Hi To Lo (RCA) Converter

[Minds]

Hi all,
Im curious for this thing. Does anybody can tell me how does it works or have the schematics for this device?

thanks all
(i already searching and found http://www.diyaudio.com/forums/showthread.php?s=&threadid=5874&highlight= but it doesn't gave me any light )

regards,
ray

 

[richie00boy]

A very cheap and nasty one will be a resistive potential divider.

A cheap one will be a cheap transformer.

A high quality one will be a good transformer with large core to as not to limit bass, and wound in such as way as to preserve high frequencies.

 

[Minds]

thanks richie for your reply

so basically it consists of just LPF/HPF ?
do the capacitors - resistors combo will work?
because i already take a look on clif designs amps, their hi input use the MKP caps and some resistors.

 

[richie00boy]

No it's not a filter, it just looses some bass and some treble depending on the quality of the transformer/attenuator, as a side effect.

The aim of the converter is to reduce down the high speaker level voltage to lower line level voltage.

 

[davidsrsb]

There is nothing wrong with a 20~30dB two resistor potential divider if you don't have any ground loop problems. After all the speaker output is low impedance and the rca input is probably >10k high impedance.

If hum is a problem I would use a 1:1 microphone transformer and build a 600R attenuator pad in front of it. It is much easier to make a good transformer if you keep the turns ratio near unity.

 

[richie00boy]

The danger with a simple potential divider is that both speaker output wires have alternating voltage on them. If you make one of these ground then you blow up your head unit.

You can make a suitable attenuator using 3 resistors, or 2 if you know the amp input impedance.

 

[Minds]

sorry but i don't get your idea richie
can you make a simple schematic ?

 

[richie00boy]

Put 3 resistors in series. The two outer ones 5.1k each and the middle one 1k. The headunit speaker connections go to the two outer ends, the amp connects to the 1k inner resistor.

This gives approx 10 times attenuation. You must connect left and right exactly the same or you will get out of phase channels.

 

[lineup]

It is okay with only 2 resistors
as long as you keep them rather low in value.

For example a divider of two resistors between + and - output.
1.000 / 100 Ohm will give -20dB
2.200 / 220 Ohm will also give -20dB.

The 1.000 (or 2.200) may need to be 1 Watt or 2 Watt resistors
if your amplifier max output is very high.
Max voltage across those resistors will be almost same as positive supply voltage.

If you do not have any nice 1 or 2 Watt resistors,
you can use two 1/2 Watt resistors in series to make one 1 Watt.

You can even make one 990 Ohm resistor using 3x330 Ohm.
Here I have replaced the 1000 Ohm with two. 470+470 = 940 Ohm.
from the + terminal:
470 Ohm
470 Ohm
100 Ohm
here is - terminal

The output is taken between 100 and 470 Ohm resistor.
If -20dB ( 1/10 ) is not low enough
then make 100 Ohm resistor lower,
maybe 47 or 33 or 22 Ohm.

 

[richie00boy]

No you cannot use a simple 2 resistor devider because

The danger with a simple potential divider is that both speaker output wires have alternating voltage on them. If you make one of these ground then you blow up your head unit.

 

[davidsrsb]

I think Richi00boy is trying to explain that car audio often uses bridged outputs, so both speaker terminals are hot and cannot be grounded.
A bit of ascii art:

1:1
A--/\/\/\------------- ------------
1k5 | ) (
/ ) (
620 \ ) ( -> 600R
/ ) (
1k5 | ) (
B--/\/\/\------------ ------------

No need to go to silly lengths with to get ideal resistor values, the sketch above is near enough a 20dB pad.

 

[davidsrsb]

something is eating the spaces

 

[richie00boy]

Yes thank you david.