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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 7th October 2018, 03:58 AM   #3171
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
The two pots output impedance will add up. That impedance is source to the preamp and augments the R element of its RC input filter. The more RC slows down the slew rate response and narrows the HF -3dB frequency response point. You would want the total to stay within the range of the 20K-50K recommendation for DCG3. The article's Fig.7 standard configuration that says below it "BAL = 2.5 VOL. For example: VOL = 10k log, BAL = 25k linear" should be like a 35K standalone pot for output impedance.
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Old 7th October 2018, 09:53 PM   #3172
Atom666 is offline Atom666  Canada
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Thanks Salas. I actually meant a 20K log for volume and a 50K linear with the added resistor for balance with a switch to short out the balance control until needed.
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Old 11th October 2018, 09:00 PM   #3173
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Set up that pots system alone first and measure its resistance from input to output when rotating so to find the max. See if it falls in the recommended range or to change pot values. The equivalent max for series type 20k-50k nominal pots is 5k-12.5k when at half point value travel.
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Old Yesterday, 06:09 AM   #3174
quan is offline quan  Australia
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Hi Nick, any advice re reducing noise level on the DCG3 headphone amp?. I can hear the noise on the back ground noise btw skipping cd tracks. . Thank you .
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Old Yesterday, 11:10 AM   #3175
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
What kind of noise with what kind of headphones? Your ATH? Some hum? Because I can't hear any hiss or hum with a gamut of headphones on my build
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Old Yesterday, 12:35 PM   #3176
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
In any case, if its not about some low level hum to solve but its hiss, you can reduce the gain to x2.33 with R7=750R. That's when the standard x3 is inadequately loud for your system and your headphones 115dB/V sensitivity regarding useful volume pot range and/or background noise creeping up.

Maybe its an opportunity to test with the alternative BC327-40 Q1 Q2 also. You may put female header pins for those components to can swap them with the BC560C originals and compare. The DC offset setting up procedure with VR1 must be repeated when changing Q1 Q2.
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