Hi Sangram,
the PSU is single rail dual mono and each winding/rectifier/CRC filter powers its own channel of the amplifier. the two wires of one winding are connected to the AC input of the rectifier. the +ve out is connected to the +ve terminal of the first capacitor in the CRC filter and the -ve out to the -ve terminal of that cap. the -ve rail forms the 0v reference for the circuit. the two rectifiers or CRC filters are not directly connected together in any way. the 0v rails are connected through two CL60 thermistors with the chassis connected between the thermistors.
hope this makes the setup clearer
the PSU is single rail dual mono and each winding/rectifier/CRC filter powers its own channel of the amplifier. the two wires of one winding are connected to the AC input of the rectifier. the +ve out is connected to the +ve terminal of the first capacitor in the CRC filter and the -ve out to the -ve terminal of that cap. the -ve rail forms the 0v reference for the circuit. the two rectifiers or CRC filters are not directly connected together in any way. the 0v rails are connected through two CL60 thermistors with the chassis connected between the thermistors.
hope this makes the setup clearer
Hi all,
Been off the forums for a while because i was involved in the commonwealth games happening here in Delhi.
I added the smoothing caps and the psu voltage was a nominal 24v (thank god)
I powered it up using a mains bulb tester (with a 230v/60W bulb) and the bulb came on for a second at power on, and then faded out. it then stayed off.
Wired up the rest of the connections and the amp works, hum is gone! i suppose the culprit was the mis-wired primaries.
Thanks to all who helped solve this for me. i am very grateful.
a small problem has come to my notice though. about 7-8 seconds after power on (i think it is the moment when the ccs cap is charged) my speaker cones (fe206e) move outwards slowly. the motion from rest to approx. 3mm excursion takes about a second after which it returns to rest and music starts playing. when i switch the amp off, the cones move inwards by the same amount and then return to rest. this didnt happen when the amp was wired as earlier (mis-wired primaries). any clues?
EDIT: i get +2vdc at the speaker outputs 7-8 seconds after turn on, and -2vdc at turn off. it only lasts for a second and then goes away. how is it possible for the dc to pass through the output which is capacitor coupled (15000uf)?
it probably wont be noticeable on less sensitive drivers but i am worried about damaging my delicate fe206e's
cheers, and thanks again
mymindinside
Been off the forums for a while because i was involved in the commonwealth games happening here in Delhi.
I added the smoothing caps and the psu voltage was a nominal 24v (thank god)
I powered it up using a mains bulb tester (with a 230v/60W bulb) and the bulb came on for a second at power on, and then faded out. it then stayed off.
Wired up the rest of the connections and the amp works, hum is gone! i suppose the culprit was the mis-wired primaries.
Thanks to all who helped solve this for me. i am very grateful.
a small problem has come to my notice though. about 7-8 seconds after power on (i think it is the moment when the ccs cap is charged) my speaker cones (fe206e) move outwards slowly. the motion from rest to approx. 3mm excursion takes about a second after which it returns to rest and music starts playing. when i switch the amp off, the cones move inwards by the same amount and then return to rest. this didnt happen when the amp was wired as earlier (mis-wired primaries). any clues?
EDIT: i get +2vdc at the speaker outputs 7-8 seconds after turn on, and -2vdc at turn off. it only lasts for a second and then goes away. how is it possible for the dc to pass through the output which is capacitor coupled (15000uf)?
it probably wont be noticeable on less sensitive drivers but i am worried about damaging my delicate fe206e's
cheers, and thanks again
mymindinside
Last edited:
Hi
That's great news regarding the loss of hum! Have you measured the DC offset recently?
No. I've just been listening to music recently
(I'd almost forgotten what it was)A friend popped over with his new speakers recently and he could barely hear it. I can...but its not much of an issue.
I am going the rewire the amp in a couple of weeks so I'll have another look then.
Just a guess - what you are seeing is probably the charging current. The speaker forms the circuit through which the cap charges up for the first time. Better to use a protection relay if you plan to stick with that cap. You will need a small load resistor for the cap to charge, once charged it can be switched to the speaker (say 5s).
Hi Sangram,
i have attached the schematic of the amplifier (it is a diy iteration of the First Watt F2). perhaps you could look at the schematic and tell me what you think the problem is. As far as i am aware, none of the other builders of this amp have had this problem. it is probably something i have done wrong.
let me know if you have an idea,
cheers,
mymindinside
i have attached the schematic of the amplifier (it is a diy iteration of the First Watt F2). perhaps you could look at the schematic and tell me what you think the problem is. As far as i am aware, none of the other builders of this amp have had this problem. it is probably something i have done wrong.
let me know if you have an idea,
cheers,
mymindinside
Attachments
It's odd that an amplifier with no negative supply voltage is generating a negative voltage at the output. I'm not at all familiar with the circuitry but would assume that the output voltage is held close enough to zero volts by the three 47 ohm resistor and the large capacitors in the 9240 biasing network take care of the switching transients.
Maybe you can examine the behaviour at the gate of the 9240 when being switched on and off. The only way you can get a negative voltage is if the C4+C6 capacitor discharges through the power supply, my abilities to debug schematics stops there. I would simply use a relay with a 4-5 second time lag to connect the speaker, and wire it so it switches off instantly on power-down (separate supply with just 1 47 or 22uF capacitor as reservoir).
Maybe you can examine the behaviour at the gate of the 9240 when being switched on and off. The only way you can get a negative voltage is if the C4+C6 capacitor discharges through the power supply, my abilities to debug schematics stops there. I would simply use a relay with a 4-5 second time lag to connect the speaker, and wire it so it switches off instantly on power-down (separate supply with just 1 47 or 22uF capacitor as reservoir).
Sangram is correct.
Charging current.
What is the DC bias voltage across the output capacitor when the amplifier has been on for 30seconds?
The capacitor has to charge from 0Vdc to bias voltage at start up. It then has to discharge from bias voltage to 0Vdc at shut down.
This is typical of all single ended amplifiers running on single supply.
It also happens with single supply push pull amplifiers, but these are much less common.
You either accept that charging/discharging current passing through your speaker or you fit a speaker isolation switch or relay to provide an alternative current path. You must have a current path. There is no charging/discharging if you leave output open ended during the switching.
Charging current.
What is the DC bias voltage across the output capacitor when the amplifier has been on for 30seconds?
The capacitor has to charge from 0Vdc to bias voltage at start up. It then has to discharge from bias voltage to 0Vdc at shut down.
This is typical of all single ended amplifiers running on single supply.
It also happens with single supply push pull amplifiers, but these are much less common.
You either accept that charging/discharging current passing through your speaker or you fit a speaker isolation switch or relay to provide an alternative current path. You must have a current path. There is no charging/discharging if you leave output open ended during the switching.
The only difference between my build and the schematic is that i have not populated C6. C4 is 15000uf. i recall Nelson Pass saying that the purpose of C4+C6 is to avoid turn on transients. should i try adding some capacitance at C6? what confuses me is the -2vdc at turn off.
cheers,
mymindinside
cheers,
mymindinside
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