Would it be detrimental to the signal to add an RCA output directly after the volume pot on a tube amp? I want to add an output I can use for a subwoofer.
The question is: would having a 10 foot RCA cable connected to that point in the circuit be a high risk of adding noise?
I know there are speaker to line level converters and subwoofers that have speaker level inputs and I've heard the argument that using high level inputs gets you the 'sound of the amplifier' from the subwoofer. But since low frequencies tend to be tough for tube amps, especially SE ones, why feed the subwoofer that version of the signal when it can have the original version? My subwoofer sounds completely different with line level connection to a SS amp compared to a high level connection to the tube amp. I'd love to have the solid and defined bass to go with the tube amp.
The amp has a built in volume control and it seems pretty easy to tap connection off of the output on the volume control to feed the sub(s).
The question is: would having a 10 foot RCA cable connected to that point in the circuit be a high risk of adding noise?
I know there are speaker to line level converters and subwoofers that have speaker level inputs and I've heard the argument that using high level inputs gets you the 'sound of the amplifier' from the subwoofer. But since low frequencies tend to be tough for tube amps, especially SE ones, why feed the subwoofer that version of the signal when it can have the original version? My subwoofer sounds completely different with line level connection to a SS amp compared to a high level connection to the tube amp. I'd love to have the solid and defined bass to go with the tube amp.
The amp has a built in volume control and it seems pretty easy to tap connection off of the output on the volume control to feed the sub(s).
There are a couple of issues. By adding 10ft of cable which would have 300pf or more of capacitance, you will likely cause a roll off of high frequencies at the input to your first stage. This is more of a problem if the volume pot is 100k than 25k and you would need to calculate the impact of adding all that capacitance in your particular amplifier. Second, you are attaching a 10ft long cable to a variable impedance point in the amplifier. The impedance is highest when the volume control is at -6db where it is equal to 1/4 the volume control value in parallel with the tube input resistor and capacitance. So for a 100k pot you have maybe a 20k input/ output impedance at that point. The other end of the cable, attached to a line input on a subwoofer should be a high impedance input. So at working volume control settings the cable is not driven or terminated by a low impedance and hum pickup is a good possibility.
If you have low voltage power inside the amp, you could build a Jfet or op amp buffer for the sub output. Alternately you could build or buy an external buffer and place it close to the tube amp, connected by a short cable.
When building small tube power amps I usually build in a HPFilter with a bypass switch. That way you have some options if you want to add a subwoofer driven by the system preamp output.
If you have low voltage power inside the amp, you could build a Jfet or op amp buffer for the sub output. Alternately you could build or buy an external buffer and place it close to the tube amp, connected by a short cable.
When building small tube power amps I usually build in a HPFilter with a bypass switch. That way you have some options if you want to add a subwoofer driven by the system preamp output.
You could add a single ZVN0545A Zetex N-channel MOSFET source follower after your volume regulator to feed your subwoofer. The extra load will be minimal and you could feed this stage from the B+, since the MOSFET can take 450 VDC. So you have no need for an extra low voltage power supply.
Regards, Gerrit
Regards, Gerrit
2 or 3 resistors, two capacitors, a zenerdiode and a cheap MOSFET. No heater voltage... Using your existing B+... For stereo, double the components. Could be worth trying!
Regards, Gerrit
Regards, Gerrit
I have a single tube mono output preamp, which can have it's own volume control, designed for a center channel out, which can be used as a powered sub driver.
This was designed to be used with one of our new generation PAS kits we sell, but can be used in pretty much any tube preamp.
Let me know if you're interested and I can 'pm' you some details
This was designed to be used with one of our new generation PAS kits we sell, but can be used in pretty much any tube preamp.
Let me know if you're interested and I can 'pm' you some details
I don't tend to have as much luck with SS components but it is definitely worth looking into.
I'm looking to cut tubes out of the signal path for the subwoofer to see what it sounds like because that seems to be an area that they don't always excel in.
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Thanks, Is there a schematic you can recommend for that?
I can solder things together and follow a schematic but calculating for parts values is beyond my level.