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Old 15th November 2012, 11:47 AM   #12681
udailey is offline udailey  United States
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Quote:
Originally Posted by tolikas View Post
Hi,

any ideas how to fight F5 Hum problems? I use 1 torroidal trafo (600w), is it possible for him to be the source of AC line humming? I am 100% sure that audio boards, power supplies, grounds are ok.

Would AC line filter before trafo help?

Thanks
100% sure is a sure way to miss a problem. Leave it for a day or two then cone inspect again. It's a grounding problem. I'm 99% sure
Get a few long wires and put alligator clips on them. Attach to earth and poke around other grounds while listening. Works for me.
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Old 15th November 2012, 12:00 PM   #12682
Marra is online now Marra  United Kingdom
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Don't signal and speaker ground connect to the pcb's with a single wire then going to power supply ground.Thats how I did mine with cvillers boards and its as quiet as a mouse.

http://www.diyaudio.com/forums/blogs...ck_f5_rev2.jpg

Last edited by Marra; 15th November 2012 at 12:03 PM.
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Old 15th November 2012, 12:02 PM   #12683
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Originally Posted by udailey View Post
Get a few long wires and put alligator clips on them. Attach to earth and poke around other grounds while listening. Works for me.
very good advice! worked for me too.
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Old 15th November 2012, 01:14 PM   #12684
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Look at the picture attached. The purple lines indicate the 0V star point. It is very important. connect both supply 0V points to the star point. From the star point all 0V connections run to individual channels. From the star point run wires to RCA inputs 0V (RCA's are isolated from chassis). keep wire lengths for left and right channels equal length. The only ground (earth) connection is indicated by blue. The mains earth is connected to the chassis there. On the power supply I have a 10ohm connecting chassis earth to the 0V point.

If you do exactly this, you will have a dead dead quiet F5 amplifier.
Actually my F5's internals look even better no offence,but leads are much shorter, star ground is at PSU PCB, ground runs only to diode bridges, and to audio PCB's from there...Plus one lead to chassis, via thermistor 4.7ohm.
I have a suspition , that trafo secondaries are catching noice from primary windings...
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Old 15th November 2012, 01:18 PM   #12685
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Quote:
Originally Posted by udailey View Post
100% sure is a sure way to miss a problem. Leave it for a day or two then cone inspect again. It's a grounding problem. I'm 99% sure
Get a few long wires and put alligator clips on them. Attach to earth and poke around other grounds while listening. Works for me.
Sounds easy and promissing, will post about results Thanks
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Old 15th November 2012, 01:21 PM   #12686
udailey is offline udailey  United States
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No. Secondaries will only pick up 60hz from primaries or 50hz, which they already have. Supply could pick it up but it gets rectified, then caps and series resistance should filter it. Other chance might be bad solder joint.
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Last edited by udailey; 15th November 2012 at 01:26 PM.
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Old 15th November 2012, 01:25 PM   #12687
udailey is offline udailey  United States
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Make sure to use test leads from ground in F5 to preamp as well.
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Old 15th November 2012, 02:05 PM   #12688
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Quote:
Originally Posted by tolikas View Post
Actually my F5's internals look even better no offence,but leads are much shorter, star ground is at PSU PCB, ground runs only to diode bridges, and to audio PCB's from there...Plus one lead to chassis, via thermistor 4.7ohm.windings...
No offence but its not how it looks on the inside it is how it sounds. Sometimes in trying to keep things neat and tidy the best grounding practices are not followed. I did initially wire the PCB's amp and PS according to layout and I did have hum / buzz. Its only when you start pulling things apart that you find the solution.
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Old 15th November 2012, 04:30 PM   #12689
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Quote:
Originally Posted by tolikas View Post
Actually my F5's internals look even better no offence,but leads are much shorter, star ground is at PSU PCB, ground runs only to diode bridges, and to audio PCB's from there...Plus one lead to chassis, via thermistor 4.7ohm.
I have a suspition , that trafo secondaries are catching noice from primary windings...
do not make a starground on the PSU pcb. thats a dirty ground.
can it be a groundloop you have? if its 2 ch amp with common PSU.
if thats the case. try a short fat cable between the 2 amp's GND.
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Old 15th November 2012, 04:52 PM   #12690
flg is offline flg  United States
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Originally Posted by udailey View Post
No. Secondaries will only pick up 60hz from primaries or 50hz, which they already have. Supply could pick it up but it gets rectified, then caps and series resistance should filter it. Other chance might be bad solder joint.
I would like to comment that a typical toroid will pass likely the whole audio band albeit not flat, thru it's primary - core and secondary windings if that's what the line has to offer. What I just read makes it sound like a 50-60Hz bandpass filter which it is far from

Quote:
Originally Posted by AudioSan View Post
do not make a starground on the PSU pcb. thats a dirty ground. can it be a groundloop you have? if its 2 ch amp with common PSU. if thats the case. try a short fat cable between the 2 amp's GND.
The forever argument? There are high current transients thru the diodes, first caps and back to the xfrmr. One recomended spot for the GND is at the -connection of the second cap(likely still on the Pwr Supply board). The reason is simple, you dont' want all that current going thru the extra wire to the amp circuit board GND having a resistnce that makes your low esr caps have the DSR/ESR of that wire added to the Vcc or Vee... But, the circuit board GND is also a good place IMHO
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Last edited by flg; 15th November 2012 at 04:58 PM.
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