MrShhh
Well-known member
Hi everyone, I was after a super-clean active DI box, to have a different sound from transformer or valve based DI so I built the following using a BB OPA134 buffer stage driving a BB DRV134 line driver:
DI Box Schematic:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DRV134DIbox.jpg
Photos:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DSCF0935.jpg
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DSCF0942.jpg
This is the first attempt I've made at designing something myself so I was hoping if people could please have a look and see if there's anything I've done that's not quite right or could be improved.
It sounds pretty good although there's couple of things I noticed when "measuring" it:
1. DRV134 Signal balance ratio: SBR = -20log(Vo/Vi) using this test circuit:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DRV134SBRTestCircuit.jpg
Vi = 0.775Vrms sinewave (z=50ohm)
My measurements:
Hz.....Vo (mV rms)....SBR (dB)
250..........6...............42.2
1k............5.7............42.7
5k............5.9............42.4
10k..........6.2............41.9
15k..........6.7............41.5
17.5k.......6.9............41.0
The datasheet SBR for the DRV134 is 54dB best, 35dB worst @ 1kHz, so is 42.7dB ok? Looking at my schematic, could this be improved or am I up against the limitations of the DRV134? The figures are much the same for both channels.
2. Leaving out R3 (so the OPA134 become a unity gain buffer) causes the output to become unstable on the scope. The scope has a hard time locking onto the waveform, it looks "messy" & the sound gets a bit duller. Does anyone know what is happening here?
Thanks for your help
DI Box Schematic:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DRV134DIbox.jpg
Photos:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DSCF0935.jpg
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DSCF0942.jpg
This is the first attempt I've made at designing something myself so I was hoping if people could please have a look and see if there's anything I've done that's not quite right or could be improved.
It sounds pretty good although there's couple of things I noticed when "measuring" it:
1. DRV134 Signal balance ratio: SBR = -20log(Vo/Vi) using this test circuit:
http://i985.photobucket.com/albums/ae333/MrShhh_2009/DRV134SBRTestCircuit.jpg
Vi = 0.775Vrms sinewave (z=50ohm)
My measurements:
Hz.....Vo (mV rms)....SBR (dB)
250..........6...............42.2
1k............5.7............42.7
5k............5.9............42.4
10k..........6.2............41.9
15k..........6.7............41.5
17.5k.......6.9............41.0
The datasheet SBR for the DRV134 is 54dB best, 35dB worst @ 1kHz, so is 42.7dB ok? Looking at my schematic, could this be improved or am I up against the limitations of the DRV134? The figures are much the same for both channels.
2. Leaving out R3 (so the OPA134 become a unity gain buffer) causes the output to become unstable on the scope. The scope has a hard time locking onto the waveform, it looks "messy" & the sound gets a bit duller. Does anyone know what is happening here?
Thanks for your help