BZLS (aka, BoSoZ?) Blocking Capacitors...what am I missing??? - diyAudio
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Old 1st February 2005, 09:04 PM   #1
NV&H is offline NV&H  United States
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Question BZLS (aka, BoSoZ?) Blocking Capacitors...what am I missing???

Can someone help me understand how the output stage of the BZLS gets it's signal to the outside world?

It seems that only if either C1 or C2 is left out can the output stage of the circuit pass voltage/current to the outside world (i.e., a power amp input). But with both C1 AND C2, it seems that the signal is "bottled up" between the caps.

HELP.

Thanks!
Hallque
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Old 1st February 2005, 09:11 PM   #2
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You're thinking DC. The caps can pass AC (the signal) while blocking the roughly 30 V DC at the drains.
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Old 1st February 2005, 09:12 PM   #3
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Both C1 and C2 are there to block DC. Speakers don't like DC.
So only AC which of course would be the sound will pass trough the caps.
Cap: Quasi infinite resistance for DC, better conductance with increasing AC.
Coil: the opposite.

/Hugo
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Old 2nd February 2005, 08:24 AM   #4
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Yes, yes... I know WHY they are there and I AM thinking AC.

It is my understanding that nothing passes THROUGH a capacitor (AC or DC), per se. But the periodic charging and discharging of each plate inside the capacitor in a loop results in an oscillating current in that loop; hence my question.

I'm not seeing how the gain stage has access to both sides of the C1 and C2 capacitors in any sort of loop the BoSoZ circuit in order to charge and discharge both the inboard and outboard sides of the caps.

I'm still scratching my head.
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Old 2nd February 2005, 09:11 AM   #5
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The voltage (V1) on the capacitor connection close to the MOSFET is altered. The output (on the other side of the capacitor) is referenced to ground (GND), which of course is a fixed 0V in our circuit. Now you can see that there is an AC voltage when V1 is altered in relation to GND (v1). This AC component, v1, is passed through the capacitor.

Not sure if I managed to make anything clearer than the above posterns already have.

/Niclas
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Old 2nd February 2005, 09:28 AM   #6
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The inboard goes through the resistor(s), +rail (-rail) and PSU capacitors to the ground. Meanwhile, the outboard goes through the resistor(s) to the ground. Therefore, at least one loop is formed for the charginging and discharging. There could be more than one loop.
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Old 2nd February 2005, 10:40 AM   #7
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Even without a reference to ground, the signal has a loop, (remembering that the signals at the two drains are opposite polarity):


Q1 drain - C1 - R9 - amp balanced input - R10 - C2 - Q2 drain - Q2 source - p5/R15 - Q1 Source - Q1 Drain.

Hope this helps
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Old 5th February 2005, 08:03 PM   #8
NV&H is offline NV&H  United States
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Thanks for the responses everyone.

As it turns out, my concept of a capacitor was incorrect. Although it is correct that current does not pass through the cap (AC or DC) it just SEEMS to do so for AC. What I was missing was the fact that when electrons are all bunched up on one plate, the field force from their collective charge reaches through the dielectric and pushes electrons off the opposite plate. In this way, the two cap terminals don't have to be part of the same loop.

So BINGO, this allows me see how the blocking caps in BoSoZ circuit works.

I feel much better now!!
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