Moderators isaac42 Posted November 28, 2012 Moderators Share Posted November 28, 2012 Puttering around... I have several old amplifiers about. None have a line out, preamp out, or anything like that. Some time back, I wanted a line out, so I built one. Speaker cord out to the line box. In the line box, there is an input jack and an output jack, which are really just parallel jacks. From the hot side of the input jack, there is a 10K dropping resistor going to the line out jack, then a 1K load resistor to the common. A couple of nights ago, I decided to add a bass boost. In series with the load resistor, I installed a 2.2 ?F capacitor. That adds a boost from about 80 Hz on down. Then, I put a 2.2K resistor in parallel with the cap, to limit the boost below 40 Hz. It ought to be shielded, I suppose, but I did it all in a plastic deli tub. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 28, 2012 Members Share Posted November 28, 2012 I've installed speaker emulated line out jacks in all my older tube amps. Comes in handy for direct recording. Theres an extra cap in there to remove the harshness you get from a normal line out. Much better for recording. It can easily be put into a separate box too but theres less hum exposure if the cord between the amp and the DI box are short. [ATTACH=CONFIG]350193[/ATTACH] [ATTACH=CONFIG]350194[/ATTACH] Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted November 28, 2012 Author Moderators Share Posted November 28, 2012 Doesn't that cap impose a 6 dB/octave rolloff starting at about 1.5 KHz? Seems awfully low to me. Have I miscalculated? I hesitate to modify my old tube amps, even mods I know I should do, such as a three-prong power cord. They're not worth much, so I shouldn't hesitate, just go ahead. I tell myself this, but I keep not doing it. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted November 28, 2012 Author Moderators Share Posted November 28, 2012 I'm also thinking I should add in a switch, bypassing the bass boost. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 28, 2012 Members Share Posted November 28, 2012 Well theres a resistor between the amps output and the line out jack it straddles so whatever load the cap puts on the amp at 8 ohms is infatesimal. The cap value is perfect for what it does. The resistor values are good for a 50W head running at normal volume. A higher or lower wattage amp may need different values. I thought about putting a 500K pot in series with the 470 ohm resistor to vary the level dowmn a bit. I suppose I could just put it across the output jack too. You could wire the cap like a guitars tone control and vary the speaker emulation, but I never saw the need to. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted November 30, 2012 Author Moderators Share Posted November 30, 2012 Tried it out at rehearsal this evening. Worked great. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.