Forums

Signal amplifier works

Started by Uncle Steve February 8, 2013
... unless there is no signal at the input.

I started with some information at the following two URLS:

http://www.mysticmarvels.com/amplifier.html
http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P1.html

The first URL goes through the process of building a high-gain
amplifier, and it works O.K. with the exception that there is no
power.  The second URL goes into more detail and shows how to deliver
some power to the speaker as in figure 16.  I have different parts on
hand, and I am working with a 12V supply instead of 9V as in the first
URL.  Since I am looking to deliver big chunky volts to my speaker,
I went ahead and modified Figure 16 and the example in the first URL
to obtain the following circuit:


    12V +---+----------+----------+      R1 = 510K
        |   |          |          |      R2 = 5.9K
        |   > R2       > R3       |      R3 = 220
     R1 >   <          <          |      C1 = 1uF
        <   |          |          |      Q1, Q2 = 2N2222
        |   +--        |          |      Q3 = 2N3055
input   |   |  \    b  |c         |
 o---||-+-(Q1)  -----(Q2)  -----(Q3)
      C1    |          |e /       |
      1uf   |          ---       SPKR
            |                     |
            |                     |
 o----------+---------------------+

SPKR is a ribbon tweeter with a 2 Ohm, 10 Watt resistor in series.

R2 ought to be 6K, but 5.9 is what I have on hand.


Driving the circuit with a 50KHz signal produces 10V across the
speaker, which decreases to about 8V as the power transistor heats up.
I had a problem with thermal runaway until I got a sufficiently beefy
heatsink on Q3 and the 7812 supplying the 12V rail.  Q3 runs quite
hot, but I think I can fix that by substituting a TO-3 package for
the TO-220 currently in the circuit, or by reducing the current.
Not sure which is the proper solution, but the speaker handles
the existing power.

220 Ohms for R3 was derived by guessing, and noting that 1K
attenuates the signal too much, but I don't really know how I should
be calculating the proper value.  The speaker is usually paired with a
5.1 Ohm, 5W resistor, but I found it got too warm in this circuit, so
I used the 10W part instead.  I have no idea what the speaker
impedance really is in operation.

The horrible fact is that this circuit works as long as there is a
signal present at the input.  I am using a simple signal generator
from my DSO, but it doesn't allow the amplitude to be changed, so I
put a 100K trim pot on the positive side of C1.  Before I modified the
circuit by adding Q2, the trim pot worked as expected.  Now,
attenuating the signal even a little causes the output across the
speaker to fall off very quickly, with serious distortion occurring as
it falls (it seems the duty cycle goes from 50 to 90%, but that is
occurring somewhere in-circuit.)

If there is no signal present at the input, the circuit goes nuts very
quickly and ends up producing a much-distorted 9KHz signal at full
power at the speaker.  This seems to be occurring at Q3, but I don't
really understand what is going on.  My thinking is that with Q1c-Q2b
at ~6V, the DC load through the speaker is too much for Q3, but when
a signal is present, it 'works'.

What I'd like to do:

In the original form of the circuit, the speaker is driven through a
capacitor connected at Q2c (3300uF, 50V), but of course there is no
power available, and the voltage drops from 11V to 1 or 2 volts at the
positive terminal of the speaker.  With the above circuit, it is not
obvious to me how I should rearrange things to decouple the speaker
from the DC signal.

I would like to figure out why the circuit only works at 'full on',
and blows up otherwise.  The last problem is the power-on state, which
launches a huge spike through the speaker driver, and indeed, changing
the input signal frequency on the DSO causes a similar discontinuity
that is being amplified quite a bit as well.  Suggestions as to how to
reduce this spike would be appreciated.  Off the top of my head, I
suppose I could install an SCR in line with the speaker driver and
have a switch to turn on the power and another to enable the speaker
output via the SCR.  I would test this, but I don't have an SCR
available ATM.

The entire objective with this little project is to develop a simple
amplifier that I can use to drive this speaker I have, where fidelity
is not as important as stability.  Plus, it would be nice to be able
to use the parts I have on-hand.



Regards,

Uncle Steve

-- 
More than a century has passed since science laid down sound
propositions as to the origins of the universe, but how many have
mastered them or possess the really scientific spirit of criticism? A
few thousands at the outside, who are lost in the midst of hundreds of
millions still steeped in prejudices and superstitions worthy of
savages, who are consequently ever ready to serve as puppets for
religious impostors.   -- Peter Kropotkin

Uncle Steve wrote:
> > ... unless there is no signal at the input. > > I started with some information at the following two URLS: > > http://www.mysticmarvels.com/amplifier.html > http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P1.html > > The first URL goes through the process of building a high-gain > amplifier, and it works O.K. with the exception that there is no > power. The second URL goes into more detail and shows how to deliver > some power to the speaker as in figure 16. I have different parts on > hand, and I am working with a 12V supply instead of 9V as in the first > URL. Since I am looking to deliver big chunky volts to my speaker, > I went ahead and modified Figure 16 and the example in the first URL > to obtain the following circuit: > > 12V +---+----------+----------+ R1 = 510K > | | | | R2 = 5.9K > | > R2 > R3 | R3 = 220 > R1 > < < | C1 = 1uF > < | | | Q1, Q2 = 2N2222 > | +-- | | Q3 = 2N3055 > input | | \ b |c | > o---||-+-(Q1) -----(Q2) -----(Q3) > C1 | |e / | > 1uf | --- SPKR > | | > | | > o----------+---------------------+ > > SPKR is a ribbon tweeter with a 2 Ohm, 10 Watt resistor in series. > > R2 ought to be 6K, but 5.9 is what I have on hand. > > Driving the circuit with a 50KHz signal produces 10V across the > speaker, which decreases to about 8V as the power transistor heats up. > I had a problem with thermal runaway until I got a sufficiently beefy > heatsink on Q3 and the 7812 supplying the 12V rail. Q3 runs quite > hot, but I think I can fix that by substituting a TO-3 package for > the TO-220 currently in the circuit, or by reducing the current. > Not sure which is the proper solution, but the speaker handles > the existing power. > > 220 Ohms for R3 was derived by guessing, and noting that 1K > attenuates the signal too much, but I don't really know how I should > be calculating the proper value. The speaker is usually paired with a > 5.1 Ohm, 5W resistor, but I found it got too warm in this circuit, so > I used the 10W part instead. I have no idea what the speaker > impedance really is in operation. > > The horrible fact is that this circuit works as long as there is a > signal present at the input. I am using a simple signal generator > from my DSO, but it doesn't allow the amplitude to be changed, so I > put a 100K trim pot on the positive side of C1. Before I modified the > circuit by adding Q2, the trim pot worked as expected. Now, > attenuating the signal even a little causes the output across the > speaker to fall off very quickly, with serious distortion occurring as > it falls (it seems the duty cycle goes from 50 to 90%, but that is > occurring somewhere in-circuit.) > > If there is no signal present at the input, the circuit goes nuts very > quickly and ends up producing a much-distorted 9KHz signal at full > power at the speaker. This seems to be occurring at Q3, but I don't > really understand what is going on. My thinking is that with Q1c-Q2b > at ~6V, the DC load through the speaker is too much for Q3, but when > a signal is present, it 'works'. > > What I'd like to do: > > In the original form of the circuit, the speaker is driven through a > capacitor connected at Q2c (3300uF, 50V), but of course there is no > power available, and the voltage drops from 11V to 1 or 2 volts at the > positive terminal of the speaker. With the above circuit, it is not > obvious to me how I should rearrange things to decouple the speaker > from the DC signal. > > I would like to figure out why the circuit only works at 'full on', > and blows up otherwise. The last problem is the power-on state, which > launches a huge spike through the speaker driver, and indeed, changing > the input signal frequency on the DSO causes a similar discontinuity > that is being amplified quite a bit as well. Suggestions as to how to > reduce this spike would be appreciated. Off the top of my head, I > suppose I could install an SCR in line with the speaker driver and > have a switch to turn on the power and another to enable the speaker > output via the SCR. I would test this, but I don't have an SCR > available ATM. > > The entire objective with this little project is to develop a simple > amplifier that I can use to drive this speaker I have, where fidelity > is not as important as stability. Plus, it would be nice to be able > to use the parts I have on-hand.
Where did you get a speaker that works at 50 KHz?
On Fri, Feb 08, 2013 at 02:59:33PM -0500, Michael A. Terrell wrote:
> > Uncle Steve wrote: > > > > ... unless there is no signal at the input. > > > > I started with some information at the following two URLS: > > > > http://www.mysticmarvels.com/amplifier.html > > http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P1.html > > > > The first URL goes through the process of building a high-gain > > amplifier, and it works O.K. with the exception that there is no > > power. The second URL goes into more detail and shows how to deliver > > some power to the speaker as in figure 16. I have different parts on > > hand, and I am working with a 12V supply instead of 9V as in the first > > URL. Since I am looking to deliver big chunky volts to my speaker, > > I went ahead and modified Figure 16 and the example in the first URL > > to obtain the following circuit: > > > > 12V +---+----------+----------+ R1 = 510K > > | | | | R2 = 5.9K > > | > R2 > R3 | R3 = 220 > > R1 > < < | C1 = 1uF > > < | | | Q1, Q2 = 2N2222 > > | +-- | | Q3 = 2N3055 > > input | | \ b |c | > > o---||-+-(Q1) -----(Q2) -----(Q3) > > C1 | |e / | > > 1uf | --- SPKR > > | | > > | | > > o----------+---------------------+ > > > > SPKR is a ribbon tweeter with a 2 Ohm, 10 Watt resistor in series. > > > > R2 ought to be 6K, but 5.9 is what I have on hand. > > > > Driving the circuit with a 50KHz signal produces 10V across the > > speaker, which decreases to about 8V as the power transistor heats up. > > I had a problem with thermal runaway until I got a sufficiently beefy > > heatsink on Q3 and the 7812 supplying the 12V rail. Q3 runs quite > > hot, but I think I can fix that by substituting a TO-3 package for > > the TO-220 currently in the circuit, or by reducing the current. > > Not sure which is the proper solution, but the speaker handles > > the existing power. > > > > 220 Ohms for R3 was derived by guessing, and noting that 1K > > attenuates the signal too much, but I don't really know how I should > > be calculating the proper value. The speaker is usually paired with a > > 5.1 Ohm, 5W resistor, but I found it got too warm in this circuit, so > > I used the 10W part instead. I have no idea what the speaker > > impedance really is in operation. > > > > The horrible fact is that this circuit works as long as there is a > > signal present at the input. I am using a simple signal generator > > from my DSO, but it doesn't allow the amplitude to be changed, so I > > put a 100K trim pot on the positive side of C1. Before I modified the > > circuit by adding Q2, the trim pot worked as expected. Now, > > attenuating the signal even a little causes the output across the > > speaker to fall off very quickly, with serious distortion occurring as > > it falls (it seems the duty cycle goes from 50 to 90%, but that is > > occurring somewhere in-circuit.) > > > > If there is no signal present at the input, the circuit goes nuts very > > quickly and ends up producing a much-distorted 9KHz signal at full > > power at the speaker. This seems to be occurring at Q3, but I don't > > really understand what is going on. My thinking is that with Q1c-Q2b > > at ~6V, the DC load through the speaker is too much for Q3, but when > > a signal is present, it 'works'. > > > > What I'd like to do: > > > > In the original form of the circuit, the speaker is driven through a > > capacitor connected at Q2c (3300uF, 50V), but of course there is no > > power available, and the voltage drops from 11V to 1 or 2 volts at the > > positive terminal of the speaker. With the above circuit, it is not > > obvious to me how I should rearrange things to decouple the speaker > > from the DC signal. > > > > I would like to figure out why the circuit only works at 'full on', > > and blows up otherwise. The last problem is the power-on state, which > > launches a huge spike through the speaker driver, and indeed, changing > > the input signal frequency on the DSO causes a similar discontinuity > > that is being amplified quite a bit as well. Suggestions as to how to > > reduce this spike would be appreciated. Off the top of my head, I > > suppose I could install an SCR in line with the speaker driver and > > have a switch to turn on the power and another to enable the speaker > > output via the SCR. I would test this, but I don't have an SCR > > available ATM. > > > > The entire objective with this little project is to develop a simple > > amplifier that I can use to drive this speaker I have, where fidelity > > is not as important as stability. Plus, it would be nice to be able > > to use the parts I have on-hand. > > > Where did you get a speaker that works at 50 KHz?
It's a ribbon tweeter, ostensibly rated to 65KHz. It is difficult to say what it's actual output is at those frequencies, but I can put two of them face-to-face, drive one of them, and get signal from the other with a scope. With the above circuit operating as described, the second driver shows 54mV at the terminals -- using ribbons which are sub-optimal. So I guess it works. Regards, Uncle Steve -- More than a century has passed since science laid down sound propositions as to the origins of the universe, but how many have mastered them or possess the really scientific spirit of criticism? A few thousands at the outside, who are lost in the midst of hundreds of millions still steeped in prejudices and superstitions worthy of savages, who are consequently ever ready to serve as puppets for religious impostors. -- Peter Kropotkin
On Fri, Feb 08, 2013 at 03:36:30PM -0500, Uncle Steve wrote:
> On Fri, Feb 08, 2013 at 02:59:33PM -0500, Michael A. Terrell wrote: > > > > Where did you get a speaker that works at 50 KHz? > > It's a ribbon tweeter, ostensibly rated to 65KHz. It is difficult to > say what it's actual output is at those frequencies, but I can put two > of them face-to-face, drive one of them, and get signal from the other > with a scope. With the above circuit operating as described, the > second driver shows 54mV at the terminals -- using ribbons which are > sub-optimal. So I guess it works.
Actually, here's someting wierd. At 4MHz, I measure 200mV, almost nothing at 6MHz, and 60mV or so at 8MHz. 4MHz may be a resonant frequency of the ribbon, given the speed of sound in copper, but that's just a guess. Regards, Uncle Steve -- More than a century has passed since science laid down sound propositions as to the origins of the universe, but how many have mastered them or possess the really scientific spirit of criticism? A few thousands at the outside, who are lost in the midst of hundreds of millions still steeped in prejudices and superstitions worthy of savages, who are consequently ever ready to serve as puppets for religious impostors. -- Peter Kropotkin
What's the specific ribbon tweeter? What will be used to
drive the amplifier when in practical use? (It's output
impedance, Vpp.) What's the application? (Pestering bats?)
How much power output do you expect? What's the range of
frequencies to be emitted? A pure tone of 50kHz?

The first stage looks all wrong to me, anyway. Are you saying
it worked? That's hard to imagine. All I see is that Q1 is
hard-saturated with its collector very near ground and the
Darlington emitter follower not doing much of anything. What
in heck were you driving that thing with via C1??? Do you
have your design notes that you might share?

Jon
On Fri, 08 Feb 2013 14:59:33 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

> >Uncle Steve wrote: >> >> ... unless there is no signal at the input. >> >> I started with some information at the following two URLS: >> >> http://www.mysticmarvels.com/amplifier.html >> http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P1.html >> >> The first URL goes through the process of building a high-gain >> amplifier, and it works O.K. with the exception that there is no >> power. The second URL goes into more detail and shows how to deliver >> some power to the speaker as in figure 16. I have different parts on >> hand, and I am working with a 12V supply instead of 9V as in the first >> URL. Since I am looking to deliver big chunky volts to my speaker, >> I went ahead and modified Figure 16 and the example in the first URL >> to obtain the following circuit: >> >> 12V +---+----------+----------+ R1 = 510K >> | | | | R2 = 5.9K >> | > R2 > R3 | R3 = 220 >> R1 > < < | C1 = 1uF >> < | | | Q1, Q2 = 2N2222 >> | +-- | | Q3 = 2N3055 >> input | | \ b |c | >> o---||-+-(Q1) -----(Q2) -----(Q3) >> C1 | |e / | >> 1uf | --- SPKR >> | | >> | | >> o----------+---------------------+ >> >> SPKR is a ribbon tweeter with a 2 Ohm, 10 Watt resistor in series. >> >> R2 ought to be 6K, but 5.9 is what I have on hand. >> >> Driving the circuit with a 50KHz signal produces 10V across the >> speaker, which decreases to about 8V as the power transistor heats up. >> I had a problem with thermal runaway until I got a sufficiently beefy >> heatsink on Q3 and the 7812 supplying the 12V rail. Q3 runs quite >> hot, but I think I can fix that by substituting a TO-3 package for >> the TO-220 currently in the circuit, or by reducing the current. >> Not sure which is the proper solution, but the speaker handles >> the existing power. >> >> 220 Ohms for R3 was derived by guessing, and noting that 1K >> attenuates the signal too much, but I don't really know how I should >> be calculating the proper value. The speaker is usually paired with a >> 5.1 Ohm, 5W resistor, but I found it got too warm in this circuit, so >> I used the 10W part instead. I have no idea what the speaker >> impedance really is in operation. >> >> The horrible fact is that this circuit works as long as there is a >> signal present at the input. I am using a simple signal generator >> from my DSO, but it doesn't allow the amplitude to be changed, so I >> put a 100K trim pot on the positive side of C1. Before I modified the >> circuit by adding Q2, the trim pot worked as expected. Now, >> attenuating the signal even a little causes the output across the >> speaker to fall off very quickly, with serious distortion occurring as >> it falls (it seems the duty cycle goes from 50 to 90%, but that is >> occurring somewhere in-circuit.) >> >> If there is no signal present at the input, the circuit goes nuts very >> quickly and ends up producing a much-distorted 9KHz signal at full >> power at the speaker. This seems to be occurring at Q3, but I don't >> really understand what is going on. My thinking is that with Q1c-Q2b >> at ~6V, the DC load through the speaker is too much for Q3, but when >> a signal is present, it 'works'. >> >> What I'd like to do: >> >> In the original form of the circuit, the speaker is driven through a >> capacitor connected at Q2c (3300uF, 50V), but of course there is no >> power available, and the voltage drops from 11V to 1 or 2 volts at the >> positive terminal of the speaker. With the above circuit, it is not >> obvious to me how I should rearrange things to decouple the speaker >> from the DC signal. >> >> I would like to figure out why the circuit only works at 'full on', >> and blows up otherwise. The last problem is the power-on state, which >> launches a huge spike through the speaker driver, and indeed, changing >> the input signal frequency on the DSO causes a similar discontinuity >> that is being amplified quite a bit as well. Suggestions as to how to >> reduce this spike would be appreciated. Off the top of my head, I >> suppose I could install an SCR in line with the speaker driver and >> have a switch to turn on the power and another to enable the speaker >> output via the SCR. I would test this, but I don't have an SCR >> available ATM. >> >> The entire objective with this little project is to develop a simple >> amplifier that I can use to drive this speaker I have, where fidelity >> is not as important as stability. Plus, it would be nice to be able >> to use the parts I have on-hand. > > > Where did you get a speaker that works at 50 KHz?
The amplifier clearly needs a bootstrap >:-} ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Fri, Feb 08, 2013 at 12:56:20PM -0800, Jon Kirwan wrote:
> What's the specific ribbon tweeter? What will be used to > drive the amplifier when in practical use? (It's output > impedance, Vpp.) What's the application? (Pestering bats?) > How much power output do you expect? What's the range of > frequencies to be emitted? A pure tone of 50kHz?
The driver is a proprietary design; the label sez "Quadral / 923 112 / 6 ohms", but it is normally attached to a crossover with a 5.1 ohm 5W resistor. Practical use is in a speaker cabinet powered by a conventional stereo system, but as I'm trying to replace the ribbons, I need a way to test the thing without installing it in the cabinet. Now that you mention it, there is a vampire infestation in Toronto so I may use one as a perimeter defense weapon, but that's after I prove A replacement ribbon. In practice the device is intended to produce audible audio frequencies, but for testing purposes I'm happy to use ultrasonics to keep the workbench noise level down.
> The first stage looks all wrong to me, anyway. Are you saying > it worked? That's hard to imagine. All I see is that Q1 is > hard-saturated with its collector very near ground and the > Darlington emitter follower not doing much of anything. What > in heck were you driving that thing with via C1??? Do you > have your design notes that you might share?
You're correct to be surprised it worked, and I still don't know exactly what happened. I wired up a TO-3 version of Q3 and substituted it into the circuit and found out that the old Q3 had let some of it's Magic Smoke out, but was still working as I described. I have no idea how that happened. Ah, it seems I miswired Q2; emitter to GND, collector to the base of Q3, and to +12 through R3. Again, wired correctly, and without Q3, I have 10.6V square wave at the collector of Q1, and 3.6V at the emitter of Q2, open circuit. Is it safe to apply the output of Q1 to the base of Q3? Oh, and I'm driving it with the signal generator output of a DSO Quad, which is a handheld 4-channel scope which retails about $220. Regards, Uncle Steve -- More than a century has passed since science laid down sound propositions as to the origins of the universe, but how many have mastered them or possess the really scientific spirit of criticism? A few thousands at the outside, who are lost in the midst of hundreds of millions still steeped in prejudices and superstitions worthy of savages, who are consequently ever ready to serve as puppets for religious impostors. -- Peter Kropotkin
Jim Thompson wrote:
> > Michael A. Terrell wrote: > > > > Where did you get a speaker that works at 50 KHz? > > The amplifier clearly needs a bootstrap >:-}
If it can hit 50 KHz, it's too late for a jock strap. ;-)
On Feb 8, 3:56=A0pm, Jon Kirwan <j...@infinitefactors.org> wrote:
> What's the specific ribbon tweeter? What will be used to > drive the amplifier when in practical use? (It's output > impedance, Vpp.) What's the application? (Pestering bats?) > How much power output do you expect? What's the range of > frequencies to be emitted? A pure tone of 50kHz? > > The first stage looks all wrong to me, anyway. Are you saying > it worked? That's hard to imagine. All I see is that Q1 is > hard-saturated with its collector very near ground and the > Darlington emitter follower not doing much of anything. What > in heck were you driving that thing with via C1??? Do you > have your design notes that you might share? > > Jon
It looked crazy to me too. Uncle Steve, you need to find some better websites. You could try an opamp with a push pull output stage. Or just a power opamp. Hey Jan had a nice audio amp... If you want to do a class A thing, then google the Zen amplfier. George H.
On Fri, Feb 08, 2013 at 03:13:36PM -0800, George Herold wrote:
> On Feb 8, 3:56&#2013266080;pm, Jon Kirwan <j...@infinitefactors.org> wrote: > > What's the specific ribbon tweeter? What will be used to > > drive the amplifier when in practical use? (It's output > > impedance, Vpp.) What's the application? (Pestering bats?) > > How much power output do you expect? What's the range of > > frequencies to be emitted? A pure tone of 50kHz? > > > > The first stage looks all wrong to me, anyway. Are you saying > > it worked? That's hard to imagine. All I see is that Q1 is > > hard-saturated with its collector very near ground and the > > Darlington emitter follower not doing much of anything. What > > in heck were you driving that thing with via C1??? Do you > > have your design notes that you might share? > > > > Jon > > It looked crazy to me too.
I suppose so. It just doesn't seem to have enough discreet components. The first stage is simple enough. The bias resistor, R1 and load resistor R2 specify that the voltage at Q1 collector is about 6V with no input signal, and allows the output to swing about 10V. The second transistor is used to boost the current, and then in theory Q3 does the heavy lifting. I'm not really clear on how Q2 does its thing, but that's what the experimentation is for. It may help to know that initially, I started with C1, R1, R2, Q3, and a capacitor coupling the collector with the speaker + terminal. That's when I discovered there was no power available to drive the speaker. I substituted a 2N2222, and then made the circuit above. It didn't work properly because I wired it wrong (see previous message) but as I described it did output something like the the input signal once the 2N3055 halfway burned out.
> Uncle Steve, you need to find some better websites.
Maybe. There's no shortage of crap out there.
> You could try an opamp with a push pull output stage. > Or just a power opamp. > Hey Jan had a nice audio amp...
Hey, I have all these transistors lying around and since I hear they're good for amplifying signals, I thought I might as well use them.
> If you want to do a class A thing, then google the Zen amplfier.
Googling... Interesting, but I don't care about linearity all that much. This is just something to run one frequency through the driver at any given time, and therefore does not have to be special or complex. Regards, Uncle Steve -- More than a century has passed since science laid down sound propositions as to the origins of the universe, but how many have mastered them or possess the really scientific spirit of criticism? A few thousands at the outside, who are lost in the midst of hundreds of millions still steeped in prejudices and superstitions worthy of savages, who are consequently ever ready to serve as puppets for religious impostors. -- Peter Kropotkin