Hi,
I have a question about B2031a.
They are four potentiometer on the pcb - VR1,2,3,4.
All available from outside.
VR4 is input level
VR3 is bass speaker level ?
VR1 and VR2 are in HT part.
What are VR1 and VR2 doing ?
One is for HT level (VR2 ?), another one (VR1 ?) for 17KHz boost ?
Am I right ?
I just would like to reduce HT level.
Look at the attached crossover picture.
Thank you 🙂
I have a question about B2031a.
They are four potentiometer on the pcb - VR1,2,3,4.
All available from outside.
VR4 is input level
VR3 is bass speaker level ?
VR1 and VR2 are in HT part.
What are VR1 and VR2 doing ?
One is for HT level (VR2 ?), another one (VR1 ?) for 17KHz boost ?
Am I right ?
I just would like to reduce HT level.
Look at the attached crossover picture.
Thank you 🙂
Last edited:
VR1 adjusts the Q value of the 18kHz low-pass filter. The Q value determines whether the attenuation at the cutoff frequency remains flat or exhibits a peak. In other words, adjusting the Q value modifies the gain of the frequency response at the cutoff frequency. A high Q value can enhance the extended ultra-high-frequency response. The B2031A employs two circuits for high-frequency enhancement: one is this Q-adjustable low-pass filter (IC8B + VR1), and the other is the IC6A 5kHz high-pass filter, which boosts frequencies starting from 4kHz. The boost magnitude is determined by the VR2//R64 ratio, with a factory setting of up to +5dB at approximately 18kHz. This is the root cause of the harsh high frequencies in the B2031A. Given the inherently poor quality of its tweeter, which should require significant high-frequency reduction, it’s puzzling why the designers opted for aggressive boosting instead. This is akin to cutting off the less sweet end of a sugarcane to improve its taste.
Can disconnecting R64 reduce high-frequency signals? What are the effects?
Can disconnecting R64 reduce high-frequency signals? What are the effects?
The B2031A’s circuit architecture features two notable highlights:
The original tweeter’s poor performance produces distorted, fatiguing highs. Replacing it with a high-quality full-range driver (conveniently available to me) would leverage the B2031A’s existing high-frequency boost circuits to compensate for the full-range driver’s natural 8kHz–12kHz dip—a perfect synergy. If power handling is insufficient, dual parallel drivers can be used. I successfully replaced the original tweeter with two AURA NSW2-326-8A units in parallel. Adjustments to VR2/VR3 would balance loudness levels, with finer corrections like disconnecting or increasing R64. This compromise sacrifices extended high-frequency response上限 to improve tonal quality, effectively trimming the "flavorless" harsh highs. This full-range solution excels in vocal and string instrument reproduction, though large-scale orchestral works still demand high-sensitivity metal dome tweeters.
Circuit simulations verify these observations. Having not deeply studied analog circuits for decades, much of my knowledge has faded. I welcome corrections and insights from experienced circuit designers—your guidance would be greatly appreciated!
- A high-Q 40Hz high-pass filter serving dual purposes: attenuating ultra-low frequencies while extending the low-frequency下限.
- The 18kHz low-pass filter that removes ultra-high frequencies. However, I believe adjusting the cutoff frequency to 15kHz or lower could significantly improve high-frequency listening quality.
The original tweeter’s poor performance produces distorted, fatiguing highs. Replacing it with a high-quality full-range driver (conveniently available to me) would leverage the B2031A’s existing high-frequency boost circuits to compensate for the full-range driver’s natural 8kHz–12kHz dip—a perfect synergy. If power handling is insufficient, dual parallel drivers can be used. I successfully replaced the original tweeter with two AURA NSW2-326-8A units in parallel. Adjustments to VR2/VR3 would balance loudness levels, with finer corrections like disconnecting or increasing R64. This compromise sacrifices extended high-frequency response上限 to improve tonal quality, effectively trimming the "flavorless" harsh highs. This full-range solution excels in vocal and string instrument reproduction, though large-scale orchestral works still demand high-sensitivity metal dome tweeters.
Circuit simulations verify these observations. Having not deeply studied analog circuits for decades, much of my knowledge has faded. I welcome corrections and insights from experienced circuit designers—your guidance would be greatly appreciated!