I finally have a Hum free F5t thanks to the help from members here, Its not wired Idealy yet but can only hear hum when my ears are close to the speakers, well its not really hum and that might be coming from my Laptop! so all good.
thanks to those who suggested I use Tea-Bag's PSU boards.
thanks to those who suggested I use Tea-Bag's PSU boards.
Ok thanks a lot, as long as that body can not conduct and into the chassis ground then all good 
Actualy the thermistors have a grainy type surface, I couldn't find the type you guys and nelson use Orange/brown mine are.
also second prob is I have 2x 5A Slow Blow fuses 1 on each wire after the transformer. they blow when I turn the amp on with the inrush current so I Put in some household 13A fuses and problem temporarily solved
I think I even tried an 8A fuse and that blew! lol so at this moment I might just buy some 13A that fit.
Actualy the thermistors have a grainy type surface, I couldn't find the type you guys and nelson use Orange/brown mine are.
also second prob is I have 2x 5A Slow Blow fuses 1 on each wire after the transformer. they blow when I turn the amp on with the inrush current so I Put in some household 13A fuses and problem temporarily solved
I think I even tried an 8A fuse and that blew! lol so at this moment I might just buy some 13A that fit.
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Hold on, that doesn't sound right. Don't put in fuses that are higher rated than needed.
You might want to build one of those light bulb testing rigs. Put the bulb in seris with the primary. There are some examples somewhere around here.
Did you try some CL60 NTC thermistors on the primary side of the transformer? These will allow a slow turn-on. As the thermistor warms up, it passes more current.
See PS schem for F4 in PDF attached. Use the 240 version for UK, if that's needed.
Be safe!
Vince
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Light Bulb Testing Rig - For Electronics testing
For safty, be sure all connections in the testing rig are fully insulated.
Only thing missing from the sketch is the earth ground. Include it as well.
If the bulb lights bright, there is something wrong, but circuit will be protected.
Some with better theory can explain it better.
For safty, be sure all connections in the testing rig are fully insulated.
Only thing missing from the sketch is the earth ground. Include it as well.
If the bulb lights bright, there is something wrong, but circuit will be protected.
Some with better theory can explain it better.
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To me it sounds like you have fuses on the secondary side of the transformer, possibly in the DC after the rectifiers.
You need only ONE fuse and it can go in series with one of the primary wires. This will be a lower rated fuse because the power coming in is at 120V, so you only need a few amps of current, then the transformer reduces voltage and increases current on the secondary side. This is why I suspect you are using fuses on the secondary. Also using one single fuse on the primary means that if it blows EVERYTHING shuts down all at once. You dont have to worry about one rail being on while other is off.
Edit: I see you DO have a fuse on each rail. Dont do this. Its bad juju.
You need only ONE fuse and it can go in series with one of the primary wires. This will be a lower rated fuse because the power coming in is at 120V, so you only need a few amps of current, then the transformer reduces voltage and increases current on the secondary side. This is why I suspect you are using fuses on the secondary. Also using one single fuse on the primary means that if it blows EVERYTHING shuts down all at once. You dont have to worry about one rail being on while other is off.
Edit: I see you DO have a fuse on each rail. Dont do this. Its bad juju.
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If the F5 misses a rail, it puts out a full-rail DC offset for a half second, and then the offset stabilises pretty close to zero and music plays just fine. There is some discussion on this in one of the posts on this thread.
Found out the hard way when one of the rail cables worked loose, my speaker took it on the chin and survived.
You should worry. I smoked my first F5 build due to a crack in the paint on a thermistor that caused a short to the MOSFET drain lead. In subsequent builds I have used thermal epoxy and a tiny piece of mica between the thermister and the drain lead.
Hi, there is a CL60 NTC on the power in to primary of the transformer
vdi_nenna, my PSU has only a single centre tap wire so cant put the 2 NTC on.
Amp works fine i presume that just the inrush is blowing fuses.
udailey, I have fuses on the secondary one on each secondary wire before caps, I have 2 secondary green wires and 1x black centre tap. I have a fuse on the primary too before the thermistor. that was blowing too at 6A. Im on 240v here.
Ok i shall remove fuse on the rails and just have one main fuse on primary side.
sangram, yes when I was putting the oversized 13A fuses in I noticed one didnt go in properly. I ended up with the amp playing only the positive rail, as you say still played music but was half missing a bit distorted.
vdi_nenna, my PSU has only a single centre tap wire so cant put the 2 NTC on.
Amp works fine i presume that just the inrush is blowing fuses.
udailey, I have fuses on the secondary one on each secondary wire before caps, I have 2 secondary green wires and 1x black centre tap. I have a fuse on the primary too before the thermistor. that was blowing too at 6A. Im on 240v here.
Ok i shall remove fuse on the rails and just have one main fuse on primary side.
sangram, yes when I was putting the oversized 13A fuses in I noticed one didnt go in properly. I ended up with the amp playing only the positive rail, as you say still played music but was half missing a bit distorted.
Exactly my point, this is my plan then, thanks
and my washers fill the whole Mosfet so I cant lay the thermistor against it as all there is is washer.I'm not sure what you are describing. This pic shows two extra thermistors for a cooling system, but they all work well on the washer.
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Yes, no problem there mine looks like yours, i was going to have thermistor touch the black Mosfet case but cant as washer is massive so will have thermistor with a small slice of mica in-between.
I Don't want to make same mistake as post #13272
There is a simple but effective way of protecting your speakers from large DC offset caused by a blown supply fuse, don't use them.
However this does not help in the case of a faulty amplifier or PSU; and that is where an appropriately sized polyswitch is useful.
Buy Resettable Wire Ended Fuses RHEF polyswitch resettable fuse, 0.5A TE Connectivity RHEF050 online from RS for next day delivery.
Resettable fuse - Wikipedia, the free encyclopedia
Fit the polyswitch in the 0V connection between star earth and connection back to the rectifiers or center tap of the transformer; most amplifiers are fairly symmetrical in +/- supply rail current consumption, meaning that very little current runs through the 0V connection back to the transformer; in the event of a fault, large currents will run through the 0V connection, tripping the polyswitch and preventing damage to your speakers.
Only getting mono from my stereo F5
I finished the basic F5 a couple of years ago and really like the sound but felt that the imaging was lacking. Recently played it with a new pair of open baffle speakers for a friend and he said he thought the sound was mono. I got some test tones and sure enough when each channel was supposed to play by itself they both played and the sound was straight down the middle. So I started changing components and cables to isolate the problem. I tried an older receiver with similar results and then a third just for the heck of it and there was the stereo. At this point when using all my original setup, except the F5, I have stereo. It would seem that the F5 and also the second amplifier have a problem. I rebiased the F5, tried hooking up speakers out of phase, checked the star ground setup and as far as I can tell I have wired correctly. I am at a loss and wonder if anyone could give me some advice, aside from having my hearing checked so I might tell the difference between mono & stereo.
I finished the basic F5 a couple of years ago and really like the sound but felt that the imaging was lacking. Recently played it with a new pair of open baffle speakers for a friend and he said he thought the sound was mono. I got some test tones and sure enough when each channel was supposed to play by itself they both played and the sound was straight down the middle. So I started changing components and cables to isolate the problem. I tried an older receiver with similar results and then a third just for the heck of it and there was the stereo. At this point when using all my original setup, except the F5, I have stereo. It would seem that the F5 and also the second amplifier have a problem. I rebiased the F5, tried hooking up speakers out of phase, checked the star ground setup and as far as I can tell I have wired correctly. I am at a loss and wonder if anyone could give me some advice, aside from having my hearing checked so I might tell the difference between mono & stereo.
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