Linkwitz Transforms

[sreten]

Originally Posted by anthonyderosa

Hey guys,


1. What is the difference between an opamp and amp? What would a traditional car amp be considered? What would a traditional home amp be considered?
2. Where exactly does this circuit get placed in regards to the signal source, amp, and driver? If the placement is between the amp and driver, as I believe it to be, how many watts can this circuit handle? How can I determine and appropriate this?
3. When selecting components for the circuit, what is the best way to determine the necessary component values to approximate calculated values with the least error?
4. When selecting resistors, how do I determine whether the resistors need to be 1W, 2W, 5W, etc? How do I determine whether the resistors need to be carbon, flameproof, etc?
5. Same question but in regards to the capacitors and their appropriate differences.
6. Where could I go to have this circuit built or bought without purchasing it from Australia?

Even if you can only answer one, or part of one, question I would appreciate it.

Thanks,

Tony

Hi,

1) Op amps are line level not speaker level.

2) Its placed before the amplifier. It can be built into some amplifiers
by treating the inverting input as a unity gain point, advanced stuff.
(Assuming a differential LTP input topology.)

3) Sensitivity of circuits to component variation is an advanced topic.
Download the free TinaTi SPICE emulator, it does sensitivity analysis.

4) A question based on a wrong assumption.
Typical line level type components.

5) same as 4).

6) Lots of options, as the circuit is nowhere near as exotic as
you imagine. You need to understand why what is does can
be done pre the power amplifier easily, and why considering
doing it after the power amplifier is simply wrong on all counts.

FWIW LT's have nothing to do with low Q sealed boxes at all.

For these all you need is bass boost. LT's are for high Q sealed
boxes, where you first compensate for the high Q roll-off and
then define a new roll-off regimen of your choice.

Component values hardly describe what you are attempting to do.

rgds, sreten.

[CharlieLaub]

Originally Posted by sreten

FWIW LT's have nothing to do with low Q sealed boxes at all.

For these all you need is bass boost. LT's are for high Q sealed
boxes, where you first compensate for the high Q roll-off and
then define a new roll-off regimen of your choice.

Actually, what's quoted above is not correct. Using the LT with a high Q sealed box is just one potential application of the circuit.

The LT generates a "response" that includes changes to both the signal amplitude and phase. The amplitude change can include boost and/or cut. It can be considered as a way to "transform" any second order response into any other one, and whether the original response has high Q or low Q doesn't matter at all.

-Charlie

[rcw666]

I have a subwoofer electronics box that uses a 17VAC plug pack and a dual rail voltage doubler circuit, (also described at ESP), this removes any need to touch mains power.

The L-T circuit described is basically the one described on the Linkwitz site, and is constrained in what it can do by the expression he gives, to do anything outside that you need a more complex three op amp biquad circuit.

Classically an op amp was used in analogue computers to do operations and was a d.c. coupled amplifier with a inverting and non inverting input, the two rail power supply was to allow a lot of them to be d.c. connected with an acceptable offset voltage. Most of the cold war era military electronics was based upon analogue computers with op amps, and the integrated op amp was originally developed for this.
rcw

[Calvin]

Hi,

I partly disagree with these defs.

1) Op amps are line level not speaker level.
2) Its placed before the amplifier. It can be built into some amplifiers
by treating the inverting input as a unity gain point, advanced stuff.
(Assuming a differential LTP input topology.)

The basic definition of an OPamp is a blackbox or building block featuring 2 inputs (one noninverting and one inverting) and one output. Additional inputs and outputs, say for power supply or reference pins may be omitted with in a first consideration.
The external circuitry connected to the Inputs and the output fully define the behaviour of the whole circuit. Voltage, current or power leves are not part of the definition.
So 1) and 2) describe at best half the truth. (Have read a lot of stuff about OPamps, but never came across an inv input defined as unity gain point???)

OPamps may be configured by their internal structure and external circuitry as amplifiers and the majority of amplifiers is constructed as Opamp.
But not every amplifier is constructed as OPamp, as well as not every Opamp works as amplifier (but differentiator, Integrator, Filter, Comparator, etc).
OPamps may come in discrete building form, as integrated circuit or a combination of both (e.g audio power amplifiers with integrated input stage and discrete power stage).

A expanded definition decribes the basic behaviour of an Opamp which in ideal theory are:
infinite gain, infinite input input impedance, and 0 output ipedance and no parasitic effects like noise, distortion etc.


jauu
Calvin

[sreten]

Hi,

Some people are being picky about the details :

1) A LT is simply not needed for a low Q sealed box
ans its complicating a very simple bass boost facility.
LT in this case is the wrong way of looking at it.

2) The circuit described is clearly a line level op-amp circuit.

3) Typical unity gain op-amp high pass filter functions
can be built into amplifiers with gain by treating the
inverting input as the unity gain point.
Whether you've heard of this or not, some thought
will indicate its true, gain =1 at the inverting input
for series feedback. (Feedback path has to be
low enough impedance to drive the filter).

rgds, sreten.

[Ken Newton]

Please take the following advice in the constructive manner in which I intended it. Many of your questions are of such as basic nature that I would have serious reservations about attempting to implement a circuit such as the Linkwitz Transform, if I were you. If you are truly serious about experimenting with DIY electronics, not merely building kits, than you really should take a formal course in electronics. Trade/vocational schools offer such programs. You don't to earn a degree, but a one year long part-time program could do wonders for your ability to do the things you seem to want to do.

Meanwhile, the following link to Elliot Sound Products could be of help for you immediate project. It's a Linkwitz Transform project for which where ESP offers a dedicated PCB.
Linkwitz Transform Subwoofer Equaliser

[CharlieLaub]

Marchand Electronics sells what they call the "BASSIS", which is a fully adjustable LT equalizer type circuit. You can buy the populated circuit board from them for $90 including all pots for adjustment, etc. ready to use, or even one built with power supply and in a case if you want that. I have used them in the past and they work as advertised for low Q or high Q speaker applications!

subwoofer equalizer, bass correction equalizer, bass boost

-Charlie

[Ken Newton]

As far as the performance parameters which define an ideal op-amp are concerned, input impedance, output impedance, gain, etc., those may be found widely on the internet.

In addition to those is that 'op-amp' is short for, 'operational amplifier'. 'Operational', refers to mathematical operations. Addition (summing), algebraic subtraction (difference), multiplication (logarithmic addition), division (logarithmic subtraction), integration and differentiation. The op-amp was invented to be the basic building block of analog computers. The first op-amp was built from vacuum tubes. While very susceptable to noise and other errors, analog computers can be exceedingly fast in performing such basic math operations. Digital computers are not nearly so susceptable to noise and other errors, and have replaced analog computers for those and other reasons, such as ease of programing. Op-amps are widely used today because they make for cheap and easy to implement linear gain blocks, mostly intended for signal amplification.

[Calvin]

Hi,

@sreten

3) Typical unity gain op-amp high pass filter functions
can be built into amplifiers with gain by treating the
inverting input as the unity gain point.
Whether you've heard of this or not, some thought
will indicate its true, gain =1 at the inverting input
for series feedback. (Feedback path has to be
low enough impedance to drive the filter).

Its not a matter of what I might have heard, but simply a matter of general conventions. If You had talked about ´configuring the OPamp as unity gain amplifier´ everybody with the slightest knowledge would have understood.
Its for sure not useful to confuse noobs by introducing Your personal set of conventions instead of common textbook conventions.
I´m surely no noob but I´n still not sure what You mean with unity gain point. Your explanation in 3) doesn´t help to clear the matter. What do You mean with gain=1 at the inverting input for series feedback and low impedance? The factor of "1" and "series feedback" define a noninverting configuration with only a connection between output and inverting input (no ground referencing for invIn) . So the signal is fed into the noninverting Input. Also the inputs themselves don´t feature a characteristic called ´gain´. The gain is a result of the OPs internal or openloop gain, feedback characteristics and which Input used as signal input.

jauu
Calvin

ps. after textbook convention the "unity gain point" defines the frequency where the OpenLoop Amplitude response has dropped to 1.

[Chris Hornbeck]

He means that the inverting input of a (modern) power amplifier will have essentially a replica of the non-inverting input's signal. Because it's at a relatively low impedance it can be used as if it were the output of a unity gain opamp for making active filters with the power amp.

Thanks,
Chris