Hi guys,
I have been working in the past days in prototyping a Jensen Twin Servo Preamp based in the original Jensen Design:
http://www.jensen-transformers.com/as/as083.pdf
So far everything works and the sound is awesome. Warm, full, 3D and punchy.
So here is the problem: I would like to add a switch for 1 or 2 stage gain. Putting a simple true bypass switch between the output from the 1st Stage to the output transformer will produce the expected loud "pop" due to DC offset changes, capacitances, etc. The design must be free of capacitors in the audio path so a coupling capacitor between stages is not an option (even though I tried a capacitor to block the DC and popping was minimun... but there was color on the sound and sound quality was not the same) There are some conventional and popular fixes like bleed resistors and capacitors... the ones people do in guitar amps, but I think were are talking here about something a little different because we are talking about Discrete Opamps, DC voltages present sometimes in the audio path and a servo DC Offset servo compensation circuit.
The goal is a clean switching between 1 stage and 2 stage preamp.
Any of you people with experience in Op Amps circuits have a sugestion?
Picture:
I have been working in the past days in prototyping a Jensen Twin Servo Preamp based in the original Jensen Design:
http://www.jensen-transformers.com/as/as083.pdf
So far everything works and the sound is awesome. Warm, full, 3D and punchy.
So here is the problem: I would like to add a switch for 1 or 2 stage gain. Putting a simple true bypass switch between the output from the 1st Stage to the output transformer will produce the expected loud "pop" due to DC offset changes, capacitances, etc. The design must be free of capacitors in the audio path so a coupling capacitor between stages is not an option (even though I tried a capacitor to block the DC and popping was minimun... but there was color on the sound and sound quality was not the same) There are some conventional and popular fixes like bleed resistors and capacitors... the ones people do in guitar amps, but I think were are talking here about something a little different because we are talking about Discrete Opamps, DC voltages present sometimes in the audio path and a servo DC Offset servo compensation circuit.
The goal is a clean switching between 1 stage and 2 stage preamp.
Any of you people with experience in Op Amps circuits have a sugestion?
Picture: