different gain levels and a PLLXO´s impedance - diyAudio
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Old 8th March 2011, 11:36 AM   #1
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Default different gain levels and a PLLXO´s impedance

I have been using a passive line level crossover for years now, only a capacitor in parallel for high pass and one in series for low pass. I added an opamp before the crossover to increase overall gain since the insertion loss was quite high.
I followed the schematic for a booster as appeared in AudioXpress. It works flawlessly and I hear no apparent distortion but I believe I hear a different tonal balance with increased gain (even when listening at the same volume) and wonder if impedance variations would result from the different gain settings and thus affect the crossover point yielded by the capacitor.
Is this a possibility?
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Old 23rd March 2011, 01:16 PM   #2
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After further listening and comparisons at different gain settings I realized that what I thought was a different tone balance is indeed distortion.
Engaging R4, 5 and 6 gives a total gain of 8db. and a great sound. Adding R3 raises gain to 15db but brings the distortion I was hearing.
I do need those 15db, (20 would be better)gain specially for movie duties.

The opamps are opa2134 and are being powered by the same dual 15v supply I use for the bass equalization.There is no hum whatsoever.
Anybody knows of a simple stage of some sort to provide an extra clean 10db boost from the output of this circuit, running on the same 15v supply?
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Old 23rd March 2011, 03:41 PM   #3
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Quote:
Originally Posted by poldus View Post
...only a capacitor in parallel for high pass and one in series for low pass...
other way round?

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Old 23rd March 2011, 03:57 PM   #4
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Originally Posted by poldus View Post
After further listening and comparisons at different gain settings I realized that what I thought was a different tone balance is indeed distortion.
If that buffer is in front of the PLLXO, then you should check the corner of the R2/C2 low pass filter. I calculate it at 1.6 kHz.

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Old 24th March 2011, 02:06 PM   #5
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Quote:
other way round?
My bad, parallel for low pass, series for high pass.
Mmmm, should I try removing R2C2? The crossover comes after the opamp.´
The boost is only needed for the higher frequencies. I am using pots to turn the lower frequencies´level down (by a big margin) again after the opamps.
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Old 24th March 2011, 07:13 PM   #6
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I don't know as i'd remove it, but it should at least be outside the audio band.

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