Hi!
I have made some measurements, with the multimeter in ac voltage mode. I run a 1khz test tone, and both channels measured exactly the same at every point i tested. Up to the xlr output connectors. But when the signals reach the soundcard, (an old wt192m), the input meters of the card, and soundforge show 5 db imbalance!!!. So, maybe the main suspect are the souncard inputs, because the outputs have the same output levels.
Jay x
I have made some measurements, with the multimeter in ac voltage mode. I run a 1khz test tone, and both channels measured exactly the same at every point i tested. Up to the xlr output connectors. But when the signals reach the soundcard, (an old wt192m), the input meters of the card, and soundforge show 5 db imbalance!!!. So, maybe the main suspect are the souncard inputs, because the outputs have the same output levels.
Jay x
Hi again!
What an afternoon!!!...after playing some music thru the mixer, at -18db input level, one opamp get smoke!!! In a channel that was not receiving any signal. After switch off. I noticed that. The boards were warm, the power rails, and even the output transformers. The psu also, smmothing caps and regulators, and the toroidal transformer....bufff...
mains voltage is ok. 228v ac.
What an afternoon!!!...after playing some music thru the mixer, at -18db input level, one opamp get smoke!!! In a channel that was not receiving any signal. After switch off. I noticed that. The boards were warm, the power rails, and even the output transformers. The psu also, smmothing caps and regulators, and the toroidal transformer....bufff...
mains voltage is ok. 228v ac.Hi,
The magic word is power dissipation. Current flow causes power losses on every device (except pure reactance or zero ohmic devices, but both don´t exist in reality), that means electr. energy is transduced to thermal energy (=device gets warm).
your opamps ~0.1W - 0.2W each (without load)
regulators (TO220 case?) ~1W, without heatsink I estimate junction temp. about 90°C !
If you still use the 10VA transformer, of course it runs hot.
The psu caps shouldn´t get significantly warm, except the regs are very close to them.
o.k., a burned opamp is not usual, but without knowing any details of your circuit it´s hard to say anything about it. The only hint I can give is, to watch for oscillation on your boards.
The magic word is power dissipation. Current flow causes power losses on every device (except pure reactance or zero ohmic devices, but both don´t exist in reality), that means electr. energy is transduced to thermal energy (=device gets warm).
your opamps ~0.1W - 0.2W each (without load)
regulators (TO220 case?) ~1W, without heatsink I estimate junction temp. about 90°C !
If you still use the 10VA transformer, of course it runs hot.
The psu caps shouldn´t get significantly warm, except the regs are very close to them.
o.k., a burned opamp is not usual, but without knowing any details of your circuit it´s hard to say anything about it. The only hint I can give is, to watch for oscillation on your boards.
Hi Andreas!
The trafo is a 30va toroidal. But among the conditions during the failure, there were two output leads not connected to any input of an audio interface, to measure output voltages.
All ti MC33078 bipolar opamps were affected ( i noticed a change in package colour). Drivers and line receiver were not affected nor the two opa2134.
As i have a bunch of lm833p and also ne5532, i will try to replace these in each position, and see what happens. If for each opamp replaced there is an increase in temperature of the psu or the boards in a section, this may give a clue...
Still pending a picture of the setup...i know!!
jay x
The trafo is a 30va toroidal. But among the conditions during the failure, there were two output leads not connected to any input of an audio interface, to measure output voltages.
All ti MC33078 bipolar opamps were affected ( i noticed a change in package colour). Drivers and line receiver were not affected nor the two opa2134.
As i have a bunch of lm833p and also ne5532, i will try to replace these in each position, and see what happens. If for each opamp replaced there is an increase in temperature of the psu or the boards in a section, this may give a clue...
Still pending a picture of the setup...i know!!
jay x
Hi Jay,
Wow, all your opamps get burned, really amazing! How many pieces?
Sorry if I behaved like a "schoolmaster" in my last post, but I thought because of your description: "Hey, what´s his problem, it´s pretty normal that things heat up during operation.".
Now I see you meant it´s above of that, what we would denote normal.
Yes, the pictures........
Andreas
Wow, all your opamps get burned, really amazing! How many pieces?
Sorry if I behaved like a "schoolmaster" in my last post, but I thought because of your description: "Hey, what´s his problem, it´s pretty normal that things heat up during operation.".
Now I see you meant it´s above of that, what we would denote normal.
Yes, the pictures........
Andreas
Hi!
Finally i discovered what happened: The heatsinks of the lm317/337 regulators touched each other, creating an overvoltage and reversing the supply on the rails, consequently frying the opamps.... not fish&chips exactly... but pretty close to that!!
Seems that things are going better this time... I checked all voltages, and power consumptions are balanced at 126ma per rail with a max of 313 ma depending on the relays switched. c'mon!!
jay x
Finally i discovered what happened: The heatsinks of the lm317/337 regulators touched each other, creating an overvoltage and reversing the supply on the rails, consequently frying the opamps.... not fish&chips exactly... but pretty close to that!!
Seems that things are going better this time... I checked all voltages, and power consumptions are balanced at 126ma per rail with a max of 313 ma depending on the relays switched. c'mon!!
jay x
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Hi,
Bon appètit!
Small cause, large effect. It´s good to hear that everything is running now, hope your opamps are on sockets otherwise you had a painful work with desoldering them.
Hi!
I don't know why... but i still have a random problem with a FET opamp fader amplifier. I used OPA2134, OP275, and TLO72. Sometimes it works fine, but sometimes it makes a harsh "reverbered" "tunnel like" sound...
I checked all wires are ok...all gnds ok....
It is a typical stage non inverting fet opamp with a gain of 3. No coupling caps, no bias resistor to gnd.... and it is placed in between two AC coupled summing amps, with 100uf25v electrolytics and 22k to gnd at output.
I could solder a 47k resistor to gnd...at the non inverting input, but i cannot do AC coupling. I will try an LM4562..(low bias current).. or...don't know what!...
It is not the first time i build this fader amp...and it worked fine always!!
Still have to investigate....!!
jay x
I don't know why... but i still have a random problem with a FET opamp fader amplifier. I used OPA2134, OP275, and TLO72. Sometimes it works fine, but sometimes it makes a harsh "reverbered" "tunnel like" sound...
I checked all wires are ok...all gnds ok....
It is a typical stage non inverting fet opamp with a gain of 3. No coupling caps, no bias resistor to gnd.... and it is placed in between two AC coupled summing amps, with 100uf25v electrolytics and 22k to gnd at output.
I could solder a 47k resistor to gnd...at the non inverting input, but i cannot do AC coupling. I will try an LM4562..(low bias current).. or...don't know what!...
It is not the first time i build this fader amp...and it worked fine always!!
Still have to investigate....!!
jay x
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