Hi,
I'm would be grateful for some advise for a diy novice. I have reconditioned my A100 following other threads here and info on Mark Hennesseys site.
I have replaced: electrolytic caps, output devices, a couple of resistors in the power amp, zener diodes, the preamp and selector switch, and IC2. I also replaced the speaker terminals and added an IEC connector. Its working OK apart from these issues
1. Fans bearings are shot, quite noisy, intrusive at low listening levels, and still need replacing but are 12V AC and its proving impossible to find a direct replacement, but there are plenty of DC fans available. Is is possible to amend the supply circuit to use DC fans instead?
2. When switching off, I hear strange low level electonic noise of rising pitch (a capacitor discharging?). How can I determine where this might this be coming from and how can I eliminate it?
3. The speaker output cut out a couple of times (amp power indicator was still lit) but the sensor housing mounting point broke when rebuilding it so I'm ptting this down to that until I replace the housing.
4. Temperature on the heatsink is about 60degC - can anyone confirm if this the normal operating temperature for these amps.
thanks
Adrian
I'm would be grateful for some advise for a diy novice. I have reconditioned my A100 following other threads here and info on Mark Hennesseys site.
I have replaced: electrolytic caps, output devices, a couple of resistors in the power amp, zener diodes, the preamp and selector switch, and IC2. I also replaced the speaker terminals and added an IEC connector. Its working OK apart from these issues
1. Fans bearings are shot, quite noisy, intrusive at low listening levels, and still need replacing but are 12V AC and its proving impossible to find a direct replacement, but there are plenty of DC fans available. Is is possible to amend the supply circuit to use DC fans instead?
2. When switching off, I hear strange low level electonic noise of rising pitch (a capacitor discharging?). How can I determine where this might this be coming from and how can I eliminate it?
3. The speaker output cut out a couple of times (amp power indicator was still lit) but the sensor housing mounting point broke when rebuilding it so I'm ptting this down to that until I replace the housing.
4. Temperature on the heatsink is about 60degC - can anyone confirm if this the normal operating temperature for these amps.
thanks
Adrian
1. buy any 12V DC fans with adequate dimensions ; wire them in series , make small dedicated Graetz+C filter+7824 reg chip for them , using one half of secondary for Graetz
2.something you didn't change ? is it in both channels or just in one ?
3. overheating ? you need thorough checking of that ; I presume you put fresh thermal grease everywhere ?
4. yes
2.something you didn't change ? is it in both channels or just in one ?
3. overheating ? you need thorough checking of that ; I presume you put fresh thermal grease everywhere ?
4. yes
Hi Zen,
thanks for your quick reply. When I said novice I really meant it and to show my ignorance I hadnt hearde of Graetz.
But I guess you mean a diode bridge like this Diode bridge - Wikipedia, the free encyclopedia, with a smoothing capacitor as per the circuit diagram. What values should I use for the diodes (I have 12V 1.3W BZX85) & the capacitor (I have 1000uF, 470uF or 47uF spare).
Shouldn't the reg chip be 7812 for 12V output? and I assume this goes in series after the cap (with centre pin to GND) followed by the fans in series as the load?
Alternatively, could I use a regulator circuit kit like this http://www.quasarelectronics.com/3060-universal-power-supply-board-for-78xx-regulators.htm and connect the +12v, 0v points from the mains transformer to the input, and the DC fans in series as the load on the output?
However, I cant help thinking this is replicating the existing bridge rectifier circuit?
2. I didnt think to check this but the noise only seems to be coming from the left channel, so that will help to narrow it down. But I changed the caps and resistors for higher spec components with the same values. FYI This noise wasnt there before the component upgrade, or the first few occasions when I switched off and isnt audible unless I switch off. Still no wiser.
3. I immediately thought about overheating too . I did put new thermal grease where is was previously (top of the heatsink, join of the top plates, back of the sensor). It could be that the fans arent working very efficiently as it hasnt cutout after removing the side panels. but I thought operaton of the the cutout would disconnect power completely . i.e. to the power LED as well?
4. Thanks for that
thanks for your quick reply. When I said novice I really meant it and to show my ignorance I hadnt hearde of Graetz.
But I guess you mean a diode bridge like this Diode bridge - Wikipedia, the free encyclopedia, with a smoothing capacitor as per the circuit diagram. What values should I use for the diodes (I have 12V 1.3W BZX85) & the capacitor (I have 1000uF, 470uF or 47uF spare).
Shouldn't the reg chip be 7812 for 12V output? and I assume this goes in series after the cap (with centre pin to GND) followed by the fans in series as the load?
Alternatively, could I use a regulator circuit kit like this http://www.quasarelectronics.com/3060-universal-power-supply-board-for-78xx-regulators.htm and connect the +12v, 0v points from the mains transformer to the input, and the DC fans in series as the load on the output?
However, I cant help thinking this is replicating the existing bridge rectifier circuit?
2. I didnt think to check this but the noise only seems to be coming from the left channel, so that will help to narrow it down. But I changed the caps and resistors for higher spec components with the same values. FYI This noise wasnt there before the component upgrade, or the first few occasions when I switched off and isnt audible unless I switch off. Still no wiser.
3. I immediately thought about overheating too . I did put new thermal grease where is was previously (top of the heatsink, join of the top plates, back of the sensor). It could be that the fans arent working very efficiently as it hasnt cutout after removing the side panels. but I thought operaton of the the cutout would disconnect power completely . i.e. to the power LED as well?
4. Thanks for that
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you can use pcb like that ;
using 2pcs of 12V fans in series , along with one 7824 reg will put less stress on reg chip itself
in fact - depending of fans used and final adequate speed of same , you can finish with :
-no chip reg ( just graetz +cap ) for full speed ( considering that final voltage is in range of 24Vdc ; dunno exactly for A100 , but considering that A1 have 18Vac secondaries)
-7818 chip for decreased speed
7815 chip for even more decreased speed
using 2pcs of 12V fans in series , along with one 7824 reg will put less stress on reg chip itself
in fact - depending of fans used and final adequate speed of same , you can finish with :
-no chip reg ( just graetz +cap ) for full speed ( considering that final voltage is in range of 24Vdc ; dunno exactly for A100 , but considering that A1 have 18Vac secondaries)
-7818 chip for decreased speed
7815 chip for even more decreased speed
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