by carefully reading after months, i finally had it assembled.
BT(bulb test) passed with the recitifer bridge.
measured with 32(+)-0(G)-32(-).
I had check the DAC output with 0.3mv - 0.35mv dc output which i guess is fine. However, i got -32v DC at speaker output...
the chip get a bit warm when i power up. touchable.
connect with a test speaker, i can see the speaker got "sucked" in then i immediately turn it off.
my god, i need some help to solve the situtation.
please help...pls...
BT(bulb test) passed with the recitifer bridge.
measured with 32(+)-0(G)-32(-).
I had check the DAC output with 0.3mv - 0.35mv dc output which i guess is fine. However, i got -32v DC at speaker output...
the chip get a bit warm when i power up. touchable.
connect with a test speaker, i can see the speaker got "sucked" in then i immediately turn it off.
my god, i need some help to solve the situtation.
please help...pls...
It could be oscillating and unstable but that's hard to check without a scope. Is the 2.7 ohm getting warm ? Has it gone open circuit ? Check voltage on the chip but be careful. Make sure both the supplies are reaching the chip. Its possible the IC could be faulty/failed due to connecting the speaker in a faulty state.
As Mark says... a photo might give a clue.
As Mark says... a photo might give a clue.
hopefully i had the schematic draw correctly.
I had checked +32vdc & -32vdc reaching the chips.
I read somewhere before saw if the 3886 chip is dead, no ohm values can be measured between pin3&4. i got > 9.7M ohm.
The chip get a bit hot after a few seconds switched on. i guess is somewhat 55c degree above (ambient temp is around 22c degree)
Sorry Mooly, that was the old schematic, the resistor u were asking 2.7r is a 2.2R/5w, is not getting warm.
If i had the chip fried, will it get hot? How to test if i had fried the chip?
Any thoughts or comments are welcome , please.
After i had add a 4R7-0.25w resistor between power gnd and signal input gnd, the -32vdc output on spk out suddently disappear and it works ! the spk protection board no longer kicks in & start singing my favourite songs!
I would like to thanks Mooly, Mark, Andrew, gotee and rest of members in diyaudio which share so much knowledge to help out layman like me who knew nothing about electronics.
the layout looks horrible, dangerous, crappy & heatsink is hot(8ohm load)... no fuse/switch/enclosure..but i will keep learning & improve later on.
1 final question:
I want to reduce rail voltages, now is +/- 33.2 from a twin 25ac,
can i create dual rectifier diodes like this to get voltage forward drop (easier to build if this work)?
or shall i build add an lm338 to reduce voltage like this?
and it works ! the spk protection board no longer kicks in & start singing my favourite songs! I would like to thanks Mooly, Mark, Andrew, gotee and rest of members in diyaudio which share so much knowledge to help out layman like me who knew nothing about electronics.
the layout looks horrible, dangerous, crappy & heatsink is hot(8ohm load)... no fuse/switch/enclosure..but i will keep learning & improve later on.
1 final question:
I want to reduce rail voltages, now is +/- 33.2 from a twin 25ac,
can i create dual rectifier diodes like this to get voltage forward drop (easier to build if this work)?
or shall i build add an lm338 to reduce voltage like this?
Great to hear you have it all working.
If your rails are around -/+ 33 volts then I don't really see a problem in practice. Losing a couple of volts isn't going to make any real difference imo. The LM3886 is capable of driving 4 ohms.
From the data sheet:
68W cont. avg. output power into 4Ω at VCC = ±28V
38W cont. avg. output power into 8Ω at VCC = ±28V
50W cont. avg. output power into 8Ω at VCC = ±35V
I don't see a problem in practice.
If your rails are around -/+ 33 volts then I don't really see a problem in practice. Losing a couple of volts isn't going to make any real difference imo. The LM3886 is capable of driving 4 ohms.
From the data sheet:
68W cont. avg. output power into 4Ω at VCC = ±28V
38W cont. avg. output power into 8Ω at VCC = ±28V
50W cont. avg. output power into 8Ω at VCC = ±35V
I don't see a problem in practice.
does droping a few volts helps the following?
1. safe for 6Ω ±33V rail at VCC?
2. less heat on heatsink.
A silly question, preventing from reaching maximum power, does this help to reduce the volume? The amp volume sounds way too loud to me (no input pot, rely adjust the volume output on dac, i only turn up 1/5 of it.)
And i hear a little noise on upper end.
the setup right now is:
avel lindberg tord. 330va, 25ac twin secdonary. Y236801E
test speaker 8Ω Printed: Nom 30W (max 80W)
10,000uf per rail.
heatsink: 13cm * 8cm * 1cm (i know is a bit small...)
1. safe for 6Ω ±33V rail at VCC?
2. less heat on heatsink.
A silly question, preventing from reaching maximum power, does this help to reduce the volume? The amp volume sounds way too loud to me (no input pot, rely adjust the volume output on dac, i only turn up 1/5 of it.)
And i hear a little noise on upper end.
the setup right now is:
avel lindberg tord. 330va, 25ac twin secdonary. Y236801E
test speaker 8Ω Printed: Nom 30W (max 80W)
10,000uf per rail.
heatsink: 13cm * 8cm * 1cm (i know is a bit small...)
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No. It increases the number of times that the output signal clips.
The operator controls the volume with a sensibly selected rotation of the vol pot.
If the "system" is too loud at very low rotations of the vol pot then go and read:
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html
A lot too small for a single channel of 3886. totally wrong for two channels. Check the National recommendation for your duty. Double it for two channels and I recommend you double it again for domestic use.
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