I can't understand why anyone would be concerned with the capacitive load of a dozen meters of coax cable when driving a self powered sub-woofer. Who cares? The assumed 10K Ohm load needs to be buffered from the main signal path (for valve drivers), sure, but a few thousand pF in parallel to that is completely unimportant at those frequencies.
A simple workable solution is to Y the two channels' output from your preamp with resistors sized to be easy on the preamp but not so large as to not supply enough driving voltage for the sub. Start with 50K or 100K Ohms each. Add a level control pot if needed (are there any self powered subs without a level control?). Shunt the top of the pot with a capacitor if needed.
PE ground loops are best dealt with by bringing the powered sub's power cord back to the same AC power strip that everything else is already plugged into. Surprisingly, it should be bundled along with the signal coax. This both minimizes hum injection and maximizes lightning protection.
Don't overly compulse about the electronics' contribution to the system crossover transfer function - the speakers mechanical systems completely dominate through this region. Only very elaborate (DSP) and invasive measures can make any important differences. And, until you can measure it, you can't fix it anyway.
All good fortune,
Chris
A simple workable solution is to Y the two channels' output from your preamp with resistors sized to be easy on the preamp but not so large as to not supply enough driving voltage for the sub. Start with 50K or 100K Ohms each. Add a level control pot if needed (are there any self powered subs without a level control?). Shunt the top of the pot with a capacitor if needed.
PE ground loops are best dealt with by bringing the powered sub's power cord back to the same AC power strip that everything else is already plugged into. Surprisingly, it should be bundled along with the signal coax. This both minimizes hum injection and maximizes lightning protection.
Don't overly compulse about the electronics' contribution to the system crossover transfer function - the speakers mechanical systems completely dominate through this region. Only very elaborate (DSP) and invasive measures can make any important differences. And, until you can measure it, you can't fix it anyway.
All good fortune,
Chris
In a typical "tube amp driving a speaker" scenario the speaker will have a considerable impedance peak around the driver or woofer's resonant frequency. Most tube amps have a fairly high output impedance. This will cause a rise in voltage across the speaker in the bass region even though less overall power is being delivered to the speaker. Tapping the output of the OPT to drive a powered sub will lead to a non flat bass response. Some listeners do favor this effect though.
Any follower is asymmetrical in its output drive capability. Considering the mosfet version, the follower can charge the load capacitance from it's power source (drain supply) through the on resistance of the fet (a few ohms or less). It must discharge the load capacitance through the source (cathode) resistor, which is usually larger than a few ohms. Given the frequency range needed, the source or cathode resistor here can be sized so the it doesn't matter. I'm running 5K ohms to a 150 volt supply pulling 30 mA through the fet.
I haven't tried an opamp to drive the sub, but then I only have about 6 feet of cable. I did put an opamp where it has the most benefit. My phono stage is an opamp mounted inside the turntable base.
If you are tapping into an existing tube amp, but not at the OPT output, then where are you getting your signal? I get my signal directly from the wiper of the volume pot. That feeds two separate small mosfet followers whose outputs are resistively combined and then buffered again by a larger mosfet and fed to the solid state sub.
The double buffering assures no blending of the two channels from the resistive combiner, and that nothing on the sub out line including a dead short will affect the main amp's sound.
Yes, it could be built with tubes, and if someone wanted the perfect follower, near infinite input impedance, near zero output impedance, all tube design, one should look up the augmented cathode follower design patented in the 1950's and used by Tektronix, TI, and others.
augmented cathode follower?
If you set the low pass and high pass filters to the same frequency, you are probably as close as you’ll get to right without DSP. But the tendency is just to run the mains full range, and use a sub to “add” bass. The problem with that is you end up adding a bunch where you don’t need it anyway, around 60-ish Hz, resulting in “boooooommmm”. Some people do like it that way (a LOT do). I don’t mind it myself, if the peak occurs at the very bottom octave of the program material and NOT in the middle. That’s why I’m not off-put by 40 Hz room gain, because any naturally occurring sound in the room gets the same treatment and covers almost all rock music. A boost down to the lowest possible note tends to sound “natural”. But when you get a 60 Hz haystack I want to run, barf or both. The proper way to deal with that is to turn the crossover frequency DOWN on the sub - if you *can*. When you’re stuck with factory presets you can’t. If I wasn’t willing or able to add some custom filtering I wouldn’t *buy* a sub that didn’t have an adjustable crossover frequency *on* the unit. With that you at least have a chance of taming the boom.
Followers driving capacitive loads are never a problem if the output impedance is high enough. But then the sound of cables makes a difference (if running full range). I would be using the same type followers for sub and main outs, and using 50 foot mic cables for interconnects. And not always the same equipment. Try to get the z out low enough so that cables won’t make a difference and that you can drive non-linear or frequency dependent loads without distortion, and you can end up with a STABILITY problem driving several thousand pF.
A single device follower is asymmetrical, yes. Two devices "can" be very symmetrical. The White CF already mentioned can be very close (but often isn't). And "any follower" covers a lot of turf. I've used a 20W tube speaker amp strapped to unity gain as a line amp.
Tapping: A tube amp with overall NFB often has a NFB "-" point and often this is low impedance. (Often a cathode.) And of course the same as the grid signal. Bogen, with low NFB amps, went further and paralleled multiple amps at the NFB points.
Modern subs put the variable crossover only on the speaker inputs. The line in on modern subs is full range because everyone assumes your receiver sub out (with dsp managed bass) is being plugged into there.
I don't doubt that is true. It is stupid but a lot of modern stuff is (like cars that use a computer to roll the window up and down).
Computer controlled windows are a good thing. You only need to run two thick wires to the motor and all other wiring can be thin.
My dad's old Pontiac needed number 10 wire to each switch, but my car uses like number 24 - when the switch is pressed, that line is grounded and the window operates. It's also why I can hold the unlock button on the fob and the windows and sunroof will open.
All of my older cars had manual windows - lighter and more reliable.
My dad's old Pontiac needed number 10 wire to each switch, but my car uses like number 24 - when the switch is pressed, that line is grounded and the window operates. It's also why I can hold the unlock button on the fob and the windows and sunroof will open.
All of my older cars had manual windows - lighter and more reliable.
Safety First!
If your modern car has electric windows, door locks, etc. . . .
Any accident that does one or more of these 4 things:
1. Destroys the battery, its cables, or the computer chip and circuitry
2. Causes your car to go into the water (door will not open)
3. The car catches fire
4. Your door is mashed and will not open
In any of those cases, you need a ball peen hammer to break one or more of your windows.
Put the hammer under your seat(s).
Think about it!
If your modern car has electric windows, door locks, etc. . . .
Any accident that does one or more of these 4 things:
1. Destroys the battery, its cables, or the computer chip and circuitry
2. Causes your car to go into the water (door will not open)
3. The car catches fire
4. Your door is mashed and will not open
In any of those cases, you need a ball peen hammer to break one or more of your windows.
Put the hammer under your seat(s).
Think about it!
Use the headrest.
Or a spark plug
How to break glass with a fragment of a spark plug (Part 2) - YouTube
Besides, my car has 8 inch subs under the seats.
1. The car has pyrotechnics that sever the main battery connection in the case of a roll over or the like, but still provide for power for the flashers. The airbags will probably blow out the glass in that case, too.
2. The car will open when it fills with water.
3. I had a tube amp catch fire once. It was still playing music while it was burning. A very rare situation... Or is it? James May Reacts To Top Gear Disaster As Chris Harris' Car Burns Down - Grand Tour Nation
4. If the door is mashed that bad, I might be trapped anyway, but again usually the glass breaks in that case. The Jaws of Life are a good thing
Or a spark plug
How to break glass with a fragment of a spark plug (Part 2) - YouTubeBesides, my car has 8 inch subs under the seats.
1. The car has pyrotechnics that sever the main battery connection in the case of a roll over or the like, but still provide for power for the flashers. The airbags will probably blow out the glass in that case, too.
2. The car will open when it fills with water.
3. I had a tube amp catch fire once. It was still playing music while it was burning. A very rare situation... Or is it? James May Reacts To Top Gear Disaster As Chris Harris' Car Burns Down - Grand Tour Nation
4. If the door is mashed that bad, I might be trapped anyway, but again usually the glass breaks in that case. The Jaws of Life are a good thing
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Going off of a bridge into deep water will keep the doors from opening.
Until the car fills with water, and the pressure is equalized, you might not be able to open the door.
The quickest fix for that is to break one or more windows.
I used to take a breath, and swim underwater for a 50 Meter distance without another breath.
The short time to swim 50 Meters, is not as long as waiting for the jaws of life.
Think ahead.
Until the car fills with water, and the pressure is equalized, you might not be able to open the door.
The quickest fix for that is to break one or more windows.
I used to take a breath, and swim underwater for a 50 Meter distance without another breath.
The short time to swim 50 Meters, is not as long as waiting for the jaws of life.
Think ahead.
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Sorry, but I don't plan on driving off of a bridge anytime soon so I'm not going to worry about it. Besides, I'd hope to die in the crash in that case anyway. Rather die from blunt force than drown
If you're really worried, buy this: Luxtude 2-Pack Car Window Breaker and Seatbelt Cutter
If you're really worried, buy this: Luxtude 2-Pack Car Window Breaker and Seatbelt Cutter
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And before computer control of everything I never had a car roll the windows up and lock the door on me with the keys inside. Before pulling a car into the shop my habit is to tap the window down a fraction of an inch and back up to make sure it is working. This confuses the hell out of the computer and it can be impossible to catch it before it is several inches down due to the terrible delay in the fly by wire. Not good if the window motor is jacked up and it is raining.
Then you have the computer controlled parking brake that slams on when you pop the door open to align yourself with the lift. It will be fun to watch the law suits when that system fails at highway speed.
And then there is the computer controlled transmission that won't go into drive if the door is not completely closed. Fabulous if you are trying to escape a carjacking.
I'm sorry Dave, I can't do that.
The computer controlled brake is fine these days. Harder to to an ebrake turn, but I can't do that with my parking brake anyway.
Almost any modern car that has traction control / stability control can already apply the brakes at any time it's needed. You don't hear of that system failing by turning on brakes on the highway, do you?
My windows go up and down instantly. Then again, I have a BMW and they tend to do things properly (faster computers). It's manual and from 2011 so even though there are like 36 computers connected optically, it just works. There isn't even any throttle lag even though it uses Valvetronic.
A modern car you should be able to code out the brake on opening the door, too. That's why I like modern computerized systems. My car will even raise the windows and shut the roof if it rains
Almost any modern car that has traction control / stability control can already apply the brakes at any time it's needed. You don't hear of that system failing by turning on brakes on the highway, do you?
My windows go up and down instantly. Then again, I have a BMW and they tend to do things properly (faster computers). It's manual and from 2011 so even though there are like 36 computers connected optically, it just works. There isn't even any throttle lag even though it uses Valvetronic.
A modern car you should be able to code out the brake on opening the door, too. That's why I like modern computerized systems. My car will even raise the windows and shut the roof if it rains
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I think I thought of a way to feed a modern subwoofer and get a headphone out at the same time. It involves doing away with line level solutions entirely. Doing away with cobbling together a LPF in the Amp. Doing away with coming off the OPT with all of its speaker impedance interactions being sent to the sub. Besides that solution won't let me send a low cut option to the power stage, it would have to be full range. This idea takes advantage of the fact that modern subs already have nice cutoff adjustable LPF's and level control built into their speaker input.
My thought is to simply incorporate one of the many OTL headphone amps tapped off the volume control. When you plug in phones its a headphone Amp, when you unplug them the thing reverts to feeding the speaker ins of the sub. Now the Amp itself can run its OPT selectable as full range or low cut mode, to taste. Many like to run their small satellites full range with a sub, or a some would like to run the tube OPT with some bass cut since they have a sub and maybe get more transparency by not running bass to the OPT. Versatility. You'd set your cutoff Hz at the sub and level. The volume control on the Amp controls all volumes in proportion. There are dozens of 32 to 300 ohm OTL head amps that can fit on a board. So Basically your amps headphone out is also your amps sub out when not switched to phones. To make it clear its to be attached to the subs speaker input, it would be jacked with binding posts instead of RCA, and labeled "to subwoofer speaker in". No hum problems, the cable can be two 25 foot lamp cords.
My thought is to simply incorporate one of the many OTL headphone amps tapped off the volume control. When you plug in phones its a headphone Amp, when you unplug them the thing reverts to feeding the speaker ins of the sub. Now the Amp itself can run its OPT selectable as full range or low cut mode, to taste. Many like to run their small satellites full range with a sub, or a some would like to run the tube OPT with some bass cut since they have a sub and maybe get more transparency by not running bass to the OPT. Versatility. You'd set your cutoff Hz at the sub and level. The volume control on the Amp controls all volumes in proportion. There are dozens of 32 to 300 ohm OTL head amps that can fit on a board. So Basically your amps headphone out is also your amps sub out when not switched to phones. To make it clear its to be attached to the subs speaker input, it would be jacked with binding posts instead of RCA, and labeled "to subwoofer speaker in". No hum problems, the cable can be two 25 foot lamp cords.
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From what I gather, the preamp is tube and presumably the main amp too. Of course the sub is solid state. A custom black box to drive the sub could be made - and it could easily be solid state. A full tube preamp with dedicated mono sub out does have its appeal, though, if one were willing to do the work and foot the bill.
I have one of these for when I need a "sub out"... Behringer | Product | CX2310
The higher model includes adjustable delay etc and it's on sale: Behringer Super-X Pro CX3400 V2 Multi-channel Crossover with Limiters
Tube pre -> sub crossover set to 30Hz or so -> tube power amps for full range, cheap class D board for car sub in the house.
I'm considering building a sub since I found 15" woofers for 22$.
The higher model includes adjustable delay etc and it's on sale: Behringer Super-X Pro CX3400 V2 Multi-channel Crossover with Limiters
Tube pre -> sub crossover set to 30Hz or so -> tube power amps for full range, cheap class D board for car sub in the house.
I'm considering building a sub since I found 15" woofers for 22$.
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Of course that always works, but people who use tubes are often allergic to Behringer. That’s not anything that money can’t fix - you can always buy “rider friendly” equipment if you want.
I’ve got a 3400 in my test rack - minimum crossover frequency is 44 Hz. Low enough for most practical uses. Solves your interconnect and drive problems too, co-locate the unit with the sub and drive the works with a twisted pair (even from an unbalanced source).
15” for $22? How much x-max do you get for that? Back in the early days of McGee, Eminence had a $23 12” that was 20-Hz capable (with no EQ!) in a large vented box, but 8mm x-max limited it to about 105 dB. Same unit was sold by PE in the early 90’s for $40, I still have several and the foam surrounds are still good! Pretty loud for music actually, but nothing by today’s HT standards. I didn’t know *anybody* was still making anything like that - thought they were gone for good. Last drivers I bought that were tuned like that were Scanspeak 8565/01’s which I’m still using. Unobtainium now.
I’ve got a 3400 in my test rack - minimum crossover frequency is 44 Hz. Low enough for most practical uses. Solves your interconnect and drive problems too, co-locate the unit with the sub and drive the works with a twisted pair (even from an unbalanced source).
15” for $22? How much x-max do you get for that? Back in the early days of McGee, Eminence had a $23 12” that was 20-Hz capable (with no EQ!) in a large vented box, but 8mm x-max limited it to about 105 dB. Same unit was sold by PE in the early 90’s for $40, I still have several and the foam surrounds are still good! Pretty loud for music actually, but nothing by today’s HT standards. I didn’t know *anybody* was still making anything like that - thought they were gone for good. Last drivers I bought that were tuned like that were Scanspeak 8565/01’s which I’m still using. Unobtainium now.
The minimum on the sub out on the 2310 goes to 10Hz...
I have no idea what the specs are for those woofers, but for 22$, I'm curious. Judging by the surround, xmax is about 20mm | GMI Products Speakers & Accessories Speakers & Accessories 904X-X-15C | Component Electronics Inc
It's probably for a bass amp, but I'm thinking if you make a box 48x48x12, and put 4 of them in it, and put it under the bed. It should make bass I'm also curious if I could make a subwoofer good to 10Hz using hundreds of 3" drivers...
I have no idea what the specs are for those woofers, but for 22$, I'm curious. Judging by the surround, xmax is about 20mm | GMI Products Speakers & Accessories Speakers & Accessories 904X-X-15C | Component Electronics Inc
It's probably for a bass amp, but I'm thinking if you make a box 48x48x12, and put 4 of them in it, and put it under the bed. It should make bass
I'm also curious if I could make a subwoofer good to 10Hz using hundreds of 3" drivers...
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