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Old 5th February 2009, 03:22 PM   #2701
labjr is offline labjr  United States
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Quote:
Originally posted by woodturner-fran
Something odd is going on with my F5. When I push the volume a bit I get lots of breakup distortion.

Need to investigate this.....


Fran
Are you sure you don't have a bad panel on those old Quads?
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Old 5th February 2009, 03:23 PM   #2702
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Default F5 with NS1000M Speakers

Hi,

does anyone have an opinion about the use of the F5 with NS1000M speakers?
These are rated at 6 Ohms with 90 db /1 m, at 1 watt.

I am currently using these speakers with an Aleph 5 PA and I am wondering what sort of difference (apart from power) I can expect if I were to switch to a F5.

Thanks for the advice and a great thread
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Old 5th February 2009, 05:16 PM   #2703
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No, none of those are the problem. What it is is R11 and R12 gone open circuit.

I have now lost 4 of these resistors in total. First 2 were totally my fault, I let them overheat stupidly. Now you could say the same about these but I set the bias low, carefully monitored heatsink temp and all looked ok. This happened after the amp was on for about 4 hours straight this morning. Heatsinks didn't get any hotter than usual and were stable.

So it seems the thermistors are a bit of a must. Either that or else those resistors are bad, and thats not too likely now is it!

So for now I have some 0.39R power resistors that I will fit instead. Unfortunately I broke one of the thermistors so its gonna be a bit of a wait until the next mouser order arrives here (will order tonight) to implement the heat compensation. I think though I will refit the current limiting when I'm at it.

Tell me this, the current limiting will work independantly of the heat compensation right?


Fran

This has been hard!!!
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Old 5th February 2009, 06:50 PM   #2704
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Cviller
i would like to order two F5 PCB but , as it is my first post in this forum though i read it for a while, i can't email you. May be you could email me instead? It seems that i need your email adress to send you a payment with paypal. Do i need to fill the wiki too?
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Old 5th February 2009, 09:01 PM   #2705
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you should send a message to peter on this thread
http://www.diyaudio.com/forums/showt...postid=1735972 I think he still has some f5 board and psu left
payment details can be found here http://www.diyaudio.com/forums/showt...05#post1680605
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Old 5th February 2009, 10:36 PM   #2706
Formerly "jh6you". R.I.P.
 
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Default Re: F5 with NS1000M Speakers

Quote:
Originally posted by georgebrooke


does anyone have an opinion about the use of the F5 with NS1000M speakers?
These are rated at 6 Ohms with 90 db /1 m, at 1 watt.

"It will drive a 2 ohm load without burping ...", said Papa.

>><<
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Old 5th February 2009, 10:38 PM   #2707
Formerly "jh6you". R.I.P.
 
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Quote:
Originally posted by woodturner-fran

Tell me this, the current limiting will work independantly of the heat compensation right?

Right.

>><<
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Old 5th February 2009, 10:48 PM   #2708
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Time for another post of weird problems from woodturner-fran. I swear I think me and this build is cursed.


Anyway. One channel is somehow "blowing" R11 and R12. What you hear is a gradual lessening of volume in that channel - ie soundstage shifts left. This happens say over the course of a song and it has been fine up to that. So previous to this, both channels biased up perfectly on the bench, really nicely, had offset at <5mV, match on voltage between R11 and R12 was within 5 or 10 mV and was steady once heatsink was warmed up ie not gradually creeping. This is somehow confined to this channel too - this is the second time today that the same thing has happened to the same channel.

On the "good" channel, bias is absolutely steady when playing music, in this case 0.45V (with 0.39R R11) Bias on both halves matches really well.

On the "bad" channel, bias flickers a bit running up and down by maybe 30 or 40mV(when playing music). Stop the source and the bias settles back to a steady value over a few seconds.

So after maybe 10 mins of this lower sound level you hear a little "fissp" and down the channel goes. R11 and R12 are blown open but are not hot - ie its not like they really roasted. In fact I had been watching the temp of them and it was steady on both channels at 50deg C. Swapping the ICs from the source makes no difference, swapping the speaker leads swaps the problem to the other speaker (ie its not the source and not that speaker).


It seems like it really doesn;t like playing music!!!


So could anyone advise what to do? I have to admit I am completely dumbfounded and don't know what to do.


Fran
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Old 5th February 2009, 11:01 PM   #2709
labjr is offline labjr  United States
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I haven't built the circuit yet but, I'd check all the parts to make sure they're installed properly and the values are correct .

Next, by process of elimination, I'd start swapping parts with the other channel to see if you can move the problem to the other channel. I might start with the bias pot. Then I would try moving the outputs. Maybe one of the outputs is acting flakey.

There's not much in the circuit so it shouldn't be too difficult to isolate the problem.
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Old 5th February 2009, 11:05 PM   #2710
massimo is offline massimo  Italy
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Double check o/p devices insulation too (i.e. micas, silicon pads etc.)
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