Audio limiting

[silversmith]

I thought I could gain sensitivity by reverse paralleling 2 germanium diodes to achieve a zener. I placed this zener directly across the headphone jack in the detector. I thought with this device installed, I could crank up the volume for quicker response without hurt my ears, but gained nothing. Maybe the volume at a full setting is still under 3/10 volts. Anyone have ideas on this? Thanks, Ron.

 

[Rob (IL)]

The limiter in my phones are the two diodes with a 100 ohm resistor in series with the diodes. Vary the resistor value to set how much volume control you want. Rob

 

[rbholt80]

yeah there would have to a resistor in series with the zeners to load down the current once it broke the revers bios of the zeners. Its like a flood gate that opens then eats some of the surge. The zeners have a voltage rating at witch it revers at so that voltage point is important. You not looking for the .7 or .3 tenths of bios volt your looking for the regulation voltage of the zener.

So what you want is at certain volume = volts the current breaks the diodes bios point and then dumps it. that limits the volume or voltage in the circuit.

 

[rbholt80]

One other thing you cant make a zener diode from rectifying diodes or signal diodes you have to use a zener.

 

[silversmith]

So I assume the audio from the detector goes through the 100 ohm resistor, and the bi-directional, parallel diodes basically goes in parallel across the load (earphones) ?

 

[Joe Patrick]

Ron,

Having designed and manufactured a metal detector audio limiter/compressor device about 20 years ago -- known as BlastMaster -- I have some experience with this type of device and circuit(s).

It has been my experience that standard silicon diode peak-clipping circuits do not actually work all that well for use with metal detectors.

Many metal detectors just do not produce a

 

[silversmith]

Hi Joe. I owned a Blastmaster at one time and it worked very well. But like all good stuff through time, it disappeared. What I was fooling around with, was with germanium diodes (1n34a crosses). Do you have a Blastmaster or a schematic available. My profession is Electronics (2-way) and my hobbies are Electronics (ham radio, building toys) etc. Any help appreciated. zlron44@gmail.com

 

[Joe Patrick]

Ron,

I am sorry to say that I cannot provide a schematic or any in-depth technical data about BlastMaster as it would disclose its 'secrets'. I will say that it does not use Silicon or Germanium diodes.

If you build a diode clipper, I think (in most cases) you will get better results with Germanium diodes. If battery operation is okay with you, take a look at some of the op-amp circuits that use diodes in the feedback loop. With an active design like this, you can get gain, clipping or gain and clipping at the same time when needed. Far more versatile than just using two diodes as a peak clipper.

Joe