Found in the street today !

[Jazzy_Pidjay]

thanks for this great explanation PRR !!

:thumb:

 

[Jazzy_Pidjay]

i'm a little bit confused

i have tested with the same method
a simple 220v/15v trafo
(one primary, one secondary
like the melodium, 4 wires)

with 1000Hz sine
Input : 0,30v
Output : 2,20v

with 50Hz sine
Input : 0,30v
Output : 2,60v

but 2,60/0,30 = 8,5 and 220/15 = 15

??? :?

any explanation

my melodium is really a 1:8 ?


thanks

 

[Guest]

[quote author="Jazzy_Pidjay"]i'm a little bit confused

i have tested with the same method
a simple 220v/15v trafo
(one primary, one secondary
like the melodium, 4 wires)

with 1000Hz sine
Input : 0,30v
Output : 2,20v

with 50Hz sine
Input : 0,30v
Output : 2,60v

but 2,60/0,30 = 8,5 and 220/15 = 15

??? :?

any explanation

my melodium is really a 1:8 ?


thanks[/quote]

Input capacity forms with primary inductance lowpass filter
of second order. An other example of second order system
is bass-reflex speaker enclosure.

xvlk

 

[Jazzy_Pidjay]

yes yes of course

i don't understand why :
the theorical ratio is (220/15=15) 1:15
and
my measure give me a ratio of about 1:8.5

i have also measure the OEP 1:6.45
and find about 1:6.33 so it's ok.

but i don't understand the power trafo ? :roll:
and it's make me confuse about my melodium ratio (1:8)

 

[Guest]

[quote author="Jazzy_Pidjay"]
but i don't understand the power trafo ? [/quote]
Designo of power trafo is not simple turns ratio,
There are also copper losses.
If you compute 220 to 22 V trafo, it is not 10:1.
You must include some percents (20 percent) to copper losses,
ratio will then be (10-2=8:1)
Power trafo are also not wideband. There can be (at 1 kHz) significant
leak-resonance.

xvlk

 

[Jazzy_Pidjay]

ok thanks very much !!! :grin:

 

[PRR]

> a simple 220v/15v trafo (one primary, one secondary... 4 wires)
with 1000Hz sine - Input : 0,30v - Output : 2,20v
with 50Hz sine - Input : 0,30v - Output : 2,60v

2.20/0.3= 7.33 at 1KHz
2.60/0.3= 8.66 at 50Hz
7.33/8.66= -1.5db

This is reasonable. Power transformers are designed only for 50/60Hz, not 1KHz. Most small power transformers will pass much of the audio band, and -1.5dB at 1KHz is typical. (Also: many digital meters have poor response above 400Hz.)

However, looking just at the power-frequency numbers:

Claimed: 220/15= 14.66
Observed: 2.60/0.3= 8.66

One small correction. The 220/15 rating is for Full Load. In measuring, you are probably measuring unloaded. And small power transformers will sag a lot under load. Maybe 20%. The actual turns-ratio is probably 20% less than the specification. 220/18= 12.2.

There is still something wrong. Are you reading the input voltage while reading the output voltage (using two meters)? The input voltage may sag when you apply the meter to the output.

Is this maybe what we call a "bell transformer"? Made only to power door-bells? These transformers are special high-resistance so that they can NOT over-heat if the door-bell wires are shorted.

 

[Jazzy_Pidjay]

i think the melodium is truly 1:8
because with the OEP 1:6.45 i measure
1:6.33

so i don't worry about my test with the power trafo
probably a lot of the reasons evoked.

thanks everybody.