A simple indicator of the output power of the amplifier

[Zampotech]

A simple quasilogarithmic amplifier detector was developed for the JLH amplifier.

Designed to work with arrow VU meters

Simple and cheap components are applied.

Scheme:

Amplitude characteristics

The circuit has a boost circuit

Appearance of the front and rear together with a VU meter SO-53

Can be used with almost any VU meter and any amplifier.

 

[Mark Tillotson]

Neat way to mount it - but PCB has to match the particular VU meter (or is it stripboard?)

 

[Zampotech]

Yes, this PCB is adapted for SO-53 type VU meter. But there is no special problem to adapt PCB for other VU meters.

 

[martin clark]

Nice.

I made a similar thing out of an interesting meter movement I found second-hand:

 

[Zampotech]

You have a real measuring device

In my case, these VU meters will be installed in the JLH amplifier.

 

[ICG]

I couldn't find anything about a KP1436 IC, the photo of the board shows a MC34119 Low Power Audio Amplifier. Is it indeed the MC34119?

 

[Zampotech]

Yes, KR1436UN1 and MC34119 analogues. I bought chips from the same factory with two different markings.

 

[audiofan]

I dont see why you are using a log amplifier ... the Arsonval is linear but the scale scale printed on the faceplate is a log scale ....

You should test the meter with a dc power supply and a resistor .....

maximun current for full scale +3 dB
70 % of maximum for 0 dB
50 % of maximum for -3 dB
10 % of maximum for -7 dB

otherwise

Nominal current fo 0 dB
141% of nominal for +3 dB
71 % of nominal for -3dB
50 % of nominal for -6 dB
10 % of nominal for - 10 dB

As far as I know you dont need a log amp to drive the meter .....

 

[Zampotech]

I dont see why you are using a log amplifier ... the Arsonval is linear but the scale scale printed on the faceplate is a log scale ....

You should test the meter with a dc power supply and a resistor .....

maximun current for full scale +3 dB
70 % of maximum for 0 dB
50 % of maximum for -3 dB
10 % of maximum for -7 dB

otherwise

Nominal current fo 0 dB
141% of nominal for +3 dB
71 % of nominal for -3dB
50 % of nominal for -6 dB
10 % of nominal for - 10 dB

As far as I know you dont need a log amp to drive the meter .....

I can understand that. I used the VU meter I had.
The scale of this meter can be easily replaced by a homemade. I made a quasilogarithmic amplifier for another reason.
At a comfortable volume the usual linear VU meter shows almost nothing the Arrow lies at the beginning of the scale and almost does not move.
So I applied dynamic range compression to visualize the performance of the amplifier.

 

[audiofan]

I understand your situation but then all you have is a moving needle ....
With a régular set up ( no log amplifier ) you can know how much power the amp is driving.
If you calibrate for 0 dB - 6.3 volts RMS you have 5 watts in 8 ohm
then
+3 dB - 8.9 volts RMS you have 10 watts in 8 ohm
-3 dB - 4.5 volts RMS you have 2.5 watts in 8 ohm
-7 dB - 2.8 volts RMS you have 1 watts in 8 ohm
-10 dB - 2.0 volts RMS you have 0.5 watts in 8 ohm
-20 dB - 0.63 volts RMS you have 0.05 watts in 8 ohm

 

[lcsaszar]

Nice job but one is interested in volume around peak where clipping occurs, and the stretched dB scale is more useful there. Especially at tape recorders 0...+6 dB range is most important.