siliconchip.com.au Australia’s electronics magazine April 2019 93
wind the inductor yourself in the June
2016 issue (pages 72-75; siliconchip.
com.au/Article/9965). We used 325
turns of 18-20 gauge wire on a former
with a 25mm inner diameter, 67mm
outer diameter and 25mm height. You
can also get pre-wound inductors from
http://www.soundlabsgroup.com.auMajestic Speaker
design questions
I built your Majestic Loudspeakers
(June & September 2014; siliconchip.
com.au/Series/275) in 2015 and am
still enjoying them but I have some
questions about the design.
Firstly, why is your crossover fre-
quency 1.6kHz (@6dB/octave) when
the Etone 1525 woofer can handle
frequencies up to about 2.2-2.4kHz?
On the Celestion website (https://ce-
lestion.com/product/48/cdx11730/),
they recommend that the CDX1-1370
compression tweeter is crossed over at
2.2kHz for a 6dB/octave filter. Could
1.6kHz be too low for the tweeter?
Also, why did you choose the
CDX1-1730 when the CDX1-1425 &
1430 (using the same neodymium
magnet) have flatter frequency re-Alternatively, there is the Talema
AP-1000 current transformer (RS Cat
775-4943). It appears to be similar to
the AX-1000 we specified but it’s dif-
ficult to say for sure since the AP-1000
data sheet only shows its output char-
acteristics with a 10W load. Its output
may be similar to the AX-1000 if the
load is 510W, as in our circuit.
Given its low price, you could give
it a try, although we can’t guarantee
that the AP-1000 will give equivalent
feedback control for the motor. Al-
though it appears physically identical
to the AX-1000.Inductor for Majestic
speaker crossover
I am interested in building a pair of
Majestic speakers (June & September
2014; siliconchip.com.au/Series/275)
but the 2.7mH inductor is out of stock.
Please advise where I can get a suit-
able replacement.
Also, it looks like Jaycar still has the
LF1330 former, so alternatively advise
the number of turns and wire gauge
required to create an equivalent sub-
stitute. (B. D., Ashburton, Vic)- We had an article explaining how to
than simple wire whip antennas.
While half-wave and full-wave an-
tennas are better than quarter-wave,
directional antennas are usually bet-
ter again. A 433MHz Yagi mounted up
high would probably give the best re-
sults, especially if it was high enough
to achieve line-of-sight.
Ultimately, getting reliable 433MHz
reception from such low-power mod-
ules over 60m without line-of-sight
requires careful antenna design and
arrangement.
Full-Wave Motor Speed
Controller transformer
I want to build the Full Wave
Universal Motor Speed Controller
(March 2018; siliconchip.com.au/
Article/10998) but RS Australia has the
Talema AX-1000 current sensing trans-
former on back-order until July. Other
vendors seem to have a similar stock
situation. Is there another device I can
use instead? (P. W., Keilor East, Vic)
- The AX-1000 (RS Cat 173-0057) is
currently back in stock. RS Cat 124-
3900 is a “house brand” version of the
AX-1000 transformer and is also cur-
rently in stock.