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Old 22nd May 2004, 04:20 PM   #71
Eva is offline Eva  Spain
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Raka :

I tested two 1000uF 16V capacitors in series back to back, with two strings of four 1N4007 diodes in paralell, one string on each direction, to allow up to about +-2.5V DC blocking


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DC levels on mains cannot be measured by directly connecting the multimeter to the line. You have to place a low-pass filter between the line and the DMM. I use a first order filter made of a 100K 1W resistor and a 22uF non-polar capacitor for that purpose

Non-gapped transformers must be operated on 'pure AC'. Even 50mV of DC may be enough to see signs of saturation on toroids
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Old 23rd May 2004, 09:22 AM   #72
Raka is offline Raka  Europe
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Eva,
thanks for your reply. I'm going to try this today. What would be the current capability of the caps? Will standard caps be enough, or should I use parallel+antiparallel?
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Old 23rd May 2004, 11:22 AM   #73
Eva is offline Eva  Spain
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I used Panasonic 1000uF 16V low impedance capacitors rated at 1,44 Arms ripple current, but beware that standard 1000uF 16V ones are rated at much smaller values like 100-300mA so you'll need to get high ripple current capacitors, to use several in paralell or to use higher capacitance values rated at higher ripple currents in order not to exceed their specs

About capacitive impedance issues, when the output of the transformer is rectified, most current consumption happens at 300Hz [6*F] and also at 100Hz and 500Hz [2*F and 10F], so you should calculate the voltage swing amplitude across the capacitor taking into account the peak current [roughly 3 times the average current] and 300Hz

Higher current output from the transformer requires higher capacitance [lower capacitor impedande] to reduce voltage swing across the capacitor since this voltage swing may get high enough to cause the diodes to clip and may ruin the DC blocking capability of the circuit

I calculated 1.000uF for 200W maximum output @230V input [I tested a 750VA toroid but I had nothing at hand to dissipate more than 200W]. For higher power output it would be also a good idea to use diodes rated at a higher current than 1N4007 since they will have to pass all the load current in case of capacitor failure or excessive voltage swing
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Old 23rd May 2004, 03:59 PM   #74
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The lower voltage Nichicon UHE series are good for this application; besides having good ripple current ratings, the impedance (ESR) which I measure is usally quite a bit better than specs, where as I've found Panasonic FC series caps are worse than spec.

Measurements are done using an HP4192 network analyser.

You can get 560-820 uF caps with ESR in the 30 milliohm range.

Due to current rectification occuring primarily at the peak of the waveform for capacitor input rectifiers, the current stress on the caps is higher than you might expect. Capacitor input rectifier systems have very poor power factor, which puts more stress on everything in the system.

Incorporating a DC filter should be standard IMO, with toroidal transformers. Also, if one wishes to use common mode filter chokes to improve noise isolation for the power amp, then I think this DC input filter is very necessary to prevent saturation or magnetization of the common mode baluun. This point is often overlooked.

Regards,

Jon
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Old 23rd May 2004, 05:45 PM   #75
Raka is offline Raka  Europe
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Eva,

Just to confirm, is this what you mean? Sorry for the quality of the picture.

If the concern is the current rating, could I use some 63V caps? I have some 1000uf FC series that goes to 2.7Ams.

I intend to use this circuit for a preamp, and a power amp that is biased at 250ma the output stage.
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Old 24th October 2004, 01:56 AM   #76
LydMekk is offline LydMekk  Norway
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Default Alternative layout of DC trap

Have successfully built this, removed 99-100% of all my DC noise from my amps.

Am no electronics expert, but is this similar to earlier schematics ?
Norway, I use 230V mains.

Click the image to open in full size.

If needing more DC removal than in this schematic, can I just add more diodes in serial to the existing 2 ? Do I also need more capacitors or bigger ones ? Can someone draw me a updated schema with more diodes so I will be 100% sure of what to do ?
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Old 24th October 2004, 02:05 AM   #77
LydMekk is offline LydMekk  Norway
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Forgot to post the values used in the schema above:

Axiell ellyt 2200uF/25V

and

LT10A04 diode 10A 400V
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Old 24th October 2004, 07:51 AM   #78
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Default Re: Alternative layout of DC trap

Quote:
Originally posted by LydMekk
Have successfully built this, removed 99-100% of all my DC noise from my amps.

Am no electronics expert, but is this similar to earlier schematics ?
Norway, I use 230V mains.

Click the image to open in full size.

If needing more DC removal than in this schematic, can I just add more diodes in serial to the existing 2 ? Do I also need more capacitors or bigger ones ? Can someone draw me a updated schema with more diodes so I will be 100% sure of what to do ?
This circuit is rather pointless, because if you are into this design you can do as Lars Clausen has done, a signle capacitor plus a 4.3 V tranzil. The same result is achieved. The extra capacitor in your design won't do any good at all.

When you choose the capacitor and the value of it you must know how much current you expect to have AND how much current the capacitors can take continuously. You must check the cap datasheet for this.

The idea is this:

Insert a capacitor in series with the primary winding.

Make sure that the caps won't get too much reverse voltage. This can be done in two ways, connect two in series or add a tranzil or two diodes across.

If you have two caps in series you ought to have some transient and inrush current protection (I used plain diodes but tranzils are also OK)
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Old 25th October 2004, 03:01 PM   #79
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Default nasty slow-start

Quote:
Originally posted by lucpes
Phew... finally quiet 1KVA toroids used two 2200uF caps, two diodes, one varistor and a 0.33uf cap. Combined with a slow-start circuit ( http://mitglied.lycos.de/Promitheus/...or_toroids.htm ) it made my amps ready for case placement (ok, after I change only a couple of things I have planned
This is a horrible design. The relay contacts will close slowly as the voltage across the coil builds up, most likely causing sparking, fizzing and nasty noises, and rapidly burning out the relay contacts.

This should be much better: http://sound.westhost.com/project39.htm
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Old 25th October 2004, 07:28 PM   #80
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the design works just fine! I´m using one of these to turn on two 600VA trannies with over 360000uF for over two years now. No sizzling sparking or whatever

William
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