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Old 7th December 2010, 07:54 PM   #1
Harolda is offline Harolda  Netherlands
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Default Lower capacity output CAPS on B1 buffers posible?

Hello all,

I am thinking of lowering the capacity of the output caps on my B1 buffers.I sue them in an active crossover. the low pass has 10uF and the high pass has 1uF, both PIO. Now i also have some Russian Silver Mica available (0.1264uF). These seem to sound very good.
Could i safely reduce these output capacitors?

I am driving audio sector LM4780 boards with the crossover. I am using a symmetrical PSU version of the buffers.

thankx in advance
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Old 8th December 2010, 12:18 PM   #2
AndrewT is online now AndrewT  Scotland
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Hi,
the output cap blocks DC from the next stage.
If the next stage is an active High Pass with it's own input capacitor, then it does not need an extra DC blocking cap.

Alternatively, you can use the DC blocking cap as one pole of the High Pass filter you are creating. eg. 18dB/Octave HP would have a CR passive filter followed by a 12dB/octave active High Pass filter.

Finally you can scale the RC filter created at the B1 output back far enough from the Pass Band of the next stage such that it passes all the wanted signals.
If you want a mid range filter of 300Hz to 4000Hz then the DC blocker could be set to ~30Hz and have virtually no audible effect on the midrange pass band.
Use F-3dB = 1 / [2 Pi R C]
with R=10k then C~470nF gives F-3dB~34Hz
Quote:
I am using a symmetrical PSU version of the buffers
what does this mean? B1 or DCB1 or ?
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regards Andrew T.

Last edited by AndrewT; 8th December 2010 at 12:21 PM.
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Old 8th December 2010, 04:31 PM   #3
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Let's hope that R = 300K

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Old 8th December 2010, 06:40 PM   #4
Harolda is offline Harolda  Netherlands
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Hello Andrew,

we discussed the crossover i am using some time ago. it is based on a design of prooptiki. see this thread: Two B1 and a crossover

I think it is a DCB1, as you can see, there are only coupling caps after the gain control of the LP and HP.

I know it is to block DC, but do i really need the 10uF and 1uF or can i go lower.

My current design is a accu powered prototype on veroboard with a fixed frequency.
The final design will be build on PCB by PCBexpress and will use an array of resistors and capacitors on the HP and LP so i can set my frequency as i need. Also a shelving filter is added for baffle step compensation also with capacitor and resistor array to set frequencies and resistors. Everything is selectable by jumpers. The whole setup is balanced and i can select between 12db or 24db.

regards.

Last edited by Harolda; 8th December 2010 at 06:43 PM.
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Old 15th December 2010, 06:25 PM   #5
Harolda is offline Harolda  Netherlands
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anybody?
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