I have started a new project: building a Ladegaard. I have read the articles of Poul Ladegaard, Jeremy Epstein and Thomas Dunker which answer most questions.
However some issues remain:
About the smoothing tank: Is it important where it is placed. Near the pump or near the arm?
And about the pump: is there anybody in Holland who has build this thing who has some advice about which pump is best?
hope you can help me,
However some issues remain:
About the smoothing tank: Is it important where it is placed. Near the pump or near the arm?
And about the pump: is there anybody in Holland who has build this thing who has some advice about which pump is best?
hope you can help me,
Look at the hose as a resistor and the tank as a capacitor. We'll
assume that the arm looks like a constant current drain and that
the overall air flow that can be provided by the pump far exceeds
the requirement of the arm.
Thus, in circuit terms you have a Voltage source (pump) driving
a series R (hose) a shunt C (tank), another series R (more hose)
and a shunt load (arm, probably modelable as a relatively high
R in this case).
Thus, for maximum attenuation of high frequencies (pulsing of
the pump) you want the R (hose) between the pump and the
tank to be fairly high.
Conclusion: One should probably put the tank reasonably
close to the arm.
assume that the arm looks like a constant current drain and that
the overall air flow that can be provided by the pump far exceeds
the requirement of the arm.
Thus, in circuit terms you have a Voltage source (pump) driving
a series R (hose) a shunt C (tank), another series R (more hose)
and a shunt load (arm, probably modelable as a relatively high
R in this case).
Thus, for maximum attenuation of high frequencies (pulsing of
the pump) you want the R (hose) between the pump and the
tank to be fairly high.
Conclusion: One should probably put the tank reasonably
close to the arm.
Well electrical analogies are fine if they are appropriate.
I was thinking along the lines once the system is up to pressure
due the net airflow the "resistance" of the tubing would not be
particularly significant, I may be wrong here.
And whilst the analogy uses an RCR filter it neglects to point
out they are usually added to capacitive smoothed rails,
driven by a rectified half sine wave performance is awful.
IMO you should use a large tank near the pump, to reduce
pulsing in the tubes and hence transmission of mechanical
noise to the arm.
If the airflow of the tubing is restrictive the electrical analogy
indicates a smaller subtank somewhere along the tubing is
a possibility, this is equivalent to a CRCR fiter.
Perhaps a car petrol line filter would be ideal ? With its
built fine gauze I can't think of anything better off hand.
The smaller extra tank with restrictive tubing will only work if
you have plently of excess pressure and even with the small
tubing enough airflow (current) is provided for the arm.
IMO the main tank should be near the pump, unless
of course the pump already has its own built in tank.
(Or the main capacitor bank near the transformer,
which is always the case in amplifiers AFAIK)
sreten.
I was thinking along the lines once the system is up to pressure
due the net airflow the "resistance" of the tubing would not be
particularly significant, I may be wrong here.
And whilst the analogy uses an RCR filter it neglects to point
out they are usually added to capacitive smoothed rails,
driven by a rectified half sine wave performance is awful.
IMO you should use a large tank near the pump, to reduce
pulsing in the tubes and hence transmission of mechanical
noise to the arm.
If the airflow of the tubing is restrictive the electrical analogy
indicates a smaller subtank somewhere along the tubing is
a possibility, this is equivalent to a CRCR fiter.
Perhaps a car petrol line filter would be ideal ? With its
built fine gauze I can't think of anything better off hand.
The smaller extra tank with restrictive tubing will only work if
you have plently of excess pressure and even with the small
tubing enough airflow (current) is provided for the arm.
IMO the main tank should be near the pump, unless
of course the pump already has its own built in tank.
(Or the main capacitor bank near the transformer,
which is always the case in amplifiers AFAIK)
sreten.Peterr,
meanwhile i am on the Ladegaard path, too.
Makes sense what has been said here already.
CRCR-Filter:
1st,
the air hose itself is a resistor with its length affecting resistance in 1st order and inner diameter in 3rd order. Means: don't use a thicker hose than you need.
2nd,
For a fixed air flow resistor you can take whatever you use to connect two hoses together. Make a plug of silicone rubber seleing the orifice and after curing of the rubber, pierce the plug with a hypodermic needle. Done.
If you want to change resistance, just take another hypodermic needle with a different diameter or length.
Cutting off the sharp / adjusting the length can be done with a Dremel's cutting disc.
Beauty of this method is that once you've chosen the right air flow resistance, just forget it, will never change its value.
Air pump:
if you manage to use an old fridge's compressor, fine. I didn't, it would refuse to start. On several occasions.
What i choose: a small airbrush compressor. It is even less noisy than a fridge and and not too expensive. And it has the excess pressure to alow a CRCR filter and get the air flow ultra smooth.
And it would not be wrong to give the filter enough capacity to provide air for atleast one records side and to equip the compressor with a switch forcing the compressor to blow its tank up to full pressure.
Having experienced a cheap aquarium pump on a Dennesen ABLT, i would not even think of using such. This is a cheap solution with any negative properties cheap solutions usually have.
meanwhile i am on the Ladegaard path, too.
Makes sense what has been said here already.
CRCR-Filter:
1st,
the air hose itself is a resistor with its length affecting resistance in 1st order and inner diameter in 3rd order. Means: don't use a thicker hose than you need.
2nd,
For a fixed air flow resistor you can take whatever you use to connect two hoses together. Make a plug of silicone rubber seleing the orifice and after curing of the rubber, pierce the plug with a hypodermic needle. Done.
If you want to change resistance, just take another hypodermic needle with a different diameter or length.
Cutting off the sharp / adjusting the length can be done with a Dremel's cutting disc.
Beauty of this method is that once you've chosen the right air flow resistance, just forget it, will never change its value.
Air pump:
if you manage to use an old fridge's compressor, fine. I didn't, it would refuse to start. On several occasions.
What i choose: a small airbrush compressor. It is even less noisy than a fridge and and not too expensive. And it has the excess pressure to alow a CRCR filter and get the air flow ultra smooth.
And it would not be wrong to give the filter enough capacity to provide air for atleast one records side and to equip the compressor with a switch forcing the compressor to blow its tank up to full pressure.
Having experienced a cheap aquarium pump on a Dennesen ABLT, i would not even think of using such. This is a cheap solution with any negative properties cheap solutions usually have.
I've finished with my tank made from 4" plastic sewage tube (use new one or clean thoroughly ) 1.5 meter long, filled with syntetic fibres, using for soft furniture stuffing. Why such long? I'm using two aquarium pumps - they are placed into MDF box, filled again with syntetic fibres - absolutely quiet. The pump produces strong 50 Hz pulsation, but, there is at least partial phase cancellation, due to parallel connection, and the rest is very effectively damped at quater wave peak (50 hz wave length is about 6 meters).
Works very well for me
) 1.5 meter long, filled with syntetic fibres, using for soft furniture stuffing. Why such long? I'm using two aquarium pumps - they are placed into MDF box, filled again with syntetic fibres - absolutely quiet. The pump produces strong 50 Hz pulsation, but, there is at least partial phase cancellation, due to parallel connection, and the rest is very effectively damped at quater wave peak (50 hz wave length is about 6 meters). Works very well for me
Probably got the wrong aquarium pump because it could not get the arm lifted. Not even the arm bearer alone! So I used an old fridge pump. Works fine with a bit of bleeding. A few 2l soft drink bottles as buffer coming after the radiator of the compressor and its small buffertank. You will need a water separator if you recycle a fridge compressor as they may spit out some oil.
My problem lies in the holes I drilled. Didn't like the perforated tape, so I drilled the 0.3mm holes through the Al profile. This creates a lot more flow resistance.
Dice: you didn't forgot the capacitor when trying the fridge compressor?
My problem lies in the holes I drilled. Didn't like the perforated tape, so I drilled the 0.3mm holes through the Al profile. This creates a lot more flow resistance.
Dice: you didn't forgot the capacitor when trying the fridge compressor?
Hi,
I'd just put it in the vecinity the arm.
The hose is already smoothing most of the pumps' turbulences caused by the push-pull action of the pumps' membrane.
Having the tank closer to the arm allows for a slow drainage of any air left in it in case of an accidental cut-off of the air supply giving you enough time to lift the arm of the record or correct the problem at the supply side.
Possible scenarios:
Power outage.
Someone stepping on the air hose cutting of the air supply.
A hose connection coming lose.
Most of the time, if the hose is long enough a smoothing tank isn't even needed and in any case it really doesn't have to be big to be effective.
Someone suggested a fuel filter and that's what's often supplied with commercial airbearing arms.
Aquarium shops also carry hose clamps, T-connectors and all kinds of related accessories but I think the important part is to have a system where the pump(s) don't interfere or add any noise so you can enjoy the music to the full.
For the most part a system like this just runs by itself and other than an occasional cleaning of parts it should run fine without any special attention from the user.
Cheers,
I'd just put it in the vecinity the arm.
The hose is already smoothing most of the pumps' turbulences caused by the push-pull action of the pumps' membrane.
Having the tank closer to the arm allows for a slow drainage of any air left in it in case of an accidental cut-off of the air supply giving you enough time to lift the arm of the record or correct the problem at the supply side.
Possible scenarios:
Power outage.
Someone stepping on the air hose cutting of the air supply.
A hose connection coming lose.
Most of the time, if the hose is long enough a smoothing tank isn't even needed and in any case it really doesn't have to be big to be effective.
Someone suggested a fuel filter and that's what's often supplied with commercial airbearing arms.
Aquarium shops also carry hose clamps, T-connectors and all kinds of related accessories but I think the important part is to have a system where the pump(s) don't interfere or add any noise so you can enjoy the music to the full.
For the most part a system like this just runs by itself and other than an occasional cleaning of parts it should run fine without any special attention from the user.
Cheers,
sreten,
"Electrical analogies are fine if they are appropriate" ????
Whether it's plumbing or electrical circuits, it all works out the same.
And given the 1:1 correspondence of the two "domains", my
analogy is, in fact, correct. The only thing open to debate is
the exact values of the various components. And if you go back
and more carefully read my posting you'll see that your "what-if's"
are already considered. In fact, the pump's output really is
a good pneumatic analogy to half-wave rectified power. pfft...pfft...
pfft...pfft...
And yes, people have been using the multiple resorvoir approach
for many years RCRCR. I don't recall if it was a DIYer in Audio
Amateur or people tweaking various early air-bearing arms, but
in any case it was tried a good 20 years ago. So go ahead and
put a reservoir at each end.
If I were doing this arm, I'd have the pump in some acoustically
isolated out-of-the-way place with a reservoir relatively close
to it, and then another reservoir a few feet from the arm.
Remember that VERY LITTLE air actually blows out the holes
of the arm.
"Electrical analogies are fine if they are appropriate" ????
Whether it's plumbing or electrical circuits, it all works out the same.
And given the 1:1 correspondence of the two "domains", my
analogy is, in fact, correct. The only thing open to debate is
the exact values of the various components. And if you go back
and more carefully read my posting you'll see that your "what-if's"
are already considered. In fact, the pump's output really is
a good pneumatic analogy to half-wave rectified power. pfft...pfft...
pfft...pfft...
And yes, people have been using the multiple resorvoir approach
for many years RCRCR. I don't recall if it was a DIYer in Audio
Amateur or people tweaking various early air-bearing arms, but
in any case it was tried a good 20 years ago. So go ahead and
put a reservoir at each end.
If I were doing this arm, I'd have the pump in some acoustically
isolated out-of-the-way place with a reservoir relatively close
to it, and then another reservoir a few feet from the arm.
Remember that VERY LITTLE air actually blows out the holes
of the arm.
Thank you all for your answers. I think I will try it both ways and see wich is best.
Meanwhile I have another question, this time about horizontal moving mass (a real snakepit it seems):
Poul Ladegaard states it can be (or even should be) quite high, in the order of 250gr, to get horizontal resonance frequency far down. In his paper he backs this up with measurements and facts.
Also Jeremy Epstein built his along these lines and I think I read somewhere that Dice45 believes this to be the best way too.
In other places I have read it should be as light as possible and that the higher horizontal moving mass is the biggest drawback of a linear tracking arm.
Any facts to shed some light?
Thanks.
Meanwhile I have another question, this time about horizontal moving mass (a real snakepit it seems):
Poul Ladegaard states it can be (or even should be) quite high, in the order of 250gr, to get horizontal resonance frequency far down. In his paper he backs this up with measurements and facts.
Also Jeremy Epstein built his along these lines and I think I read somewhere that Dice45 believes this to be the best way too.
In other places I have read it should be as light as possible and that the higher horizontal moving mass is the biggest drawback of a linear tracking arm.
Any facts to shed some light?
Thanks.
Hi,
The thing about linear arms is that the lateral mass actually IS your effective mass as they don't pivot.
It then follows that lateral mass is always higher than vertical mass as it is with pivoted arms.
Tangential arm design is a compromise between too-low vertical mass and too-high horizontal mass.
Cheers,
The thing about linear arms is that the lateral mass actually IS your effective mass as they don't pivot.
It then follows that lateral mass is always higher than vertical mass as it is with pivoted arms.
Tangential arm design is a compromise between too-low vertical mass and too-high horizontal mass.
Cheers,
keep horizontal resonance above 4.5Hz
Peterr,
on a Ladegaard design, i would not panic concerning horizontal mass. If you can keep the horizontal resonance above say 4.5Hz, your arm will work fine.
Lateral run error frequency is 33rpm/60sec: 0.55Hz
So 4.5Hz is more than 3 octaves away: supercritical damping will give you a nice insulation from the run error's excitation.
Assumed the cartridge's compliance will be vertically and laterally equal and constant, resonance frequency increases with the square root of mass. And as the Ladegaard's slider is not adding to vertical effective mass, you can shove vertical and lateral resonance to desired frequencies, within limits of course.
After all, a Ladegaard slider is not be a heavy-weight component and a total lateral mass of 36gr without the counterweight (compare the AirTangent) should be within reach.
A higher lateral mass should lead to superior tracking provided the resonance is not too low.
Peterr,
on a Ladegaard design, i would not panic concerning horizontal mass. If you can keep the horizontal resonance above say 4.5Hz, your arm will work fine.
Lateral run error frequency is 33rpm/60sec: 0.55Hz
So 4.5Hz is more than 3 octaves away: supercritical damping will give you a nice insulation from the run error's excitation.
Assumed the cartridge's compliance will be vertically and laterally equal and constant, resonance frequency increases with the square root of mass. And as the Ladegaard's slider is not adding to vertical effective mass, you can shove vertical and lateral resonance to desired frequencies, within limits of course.
After all, a Ladegaard slider is not be a heavy-weight component and a total lateral mass of 36gr without the counterweight (compare the AirTangent) should be within reach.
A higher lateral mass should lead to superior tracking provided the resonance is not too low.
Basically agree except for a couple of minor points.
Critical damping of the horizontal resonant frequency as far
as I can tell is not required. In fact Q doesn't really come into it.
Nor is critical damping of the vertical frequency particularly relevant.
Horizontal stylus deflection for moving the slide is related to
compliance only i.e. resonant frequency.
Scale the following graph down in frequency by x100, full scale = 10Hz.
Shown are two Q's for 4.5 Hz (one "critical"), also
1.5Hz, 3Hz and 6Hz, level at 0.55Hz (55Hz) matters.
What this shows is 4Hz to 5Hz is an excellent minimum
and as stated not difficult to achieve with correct mass.
sreten.
Critical damping of the horizontal resonant frequency as far
as I can tell is not required. In fact Q doesn't really come into it.
Nor is critical damping of the vertical frequency particularly relevant.
Horizontal stylus deflection for moving the slide is related to
compliance only i.e. resonant frequency.
Scale the following graph down in frequency by x100, full scale = 10Hz.
Shown are two Q's for 4.5 Hz (one "critical"), also
1.5Hz, 3Hz and 6Hz, level at 0.55Hz (55Hz) matters.
What this shows is 4Hz to 5Hz is an excellent minimum
and as stated not difficult to achieve with correct mass.
sreten.Attachments
Supercritical damping
sreten,
i did not mean "critical" damping, adressing any possible Q, i meant super-critical damping:
Put the lowest interesting frequency way above the exciting frequency as the gain of the excitation transfer function is
unity below resonance,
way above unity (depending on Q) in proximity of and at the resonance and
way **below** unity above the resonance frequency (how much is again depending on Q).
This means that the excitation amplitude will be transferred with a gain of way below unity i.e. damped to a high extent.
It is the way most turntable suspensions work.
sreten,
i did not mean "critical" damping, adressing any possible Q, i meant super-critical damping:
Put the lowest interesting frequency way above the exciting frequency as the gain of the excitation transfer function is
unity below resonance,
way above unity (depending on Q) in proximity of and at the resonance and
way **below** unity above the resonance frequency (how much is again depending on Q).
This means that the excitation amplitude will be transferred with a gain of way below unity i.e. damped to a high extent.
It is the way most turntable suspensions work.
Re: Supercritical damping
But as I've shown - damping (engineering definition) is not
the issue, that is Q is not relevant - you don't make sense.
"Critical" damping for a resonant system is explicitly defined,
so your "super-critical" definition is way off interpretable for
me, nevermind anyone else struggling to follow you.
There is no such thing in engineering terms.
You are quite correct my graphs with appropriate scaling are
applicable to turntables but "super-critical" is not relevant.
Unless you mean a Q of above critical, "super-critical"
is a totally a very poor way of describing this IMO.
sreten.
dice45 said:
But as I've shown - damping (engineering definition) is not
the issue, that is Q is not relevant - you don't make sense.
"Critical" damping for a resonant system is explicitly defined,
so your "super-critical" definition is way off interpretable for
me, nevermind anyone else struggling to follow you.
There is no such thing in engineering terms.
You are quite correct my graphs with appropriate scaling are
applicable to turntables but "super-critical" is not relevant.
Unless you mean a Q of above critical, "super-critical"
is a totally a very poor way of describing this IMO.
sreten.sreten,
i am not an Englisch native speaker and in German engineering terms the crititical frequency is the frenquency at which the resonance peak, the so-called resonance catastrophe is happening (at zero damping/ infinte Q of course), hence the term "super-critical damping" for positioning the lowest interesting system frequency way above the critical frequency.
So, i don't make sense, huh?
I described exactly what i meant (i re-read my post) and you obviously enjoy to split hairs on technical terms
I do not enjoy that sort of fruitless discussion; i had way more than my share of it already (particularly here@diyAudio). Back to lurking mode. Bye.
Bernhard
i am not an Englisch native speaker and in German engineering terms the crititical frequency is the frenquency at which the resonance peak, the so-called resonance catastrophe is happening (at zero damping/ infinte Q of course), hence the term "super-critical damping" for positioning the lowest interesting system frequency way above the critical frequency.
So, i don't make sense, huh?
I described exactly what i meant (i re-read my post) and you obviously enjoy to split hairs on technical terms
I do not enjoy that sort of fruitless discussion; i had way more than my share of it already (particularly here@diyAudio). Back to lurking mode. Bye.
Bernhard
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