An illustrated guide to building an F5

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6L6

6L6

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Joined 2010
Paid Member
AndrewT said:
Speaker negatives they are not.
You mean speaker ground or as I prefer to call them speaker Return..
You can locate the Main Audio Ground somewhere between all the other Audio Grounds.
But, not on the smoothing Caps link.
Click to expand...


Trying this has been in the queue for a bit longer than I was hoping. Sorry.

Long story made short, Andrew is quite correct -- placing the speaker Negative at the point where the input and the PSU all connect has made it quieter by an order of magnitude. :eek::)

Even the transformer even has less mechanical hummm.

So, the scheme is -

PSU GND to circuit board GND. Input and speaker negative all attach at that point.

In the photo;
PSU GND (white)
Speaker Negative (black)
Speaker Positive (red)
V+ (green)
V- (blue)

F5newMAG.jpg


F5newMAGclose.jpg


It looks a bit kludgey, but remember that the PCB is quite small (2x3 inches)
 
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U

Uunderhill

Member
Joined 2008
6L6 said:
-- placing the speaker [Gnd] at the point where the input and the PSU all connect has made it quieter by an order of magnitude. :eek::)

Even the transformer even has less mechanical hummm.

So, the scheme is -

PSU GND to circuit board GND. Input and speaker [Gnd] all attach at that point.
Click to expand...

6L6,

Thanks for rewiring the Gnd's on your F5

and letting us know the star Gnd node should be on the Amp board.

Pleased to know it worked so well.
.
 
A

AndrewT

R.I.P.
Joined 2004
It does not have to be on the amp board.
Where it must not be is on the PSU where the smoothing caps join together.

If you look at post 401 you can see two connections on a wire link standing out from the PCB. One from PSU and one from Speaker.

I can't see where the signal screen is connected.
 
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A

AndrewT

R.I.P.
Joined 2004
are both the pads GND,
I can't tell by the pic.
Could those two adjacent pads be GND and signal return/ground?

I would expect signal hot and signal return to be adjacent.
Then power ground to be elsewhere.
the pic in post402 & post404 show that the two pads are different, one for power ground and the other (middle pad) for signal ground. The third pad is signal hot.
 
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A

AndrewT

R.I.P.
Joined 2004
Ah!
breaks my rule of keeping Sig Gnd separate from Power Gnd.

But with the star ground so close (at the other end of that short wire) the effect is very small. I would still prefer to see sig gnd separate though. That keeps the option to insert a resistor, or to insert a link to maintain the voltage reference from in to out..
 
A

AndrewT

R.I.P.
Joined 2004
No, the input socket is connected directly to the +IN and -IN pins of the amplifier.
The NFB if any is also connected to the signal -IN pin

The Power Ground is completely separate.

Then one finally references the signal ground to the power ground at the Main Audio Ground. The signal ground connection to this MAG can have a series resistor since it carries virtually no current (I'm talking pA here).

To allow this to happen the sig gnd must be separate from the amp Power Gnd. Many amplifier layouts maintain this separation.
 
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