I am about to build a tube amp (Simple SE... ~6-7 watts) and attempt to mate it with a sub-amp. The mains are high-efficiency fullrange (~98db) and the sub-amp is of the silicon variety. The source is a Rega Planet CDP.
Hopefully these questions are not too over-generalized and basic:
1.) Can I do a direct split of my analog source output and send one set to the sub amp and one to the tube amp (i.e. will it cause load or grounding issues on either amp or the CDP)?
2.) Will putting a cap on the tube amp input increase the tube amp's apparent gain or lower distortion at all (since the lower frequencies that require the most power will now be attenuated from the onset)?
3.) Is there a better way of mating the two amps?
Thank you very much,
Kevin
Hopefully these questions are not too over-generalized and basic:
1.) Can I do a direct split of my analog source output and send one set to the sub amp and one to the tube amp (i.e. will it cause load or grounding issues on either amp or the CDP)?
2.) Will putting a cap on the tube amp input increase the tube amp's apparent gain or lower distortion at all (since the lower frequencies that require the most power will now be attenuated from the onset)?
3.) Is there a better way of mating the two amps?
Thank you very much,
Kevin
If you simply split the signal, bass will be sent to your mains.
Having a dedicated subwoofer means you can prevent this, allowing the mains to reproduce the midrange cleanly - cone excursion is the last thing you want for a driver trying to reproduce the rest of the frequency range.
1 - you can, but it won't yield best results. You might get a ground loop issue, but this is easily rectified.
2 - you'd lower the distortion a little, but a series cap is a mere first order crossover - not really enough (IMO) to relieve full-range drivers of flapping around when it comes to the low stuff.
3 - I'd say build an active crossover. There's plenty of information around on them, their advantages are well-known, and they allow the use of steep crossovers.
Chris
Having a dedicated subwoofer means you can prevent this, allowing the mains to reproduce the midrange cleanly - cone excursion is the last thing you want for a driver trying to reproduce the rest of the frequency range.
1 - you can, but it won't yield best results. You might get a ground loop issue, but this is easily rectified.
2 - you'd lower the distortion a little, but a series cap is a mere first order crossover - not really enough (IMO) to relieve full-range drivers of flapping around when it comes to the low stuff.
3 - I'd say build an active crossover. There's plenty of information around on them, their advantages are well-known, and they allow the use of steep crossovers.
Chris
Chris,
Excellent answers, thank you very much. I am hesitant to add any crossover (or even a cap on the input for that matter) because of the adverse affect it will almost certainly have on the sound quality. I have no crossover as it is (single driver full range) and they sound very pure. I like the idea of the Simple SE tube amp because of the general lack of components. Truth be told, I HATE the sound of capacitors. Maybe I just haven't found the right ones.
I like your assessment, though, that bass frequencies can and do muddy and distort the higher frequencies, especially when the single driver is trying to push the entire range. That's why I was thinking of the single cap on the input... maybe it would be small enough to where I could get a high end cap but not spend half my paycheck. How do you think the active crossovers would affect the sound (i.e. mid and highs)?
Hi bermtoog,
Without knowing your room, setup, music preference, or listening level it is basically impossible to respond to your questions, anyway:
to 1: Yes. Just make sure that you're not overloading the output drive capacity of the Rega Planet CD player. The sub amp should not be a problem, and you are the one building the tube amp. I would suggest evaluating the effect of e.g.: the series capacitor through listening tests, you might be surprised at what you'll find.
to 2: adding a series capacitor between the Rega and your tube amp should give you a 1st order filter consisting of the capacitor, and the amplifiers input impedance; the higher the input impedance, the smaller the necessary capacitor. This should not affect the midband gain of the amplifier, but should reduce the amount of low frequency energy send to the fullrange speakers.
to 3: what is better or not depends on what you like to hear. From your answer in Post #3 you seem to like the sound of your current fullrange setup. If you are interested in playing around with other alternatives, you could build or buy an active analog crossover, as chris661 suggested; or maybe research the MiniDSP kits Home | miniDSP.
Also, take a look at this thread (for a quick look, Post #5) http://www.diyaudio.com/forums/subwoofers/134568-multiple-small-subs-geddes-approach.html. It seems that Dr. Geddes runs his main speakers without low-cut (they are not small fullrange speakers though), and adds three subs to fill in the low end, and take care of room irregularities.
Regards,
Without knowing your room, setup, music preference, or listening level it is basically impossible to respond to your questions, anyway:
to 1: Yes. Just make sure that you're not overloading the output drive capacity of the Rega Planet CD player. The sub amp should not be a problem, and you are the one building the tube amp. I would suggest evaluating the effect of e.g.: the series capacitor through listening tests, you might be surprised at what you'll find.
to 2: adding a series capacitor between the Rega and your tube amp should give you a 1st order filter consisting of the capacitor, and the amplifiers input impedance; the higher the input impedance, the smaller the necessary capacitor. This should not affect the midband gain of the amplifier, but should reduce the amount of low frequency energy send to the fullrange speakers.
to 3: what is better or not depends on what you like to hear. From your answer in Post #3 you seem to like the sound of your current fullrange setup. If you are interested in playing around with other alternatives, you could build or buy an active analog crossover, as chris661 suggested; or maybe research the MiniDSP kits Home | miniDSP.
Also, take a look at this thread (for a quick look, Post #5) http://www.diyaudio.com/forums/subwoofers/134568-multiple-small-subs-geddes-approach.html. It seems that Dr. Geddes runs his main speakers without low-cut (they are not small fullrange speakers though), and adds three subs to fill in the low end, and take care of room irregularities.
Regards,
I went from running just the Fostex cabinets with the tripath amplifier (see my signature) to adding the subwoofers.
For me, the potential sacrifice in adding more components was far outweighed by the much improved dynamic range and "oomph" to the music that was previously missed.
I can see your point of view entirely - I really like the sounds that simple systems can make. My problem with such systems is that you end up (IMO) a little limited in what you can listen to and enjoy:
for example, the Fostexes alone sounded nice enough for things like choirs, singers with acoustic guitars, stuff like that.
Then play something like Put Your Lights On by Santana. At reasonably low levels, it sounded decent enough, perhaps a touch bass light. Crank it up so the cones start moving and the presentation fell apart.
Cross them over, and they'll stand much louder, more (dare I say it?) complex music.
So, it all depends on what you want from the system.
Here's the crossover I use...
Active Filters
Its 4x TL072 op-amps, and a handful of resistors and capacitors. The op-amps can (for a test) run off a wall-wart.
Oh, you might need to buffer the input. Nothing dangerous, just another op-amp (use another TL072) set to unity gain.
The cost for the lot (not including a nice box) would be maybe £10, just add connectors.
IMO, its a very cost-effective thing to try. I used cheap polyester film caps. You could upgrade to something more expensive if you like, but as a try-it-and-see project, such capacitors would be fine.
In fact, if your computer has a multi-channel sound output, you could run the crossover plugin on Foobar2000.
In your position, I'd...
Build the amplifier, see how it all sounds.
If you find the system lacking, try adding a subwoofer.
Chris
PS - remember it also means the low-power amplifier won't have to do the bass either, so the amplifier will be running "cleaner".
Hey Chris,
I can't see your signature and when I go to your profile pictures it tells me I don't have permission. Again, thank you very much for your input. Which Fostex drivers do you have? I've thought about trying them before. I'm using the Audio Nirvana Super 8's in custom cabinets. They actually did very well with the entire spectrum on my transistor amp when they were mounted in 1/4 wave TL's. The problem was, they were trying to do too much so I built a cabinet tuned to ~95Hz and added a 12" sub to the room.
My whole issue is the main amp completely loses the texture of the sound. This is even after I soldered directly from one input to the volume control to the power amp... bypassing all switches, tone controls, and other components that the signal passes through. This greatly increased clarity but I'm still hungering for a more minimalist sound approach. I need the mids to sing and the highs to sizzle but the more components you add to the mix, the more electronic, dull, and flat the texture becomes.
However, I'm going to look into the active filter you mentioned because I really want the bass completely out of the tube amp side of the system. Like you said, it's less for the amp to do and less for the speaker to do so it should increase stability and clarity by a significant amount.
Thanks Chris,
Kevin
I can't see your signature and when I go to your profile pictures it tells me I don't have permission. Again, thank you very much for your input. Which Fostex drivers do you have? I've thought about trying them before. I'm using the Audio Nirvana Super 8's in custom cabinets. They actually did very well with the entire spectrum on my transistor amp when they were mounted in 1/4 wave TL's. The problem was, they were trying to do too much so I built a cabinet tuned to ~95Hz and added a 12" sub to the room.
My whole issue is the main amp completely loses the texture of the sound. This is even after I soldered directly from one input to the volume control to the power amp... bypassing all switches, tone controls, and other components that the signal passes through. This greatly increased clarity but I'm still hungering for a more minimalist sound approach. I need the mids to sing and the highs to sizzle but the more components you add to the mix, the more electronic, dull, and flat the texture becomes.
However, I'm going to look into the active filter you mentioned because I really want the bass completely out of the tube amp side of the system. Like you said, it's less for the amp to do and less for the speaker to do so it should increase stability and clarity by a significant amount.
Thanks Chris,
Kevin
Oliver,
1.) Would adding a simple resistance on one or both sides of the split insure the safety (and low distortion) of the Rega output or would a volume control be sufficient?
2.) Thank you, this is exactly what I needed.
-Kevin
Should be working now.
Hmmm... If bypassing those controls made such a difference, I'd be seriously questioning the quality of said controls.
From what I've read of the Audio Nirvana drivers, they ought to be comparable in quality to the Fostex drivers. The Fostex drivers take quite a lot of work to tame - have a look at the frequency response charts for the FE126En. Note the rising response leading to a peak at ~7kHz. This leads to a very forward, sibilant sound.
Mine have cone treatments, phase plugs, and an electrical filter to try to combat this.
Once you get it right, they do sing, though.
Chris
Hi Kevin,
Post #7:
to 1.): I'm assuming that you are using a stereo setup, and that you are starting out with a single subwoofer. You can just tap the lines going to the input of the tube amplifiers, and run that signal into a summing amplifier (simple single inverting opamp), using e.g.: the TL072 that Chris recommends, the input resistors of the summing amplifer should be high enough to prevent any interaction between the amplifers, and to prevent loading. Now you have a full range sum of the Rega outputs. You'll run that signal through your filter of choice, and into the subamp. Here is another source for opamp circuits, including the inverting summer: Audio Designs With Opamps - 3 . Take a look at the References in that article, and at the rest of the Elliott Sound website, they even have a Passive Crossover Design Spreadsheet (under downloads: ESP Download Page ). Anyway, that would give you the subwoofer signal you need, than you still have to decide what to do with the tube amplifier inputs.
Chris seems to be the one to listen to, as he has battled the same problem you are trying to address.
Regards,
Post #7:
to 1.): I'm assuming that you are using a stereo setup, and that you are starting out with a single subwoofer. You can just tap the lines going to the input of the tube amplifiers, and run that signal into a summing amplifier (simple single inverting opamp), using e.g.: the TL072 that Chris recommends, the input resistors of the summing amplifer should be high enough to prevent any interaction between the amplifers, and to prevent loading. Now you have a full range sum of the Rega outputs. You'll run that signal through your filter of choice, and into the subamp. Here is another source for opamp circuits, including the inverting summer: Audio Designs With Opamps - 3 . Take a look at the References in that article, and at the rest of the Elliott Sound website, they even have a Passive Crossover Design Spreadsheet (under downloads: ESP Download Page ). Anyway, that would give you the subwoofer signal you need, than you still have to decide what to do with the tube amplifier inputs.
Chris seems to be the one to listen to, as he has battled the same problem you are trying to address.
Regards,
In my opinion, the treatment probably only adds mass to the cone, in order to (mainly) re-inforce it.
The measurements I remember seeing showed that the driver lost some of its top end extension, which would give the impression of a smoother (ie, less sibilant/piercing, etc) sound.
Whether that suits you or not is entirely subjective - I like the sound of mine, but they took some work (most of which was by Planet10) to get right. If it ain't broke, fix it until it is. No, wait. You know the one I mean. I'd work on getting the subwoofer done first before looking at what else you might want to change. One at a time!
There's a big thread around here somewhere about EnABL - that will almost certainly have graphs in there.
Chris
Hi,
There are two huge pointless threads about UnABL(e).
Read them if you really want to lose the will to live.
Replacing the valve amplifiers input capacitor with a smaller value
works far better than nothing, it makes a big difference. Once you
know the roll-off you can make a passive inverse filter / attenuator
to drive the subamp from the valve amplifier outputs if desired.
You then won't have any loading / splitting issues.
It doesn't give as much power handling advantage as an active
crossover*, but it works, it is simple, and relatively pure. It will
reduce the change in amplifier character for the low bass.
Whilst your at it also consider a line level BSC circuit for the FR's,
far more effective and far cheaper than pretty patterns on drivers.
http://sound.westhost.com/bafflestep.htm
The only sensible way to do BSC for expensive flea powered amplifiers.
rgds, sreten.
* because its only 6dB/octave on the FR, that roll-off is corrected
by the passive inverse filter, and you then use the sub settings to
control its roll-off, it is more flexible than a fixed active x/o.
TL072's op-amps driving valve amplifiers ? Surely that is heresy.
There are two huge pointless threads about UnABL(e).
Read them if you really want to lose the will to live.
Replacing the valve amplifiers input capacitor with a smaller value
works far better than nothing, it makes a big difference. Once you
know the roll-off you can make a passive inverse filter / attenuator
to drive the subamp from the valve amplifier outputs if desired.
You then won't have any loading / splitting issues.
It doesn't give as much power handling advantage as an active
crossover*, but it works, it is simple, and relatively pure. It will
reduce the change in amplifier character for the low bass.
Whilst your at it also consider a line level BSC circuit for the FR's,
far more effective and far cheaper than pretty patterns on drivers.
http://sound.westhost.com/bafflestep.htm
The only sensible way to do BSC for expensive flea powered amplifiers.
rgds, sreten.
* because its only 6dB/octave on the FR, that roll-off is corrected
by the passive inverse filter, and you then use the sub settings to
control its roll-off, it is more flexible than a fixed active x/o.
TL072's op-amps driving valve amplifiers ? Surely that is heresy
.
Last edited:
That's what I started thinking. The complete lack of empirical evidence gave it away. I bet you could paint dots on your car engine too, to improve gas mileage.
Yes, I was trying to figure out how to control the volume with one knob. Could I use the sub-amp's built-in LPF instead?
What do you mean by power handling advantage? Would an active crossover enable more power to get to the speakers before the onset of major distortion? In other words, I'm really asking how much input could the tube amp handle (in relative terms) before distorting significantly?
Thank you for your reply,
Kevin
Hi,
No not really. The issue is how much power can your FR's take
from the tube amp without distorting. If they can handle the
amplifiers output you won't gain much by using an active
arrangement. Driver excursion increases for flat response
by 12dB/octave, as you go down, with 6dB/octave filtering
it still increases at 6dB/octave as you go down.
If you talking about the amplifier giving up the ghost before
the drivers then 6dB/octave filtering will likely be fine and
make a huge difference to the apparent bass power handing.
Driving the sub amplifier from the tube amp outputs via an
inverse filter / attenuator means only one volume control.
The inverse filter allows you to use the sub amps LPF.
rgds, sreten.
The passive inverse filter corrects the bass roll off at
the tube amps output for a flat drive to the sub.
You then have use the subs controls for its rolloff.
Last edited:
bermtoog, I'm wondering:
-what speakers you are running (there was something posted, but more description, especially how low they go in bass and are they sealed, vented, transmission line...)
-what the heck do you use for a volume control?
Anyway, passive crossovers can be made to feed the amplifiers. From a power point of view, the steepness of the filter doesn't really matter
AES E-Library Power Transmission Through Crossover Networks
because while a steeper slope cuts more power below the filter frequency, the sharper "knee" lets more power through above the filter frequency. Since these slopes are logarithmic, the power transmitted remains more or less the same regardless of 1st or 2nd or 3rd etc order.
The steeper filters will, however, reduce excursion more...unless it is already being limited by a sealed box rolloff.
You really DO want to filter the highs out of the fullranges. It will reduce the excursion and modulation distortion. Also, it will effectively free up more power. Imagine a 500 Hz 10 volt tone (25W@4ohms), simultaneous with a 20 Hz 10 volt tone. This requires the amp to swing 20V (100W@4ohm amp needed to put out just 50W total). If the 20 Hz was filtered down to nothing, you could swing 20V at 500Hz...=100W, or +6dB compared to unfiltered!
The suggestion to replace the input capacitor (if there is one) is quite good. You could also parallel a coil to get 2nd order, hopefully without induced crud.
The subwoofer side will need some way to tune the lowpass. Ideally you would also be able to adjust the shape of the rolloff knee and the phase, for better summation to the fullranges.
One thing about passives-they can be much simpler than opamps (at least to my unelectronic leanings) BUT watch if the phase of the input impedances doesn't make your source unhappy, especially since the full+sub may have a weird total impedance.
-what speakers you are running (there was something posted, but more description, especially how low they go in bass and are they sealed, vented, transmission line...)
-what the heck do you use for a volume control?
Anyway, passive crossovers can be made to feed the amplifiers. From a power point of view, the steepness of the filter doesn't really matter
AES E-Library Power Transmission Through Crossover Networks
because while a steeper slope cuts more power below the filter frequency, the sharper "knee" lets more power through above the filter frequency. Since these slopes are logarithmic, the power transmitted remains more or less the same regardless of 1st or 2nd or 3rd etc order.
The steeper filters will, however, reduce excursion more...unless it is already being limited by a sealed box rolloff.
You really DO want to filter the highs out of the fullranges. It will reduce the excursion and modulation distortion. Also, it will effectively free up more power. Imagine a 500 Hz 10 volt tone (25W@4ohms), simultaneous with a 20 Hz 10 volt tone. This requires the amp to swing 20V (100W@4ohm amp needed to put out just 50W total). If the 20 Hz was filtered down to nothing, you could swing 20V at 500Hz...=100W, or +6dB compared to unfiltered!
The suggestion to replace the input capacitor (if there is one) is quite good. You could also parallel a coil to get 2nd order, hopefully without induced crud.
The subwoofer side will need some way to tune the lowpass. Ideally you would also be able to adjust the shape of the rolloff knee and the phase, for better summation to the fullranges.
One thing about passives-they can be much simpler than opamps (at least to my unelectronic leanings) BUT watch if the phase of the input impedances doesn't make your source unhappy, especially since the full+sub may have a weird total impedance.
They were TL's until recently I built them into standard, single ported reflex... tuned to around 90-100Hz. They are 8" Audio Nirvana single fullrange drivers, no crossover or notch filters of any kind.
George Anderson suggests a 50k pot for the Simple SE, I haven't purchased it yet... still trying to get all the parts on order.
(I'm assuming you meant filter out the "lows") Yes! This is exactly what I was getting at with the OP. So then it would affect the apparent gain to filter out as much of the power hogging lows as possible?
Yes, I want absolutely as few components in the audio path as is possible. I understand what your saying about phase differences. This would be very hard to measure without a scope. But, the impedance should go up below the cut-off frequency, right (on the FR side)? And the sub input impedance will be high anyway.
What do you think about going from the Rega to the volume control and then splitting: one stereo set to the subamp, one set to the filter caps on the tube amp. Would that work?
Thank you for your response,
Kevin
Hi bermtoog,
Here is a link to a schematic by Steve Bench for a tube solution of a crossover, maybe something in there can be used for your application. By the way, Steve has an excellent tube website.
http://greygum.net/sbench/sbench101/Crossover/xover.gif
I also would recommend stuffing the port when using your fullrange with a subwoofer. It is much easier to integrate the signal of a sealed box with a subwoofer, but as always YMMV.
Regard,
Here is a link to a schematic by Steve Bench for a tube solution of a crossover, maybe something in there can be used for your application. By the way, Steve has an excellent tube website.
http://greygum.net/sbench/sbench101/Crossover/xover.gif
I also would recommend stuffing the port when using your fullrange with a subwoofer. It is much easier to integrate the signal of a sealed box with a subwoofer, but as always YMMV.
Regard,
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.