Hi,
I recently finished building small stereo analog processor (not an EQ). External Ac transformer, half wave rectifier psu, +/-17v One layer PCB, Singlepoint ground.. the usual practices. I also designed a metal case to fit the boards, etc... In a normal listening test you wouldn't notice there is a problem... All opamp stages (MC33078, DRV134),have a bandwidth around 100khz, each. But after testing the device with TRUE RTA, (20-20khz bandwidth) it revealed a bandwidth problem...
Many questions arise: ¿is it due to single layer layout? (pcb is flooded with gnd), Some told me about parasitic capacitances...Maybe the bandwidth filters in the opamps are not correct? ¿ wrong caps values?
In professional audio products the bandwidth is specified within +/- 0.5db in others +/- 3db variation ( within ear range..)
¿what factors can contribute to limit the bandwidth of an audio circuit? ¿how can i trooble shoot this?
because all of this, i ask some help to point the cause of the problem.
Thank you for your help!
Jay x.
input test signal level: 1khz , 775mv @ 0dbu
freq dbu
20.000 -3,700
50.397 -2,085
100.794 0.000
201.587 0.647
403.175 0.782
1.015.937 0.138
1.140.350 -0,037
2.031.873 -1,199
3.225.398 -2,470
4.063.747 -2,260
5.120.000 -2,210
6.450.796 -3,560
10.240.000 -3,250
16.254.987 -3,780
20.480.000 -4,660
I recently finished building small stereo analog processor (not an EQ). External Ac transformer, half wave rectifier psu, +/-17v One layer PCB, Singlepoint ground.. the usual practices. I also designed a metal case to fit the boards, etc... In a normal listening test you wouldn't notice there is a problem... All opamp stages (MC33078, DRV134),have a bandwidth around 100khz, each. But after testing the device with TRUE RTA, (20-20khz bandwidth) it revealed a bandwidth problem...
Many questions arise: ¿is it due to single layer layout? (pcb is flooded with gnd), Some told me about parasitic capacitances...Maybe the bandwidth filters in the opamps are not correct? ¿ wrong caps values?
In professional audio products the bandwidth is specified within +/- 0.5db in others +/- 3db variation ( within ear range..)
¿what factors can contribute to limit the bandwidth of an audio circuit? ¿how can i trooble shoot this?
because all of this, i ask some help to point the cause of the problem.
Thank you for your help!
Jay x.
input test signal level: 1khz , 775mv @ 0dbu
freq dbu
20.000 -3,700
50.397 -2,085
100.794 0.000
201.587 0.647
403.175 0.782
1.015.937 0.138
1.140.350 -0,037
2.031.873 -1,199
3.225.398 -2,470
4.063.747 -2,260
5.120.000 -2,210
6.450.796 -3,560
10.240.000 -3,250
16.254.987 -3,780
20.480.000 -4,660