I'm pretty sure these are easy to make, but wanted to know if anyone could give me some advice on how to do it for best sound, and also what values to use. I want to build a device that will replicate the many, for instance, car high level to low level signal devices, which are normally a set of resistors. I'm not really sure what else, if anything, goes into them. However my complication is that this is to go from the speaker level outputs of a tube SET integrated amp into a subwoofer, and I would like to have the the SET amp see a nice even load, but I dont know what load is best, and how much resistance I need to turn all that current and voltage into 2 volts and a few ma of current. I was also originally considering building a simple lowpass crossover into it, but now I dont see a real advantage to that, since the sub has a built in crossover in the amp. If I'm wrong, let me know, and why.
An alternative method might be to hook a set of RCA's onto the volume control, allowing it to act as a passive preamp, but I was worried that because it has to drive a 15-20ft long pair of RCA's, it might not work so well. I know passive preamps are picky about the loads they are matched with, and I'm not sure what type of load a sub amp presents. I also considered, since I believe the amp is essentially a preamp at the 12au7-second tube in the chain, 4th triode (Correct?) that I could somehow tap in at that point and have an active preamp driving it as well. However, I was worried about how that might affect the amp.
The final option is to bypass the volume control, which I already added a switch to do that, and use it like a power amp, then use a tube preamp to control volume and feed the sub as well. However, thats an extra expense I don't really want I don't think.
An alternative method might be to hook a set of RCA's onto the volume control, allowing it to act as a passive preamp, but I was worried that because it has to drive a 15-20ft long pair of RCA's, it might not work so well. I know passive preamps are picky about the loads they are matched with, and I'm not sure what type of load a sub amp presents. I also considered, since I believe the amp is essentially a preamp at the 12au7-second tube in the chain, 4th triode (Correct?) that I could somehow tap in at that point and have an active preamp driving it as well. However, I was worried about how that might affect the amp.
The final option is to bypass the volume control, which I already added a switch to do that, and use it like a power amp, then use a tube preamp to control volume and feed the sub as well. However, thats an extra expense I don't really want I don't think.
Hi,
taking the speaker outlet signal and converting it to drive a line level is not the best way, but for a sub it might be adequate.
What impedance can the tube amp feed? I am guessing 8ohm.
Adding a 10k resitor in parallel to the speaker will make almost no difference to the load the tube output sees.
Now add a resistor ladder in parallel to the speaker to give the attenuation you need.
The attenuation will depend on the relative sensitivities of the sub and mains and on the gain in the sub.
-20db (=1/10) may be about right but it could vary a lot from this guesstimate.
taking the speaker outlet signal and converting it to drive a line level is not the best way, but for a sub it might be adequate.
What impedance can the tube amp feed? I am guessing 8ohm.
Adding a 10k resitor in parallel to the speaker will make almost no difference to the load the tube output sees.
Now add a resistor ladder in parallel to the speaker to give the attenuation you need.
The attenuation will depend on the relative sensitivities of the sub and mains and on the gain in the sub.
-20db (=1/10) may be about right but it could vary a lot from this guesstimate.
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