Samuel Groner
Well-known member
Hi
As a first project for my discrete opamp ([removed]) I designed a mic preamp: [removed]
I'm looking for a slightly coloured, yet versatile preamp. It was important to me to have similar sound at different gains, hence the two gain stages.
The two gain stages are adjusted such that the first has twice the gain of the second (e.g. 20 dB and 10 dB) and from 6 dB to 60 dB overall. The transformer balanced output and the input transformer each add 6 dB to this.
The values of R103-R105, R109 and R111 are not final yet.
The transformer balanced output is taken from the LL1539 datasheet (1539.pdf).
The input bias cancellation of the first opamp is somewhat overkill but it reduces DC current through the transformer secondaries and perhaps clicks during gain changes as well.
I opted for on-board regulators as the PSRR of the used opamps is not as good as we are used to from ICs and I want it dead silent.
Any comments, suggestions, drawing errors?
Thanks!
Samuel
As a first project for my discrete opamp ([removed]) I designed a mic preamp: [removed]
I'm looking for a slightly coloured, yet versatile preamp. It was important to me to have similar sound at different gains, hence the two gain stages.
The two gain stages are adjusted such that the first has twice the gain of the second (e.g. 20 dB and 10 dB) and from 6 dB to 60 dB overall. The transformer balanced output and the input transformer each add 6 dB to this.
The values of R103-R105, R109 and R111 are not final yet.
The transformer balanced output is taken from the LL1539 datasheet (1539.pdf).
The input bias cancellation of the first opamp is somewhat overkill but it reduces DC current through the transformer secondaries and perhaps clicks during gain changes as well.
I opted for on-board regulators as the PSRR of the used opamps is not as good as we are used to from ICs and I want it dead silent.
Any comments, suggestions, drawing errors?
Thanks!
Samuel