Hi folks!
I've a question which is for you more experienced guys for sure easy to answer!
I changed the filter elcos of my phono board to larger ones - 2200muF instead of 470muF.
Of course space is limited, so I layed them flat down, unfortunately only some 1-2 millimeters away from an opamp (which is regulating the amplifiying opamp).
Problem is, if I crank the volume (no music playing) to the max I can hear humm in the (very low) noise quite clearly - unfortunately I don't know if this was already there before
I've no possibilty to change them back right now, so I would be happy if someone can tell me if this is reasonable (humm introduced by cap) or not!
Thanks a lot! Hannes
PS: the 2200muF cap is filtering 20V dc-voltage; the board draws less than 100mA, opamp is an opa134.
I've a question which is for you more experienced guys for sure easy to answer!
I changed the filter elcos of my phono board to larger ones - 2200muF instead of 470muF.
Of course space is limited, so I layed them flat down, unfortunately only some 1-2 millimeters away from an opamp (which is regulating the amplifiying opamp).
Problem is, if I crank the volume (no music playing) to the max I can hear humm in the (very low) noise quite clearly - unfortunately I don't know if this was already there before
I've no possibilty to change them back right now, so I would be happy if someone can tell me if this is reasonable (humm introduced by cap) or not!
Thanks a lot! Hannes
PS: the 2200muF cap is filtering 20V dc-voltage; the board draws less than 100mA, opamp is an opa134.
Um, You shouldn"t be running the OPA134 off of a +/- 20v supply as it has a Max Supply Volyage of +/-18v (If running off of a Dual Supply) ....I" don"t know if that is your problem but I thought I would point it out.....
I"m sure 20v would be ok with a Single Supply but I don"t know how stable the OPA134 is on a Single supply as the datasheet doesn"t mention anything about single supply operation.....
If the 2200uF caps you are useing are lower quality than the originals like for instance they have a Much higher Leakage current then the others than you might get more noise....
You might also try bypassing the caps with a 0.1uF to 1.0uF Poly or Metal film cap to see if that helps.....
Good luck
I"m sure 20v would be ok with a Single Supply but I don"t know how stable the OPA134 is on a Single supply as the datasheet doesn"t mention anything about single supply operation.....
If the 2200uF caps you are useing are lower quality than the originals like for instance they have a Much higher Leakage current then the others than you might get more noise....
You might also try bypassing the caps with a 0.1uF to 1.0uF Poly or Metal film cap to see if that helps.....
Good luck
Thanks a lot for your replies!
@turnA_zpoint: I'm very sorry, but I don't understand, could you please explain a bit more?
@Minion: thanks for your advice, but the opa134 is driven by +-18V voltage regulators. I'm talking about the filter elco after the rectifying diodes!
Thanks also for the tipp with the leakage current, I'm going to check that, however I'm using hiqh quality elna caps.
With kind regards, Hannes
@turnA_zpoint: I'm very sorry, but I don't understand, could you please explain a bit more?
@Minion: thanks for your advice, but the opa134 is driven by +-18V voltage regulators. I'm talking about the filter elco after the rectifying diodes!
Thanks also for the tipp with the leakage current, I'm going to check that, however I'm using hiqh quality elna caps.
With kind regards, Hannes
Hey thanks a lot to all for your replies!
First, I'm not sure what voltage I have after the diodes. It's stupid, but I don't have access to a multimeter at the moment.
Actually it's a 12V AC wall wart (12V at 200mA that is) that has higher idling voltage at low current (about 30mA (max) I guess) - that's the reason that it is possible to use +-18V regulators (that need +1.7V themselves plus 0.7V for the diode yields at least 20.7V idle voltage).
pcb is a project phonobox (see for a discussion here http://www.diyaudio.com/forums/showthread.php?s=&threadid=21833).
@peranders: well since the phonobox uses cheap components I replaced 90% of its parts with better ones (better in terms of closer tolerances and better specs) and of course I wanted to improve filtering (from original 470muF to 2200uF). The PSU powers 6 opa134 in total.
@AndrewT: well I thought about dropouts, but this hum is already present without any signal, so the current is lowest and therefore idle voltage highest. It should get far worse with music playing but it isn't!
@lineup: phono+psu schematic is right here:
http://www.angelfire.com/az3/dimitri/images/phonobox.pdf
However I found a far better solution (IMHO), if I'm lucky I can try it today in the evening.
I'm not sure that my improved solution has not this problem, but I will report.
With kind regards, Hannes
First, I'm not sure what voltage I have after the diodes. It's stupid, but I don't have access to a multimeter at the moment.
Actually it's a 12V AC wall wart (12V at 200mA that is) that has higher idling voltage at low current (about 30mA (max) I guess) - that's the reason that it is possible to use +-18V regulators (that need +1.7V themselves plus 0.7V for the diode yields at least 20.7V idle voltage).
pcb is a project phonobox (see for a discussion here http://www.diyaudio.com/forums/showthread.php?s=&threadid=21833).
@peranders: well since the phonobox uses cheap components I replaced 90% of its parts with better ones (better in terms of closer tolerances and better specs) and of course I wanted to improve filtering (from original 470muF to 2200uF). The PSU powers 6 opa134 in total.
@AndrewT: well I thought about dropouts, but this hum is already present without any signal, so the current is lowest and therefore idle voltage highest. It should get far worse with music playing but it isn't!
@lineup: phono+psu schematic is right here:
http://www.angelfire.com/az3/dimitri/images/phonobox.pdf
However I found a far better solution (IMHO), if I'm lucky I can try it today in the evening.
I'm not sure that my improved solution has not this problem, but I will report.
With kind regards, Hannes
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