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Old 6th May 2006, 06:54 PM   #1
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Default Aleph-x input-coupling-capacitors

Hello,
I implemented the BG 10uF capacitors in the two ways shown on the image. The main difference is, if they are before, or after the 10K input resistor. What suprises me is the big difference in sound. When the capacitor is in front of the resistor, voices or instruments are quite small and very precise in focus. When the capacitors are behind the 10k resistor the sound is very laid back and the timing is relaxed. But voices are much bigger and out of focus. I have no real explanation of this phänomenon, as the 68k groundresistor is responsible for the resistance the capacitor faces. Could it be the feedback is different?
This shouldn´t be a discussion about BG´s or the reasons for input caps, just a question about the influence of their position in the circuit.
Oliver
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Old 7th May 2006, 02:14 PM   #2
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Hello,
Does someone know how the iputcapacitor is implemented in the origina XA? Or do you have ideas, why the difference in the sound is so big? I know that the inputcap comes behind the input resistor normaly, but the other way voices sound much better.
Oliver
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Old 7th May 2006, 03:55 PM   #3
EUVL is offline EUVL  Europe
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If you connected the feedback capacitor to the junction of 10k/100k and before the cap in the lower figure, then you just added 10uF to the input capacitance of the input diff pair, I think.

I would connect it as per the upper figure, and I do not think you need the 100k before the cap. The 100k feedback resistor goes to the junction of 10k/68k, as in the original schematic.

Patrick

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Old 7th May 2006, 04:10 PM   #4
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Not the feedbackcapacitor, but the inputcapacitor. The difference to the inputcap of preamps is that i have the zener on the other side of the capacitor. Could this be wrong?
Oliver
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Old 7th May 2006, 04:13 PM   #5
EUVL is offline EUVL  Europe
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Sorry. Typing error. I meant the 100k feedback resistor.
The Zener is in the right place.

May I ask why you want an input cap in the first place ?

Patrick
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Old 7th May 2006, 04:22 PM   #6
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It´s just my wish to be carefull, because in a friends preamp, the outputcapacitor had a breakthrough, and the aleph-x has dc gain, if there are no inputcaps. That´s the reason for inputcaps in the XA.
The Coral chassis of my speakers are not replaceable.
Oliver
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Old 7th May 2006, 04:23 PM   #7
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In the aleph L and Aleph P the diodes are on the oposite side of the inputcaps, that´s why i´m asking.
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Old 7th May 2006, 04:28 PM   #8
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In my test circuit, I put an input cap before the 10k resistor. It works fine. The rest of the circuit stays the same if you want to remove the cap later.

Patrick
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Old 7th May 2006, 04:29 PM   #9
Netlist is offline Netlist  Belgium
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Oliver, what's the use of the 100k resistor.
I can't see it in the original AlephX.

/Hugo
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Old 7th May 2006, 04:35 PM   #10
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It´s common to have a groundresistor in front of inputcaps, in case there is some dc, i guess. Actually it doesn´t make a difference in the sound if i leave it out. I tried.
Oliver
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