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Old 9th April 2011, 07:25 PM   #21
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Do you have Thermistors soldered on place "HL" on capacitor board, and did you groung this GND trace to the right point ?
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Old 10th April 2011, 03:41 AM   #22
anilva is offline anilva  India
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Quote:
Originally Posted by komigenie View Post
Do you have Thermistors soldered on place "HL" on capacitor board, and did you groung this GND trace to the right point ?
Yes. The point is grounded to Chassis and also Power Earth, as per Papa's PS schematic.
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Old 10th April 2011, 12:20 PM   #23
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Have you tried reversing the AC leads to one of your diode bridges?
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Old 19th April 2011, 07:36 AM   #24
anilva is offline anilva  India
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Default Update on hum removal efforts

I got a chance to try around with a few things to remove the small amount of AC hum coming out of the speakers (when I place my ear close to the speaker).

Firstly I measured the AC hum at the output. It measures 7mV with input open and ~4mV with input shorted.

I tried turning the toroid 90 degrees, reversing the AC leads to the bridge rectifier, rerouting the wires. No big difference. Faint hum still exists and the hum levels measure 3.5mV at the output.

I reduced the bias to 100mV on R11/R12 to see if the capacitance I have on the PSU is the cause. Hum levels are much much lower, but not gone yet.

Hence I am unable to put my finger on what is causing the hum. I will upgrade the caps and check.
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Old 19th April 2011, 10:21 AM   #25
AndrewT is offline AndrewT  Scotland
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Is your PSU Zero Volts separate from your Main Audio Ground?

Turning down the bias reduces the mains ripple on the PSU. The F5 produces less Hum as a result.
It is either PSRR letting excessive ripple through to the output or supply rail ripple modulation that is radiating into the low level circuits.
or
something else.

A target for a hum free system is <0.1mVac at the output. A lesser target is <=0.6mVac at the output. This should just about be inaudible with medium sensitivity speakers.
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Old 19th April 2011, 03:38 PM   #26
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See posts 13 and 15......

When you tested by decreasing your bias, you reduced the current flow thru your MOSFETs. That, in turn, reduces the load on your power supply, which effectively reduces your power supply ripple--and thereby reduces your hum. Your testing suggests you are close to finding the cause.

If you have additional caps of similar mfd and voltage ratings, do a test--temporarily wire them into your power supply, to increase your filter's capacitance. If the hum is reduced/eliminated, add those caps to your final construction. (As noted in the earlier posts (13 and 15), may be prudent to roughly double the total capacitance of your cap banks.
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Old 19th April 2011, 03:45 PM   #27
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Another troubleshooting option:

1. Select the one channel with the most hum

2. Disconnect the OTHER channel from your PSU rails

3. Doing so will reduce the load on your PSU (to about half). This in turn would reduce the PSU ripple voltage accordingly.

4. Listen to the one channel that remains connected. If the hum is reduced in this channel, then I'd focus on your PSU capacitance.

5. If no difference (step 4) I'd look further for potential ground loops.
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Old 19th April 2011, 05:00 PM   #28
dazed2 is offline dazed2  Canada
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I think I already posted this somewhere else but try this (note I am not familiar with cvillers board)

1) Remove the ground wire(s) from the two boards altogether.
2) attached the ground connection from the board to the RCA ground that is inside your shielded input wire.
3) do NOT connect the shield of the input wire at the board.
4) connect the shield at the input RCA ground side.
5) connect the L and R RCA ground together. (at the inputs/binding post)
6) connect a wire at mid point of the L and R RCA wire to the PS ground.

That should eliminate hum. It did on mine.

Last edited by dazed2; 19th April 2011 at 05:06 PM.
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Old 20th April 2011, 02:16 AM   #29
anilva is offline anilva  India
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Quote:
Originally Posted by AndrewT View Post
Is your PSU Zero Volts separate from your Main Audio Ground?

Turning down the bias reduces the mains ripple on the PSU. The F5 produces less Hum as a result.
It is either PSRR letting excessive ripple through to the output or supply rail ripple modulation that is radiating into the low level circuits.
or
something else.

A target for a hum free system is <0.1mVac at the output. A lesser target is <=0.6mVac at the output. This should just about be inaudible with medium sensitivity speakers.
Andrew, thanks. In the Cvillers board, the audio ground and '0' V are connected together. The board draws the 0V from the PSU PCB, which is a standard Papa design. The 0V at PSU PCB is taken to the chassis ground through a 10ohms thermistor as per Papa's design. Pretty much standard connections like in a FW F5.

The input wires are simple thin multistrand ones, twisted together and connected from RCA inputs to the F5 PCB. No shielding. Earlier used coax cable and created a racket as well. Now I am thinking of buying a twisted pair shielded cable and try.

Quote:
Originally Posted by CanAm Man View Post
See posts 13 and 15......

When you tested by decreasing your bias, you reduced the current flow thru your MOSFETs. That, in turn, reduces the load on your power supply, which effectively reduces your power supply ripple--and thereby reduces your hum. Your testing suggests you are close to finding the cause.

If you have additional caps of similar mfd and voltage ratings, do a test--temporarily wire them into your power supply, to increase your filter's capacitance. If the hum is reduced/eliminated, add those caps to your final construction. (As noted in the earlier posts (13 and 15), may be prudent to roughly double the total capacitance of your cap banks.
CanAm Man, thanks. I do not have additional capacitors for testing. I have ordered them and once they reach me, will test with additional capacitance. I will test with one channel and see meanwhile.

Quote:
Originally Posted by dazed2 View Post
I think I already posted this somewhere else but try this (note I am not familiar with cvillers board)

1) Remove the ground wire(s) from the two boards altogether.
2) attached the ground connection from the board to the RCA ground that is inside your shielded input wire.
3) do NOT connect the shield of the input wire at the board.
4) connect the shield at the input RCA ground side.
5) connect the L and R RCA ground together. (at the inputs/binding post)
6) connect a wire at mid point of the L and R RCA wire to the PS ground.

That should eliminate hum. It did on mine.
I am confused a bit. Going by your suggestion, there seems to be a loop created with the shielded wire isn't it? Can you point out to your earlier post tha you are referring to?

Cheers.
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Old 20th April 2011, 02:53 AM   #30
dazed2 is offline dazed2  Canada
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Well since you just said that the input RCA wires are not shielded, that won't be a problem.

Basically what I did was allow any noise that the may be amplified to run away from the amp board.

Right now, what you have is any noise that the RCA picks up, go towards the amp and flows from the amp board to PS ground.
Which will lend it being amplified.
The way I did it was to have any noise that may be picked up, flow away from the amp, and have it grounded closer to the RCA posts. Thus the grounding to the PS ground between the RCA's

In the pic I have the circled my grounding scheme. The black wire to the amp board has the signal, ground, and shield. The signal is obviously connected at both ends, the ground is connected at both ends, but the shield is connected only at the RCA ground. The white wire connects the L and R RCA ground. I should have connected the white wire going to the PS ground in the middle, but that is for later mod.

Anyways please ignore the mess in there. new caps on the way.
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Last edited by dazed2; 20th April 2011 at 02:56 AM.
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