"But, I am afraid that if it goes wrong and destroys my expensive gear that I will only have myself to blame and I will have no way of replacing my lost stuff"
So build the Bryston circuit. It's good enough for them and their 20 year warranty.
Just plop a 35A bridge on the chassis and tack the caps across it.
So build the Bryston circuit. It's good enough for them and their 20 year warranty.
Just plop a 35A bridge on the chassis and tack the caps across it.
djk said:
Ok... How large should I make the caps if I am trying to supply a 1500W device? 30,000uF enough?
Hi Needy,
your 30mF cap has an impedance of 0.088ohms at 60Hz.
1/[2*Pi*F*C].
A pair in parallel will develop half the voltage of a single.
The current into your 1500W load @ 110Vac is 13.6Arms and about 19.3Apk, if a true sinewave.
The voltage across the pair of caps passing this level of AC current is I*R=0.088*19.3/2=0.85Vpk.
This is less than the Vf of that pair of series diodes, so not current bypasses the caps.
At 1.2Vf the caps should be able to pass 27Apk.
This allows a bit of crest factor at full load and considerable crest factor if the load is well below maximum.
30mF//30mF can easily carry 1500W load.
The diodes will bypass the caps at start up and if fault current flows. They should be sized to ensure they never develop any more than 2Vf under worst case conditions to protect the low voltage caps.
your 30mF cap has an impedance of 0.088ohms at 60Hz.
1/[2*Pi*F*C].
A pair in parallel will develop half the voltage of a single.
The current into your 1500W load @ 110Vac is 13.6Arms and about 19.3Apk, if a true sinewave.
The voltage across the pair of caps passing this level of AC current is I*R=0.088*19.3/2=0.85Vpk.
This is less than the Vf of that pair of series diodes, so not current bypasses the caps.
At 1.2Vf the caps should be able to pass 27Apk.
This allows a bit of crest factor at full load and considerable crest factor if the load is well below maximum.
30mF//30mF can easily carry 1500W load.
The diodes will bypass the caps at start up and if fault current flows. They should be sized to ensure they never develop any more than 2Vf under worst case conditions to protect the low voltage caps.
But audio amplifier power supplies are seldom resistive loads, you really need to design for the current peaks into the supply caps, I suspect the crest factor can be higher than mentioned above - particularly with "audiophile" high energy storage notions giveing huge reservoir caps
since the correct circuit’s clamp diodes prevent over-voltage the DC blocking caps can be low V rating but must be sized/have esr appropriate for the (primary) current which is drawn in high peaks to recharge the internal supply reservoir caps
since the correct circuit’s clamp diodes prevent over-voltage the DC blocking caps can be low V rating but must be sized/have esr appropriate for the (primary) current which is drawn in high peaks to recharge the internal supply reservoir caps
Thats the one I built... it works even with diodes being supposedly the wrong way around...
The circuit as is, is good to block .7VDC, and you can add more diodes in series to increase this.
The circuit as is, is good to block .7VDC, and you can add more diodes in series to increase this.
I would really like to know where the DC is coming from. Line voltage is transmitted through transformers which do not pass DC. My experience is that many consumers products which have internal power transformers are designed and built for low expense, that is cheap. They are designed such that the maximum flux density is very close to the saturation flux density. A good line transformer would be designed for a maximum flux density of 1/2 the saturated flux density of the material. In addition, the transformers may not have been properly impregnated with a high quality transformer varnish. The lack of varnish in and around the steel laminations and copper can cause buzzing. In addition, they may have butt stacked and welded the laminations instead of interleaving and bolting. The laminations themselves may be of a very low grade. One more thing, the conduction angle of the transformer rectifier unit with a capacitive input filter gives rise to very large and narrow current pulses. They are not sinusoidal. These sharp leading edge currents can set up sympathetic vibrations through the copper to the transformer core. The worst part of all this is that there is nothing you can do about it expect get a higher quality transformer which probably won't fit!
EchoWars said:
somewhat confused with the bryston circuit.
can you explain the connections?
thank you very much 🙂
The DC comes from the way we load up the mains supply with non resistive loads.[email]artnace@cox.net[/email] said:
These capacitor input filters, some direct off the mains voltage, trim off the top of the waveform resulting in an asymmetric waveform for the neighbours. Our TVs are really good at this. The asymmetric waveform is AC +DC and some types of transformers are particularly susceptible to DC.
I believe toroids are usually designed to minimise the core resulting in high flux, much higher than EI and others.
Can you ask specific (and clear) questions?jarthel said:
We are dealing with mains voltage and I fear ambiguity could lead to accidents.
[email]artnace@cox.net[/email] said:
Half-power setting in heaters, hot air guns etc is one pretty common cause. Cheapest and nastiest way to implement half-power is to cut off half of the cycle with power diode in series with load. Non-symmetric current then causes dc-offset because supply impedance is not zero.
I just measured 1.7V dc offset voltage from electrical outlet at my working place when using 1800W Bosch hot air gun on half-power. Also bench-top power supplies that I have on my table start to buzz loudly instantly after switching to half-power.
Edit: Bulletproof dc-blocker should be designed for nearly 5 volts offset. Electric outlet impedance can be up to 1 ohm(0.2-0.7 ohms typically) for 230v outlets, resulting in max 5 volt dc-offset if 2200W load is connected with diode.
For USA home use, typical half wave off-set is caused by Halogen lamp (300W) or Crock Pot (150W).
These are cleaned up with a simple bridge rectifier (Bryston circuit).
These are cleaned up with a simple bridge rectifier (Bryston circuit).
location of DC block
Hi all,
We normally see the DC block in the Live line and occasionally in the neutral line.
I have a twin primary for 220/240Vac operation.
Are there any reasons, safety or otherwise, against fitting the DC block between the two primary windings?
It will sit at about 110Vac with respect to safety earth and still operate as a block but allowing AC to pass.
Comments please.
Hi all,
We normally see the DC block in the Live line and occasionally in the neutral line.
I have a twin primary for 220/240Vac operation.
Are there any reasons, safety or otherwise, against fitting the DC block between the two primary windings?
It will sit at about 110Vac with respect to safety earth and still operate as a block but allowing AC to pass.
Comments please.
Some discussion on a different circuit can be found here: http://www.diyaudio.com/forums/showthread.php?s=&threadid=3924&highlight=
AndrewT said:
the bryston circuit does not show where the other wire of out the bridged rectifier goes.
also, the "line" wire of the AC mains seems to be unconnected.
Re: location of DC block
Hi Andrew,
Is there a special reason for tapping between the windings?
Regards
Jürgen
Hi Andrew,
I would prefer the more straight solution, which means treating the transformer as a building block, regardless if it has dual primaries or not.AndrewT said:
Is there a special reason for tapping between the windings?
Regards
Jürgen
"the bryston circuit does not show where the other wire of out the bridged rectifier goes. also, the "line" wire of the AC mains seems to be unconnected"
Really, you can't figure it out?
The only connection to the neutral on the power inlet is through the bridge, everything going to neutral would thus connect to the bridge. The line would therefore go to a fuse, power switch, and then the transformer.
"The Bryston circuit is not a simple bridge rectifier."
It is, and is used for it's 1.4V drop. 5V drop, as proposed by someone else, is another story (caps would need to be 4X as large and connected back-to-back). If you're not smart enough to figure out the caps are part of the circuit (and I know you are), then you shouldn't be messing with line voltage in the first place.
For those of you that can't figure it out from the thumbnail, here is the whole schematic:
http://www.bryston.ca/BrystonSite05/pdfs/SSTAmplifiers/3B-SST-SCH-1C(Oct02).pdf
Really, you can't figure it out?
The only connection to the neutral on the power inlet is through the bridge, everything going to neutral would thus connect to the bridge. The line would therefore go to a fuse, power switch, and then the transformer.
"The Bryston circuit is not a simple bridge rectifier."
It is, and is used for it's 1.4V drop. 5V drop, as proposed by someone else, is another story (caps would need to be 4X as large and connected back-to-back). If you're not smart enough to figure out the caps are part of the circuit (and I know you are), then you shouldn't be messing with line voltage in the first place.
For those of you that can't figure it out from the thumbnail, here is the whole schematic:
http://www.bryston.ca/BrystonSite05/pdfs/SSTAmplifiers/3B-SST-SCH-1C(Oct02).pdf
Hi Djk,
Note that the + is connected to the -.
Wired this way, the "bridge rectifier" is acting as a voltage limiter not as a rectifier. In fact it behaves as a bipolar voltage limiter, preventing any more than +-1.4V, at lowish currents, across it's ~ to ~ connections. At very high currents this limiting action could rise to values near +-2V.
The sole purpose of the bridge is to limit voltage across the capacitors and thus allow large value low voltage caps to be used here. And that is related to budget and space.
confirms that you are aware it is not a simple bridge rectifier.
Note that the + is connected to the -.
Wired this way, the "bridge rectifier" is acting as a voltage limiter not as a rectifier. In fact it behaves as a bipolar voltage limiter, preventing any more than +-1.4V, at lowish currents, across it's ~ to ~ connections. At very high currents this limiting action could rise to values near +-2V.
The sole purpose of the bridge is to limit voltage across the capacitors and thus allow large value low voltage caps to be used here. And that is related to budget and space.
