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Old 18th August 2013, 09:09 PM   #11
AndrewT is offline AndrewT  Scotland
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post8 diagram is wrong.

The PSU shows two links to MAG.
These two links must go to each other.
Only the right most cap pair (Zero Volts) links to MAG.

The 8 components at the right, 6caps and 2 resistors, probably do nothing to improve the output of the PSU. I suggest you delete all 8.
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Old 18th August 2013, 09:18 PM   #12
AndrewT is offline AndrewT  Scotland
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I don't like diagrams of posts 9 & 10.
Post9 shows the Zero Volts carrying charging pulses being used as the MAG. No the MAG is NEVER on the PSU Zero Volts.
Post10 shows the power connections split up into 4 single wires. The Zero Volts should be joined and the V+, V- and Zero volts must be close coupled as a power triplet to pass over the MAG on the way to each amp PCB.
Similarly the Signal Grounds are split creating a hum loop as soon as the Source to Amp Interconnects are plugged in.
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Old 18th August 2013, 09:20 PM   #13
iggy111 is offline iggy111  Croatia
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Quote:
Originally Posted by aparatusonitus View Post
Ok, so you are using single PSU to power both channels? If that's the case do it like in the images below ;-)
Edit: Take output (speaker) ground for left channel from power ground point at left channel pcb, do the same for right channel.
1. What is that between the reservoir caps in the first image?
2. Why connect speaker return to power gnd, isn't it better to connect it directly to main ground?
3. Could you explain what those antiparallel diodes do exactly?

I see that this way you make use of twisting the V+/V-/Gnd wires going to amp boards, right now I just twist V+/V- together.
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Old 18th August 2013, 11:37 PM   #14
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Quote:
Originally Posted by iggy111 View Post
which of these are you saying I should do:

1. connect signal gnd to bottom of R2 and then wire to MAG, also give nfb gnd a separate wire to MAG

OR
2. connect signal gnd directly to MAG, and connect bottom of R2 to nfb and then wire to MAG?
Its looking like your 2 is what I am suggesting. In your pic the signal ground is shaped like a letter 'T' - I'm saying cut the top left connection (IN-) to that 'T' and give that IN- node only its dedicated wire to MAG. The other connections to signal gnd to remain as is.

<edit> On your PSU wiring pic, why those particular two wires to MAG? Seems to me you do want two wires but not those, rather you want a wire from the -ve and a wire from the +ve. As it is you have fairly major charging currents (those for the 2nd cap) running through MAG. None too pretty.
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Last edited by abraxalito; 18th August 2013 at 11:40 PM.
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Old 19th August 2013, 12:36 AM   #15
iggy111 is offline iggy111  Croatia
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Quote:
Originally Posted by AndrewT View Post
post8 diagram is wrong.

The PSU shows two links to MAG.
These two links must go to each other.
Only the right most cap pair (Zero Volts) links to MAG.
Hmm, I'd have to dig up that post where I first saw those two separate wires, it's somewhere in that huge discussion about PSU quality... but then again, I'm the one usually wrong here so I'll definitely change that.

Quote:
Originally Posted by AndrewT View Post
The 8 components at the right, 6caps and 2 resistors, probably do nothing to improve the output of the PSU. I suggest you delete all 8.
I can understand removing the 3.3uF, but remove the bypass 100nF and snubbers?! Why? Isn't bypassing large capacitors a proven method, and don't snubbers remove the diode switching noise and help with the psu impedance?
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Old 19th August 2013, 08:43 AM   #16
AndrewT is offline AndrewT  Scotland
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the snubber is in the wrong place.

The bypass increases the quiescent ripple being fed to the quiescent amplifier
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Old 19th August 2013, 09:35 AM   #17
iggy111 is offline iggy111  Croatia
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I'll test it without the bypasses. Where should I put the snubbers then - before or after the first reservoir caps?
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Old 19th August 2013, 09:42 AM   #18
AndrewT is offline AndrewT  Scotland
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across the transformer tappings right next to the rectifier.
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Old 20th August 2013, 05:46 PM   #19
iggy111 is offline iggy111  Croatia
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I made some changes to the PSU:
- removed one of the wires going to MAG, connected first reservoir ground to second reservoir ground
- moved the snubbers to the transformer tappings
- removed the 3.3uF caps
- moved the 100nF bypasses directly to the pins of second reservoir caps

Can't say I hear any difference. The slight hum is exactly the same as it was, it is still a bit louder in the left channel (with some very slight buzzing), but that's basicaly irrelevant, can't be heard even at 1m from the speakers.

I still have to try the signal / nfb ground change, and decoupling MAG from chassis ground, so I'll post again.

PS - I have lots of changes going on (P2P, grounding, LDRs, paralleling Simics...) but changing the gain and adding diodes in series with V+ and V- make the greatest positive changes. Here's a link to diodes trick
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Old 20th August 2013, 07:51 PM   #20
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Quote:
Originally Posted by iggy111 View Post
1. What is that between the reservoir caps in the first image?
It's just a CMC (common mode choke)...in your amp psu you have an RC filter, you can make it a bit better if you place another R (like 0R1/10W in front of first filter capacitor so your PSU become an RCRC filter. Don't put more then 0R1, 'cos there is already dynamic impedance of diode bridge + resistance from transformer secondaries + transformer leakage inductance reactance.

Quote:
Originally Posted by iggy111 View Post
12. Why connect speaker return to power gnd, isn't it better to connect it directly to main ground?
No, in theory at least, all input, feedback and output ground should be referenced to the same point - power ground as close as posible to amp supply pins/decoupling capacitors.

Quote:
Originally Posted by iggy111 View Post
13. Could you explain what those antiparallel diodes do exactly?
It's a ground separator, protecting you from killing yourself and potential ground loops from the rest of you system (house wireing).

Quote:
Originally Posted by iggy111 View Post
Can't say I hear any difference. The slight hum is exactly the same as it was, it is still a bit louder in the left channel (with some very slight buzzing), but that's basicaly irrelevant, can't be heard even at 1m from the speakers.
Do exactly as I show you before, with lots of wire twisting of equal length for left/right channel, stay away with wireing from transformer, or place wire perpendicular to transformer radius (if it's toroidal), do not parallel line carring high current with signal lines, make them cross if you have to. If you follow this rules, you will not hear any noise or buzzing from your speaker any more.
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