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Old 13th November 2009, 06:01 PM   #5801
galop is offline galop  Slovenia
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problem solved.I was split 0 on transformer.thank you very much.
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Old 13th November 2009, 06:11 PM   #5802
tinitus is offline tinitus  Europe
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Galop, nice to hear

Oh, it was just a thought with the combined thermal switch and softstart
I have just been told that my delivery of heatsink weighs in at 45kilo, so I expect no need

Balanced F5x
I would still like some opinions about load issues with a balanced F5(X)
Sure, its a nice way to get more power, and retain the low voltage with less strain on curcuit
And I suppose we have a natural double bias, with standard settings
But amp will also "see" half impedance of actual speaker load
I do have matched quads of all, and could do it with double outputs etc
But Im not sure I want to go that way, even tho it does have some attraction
It would need complicated balanced signal
And I have never really preferred the sound of balanced gear over traditional
To me, balanced gear sounds a bit "mechanical", but I know it could have been related to something else
Any opinions appreciated

Last edited by tinitus; 13th November 2009 at 06:17 PM.
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Old 13th November 2009, 07:13 PM   #5803
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I've just built my first amp the F5 2 weeks ago and what a great feeling of accomplishment.
The fact that is sounds great makes it all worth the time and effort.
I built the B1 a couple of days after the F5 and built speaker inclosers with the help of planet10-hifi drawings on the Fonken-steen. The drivers a F120A that I bought of ebay that were already enambled! They seem to sound better since I first installed them 3 or 4 days ago.
Now for the bad news. One of my channels started to distort last night. Made crackling noises through the music. I took the speakers off and measered the dc offset. It seem to fluctuate but was around 120mV. Oh that particular channel was also cool to the touch. I checked the voltage between R11 and R12, the volts were dramatically different. I forget which one though, one was around 4mV and the other 120mV. I proceeded to adjust them down checking the resistors and the dc offset at the speaker terminals. The offset wouldn't stop flucuating and P1 for some reason took alot to see any change in volts between R11. Once the two resistors were equal I started to move the voltage back up once I got around .52 volts R11 started to go crazy and soon after both R11 and R12 burned up. Dope! Sorry this is still all very new to me. I'm not sure what could have made the dc offset to act so sporadically the way it did.
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Old 13th November 2009, 07:16 PM   #5804
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Quote:
Originally Posted by gaborbela View Post
Thanh
I think if you read the post of Mr. Pass and EUVL you get answer for your question .
By the way are you planing to use multiple power mosfet or just one pair on each board .
Or you will design a PC board to the X both half together ?
I use separate PC board like Smyslow .
I'm very happy the Master himself gave answer to our question , also Patrick answer is very valuable !
Now I will go on and each the PC boards .
Greets
Yes, I am very happy with the answer provided.
Regarding output mosfets, I will probbably go with 2 pairs or 3 pairs per half (ie total of 4 pairs or 6 pairs per channel)
However, it might end up being 6 pairs per channel, only because I have already built one working channel (regular version) with 3 pairs.
If I was building from scratch then I would probably go with 2 pairs on each half (4 pairs per channel).
However I think you mentioned you already have the devices laying around not being used, so go with what you feel comfortable with.
See how many you get matched and go with that. From what I have heard the Toshiba devices tend to be quite good in terms of them being closely matched straight from the factory.

Last edited by Melon Head; 13th November 2009 at 07:29 PM.
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Old 13th November 2009, 07:22 PM   #5805
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Hi bluewater
Check for cold solder joints.
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Old 13th November 2009, 07:36 PM   #5806
Tea-Bag is offline Tea-Bag  United States
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Quote:
Originally Posted by thanh1973 View Post
Hi bluewater
Check for cold solder joints.
I concur.

Replace 11 and 12, replace MOSFET's, re-heat questionable solder-joints. Check isolation pads or replace, test for shorts to ground before re-assebling and retry. Your not the first one to fry a channel.
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Old 13th November 2009, 07:48 PM   #5807
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Would it be good to test while I have it still mounted and connected for searching for shorts.

Thank you for the replies
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Old 13th November 2009, 08:05 PM   #5808
Tea-Bag is offline Tea-Bag  United States
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not in my mind, as it is tied into ground via the power supply. I lift that and test.
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Old 13th November 2009, 09:17 PM   #5809
Ryssen is offline Ryssen  Sweden
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Quote:
R11 started to go crazy and soon after both R11 and R12 burned up.
Sommething not so funny happend,I heard it sounded distorded
and I opened the F5 ,and at the bottom was R11 from one channel and R12 from the other laying...lose...
I have messaured on the mosfets and theres no short or opencircuit on the mosfets.
Those resistors must have been quite hot..can I just solder new ones and try?
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Old 13th November 2009, 09:52 PM   #5810
CBRworm is offline CBRworm  United States
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If they were the correct wattage resistors (5 watt?) they should be hot, but not nearly hot enough to unsolder themselves.

What is common between both channels? An external short between the two positive speaker terminals? Power supply (or ground) problem? Was the bias unreasonably high on both channels? Oscillation on both channels?

Luckily there are not very many components to troubleshoot.
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