is to accommodate the two amplifiers in a single case often with a single PSU and still provide suitable segregation for good crosstalk performance. You could use a dual-core in which case the cores would carry L & R, but it's better to keep them separate, although obviously if you have a 3-pin (signal) inlet then the screens would be connected together at both ends. I'd go for the dual core in that case. It's the ground returns in a common connector which are primarily responsible for crosstalk, as opposed to inductive pickup in conductors in close proximity. You connect one end of the screen to the common inlet terminal (sleeve) and the other end to the star ground, either at the PSU if you go for a single star or at the sleeve of the output jack if you go clean/dirty.
 
The Alps RK27 pots don't have a terminal allowing the case to be grounded, in the rare cases where this is done a flying lead is usually soldered to the pot case.
 
One side of the pot (one terminal) will, however, be connected to ground, and this connection must be made, to the star in whichever topology you choose.
 
w

 

[shake]

Haha, I think there was kinda a misunderstanding/miscommunication.  I had asked where I put the input ground since earlier in the thread, Avro said there was no ground channel because I was using a dual power supply.  I was trying to figure out if i just completely ignore the input ground (which doesn't make sense) or I just ground it at the star point.
I'm not so clueless that I don't know what to do with the input ground, but what Avro said confused me a bit .
 
Quote:

The dual rail power supply eliminates the need for a ground channel.
You just use left and right channels.

 

[Avro_Arrow]

It's pretty easy to have that happen on a forum like this where people have all levels of experience
and you have to make some assumptions about someone else's knowledge. Sorry if I caused
any confusion.
 
Quote:

Haha, I think there was kinda a misunderstanding/miscommunication.  I had asked where I put the input ground since earlier in the thread, Avro said there was no ground channel because I was using a dual power supply.  I was trying to figure out if i just completely ignore the input ground (which doesn't make sense) or I just ground it at the star point.
I'm not so clueless that I don't know what to do with the input ground, but what Avro said confused me a bit .
 

 

[shake]

Time to troubleshoot!
I flipped the power switch and the power LED didnt' turn on.  I'm measuring 60-70 VAC from the secondaries to earth ground.  Is that right?

 

[Avro_Arrow]

The Earth Ground and Transformer Secondaries should have no relationship to one another.
 
What is the AC value before the rectifier and the DC value after the rectifier?
 
Pictures?

 

[shake]

Measuring AC at the switch, I'm getting 121V.  Measuring DC output, I'm getting 22V from the + to - rail on one side, 23.5 on the other.  I'll post pics asap, but it won't look pretty and probably won't help.  The transformer should be a dual 30V.

 

[Avro_Arrow]

If you have a transformer that is rated 30 volts AC at some load, when the load
is less, then the voltage goes higher. How much higher depends on the design
of the transformer. After the AC is rectified, it goes higher still, by 1.41 times.
So, for your 30 volt AC secondaries, you could expect a minimum of 42.3 volts DC.
 
Does your voltage vary when you adjust the trim pots?
Maybe your LED is hooked up wrong...

 

[shake]

I was going through the traces and noticed that I had a bad connection from the negative terminal of one filter capacitor to the next and fixed it. Now I'm getting 14.9V on both sections after the regulator, so I think that's good.
However, I did wire the power section weird in that on the schematic, I have:

But on the board, due to carelessness at 3am, it looks like this:

Is this still ok to tie them in at the end in the middle for ground or will I now have unregulated +15v and -15v rails?
Also I misspoke, the transformer is 30VAC in series, not parallel.  And yes, the voltage is a little higher (23V) at it's output.  Then it goes through the regulators and drops to ~14.9.  I have a $30 Craftsman multimeter, so measurements are probably a little off.
What I'm trying to find out is: Is it ok to tie them in the middle like this?