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Bias design, amplifier design, filtering etc.

I been trying something new this past weekend.
I used 2 lnm317's and got the variable voltage down to between.5 and 2 volts. I am trying to use an lm340 and lm350 as a basic current limter.
So far so good... I can get the voltage in the right range and have the upper limit of the lm 340/350 set at 200ma.
Its not quite done yet...but I was able to get the values that I wanted out of the circuit. So its a good start...just gotta get it to track
 
bushwacker, when you say upper limit at 200ma, is that 200ma idle current or 200ma current limit for the bias supply?

where are you measuring the current?
 
bob85 said:
bushwacker, when you say upper limit at 200ma, is that 200ma idle current or 200ma current limit for the bias supply?

where are you measuring the current?
Click to expand...

Right now its not in the amp.... I was checking if the lm350/340 were working as a current limiting device...I set the upper limit of the lm350/340 to 200ma.

The first part of the circuit is just a LM317 regulator with the variable output lowered to .6 volts but can be adjusted as high as 2 volts. This circuit is just a voltage regulator and can pass up to 1 amp ( or so)

The second part of the circuit is a current limter. I did the calculators for setting the current limiting ( resistor value) on a lm340 and lm350. These are functioning as just a current limter. I set the upper limit to 200ma.
Still bench testing.... on the bench I hooked it up to a load ( high output LEDS, resistors ect) and adjusted the voltage.
So I have my regulator output and current limiter circuit, in series with my fluke ( for measuring current) and then the load in series with that.

The whole idea is to try keeping a regulated voltage ( adjustable) but limit ( control) the current.
So far so good... I can control voltage and current.
Its still not done...I want to be able to set an upper limit to how much current can be drawn... then control it within that range.
Its a circuit by circuit build up.
Is still in testing phase Bob
Take care
 
Last edited:
its nice to see somebody else out here experimenting bush,
imho current limit is a good idea, i used 4 parallel resistors on the bias board to give better control over current limit, having the bias voltage fold back if you overdrive the amp may ( im not sure ) give a little bit of overdrive protection.
good luck with your experiment(y)
 
bush if you intend biasing the 4x2879 snowcap with the circuit you are talking about you will need more than 200ma current limit at higher drive levels if you want to keep the amp in true class ab even if you use one bias supply per pair of transistors.
 
Bob is right, as you drive the amp, the bias voltage will drop some causing bias level to drop possible even to a class B level. I have built several bias circuits in the past and had this same exact problem in some of the circuits.
 
Matter of fact, I had one circuit in particular, was resting at around .68 volts. But when I was driving amp with just radio, it dropped to .4 volts. I remember this well, I was just experimenting with biasing and Bob was working on a bias circuit using a 723 and working out a few details. LOL
 
bob85 said:
bush if you intend biasing the 4x2879 snowcap with the circuit you are talking about you will need more than 200ma current limit at higher drive levels if you want to keep the amp in true class ab even if you use one bias supply per pair of transistors.
Click to expand...

Yes I understand . Thanks for the input
I will definatly keep that in mind when I test it in the amp

I'm still in experimental stage. This is the first time I am using a regulator IC strictly as a current limiter.
This is just testing..... nothing is set in stone...nothing is put in the amp.
But things are progressing in the right direction..
I can have a regulated voltage.
I can control current .
Next step would be to see exactly what its doing and how its functioning
I don't have any variable resistors that are the right value and size right now unfortunatly, so I am using fixed resistors. Once I have the pots then I can adjust as needed.


I think I might just try testing it in the amp next......hook it up to the amp...run it for a bit while watching what its doing on the scope. I'll just monitor bias current draw and voltage while I check out the waveform. Then at least I will have more info as to how its presently functioning and what it needs before I do anything else.

I really need to see how this thing is functioning before I make changes.
I need some parts and more time to do it also.

I will let you know what its doing when I finally get around to testing it in the amp. Your probably right about raising the limit though...I just need to check it out whats going on first before I do anymore changes.

Thanks for the input Crusher and Bob... your opinion and thoughts are always welcome.
 
bigred222 said:
how many of the 500 watts my midnight special 700 are going out at 27 megahertz
Click to expand...

2hicqxk.gif
 
You can test it with using expensive pills.;)

bushwacker said:
Yes I understand . Thanks for the input
I will definatly keep that in mind when I test it in the amp

I'm still in experimental stage. This is the first time I am using a regulator IC strictly as a current limiter.
This is just testing..... nothing is set in stone...nothing is put in the amp.
But things are progressing in the right direction..
I can have a regulated voltage.
I can control current .
Next step would be to see exactly what its doing and how its functioning
I don't have any variable resistors that are the right value and size right now unfortunatly, so I am using fixed resistors. Once I have the pots then I can adjust as needed.


I think I might just try testing it in the amp next......hook it up to the amp...run it for a bit while watching what its doing on the scope. I'll just monitor bias current draw and voltage while I check out the waveform. Then at least I will have more info as to how its presently functioning and what it needs before I do anything else.

I really need to see how this thing is functioning before I make changes.
I need some parts and more time to do it also.

I will let you know what its doing when I finally get around to testing it in the amp. Your probably right about raising the limit though...I just need to check it out whats going on first before I do anymore changes.

Thanks for the input Crusher and Bob... your opinion and thoughts are always welcome.
Click to expand...
 

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