Just don't forget that fuses usually need quite a lot of overcurrent before they blow. From the tech. specs. of fuses one finds that it is not uncommon that even fast fuses may withstand twice the mark current for up to half an hour or so, but it may also go much much quicker. Fuses seem to have exceptionally lousy tolerance figures.
I know very well short-circuit behaviour of the fuses /V = f(t), I = f(t)/ as I often participate at fuses/low voltage switchgear/ LV and HV cisrcuit breaker's short circuit tests at high power certifying testing plant.
With my very first amplifiers i had T4.0A, they were useless. I once had an ouputstage exploding (did not use genuine transistors), one transistor exploded and the complementary shorted, giving full DC at output. It took me a few seconds to pull the plug, the speaker was blown, the fuse not... 🙁 gladly it was only a testspeaker...
How long does it take for a fast blow fuse to blow ? I do not want to have blown fuse by very low frequency.
Pavel, don't you think your 6.3a fuses are too big ? In case of 8ohm speakers and above horror scenario you get only ~3.4a ?
John, 3A sounds good to me, my concern is only about fast blow, if these fuses are fast enough to be triggered by a half wave with low enough frequency ? The changes to the PCB are about supplyrails and power grounding. As symasym measures great while operating in ClassA and beeing quiet i did not want to change too much, it is only about induced even harmonics when operating ClassB which should origin from halfwaves flowing in the powersupply.
Maybe fuses with medium speed would be a good choice ?
I've been using the T2.5A for ~1.5 years now in previous amplifiers, they did not make problems yet.
Mike
How long does it take for a fast blow fuse to blow ? I do not want to have blown fuse by very low frequency.
Pavel, don't you think your 6.3a fuses are too big ? In case of 8ohm speakers and above horror scenario you get only ~3.4a ?
John, 3A sounds good to me, my concern is only about fast blow, if these fuses are fast enough to be triggered by a half wave with low enough frequency ? The changes to the PCB are about supplyrails and power grounding. As symasym measures great while operating in ClassA and beeing quiet i did not want to change too much, it is only about induced even harmonics when operating ClassB which should origin from halfwaves flowing in the powersupply.
Maybe fuses with medium speed would be a good choice ?
I've been using the T2.5A for ~1.5 years now in previous amplifiers, they did not make problems yet.
Mike
Upupa Epops said:
Do you have problems or not ?Christer, how to measure when the fuse will blow ? After knowing it the fuse is
...Mike
MikeB said:
Christer, how to measure when the fuse will blow ? After knowing it the fuse is
I suppose you have to test a large number of fuses at various currents and see how long they take to melt. That is probably not very practical to do. My comment was based on what the specs say for a number of fuses. The conclusion from the specs is that fuses are very unpredictable components, or at least the manufacturers are very careful not to promise too much.
Mike, I recomend to you read norms about consumer electronic, EN 65.... There you can find all... You will see, that problem isn't easy.... 😉 BTW, it should read every amateurs.... Some constructions, which we can see here, are very instructive from this look....
MikeB said:Hi !
New PCB is about to be finished, measuring should be done by ~tomorrow. 🙂 I hope it fixed the problem, if not, a complete redesign will be necessary...
I also added pins for REs in the input-ltp, these will become handy for versions with lower gain, suitable to be driven by preamps.
Mike
Hi Mike,
I just saw this. Are you making changes to the PCB layout? I was jsut about to etch some boards for this. Should I wait?
Thanks, Terry
still4given said:
Hi Terry, you don't need to wait, symasym sounds "wonderful" with actual layout, the problem is visible with measurements, but the distortions created are mainly even harmonics, barely audible...
It's just that layout is not perfect, and i can't sleep with that. 😀
It's possible that new layout is even worse... The existing layout is tested and built by many and definitely works without problems.
Mike
MikeB said:
Hi Mike,
I may just wait a little to see if you work it all out. I have a couple of things to work on while I wait. I want to change out the outputs in the Aleph-X I just finished to see if I can obtain the great sound that everyone seems to think it can produce. It's sure not there right now. I might take some time and see if I can troubleshoot the Leach Superamp I build and never got working as well.
I already have most, if not all of the parts I will need for your amp. I'd rather etch the "perfect" boards after you are sleeping well. 😀
Blessings, Terry
Hi !
I did some measurings today with new pcb, i attached a result...
My setup is very unlucky, the cd-player (signalsource) injects bad 50hz stuff with tons of odd harmonics. It is not caused by amp itself, if i pull the powerplug of the player everything is quiet...
H4 and H8 are caused by soundcard and player, everything else looks like it should, H2 is that big by design... (sightly bigger than in sims) PSU ripple is ~-110db, H3 is below -100db and the 17khz signal is caused by computermonitor...
Yipee, i changed the right stuff !!!
Next days i will make 2nd channel and listening, quick listening showed that the amp might sound slightly clearer/more transparent/detailed...
Mike
I did some measurings today with new pcb, i attached a result...
My setup is very unlucky, the cd-player (signalsource) injects bad 50hz stuff with tons of odd harmonics. It is not caused by amp itself, if i pull the powerplug of the player everything is quiet...
H4 and H8 are caused by soundcard and player, everything else looks like it should, H2 is that big by design... (sightly bigger than in sims) PSU ripple is ~-110db, H3 is below -100db and the 17khz signal is caused by computermonitor...
Yipee, i changed the right stuff !!!
Next days i will make 2nd channel and listening, quick listening showed that the amp might sound slightly clearer/more transparent/detailed...
Mike
Attachments
Mike, where do you get those ugly spectral lines? 😉 . Anyway, I can't see any improvement from older version, see
http://web.telecom.cz/macura/sym5_16w_4o_1k.gif
And the distortion rised for higher frequencies, 5kHz measurement would be of interest.
http://web.telecom.cz/macura/sym5_16w_4o_1k.gif
And the distortion rised for higher frequencies, 5kHz measurement would be of interest.
Hi Pavels ! 😉
Not much, this is ~5v into 8 ohms... The problem appeared the moment the amp entered ClassB.
Hmm, measuring is not my best ability, that's why you had to do it !
You need to compare it with my old measuring. Observe the even harmonics having gone. And, this is with normal 50ma bias.
My ugly spectral lines ? I should do measurings only at daylight, without thousands of dimmed lights turned on everywhere... 😀 And i did not use any buffers, everything connected straight.
I attached a 6khz measuring, the harmonics increased only very slightly, ignore the horrible spectrals ! 😉 Okay, harmonics are hard to find, my measuring setup is a disaster, but okay for just checking the problem...
Mike
Upupa Epops said:
Not much, this is ~5v into 8 ohms... The problem appeared the moment the amp entered ClassB.
PMA said:
Hmm, measuring is not my best ability, that's why you had to do it !
You need to compare it with my old measuring. Observe the even harmonics having gone. And, this is with normal 50ma bias.
My ugly spectral lines ? I should do measurings only at daylight, without thousands of dimmed lights turned on everywhere... 😀 And i did not use any buffers, everything connected straight.
I attached a 6khz measuring, the harmonics increased only very slightly, ignore the horrible spectrals ! 😉 Okay, harmonics are hard to find, my measuring setup is a disaster, but okay for just checking the problem...
Mike
Attachments
