hi,
I have a 6ch power amplifier for my active system. It has two toroidal transformers each 600w. They are buzzing occasionally, if i put my finger on them i can feel the buzzing. So i decided to make a dc blocker circuit. I made it but the noise is still there. I used 1 bridge 1000/V35A and 4 capacitors 22000uF/35v each. My circuit is like the one in the picture but i have another one pair of capacitors connected in series like the pair in the picture. The second pair have the same polarity and is paralleled to the first pair.
Despite having this circuit the transformers are still buzzing. They buzzing when i use hair dryer, microwave oven even when my neighboor use something which produce dc on the main line.
When i am measuring ac voltage across the bridge, i have about 180mVac so the diodes are not conducting. So how the dc pass through? cannot understand what is happening.
I have a 6ch power amplifier for my active system. It has two toroidal transformers each 600w. They are buzzing occasionally, if i put my finger on them i can feel the buzzing. So i decided to make a dc blocker circuit. I made it but the noise is still there. I used 1 bridge 1000/V35A and 4 capacitors 22000uF/35v each. My circuit is like the one in the picture but i have another one pair of capacitors connected in series like the pair in the picture. The second pair have the same polarity and is paralleled to the first pair.
Despite having this circuit the transformers are still buzzing. They buzzing when i use hair dryer, microwave oven even when my neighboor use something which produce dc on the main line.
When i am measuring ac voltage across the bridge, i have about 180mVac so the diodes are not conducting. So how the dc pass through? cannot understand what is happening.
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You wouldn't hear DC on the line (except maybe a clicking sound when DC is applied). The buzzing is likely from something on the mains line injecting AC noise into the circuit. Do you have bypass caps on the supply side in parallel with the filter caps? They should shunt higher frequency noise to ground. In the case of *very* dirty mains voltage, a choke in series with the primary should act as a simple low pass filter.
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hello,
yes before the dc blocker circuit i have an EMI filter which has chokes and capacitors to ground
I also have one 220nF capacitor in parallel to the dc filter capacitors.
yes before the dc blocker circuit i have an EMI filter which has chokes and capacitors to ground
I also have one 220nF capacitor in parallel to the dc filter capacitors.
Hi
There is an alternate way to wire the bridge and the caps:
join the DCs together
Join the ACs together
Add the caps in anti-parallel across the paired bridge terminals
The last part might scare you but electros can withstand tiny reverse voltage well and the total diode drop is now one diode each way instead of two.
The caps in series divide in total value where the parallel caps add. You need the highest capacitance possible. For really big toroids, 33mF caps are the usual choice, two making 66mF total. Your 4m7s are too low to be of real use and may resonate with the PT.
I learned this from Kevin O'Connor's book "The Ultimate Tone vol.4", which is aimed at people building guitar amps but it has a wicked chapter about an advanced auto-ranging linear supply.
There is an alternate way to wire the bridge and the caps:
join the DCs together
Join the ACs together
Add the caps in anti-parallel across the paired bridge terminals
The last part might scare you but electros can withstand tiny reverse voltage well and the total diode drop is now one diode each way instead of two.
The caps in series divide in total value where the parallel caps add. You need the highest capacitance possible. For really big toroids, 33mF caps are the usual choice, two making 66mF total. Your 4m7s are too low to be of real use and may resonate with the PT.
I learned this from Kevin O'Connor's book "The Ultimate Tone vol.4", which is aimed at people building guitar amps but it has a wicked chapter about an advanced auto-ranging linear supply.
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Hey
Also... The cap voltages are unimportant because the diodes limit the voltage across them. The 33mF caps are usually only 6V - the highest value at the lowest voltage possible, so they are not too big physically.
Also... The cap voltages are unimportant because the diodes limit the voltage across them. The 33mF caps are usually only 6V - the highest value at the lowest voltage possible, so they are not too big physically.
Are you sure? Depending on the cap value, you will achieve a certain impedance at 50 of 60Hz. Suppose the diode over which the cap is placed starts to conduct at 0,5 volts, the current throught the cap will be 0,5V/cap-impedance (0,145ohm at 22000uf) = 3,5amps.
When using two series diodes as many do, the current will be twice this value.
I always select a cap with a much higher ripple current than this. Which mostly leads to higher voltage caps.
DC blockers only work if there is DC on the line for them to block.
And, DC on the line is not the only cause for transformer noise.
mlloyd1
And, DC on the line is not the only cause for transformer noise.
mlloyd1
Hi
DC on the mains does not mean DC from a battery. It means there is asymmetric noise that can measure like DC, and this will cause large PTs to saturate easily if they do not have a certain minimum load on them.
The DC blocker threshold should therefore be as low as you can make it and proper ones are one diode each way NOT two. Most people are afraid of the anti-parallel cap connection because it looks wrong, and instead opt for the familiar anti-series connection. That cuts the effective C in half which is no good for a DC blocker.
As I stated above, the Cs have to be the highest possible values so the resonant frequency working against the PT inductance will be nonproblematic. Read Eliott's or O'Connor's writings and you will see this is the truth, although even Rod was afraid to use the anti-parallel cap connection.
Also, it was TUT6 not TUT4, sorry - got them all and get confused what info is where some times - 1,000s of pages...
It works ! Ot's safe ! Big manufacturers do this.
Ideally, there is current limiting but hardly anyone incorporates that and because of all the DC resistances in the AC path the caps survive well and PTs do not growl.
DC on the mains does not mean DC from a battery. It means there is asymmetric noise that can measure like DC, and this will cause large PTs to saturate easily if they do not have a certain minimum load on them.
The DC blocker threshold should therefore be as low as you can make it and proper ones are one diode each way NOT two. Most people are afraid of the anti-parallel cap connection because it looks wrong, and instead opt for the familiar anti-series connection. That cuts the effective C in half which is no good for a DC blocker.
As I stated above, the Cs have to be the highest possible values so the resonant frequency working against the PT inductance will be nonproblematic. Read Eliott's or O'Connor's writings and you will see this is the truth, although even Rod was afraid to use the anti-parallel cap connection.
Also, it was TUT6 not TUT4, sorry - got them all and get confused what info is where some times - 1,000s of pages...
It works ! Ot's safe ! Big manufacturers do this.
Ideally, there is current limiting but hardly anyone incorporates that and because of all the DC resistances in the AC path the caps survive well and PTs do not growl.
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In a residential setting most of the sources of power line asymmetry (DC offset) operate intermittently. IF the problem is not 24 by 7 then some detective work might track down the cause. Take the equipment to a friend's place in a different neighborhood and try again.
I think that much of the audiophile DC problem is actually a high AC line voltage problem.
I think that much of the audiophile DC problem is actually a high AC line voltage problem.
Hi
The functioning of the DC blocker is independent of high or low mains. On OEM equipment designed to work anywhere in the world, the DC blocker is the same at 120V or 240V.
The proof that the DC blocker is working is simply that the PT does not growl at low loadings. No need to take the unit to other places to test it.
The functioning of the DC blocker is independent of high or low mains. On OEM equipment designed to work anywhere in the world, the DC blocker is the same at 120V or 240V.
The proof that the DC blocker is working is simply that the PT does not growl at low loadings. No need to take the unit to other places to test it.
a DC blocker can only block DC offset if and when a DC offset is present.
many DC blocker circuits also drop the AC line voltage and high AC voltage may be the problem.
Taking a hi-fi component to another location, is to see if the component may have some other type of problem.
Hi ioannidis
There are many reasons that the TX may BUZZ
1. If 50Hz power and the transformer is rated for 60Hz it will BUZZ.
2. If the toroid has a HALF WAVE rectifier circuit it will BUZZ.
3. If the FW BRIDGE has an OPEN DIODE it will BUZZ.
4. If the AC LINE voltage is >10% HIGH it will BUZZ.
5. If the AC LINE has DC the transformer could BUZZ.
Toroid transformers do not have any air gap like EI types and unsymmetrical rectification will BIAS the core.
Duke
There are many reasons that the TX may BUZZ
1. If 50Hz power and the transformer is rated for 60Hz it will BUZZ.
2. If the toroid has a HALF WAVE rectifier circuit it will BUZZ.
3. If the FW BRIDGE has an OPEN DIODE it will BUZZ.
4. If the AC LINE voltage is >10% HIGH it will BUZZ.
5. If the AC LINE has DC the transformer could BUZZ.
Toroid transformers do not have any air gap like EI types and unsymmetrical rectification will BIAS the core.
Duke
Hey
From post-1:
"they buzzing when i use hair dryer, microwave oven"
Since you have an EMI filter on the mains, you should make sure there is appropriate RF filtering on the audio inputs and that a proper ground scheme has been used. EMI can enter the circuit by conduction or through the air.
Since the buzzing is reported to occur with these kind of external influences, internal design flaws like half-wave rectified circuits is not likely the source of the noise.
From post-1:
"they buzzing when i use hair dryer, microwave oven"
Since you have an EMI filter on the mains, you should make sure there is appropriate RF filtering on the audio inputs and that a proper ground scheme has been used. EMI can enter the circuit by conduction or through the air.
Since the buzzing is reported to occur with these kind of external influences, internal design flaws like half-wave rectified circuits is not likely the source of the noise.
hello ,
thank you for your answers,
the two toroids that i have in my power amp are mounted vertically. They are rated at 600VA each. When i connect the amplifier to the mains (220V 50HZ) they are occasionally buzzing, for example when i turn on the hair dryer like i already said or even when i don't turn on something in my house. But most of the time they are not buzzing.
Now, when i connect the amplifier to my MGE online UPS (3kVA double conversion ups), to which i have connected all my audio equipment, they are buzzing all the time (and louder than when connected directly to mains) even with the DC blocker circuit. So maybe the problem is not the dc? I tried to change the UPS output voltage to 240,230,220,210 at 50Hz and nothing changes but the buzz loudness. (At 60HZ the buzz is very loud - the toroids are made for 50HZ)
After each toroid (output 2x50v) i have 2 bridges with their capacitors. (one bridge + capacitors for each channel)
Because of the buzz presence i cannot have my amp connected to the UPS.
thank you for your answers,
the two toroids that i have in my power amp are mounted vertically. They are rated at 600VA each. When i connect the amplifier to the mains (220V 50HZ) they are occasionally buzzing, for example when i turn on the hair dryer like i already said or even when i don't turn on something in my house. But most of the time they are not buzzing.
Now, when i connect the amplifier to my MGE online UPS (3kVA double conversion ups), to which i have connected all my audio equipment, they are buzzing all the time (and louder than when connected directly to mains) even with the DC blocker circuit. So maybe the problem is not the dc? I tried to change the UPS output voltage to 240,230,220,210 at 50Hz and nothing changes but the buzz loudness. (At 60HZ the buzz is very loud - the toroids are made for 50HZ)
After each toroid (output 2x50v) i have 2 bridges with their capacitors. (one bridge + capacitors for each channel)
Because of the buzz presence i cannot have my amp connected to the UPS.
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Many (or most of them) UPS won't put out a true sinus. It's more like a squarewave when you're looking at it on a scope... No problem for a SMPS but toroids could start buzzing... UPS that are putting out a true sinus are usually marked as doing so.
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