Hi everyone....
I would like to share a tube mic preamp I design. I have not seen a mic preamp that can switch between SE/PP and TRI-UL-PEN. It sounds nice och has a lot of diffrent flavours. It has no NFB. The idea was also to design the preamp around cheap but good performing tubes. The russian/soviet 6J32P, 6N1P and 6N6P fit that bill.
I used the UTM-3580 PP or Carnhill WTB2291 (even if it not design as a PP transfomer it does a nice job), I guess you could use a PP transfomer from edcore if you live in US. As input transfomer anything from 1:4 to 1:10 should work fine depending on taste... headroom, s/n etc...
My build also has DI, HP, input and output PAD, phase reverse and 48V... The B+ is around 250VdC....
Picture in Post 16 shows how implement a DI that breaks the MIC connection, and how to integrate a -20dB PAD and Phantom power and polarity reverse.
At the output there can be a output PAD and a load resistor that forces the line stage to work hard and produce harmonic distortion.
I omitted the gain control switch in the input stage, because it interacts with the tri/pen controll and because the triode mode makes the input stage clean enough, more feedback makes the sound sterile in my opinion. This is a coloured pre amp...
Fre. response -3dB ca. 20Hz-30KHz.
Clean setting: TRI + PP= THD+N: 0,18% at 1KHz 0 dBu (without NFB).
Coloured setting: PEN + SE + -15dB OUTPUT PAD: THD+N: 2,7 % (without NFB).
The H2 and H3 content varies depending on mode. PP cancels H2, PEN increases H3.
The TRI/PEN and PP/SE modes can alter the preamps gain by about 20 dB.
The 1K5 dropping resistor in the PSU high voltage rail needs to be in the 7-10 W range otherwise there will be smoke...
Audio sample post #24: 4in1 tube mic preamp SE/PP TRI/PEN
I would like to share a tube mic preamp I design. I have not seen a mic preamp that can switch between SE/PP and TRI-UL-PEN. It sounds nice och has a lot of diffrent flavours. It has no NFB. The idea was also to design the preamp around cheap but good performing tubes. The russian/soviet 6J32P, 6N1P and 6N6P fit that bill.
I used the UTM-3580 PP or Carnhill WTB2291 (even if it not design as a PP transfomer it does a nice job), I guess you could use a PP transfomer from edcore if you live in US. As input transfomer anything from 1:4 to 1:10 should work fine depending on taste... headroom, s/n etc...
My build also has DI, HP, input and output PAD, phase reverse and 48V... The B+ is around 250VdC....
Picture in Post 16 shows how implement a DI that breaks the MIC connection, and how to integrate a -20dB PAD and Phantom power and polarity reverse.
At the output there can be a output PAD and a load resistor that forces the line stage to work hard and produce harmonic distortion.
I omitted the gain control switch in the input stage, because it interacts with the tri/pen controll and because the triode mode makes the input stage clean enough, more feedback makes the sound sterile in my opinion. This is a coloured pre amp...
Fre. response -3dB ca. 20Hz-30KHz.
Clean setting: TRI + PP= THD+N: 0,18% at 1KHz 0 dBu (without NFB).
Coloured setting: PEN + SE + -15dB OUTPUT PAD: THD+N: 2,7 % (without NFB).
The H2 and H3 content varies depending on mode. PP cancels H2, PEN increases H3.
The TRI/PEN and PP/SE modes can alter the preamps gain by about 20 dB.
The 1K5 dropping resistor in the PSU high voltage rail needs to be in the 7-10 W range otherwise there will be smoke...
Audio sample post #24: 4in1 tube mic preamp SE/PP TRI/PEN
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16A8701D-8667-49C8-B8BF-B431D1A10603.jpeg163.6 KB · Views: 301
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8EB5A2BB-F6EC-42BE-9C76-84018A880691.jpeg100.5 KB · Views: 233
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BBFE7EA8-AD9D-4872-B8CF-C329D5233B31.jpeg137 KB · Views: 262
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4in1 PSU.jpeg168.3 KB · Views: 261
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Mic-DI-input.jpeg115.9 KB · Views: 83
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Inputstage.jpeg187.5 KB · Views: 84
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Splitter+Line stage.jpeg175 KB · Views: 81
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Load + output PAD.jpeg138.7 KB · Views: 95
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