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From: N_Cook on 12 Jul 2010 12:05 Meat Plow <mhywatt(a)yahoo.com> wrote in message news:3tc18b.idi.17.7(a)news.alt.net... > On Mon, 12 Jul 2010 10:24:03 +0100, N_Cook wrote: > > > Seems to be a notorious problem with fan system on these, so many I > > cannot find a recognised solution in amongst the complaints. I've not > > taken apart yet,all wrapped up under the h/s, is it active or thermistor > > monitoring ? and then a cut out mechanism as well. Monitoring V to the > > 12V fan takes ages getting from 1.2V to 3V and stops there as fan starts > > taking current at 3V. Already the h/s is too hot too keep fingers on. I > > never liked the idea of slowly ramped V to fans but will ask the owner > > if they want the temp monitoring changed or fan on all the time. > > Ask the owner, chances are they will want it on all the time. I used a > Crown Microtech 1000 for a bass head for many years and it's still part > of my rig along with a BBE 383 preamp. The fan was loud and ran full > speed but the din of the audience nulled any noise it made between songs/ > sets and of course when we played all you could hear during silent > periods were your ears ringing. The other great advantage with always-on is that the user knows the fan is in working order right from the off.
From: Meat Plow on 12 Jul 2010 18:07 On Mon, 12 Jul 2010 17:05:47 +0100, N_Cook wrote: > Meat Plow <mhywatt(a)yahoo.com> wrote in message > news:3tc18b.idi.17.7(a)news.alt.net... >> On Mon, 12 Jul 2010 10:24:03 +0100, N_Cook wrote: >> >> > Seems to be a notorious problem with fan system on these, so many I >> > cannot find a recognised solution in amongst the complaints. I've not >> > taken apart yet,all wrapped up under the h/s, is it active or >> > thermistor monitoring ? and then a cut out mechanism as well. >> > Monitoring V to the 12V fan takes ages getting from 1.2V to 3V and >> > stops there as fan starts taking current at 3V. Already the h/s is >> > too hot too keep fingers on. I never liked the idea of slowly ramped >> > V to fans but will ask the owner if they want the temp monitoring >> > changed or fan on all the time. >> >> Ask the owner, chances are they will want it on all the time. I used a >> Crown Microtech 1000 for a bass head for many years and it's still part >> of my rig along with a BBE 383 preamp. The fan was loud and ran full >> speed but the din of the audience nulled any noise it made between >> songs/ sets and of course when we played all you could hear during >> silent periods were your ears ringing. > > > The other great advantage with always-on is that the user knows the fan > is in working order right from the off. I remember my sarcastic drummer calling the Crown a microwave oven :) because of the fan noise. It never bothered me. Also used a BGW prior to the purchase of the crown. Larger in size but only 700 into 8ohms. It also had a loud fan but still hefty enough to have reserve on those low 5th string bass notes without distortion. That's the main reason I snagged the Crown. And I got many compliments from my band mates on the sound.
From: N_Cook on 14 Jul 2010 03:09 17 deg C / 0.17V of lift from a SM shottke diode under the sensor is about right to get the fan turning properly at ambient 15 deg C or more. Definitely a PbF solder amp from 2007. Made in China for USA for export to the UK but presumably the same for domestic USA use , no mention of PbF on pcb or rear of casing
From: N_Cook on 16 Jul 2010 04:08 If the amp is left switched on with no input the quiescent current is enough to slightly raise the h/s temp to about 30 deg C and fan comes on now I suspect the problem is drift over time of the Vbe of the drive transistor, change of 0.01V there leads to change of 1.5V on the fan , so if Vbe drops a few mV the fan will only come on at 50 or 60 deg C, too late to be safe
From: N_Cook on 16 Jul 2010 04:42 correction so if Vbe rises a ......
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