Crown Amps

[grumpy]

looks like 4-8 (2242)... in parallel Get out your welding cables

[1audiohack]

Damn! Looks like I need one more!

[pos]

Before you burn those poor ol' 2242H to death/deaf, why not try and see what current drive mode can do for your 1200fe in its midbass configuration (ie used above Fs) ?
http://www.diyaudio.com/forums/multi...ml#post4410302

[1audiohack]

I have much smaller/safer amps that will operate in CC mode than this monster.

I have thought about the CC thing and only once tried it, by accident. If you switch one of these into CC mode without the sensor wire at the load it goes full output loooking for something coming back. It was an amazing experience. The amp itself sounded like a camera flash charging up and heat radiated out of it immediately.

I will have to reconsider CC after re-reading that thread. It's been a while.

The 7700 amp is for the shop only, I don't three phase power at the house.

Barry.

[pos]

I have much smaller/safer amps that will operate in CC mode than this monster.

What model is it?
A smaller Techron?
I have been looking for a ready-made current amp for a long time now...

[1audiohack]

Hi Thomas;

I cut this out of a manual I have. After reading it all I decided that without evidence of serious sonic benefits I would stick with CV.

CC and CV Modes
Techron amplifiers offer precise control of
current or voltage. Techron amplifiers are
designed to operate in either controlled
voltage mode or controlled current mode.
Some models provide only one mode, and
others offer selection between modes.
In controlled voltage (CV) mode (formerly
called “constant voltage”), the output voltage
is an amplified voltage representation of the
input voltage signal. (See Illustration 1.) The
input signal to the amplifier produces a
desired voltage, and the amplifier maintains
that desired voltage even if the load varies. If
the load’s impedance changes, the amplifier
seeks to maintain the desired voltage by
changing its output current. Use CV mode
when the output voltage waveform should be
like the input voltage waveform.
In controlled current (CC) mode (formerly
called “constant current”), the output current
is an amplified current representation of the
input voltage signal. (See Illustration 2.) If
the load’s impedance changes, the amplifier
seeks to maintain the desired output current
by changing the output voltage. Use CC
mode when the output current waveform
should be like the input voltage waveform.
In CC operation, the load is a critical circuit
component and must always be connected to
the amplifier! (See
Illustration 8 for a
diagram of a CC/CV
circuit inside an
amplifier.) If no
load is attached, no
current can flow.
The amplifier,
however, will vainly
seek the impossible
current
requirement by raising the
voltage as high as
possible. The
amplifier will then
operate in an
unstable and possibly
damaging
manner.
In CC operation,
not only must a load always be connected, but
it must be connected to the proper terminals.
In the 7521, 7541, 7700 family, and 8700
family amplifiers, the load must be connected
to the Output and Sampled Common
terminals. (See Illustration 9.) The shunt
resistor connecting the Common and
Sampled Common tells the amplifier how
much current is flowing through the load.
Without this vital information, the amplifier
will become unstable and possibly self-destructive
while in CC mode.
Since the load is a critical part of the circuit,
the resistance, inductance, and capacitance of
the load must be compensated to obtain
accurate CC operation. Compensation is
performed by altering the values of the
“compensation network” (a resistor and a
capacitor) inside the amplifier. (See Illustration
8.) Amplifiers are most easily compensated
to a resistive load that has an inductive
component. (For more tips on CC operation
consult the Techron publication Application
Note: Controlled Current Operation.)
In CV operation, the amount of current
flowing through the load is not crucial to the
operation of the circuit. The load may be
connected to either the Common or the
Sampled Common terminals. You must use
the Sampled Common terminal, however, if
you want to use the amplifier test points
(where applicable) to monitor the current
flowing through the load.

Impedance Matching
An amplifier transfers maximum power to a
specific load impedance. (Illustration 10 shows
a power transfer curve for a 7780 amplifier in
CV mode with a
continuous 1 kHz
sine wave input.)
Compared to this
optimal value, if a
load’s impedance is
lower (producing
high current/low
voltage), the amplifier
may become
current limited and
may start to overheat. If the load’s impedance
is higher than the optimal value (producing low
current/high voltage), the amplifier may become
voltage limited and be unable to transfer
as much power.
Maximum power transfer depends on amplifier
design, load design (relative values of resistance,
capacitance, and inductance), duty cycle,
and waveform. The optimal load impedances of
Techron amplifiers range, according to the
model, from approximately 0.25 to 100 W. (The
optimal load impedances is not the same as the
impedance at the amplifier output terminals—
typically only a few mW.)
Many loads driven by amplifiers consist of
some type of coil. Coil design is an important
factor in choosing a suitable amplifier to drive
it. A coil composed of a thick wire with few
turns can create the same magnetic field as a
coil composed of a thin wire with many turns.
However, the first coil may require more
current than an amplifier can provide while
the latter may require more voltage than the
amplifier can provide. Ideally, a coil should
be designed from the start to match its
intended power supply.


Coil impedance depends not only on its own
inductance but also on the signal frequency.
The inductive reactance (XL) of a coil equals
2pfL. For example, say an application requires
10 A through a 0.001 H coil. At 100 Hz
the coil’s inductive reactance is 0.63 W. Since
E=IR, (ignoring coil capacitive reactance and
resistance), the amplifier must be capable of
at least 6.3 V (10 A x 0.63 W) to meet the 10 A
requirement.
At 10 kHz, however,
the coil’s inductive
reactance is 62.8 W.
Then an amplifier
would need to be
capable of at least
628 V (10 A x 62.8
W) to meet the 10 A
requirement. (See
Illustration 11.)
The higher-impedance problem may also
affect applications unexpectedly since signal
frequencies often do not remain constant.
Even relatively low-frequency (on average)
signals may contain some waveforms with
rapid rise times (transitions from one voltage
amplitude to another). Rapid rise times can
temporarily boost the effective signal frequency,
coil reactance, and needed amplifier
voltage to very high levels.
All Techron amplifiers can easily handle
frequencies to 20 kHz and beyond, but none
individually can produce 628 V as needed in
the example above. A series system of amplifiers
might produce enough voltage, but a
better solution is to design the application to
operate with lower voltage. Techron application
engineers can work with you to determine
your best design in coil parameters.


This makes it look like a standard voice coil may be far from an optimized match for this method of drive so I didn't pursue it further.

In any event, the 7500 series is the slightly more sane line for CC or CV.

Sorry for struggling with the text editor. This is the best I could do in a snap.

All the best,
Barry.

[NickH]

No 3 phase in your house, what were you thinking.


How much does that boat anchor weigh?


Nick

[pos]

Hi Barry

This makes it look like a standard voice coil may be far from an optimized match for this method of drive so I didn't pursue it further.

Actually I think the opposite is true.
You can find theoretical information on this web site, as well as many threads on the diyaudio forum under the terms "transconductance" or "current drive".

You can also try for yourself using a series resistor between the amp and driver to simulate a high output impedance (ie damping factor smaller than 1).
When I tried this I got tremendous reduction in harmonic distortion (especially 3rd order), except for compression drivers where it did not seem to change a thing.
Of course the response get modified as any rise in impedance will cause a rise in magnitude (beware of the Fs...), but this can always be arranged using EQ, and you always have to use EQ in an active multiway system anyway.

Of course it is better to stay above the Fs of the driver (or use drivers with a very low Qms, but that is certainly not the case of the 1200Fe), and use EQ to reduce its effect in the stop band.

[1audiohack]

Hi Thomas!

I am unable to study this at the moment as I am away from home and out of internet contact for the most part this week but I am curious and working to understand how this CC method works via a series resistor to reduce distortion. I will be the first to admit that I don't know near as much about electronics as I would like to so I am not certain how to properly (technically) phrase this question but here goes:

I do not understand how removing an element of control (dampening) from a transducer-amplifier system could in itself have the positive effect of distortion reduction of the transducer. It seems possible though the series resistor would act as a buffer alowing the amp to operate in a more comfortable area of operation as a voltage source. When the amp and the transducer are at odds with each other, if the difference is spent as heat in the resistor rather than engaging (dramatically ?) the feedback (control loop) system in the amplifier, I think I can see my way clear to a reduction in some type of distortion in the "system". If I have it right, this would make the level of benefit system dependent eg to a particular amp and transducer.

It would seem that this will likely be a tradeoff with some other effect and which may be less offensive and desirable and that is always the secondary goal in audio if one cannot achieve the outright elimination of what ever ails it.

I don't know how to ask it any better than that. I am in hopes that you will help me understand.

Thank you,
Barry.

[pos]

Hi Barry,

I am afraid the electrical notions behind this distortion reduction are beyond my reach, but the diyaudio threads and the website I linked should give you the in-depth explanation you are looking for.
I think the benefit are solely transducer-dependant.
In my own tests I found that the older the motor structure, the higher the benefits.
It looks like current-drive fully achieve what shortcut rings and other similar mechanisms are attempting to do.

I did not keep all my measurements, but I can share data on the JBL C500G, JBL 2020H, TAD TM1201H, TAD TL1801H

[1audiohack]

Thank you Thomas.

I will look into it when I get back.

All the best,
Barry.

[bubbleboy76]

Crown-question #1.
Anyone who knows if the power-inlet of the Crown CTs-series is universal, or are there separate 110 and 220 volt versions?

[bubbleboy76]

Crown-question #2.
I do not understand the "input sensitivity switches" on my Crown CTs-600, explained in the manual like this:
The switches are in the top surface of the cavity behind the Input Panel. One 3-position switch per channel selects among these settings: 1.4V (8/4 ohms), 26 dB gain, and 1.4V (70Voperation).

From another place in the manual:
Maximum Input Level
Before input compression +20 dBu
Absolute maximum + 32 dBu

What are the different switch positions intended use?
Which one should I use with my dbx4820?
I can select a range of different output voltages in the dbx, ranging from 4dbu to 24dbu.

[1audiohack]

Hi there;

If I follow your questions correctly:

Input sensitivity, the input voltage requried to drive the amp to full power would be 1.4V or 3.46V in the 26dB position. Why they just don't say it I don't know.

The 70-140 volt operating option is for driving a distributed speaker system like in a restaurant or retail store where the speakers are each isolated from the amp via a transformer.

The dB input before limiting and absolute tell you how much voltage the input section of the amp can tolerate. This is usually about 8V.

Am I on the right page with you or are you after something else?

Barry.

[bubbleboy76]

Hi there;

If I follow your questions correctly:

Input sensitivity, the input voltage requried to drive the amp to full power would be 1.4V or 3.46V in the 26dB position. Why they just don't say it I don't know.

The 70-140 volt operating option is for driving a distributed speaker system like in a restaurant or retail store where the speakers are each isolated from the amp via a transformer.

The dB input before limiting and absolute tell you how much voltage the input section of the amp can tolerate. This is usually about 8V.

Am I on the right page with you or are you after something else?

Barry.

OK, that is kind of the right page
So which setting should I use in the Crown and in the DBX?
It is better to send as high signal as possible (without clipping the crown) from the source (dbx), right?
So optimal would be 13dBu out from dbx, 26dB position in the crown input, and then set the crown gain to lowest possible setting to reach the max spl I want?