Monitoring the signal going into a non-grounded speaker?

[N_Cook]

Without differential scope amplifier/probe, audio out is missing something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of the
speaker or some inductive/capacitive interaction with the amplifier when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to the
combo. Any simple component to put in series or parallel with the speaker to
check if an output matching problem ?

 

[Gareth Magennis]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb0pt$a4d$1@dont-email.me...

Without differential scope amplifier/probe, audio out is missing something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of the
speaker or some inductive/capacitive interaction with the amplifier when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to the
combo. Any simple component to put in series or parallel with the speaker
to
check if an output matching problem ?

Does this amp have a graphic equaliser? The line out may be pre graphic,
and one graphic fader may be faulty.



Gareth.

 

[N_Cook]

Gareth Magennis <sound.service@btconnect.com> wrote in message
news:Ea2dnSSwS_6piITMnZ2dnUVZ8h6dnZ2d@bt.com...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb0pt$a4d$1@dont-email.me...
Without differential scope amplifier/probe, audio out is missing
something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those
frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of
the
speaker or some inductive/capacitive interaction with the amplifier when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to
the
combo. Any simple component to put in series or parallel with the
speaker
to
check if an output matching problem ?




Does this amp have a graphic equaliser? The line out may be pre graphic,
and one graphic fader may be faulty.



Gareth.

Volume , tone controls etc are in the DSP sextion and as line out is fine ,
I assume not a problem in that piece of magic.

 

[Gareth Magennis]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb52k$7fb$1@dont-email.me...

Gareth Magennis <sound.service@btconnect.com> wrote in message
news:Ea2dnSSwS_6piITMnZ2dnUVZ8h6dnZ2d@bt.com...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb0pt$a4d$1@dont-email.me...
Without differential scope amplifier/probe, audio out is missing
something
in the bass range about 70-80 Hz. Line-out signal faithfully follows
the
bass guitar input signal . Shure microphone, capable of those
frequencies,
monitoring the sound from the speaker, does not match the input at
those
sort of frequencies. But is it a failing of suspension or something of
the
speaker or some inductive/capacitive interaction with the amplifier
when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to
the
combo. Any simple component to put in series or parallel with the
speaker
to
check if an output matching problem ?




Does this amp have a graphic equaliser? The line out may be pre graphic,
and one graphic fader may be faulty.



Gareth.




Volume , tone controls etc are in the DSP sextion and as line out is fine
,
I assume not a problem in that piece of magic.

Is this a Line 6?



Gareth.

 

[Jeff Liebermann]

On Mon, 11 Feb 2013 14:55:42 -0000, "N_Cook" <diverse@tcp.co.uk>
wrote:

Without differential scope amplifier/probe,

Then get a differential scope. You have one in your computah in the
form of the stereo input of your sound card. Just install an
oscilloscope emulator program. Put some large value resistors in
series with the inputs so you don't blow anything up. Favorite
software:
<http://www.sillanumsoft.org>
You'll also find it handy when troubleshooting constant voltage
speaker system.

Incidentally, looking at my pile of about 15 assorted scopes (dead and
alive), the only one that doesn't have a differential input is an
ancient Heath Vectorscope. Finding two scope probes that are matched
and/or haven't been broken by my mishandling is a bit more difficult.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Geo]

On Mon, 11 Feb 2013 14:55:42 -0000, "N_Cook" <diverse@tcp.co.uk>
wrote:

Without differential scope amplifier/probe,

Battery operated (AC) DVM?
Or the green/yellow wire in the scope plug...

 

[tm]

"Geo" <nhhu-o3hu@dea.spamcon.org> wrote in message
news:gt7ih89jsicpbd5jdua74j0jm18hgs5sob@4ax.com...

On Mon, 11 Feb 2013 14:55:42 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:

Without differential scope amplifier/probe,

Battery operated (AC) DVM?
Or the green/yellow wire in the scope plug...

NEVER do that.

 

[Jeff Liebermann]

On Mon, 11 Feb 2013 08:34:04 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Mon, 11 Feb 2013 14:55:42 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:

Without differential scope amplifier/probe,

Then get a differential scope. You have one in your computah in the
form of the stereo input of your sound card. Just install an
oscilloscope emulator program. Put some large value resistors in
series with the inputs so you don't blow anything up. Favorite
software:
http://www.sillanumsoft.org
You'll also find it handy when troubleshooting constant voltage
speaker system.

I guess I should offer a few warnings to prevent the usual disasters.
I sometimes use a sound card scope when sniffing around switching
power supplies, where the input section is usually ungrounded. It's
kinda difficult to see the waveforms due to the limited bandwidth of
the sound card, but I have a good imagination. However, there are a
few precautions.

1. Use a USB sound card dongle and not the device on the computah
motherboard. If you do something wrong, and burn up the motherboard
sound chip, you will not be very happy. A $3 dongle is essentially a
throw away device. It's also nice to have a long extension on the USB
cable, instead of a long cable on the probe.

2. Use a protective resistor in series with the input cable. It
protects against overcurrent, but also protects against idiot errors,
such as unplugging the 3.5mm jack while the probes are connected to
the AC mains. The jack will be shorted on its way out, and will make
a nifty spark.

3. Build an attenuator if you're playing with high voltages. My
guess(tm) is that the sound card input can handle about 5V peak to
peak. 10:1 for audio is fine. 100:1 for high voltage. Also, don't
count on the input capacitor, which is probably only good for about
15VDC.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[mike]

On 2/11/2013 10:37 AM, Jeff Liebermann wrote:

On Mon, 11 Feb 2013 08:34:04 -0800, Jeff Liebermann<jeffl@cruzio.com
wrote:

On Mon, 11 Feb 2013 14:55:42 -0000, "N_Cook"<diverse@tcp.co.uk
wrote:

Without differential scope amplifier/probe,

Then get a differential scope. You have one in your computah in the
form of the stereo input of your sound card. Just install an
oscilloscope emulator program. Put some large value resistors in
series with the inputs so you don't blow anything up. Favorite
software:
http://www.sillanumsoft.org
You'll also find it handy when troubleshooting constant voltage
speaker system.

I guess I should offer a few warnings to prevent the usual disasters.
I sometimes use a sound card scope when sniffing around switching
power supplies, where the input section is usually ungrounded. It's
kinda difficult to see the waveforms due to the limited bandwidth of
the sound card, but I have a good imagination. However, there are a
few precautions.

1. Use a USB sound card dongle and not the device on the computah
motherboard. If you do something wrong, and burn up the motherboard
sound chip, you will not be very happy. A $3 dongle is essentially a
throw away device. It's also nice to have a long extension on the USB
cable, instead of a long cable on the probe.

2. Use a protective resistor in series with the input cable. It
protects against overcurrent, but also protects against idiot errors,
such as unplugging the 3.5mm jack while the probes are connected to
the AC mains. The jack will be shorted on its way out, and will make
a nifty spark.

3. Build an attenuator if you're playing with high voltages. My
guess(tm) is that the sound card input can handle about 5V peak to
peak. 10:1 for audio is fine. 100:1 for high voltage. Also, don't
count on the input capacitor, which is probably only good for about
15VDC.


Can you be more descriptive about what you're doing?

If you're connecting a sound card to the line side of a switcher,
I can't imagine anything more dangerous...as in smoke/fire/death.

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb0pt$a4d$1@dont-email.me...

Without differential scope amplifier/probe, audio out is missing something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of the
speaker or some inductive/capacitive interaction with the amplifier when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to the
combo. Any simple component to put in series or parallel with the speaker
to
check if an output matching problem ?

I have a current transformer on one leg of the input to my dummy load /
power meter. This allows me to monitor non grounded amp outputs, using a bog
standard grounded scope probe into a grounded scope ...

Arfa

 

[Jeff Liebermann]

On Mon, 11 Feb 2013 13:29:03 -0800, mike <ham789@netzero.net> wrote:

Can you be more descriptive about what you're doing?
If you're connecting a sound card to the line side of a switcher,
I can't imagine anything more dangerous...as in smoke/fire/death.

Left -------------------------/\/\/\/------> hot

Right ------------------------/\/\/\/------> common

Shield ------------------------------------> ground

(For a switcher, pretend the resistor is a 100:1 attentuator network
as I'm too lazy to draw it). As long as the sound card can handle the
voltage difference between hot and ground, and common and ground,
nothing will blow up. With the 100:1 attenuator, it should be no more
than about 5V on the inputs. Incidentally, using a series capacitor
for isolation doesn't work as the initial charging current will blow
up the sound dongle.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:wghSs.9174$n95.3013@fx03.fr7...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kfb0pt$a4d$1@dont-email.me...
Without differential scope amplifier/probe, audio out is missing
something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those
frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of
the
speaker or some inductive/capacitive interaction with the amplifier when
loaded with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to
the
combo. Any simple component to put in series or parallel with the
speaker
to
check if an output matching problem ?




I have a current transformer on one leg of the input to my dummy load /
power meter. This allows me to monitor non grounded amp outputs, using a
bog
standard grounded scope probe into a grounded scope ...

Arfa

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect. I do have a scope with differential inputs but
as its not been used for 15 years I would bet good money on it having at
least corroded switch contacts.
I may sort out replacement rechargeable batteries for an ancient Tektronix
212 hand held scope
This is a Roland Cube Bass 30. There may be a faulty , going open, "shape"
switch and may sometime settle into the default at the bottom of the
resistor chain which is the Octave Bass setting which , may explain the odd
effect

 

[whit3rd]

On Tuesday, February 12, 2013 12:31:27 AM UTC-8, N_Cook wrote:

Arfa Daily <arfa.daily@ntlworld.com> wrote in message

news:wghSs.9174$n95.3013@fx03.fr7...

I have a current transformer on one leg of the input to my dummy load /
power meter. This allows me to monitor ...

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect.

A properly loaded currrent transformer can be ten millliohms, or a few
hundred microohms. There needn't be any significant effect on the system
being measured.

 

[Arfa Daily]

"whit3rd" <whit3rd@gmail.com> wrote in message
news:8b7ff2b1-acf8-4721-bb4a-daf45fcc317a@googlegroups.com...

On Tuesday, February 12, 2013 12:31:27 AM UTC-8, N_Cook wrote:
Arfa Daily <arfa.daily@ntlworld.com> wrote in message

news:wghSs.9174$n95.3013@fx03.fr7...

I have a current transformer on one leg of the input to my dummy load /
power meter. This allows me to monitor ...

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect.

A properly loaded currrent transformer can be ten millliohms, or a few
hundred microohms. There needn't be any significant effect on the system
being measured.

Quite. The one that I use is completely non-invasive to the system it's
monitoring - in this case an output stage into a dummy load. It's just a
fully encapsulated winding with a hole through the middle. One leg of the
input to my tester passes through this hole. The winding is terminated with
a couple of k, and my scope hooks directly across it, fully isolated from
the unit under test. It has zero measurable effect on the amplifier or any
networks connected in the amp's output circuit. I would not have designed it
in, and been using it without issue for some years, if it did ...

This is the exact one

http://ww.sourcingmap.co.uk/020a-input-current-epoxy-resin-embedding-precision-current-transformer-ta17-p-133281.html

Arfa

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:I_CSs.40682$D02.34944@fx16.fr7...

"whit3rd" <whit3rd@gmail.com> wrote in message
news:8b7ff2b1-acf8-4721-bb4a-daf45fcc317a@googlegroups.com...
On Tuesday, February 12, 2013 12:31:27 AM UTC-8, N_Cook wrote:
Arfa Daily <arfa.daily@ntlworld.com> wrote in message

news:wghSs.9174$n95.3013@fx03.fr7...

I have a current transformer on one leg of the input to my dummy load
/
power meter. This allows me to monitor ...

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect.

A properly loaded currrent transformer can be ten millliohms, or a few
hundred microohms. There needn't be any significant effect on the
system
being measured.


Quite. The one that I use is completely non-invasive to the system it's
monitoring - in this case an output stage into a dummy load. It's just a
fully encapsulated winding with a hole through the middle. One leg of the
input to my tester passes through this hole. The winding is terminated
with
a couple of k, and my scope hooks directly across it, fully isolated from
the unit under test. It has zero measurable effect on the amplifier or any
networks connected in the amp's output circuit. I would not have designed
it
in, and been using it without issue for some years, if it did ...

This is the exact one


http://ww.sourcingmap.co.uk/020a-input-current-epoxy-resin-embedding-precisi

on-current-transformer-ta17-p-133281.html

Arfa

So you would pass a speaker lead through the hole, ignoring the primary
sense turns.
In the meantime I may as well try a solenoid without pole piece

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kffj3m$c7h$1@dont-email.me...

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:I_CSs.40682$D02.34944@fx16.fr7...


"whit3rd" <whit3rd@gmail.com> wrote in message
news:8b7ff2b1-acf8-4721-bb4a-daf45fcc317a@googlegroups.com...
On Tuesday, February 12, 2013 12:31:27 AM UTC-8, N_Cook wrote:
Arfa Daily <arfa.daily@ntlworld.com> wrote in message

news:wghSs.9174$n95.3013@fx03.fr7...

I have a current transformer on one leg of the input to my dummy
load
/
power meter. This allows me to monitor ...

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect.

A properly loaded currrent transformer can be ten millliohms, or a few
hundred microohms. There needn't be any significant effect on the
system
being measured.


Quite. The one that I use is completely non-invasive to the system it's
monitoring - in this case an output stage into a dummy load. It's just a
fully encapsulated winding with a hole through the middle. One leg of the
input to my tester passes through this hole. The winding is terminated
with
a couple of k, and my scope hooks directly across it, fully isolated from
the unit under test. It has zero measurable effect on the amplifier or
any
networks connected in the amp's output circuit. I would not have designed
it
in, and been using it without issue for some years, if it did ...

This is the exact one


http://ww.sourcingmap.co.uk/020a-input-current-epoxy-resin-embedding-precisi
on-current-transformer-ta17-p-133281.html

Arfa



So you would pass a speaker lead through the hole, ignoring the primary
sense turns.
In the meantime I may as well try a solenoid without pole piece

Yes, a speaker lead passes straight through the middle. In this use of the
device, there is no 'primary sense turns' issue. The wire passing through
the middle represents a single turn primary. With the ratio being 2000:1,
that provides a more than adequate output level for really very small power
levels - just a few watts in fact. I dare say that if you were bothered, you
could rectify the voltage appearing across the secondary, and hang a
suitable meter and calibration pot across the output, and get a fair
indication of relative, if not absolute power levels. The transformer is
rated to 20A, which I believe is the point at which the core starts to
saturate, so the output becomes non-linear, rather than where anything nasty
starts to happen. 20A allows a pretty powerful amp to be run through it.

You can try a solenoid. I'm sure that you will get something out, but I'm
not sure how much. CTs are usually torroidal in construction - at least the
small ones that I've seen - and I guess there's a reason for that. I mean,
at the end of the day, you can drink coffee out of a shoe, but a cup works
better ...

Arfa

 

[Wild_Bill]

Basically, a coil of wire will sense electrical activity on any conductor
that passes thru the coil.
A coil also senses fields near it without having to wrap around a conductor.

A coil on a ferrous core will generally be more sensitive, but as little as
a few turns of wire will also work.
Coils with ferrous cores are used in amp-clamp-type meters and inductive
pickups, and some current probes.

Sencore marketed a product they named the Snoop Loop, which was a length of
coaxial cable with a few turns of wire at the end.. which could be attached
to a scope or other test equipment to sample signals in circuit components
such as tiny board-mounted inductors.

A suitable DIY accessory can be a few turns of wire connected to a female
BNC connector (panel type), so the loop can be easily be attached to a
common scope probe by inserting the probe tip into the connector.
When placed around a small inter-stage transformer the signal becomes
loosely coupled to the loop.

Several turns of wire placed around RF transmission cables is often
sensitive enough to get frequency or modulation readings. I used this method
and capacitive coupling (T connector) when bench testing CB radios years
ago.

--
Cheers,
WB
..............


"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:h5PSs.56655$gq.27297@fx22.fr7...

Yes, a speaker lead passes straight through the middle. In this use of the
device, there is no 'primary sense turns' issue. The wire passing through
the middle represents a single turn primary. With the ratio being 2000:1,
that provides a more than adequate output level for really very small
power levels - just a few watts in fact. I dare say that if you were
bothered, you could rectify the voltage appearing across the secondary,
and hang a suitable meter and calibration pot across the output, and get a
fair indication of relative, if not absolute power levels. The transformer
is rated to 20A, which I believe is the point at which the core starts to
saturate, so the output becomes non-linear, rather than where anything
nasty starts to happen. 20A allows a pretty powerful amp to be run through
it.

You can try a solenoid. I'm sure that you will get something out, but I'm
not sure how much. CTs are usually torroidal in construction - at least
the small ones that I've seen - and I guess there's a reason for that. I
mean, at the end of the day, you can drink coffee out of a shoe, but a cup
works better ...

Arfa

 

[Arfa Daily]

"Wild_Bill" <wb_wildbill@XSPAMyahoo.com> wrote in message
news:L9QSs.419305$OJ2.382458@en-nntp-11.dc1.easynews.com...

Basically, a coil of wire will sense electrical activity on any conductor
that passes thru the coil.
A coil also senses fields near it without having to wrap around a
conductor.

A coil on a ferrous core will generally be more sensitive, but as little
as a few turns of wire will also work.
Coils with ferrous cores are used in amp-clamp-type meters and inductive
pickups, and some current probes.

Sencore marketed a product they named the Snoop Loop, which was a length
of coaxial cable with a few turns of wire at the end.. which could be
attached to a scope or other test equipment to sample signals in circuit
components such as tiny board-mounted inductors.

A suitable DIY accessory can be a few turns of wire connected to a female
BNC connector (panel type), so the loop can be easily be attached to a
common scope probe by inserting the probe tip into the connector.
When placed around a small inter-stage transformer the signal becomes
loosely coupled to the loop.

Several turns of wire placed around RF transmission cables is often
sensitive enough to get frequency or modulation readings. I used this
method and capacitive coupling (T connector) when bench testing CB radios
years ago.

--
Cheers,
WB
.............

All that you say is of course true, but the key to the whole thing is
sensitivity. For sure, you can sense RF fields with just a few turns of
wire, but sensing small currents at audio frequencies is a whole different
ball game. Before settling on the CT that I used in my dummy load / power
meter, I tried all sorts of DIY solutions such as messing about with ready
wound solenoids as Nigel is proposing, and wrapping turns around a piece of
wire and so on. None of those trials produced anything like a sufficiency of
output as to be useful for much. The CT that I used is small, neat, readily
available, cheap, and very sensitive with its 2000:1 ratio. Basically, it
does the job it's designed to do, much like that coffee cup that I
mentioned, and I don't really see the point in trying to bodge up some other
device to serve the same purpose ...

Arfa

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:h5PSs.56655$gq.27297@fx22.fr7...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kffj3m$c7h$1@dont-email.me...
Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:I_CSs.40682$D02.34944@fx16.fr7...


"whit3rd" <whit3rd@gmail.com> wrote in message
news:8b7ff2b1-acf8-4721-bb4a-daf45fcc317a@googlegroups.com...
On Tuesday, February 12, 2013 12:31:27 AM UTC-8, N_Cook wrote:
Arfa Daily <arfa.daily@ntlworld.com> wrote in message

news:wghSs.9174$n95.3013@fx03.fr7...

I have a current transformer on one leg of the input to my dummy
load
/
power meter. This allows me to monitor ...

I suspect a current transformer would affect any PA/speaker/Zobell
resonance/interaction effect.

A properly loaded currrent transformer can be ten millliohms, or a
few
hundred microohms. There needn't be any significant effect on the
system
being measured.


Quite. The one that I use is completely non-invasive to the system it's
monitoring - in this case an output stage into a dummy load. It's just
a
fully encapsulated winding with a hole through the middle. One leg of
the
input to my tester passes through this hole. The winding is terminated
with
a couple of k, and my scope hooks directly across it, fully isolated
from
the unit under test. It has zero measurable effect on the amplifier or
any
networks connected in the amp's output circuit. I would not have
designed
it
in, and been using it without issue for some years, if it did ...

This is the exact one



http://ww.sourcingmap.co.uk/020a-input-current-epoxy-resin-embedding-precisi
on-current-transformer-ta17-p-133281.html

Arfa



So you would pass a speaker lead through the hole, ignoring the primary
sense turns.
In the meantime I may as well try a solenoid without pole piece


Yes, a speaker lead passes straight through the middle. In this use of the
device, there is no 'primary sense turns' issue. The wire passing through
the middle represents a single turn primary. With the ratio being 2000:1,
that provides a more than adequate output level for really very small
power
levels - just a few watts in fact. I dare say that if you were bothered,
you
could rectify the voltage appearing across the secondary, and hang a
suitable meter and calibration pot across the output, and get a fair
indication of relative, if not absolute power levels. The transformer is
rated to 20A, which I believe is the point at which the core starts to
saturate, so the output becomes non-linear, rather than where anything
nasty
starts to happen. 20A allows a pretty powerful amp to be run through it.

You can try a solenoid. I'm sure that you will get something out, but I'm
not sure how much. CTs are usually torroidal in construction - at least
the
small ones that I've seen - and I guess there's a reason for that. I mean,
at the end of the day, you can drink coffee out of a shoe, but a cup works
better ...

Arfa

I tried a solenoid but not enough output and poor at sub 100Hz. Do you know
what the response is like below 100Hz on your pass-thru Tx ?
Dug out a couple of microphone Tx and checked they worked down to 40Hz ,
taking readings, less response but not too much. Then some more important
jobs came in.
One for the phones out line ( so same f response) and one with series 1K or
so over the speaker, should work fed to a normal dual channel scope

 

[N_Cook]

I tried a couple of physically larger microphone Tx and the response is
essentially flat from 2Hz (the bottom limit of my sine gen ) and about 20KHz
, rapid tail-off after 30KHz.
So will try one or both of them when I get back to this speaker/PA problem.
RTFM time : the "shape" switch on a Roland cube 30 bass does not switch in
and
out the COSM selection. I think there was a problem in this sw and when the
wiper disconnects then the function stays with whatever was selected before,
the control lines stay high.
Incidently if o/c at switch on then disables the amp totally. The speaker/PA
is perhaps fine after all , but will try comparing at some point , to at
least see if microphone Txs are useful for this