I am teaching myself how to design and build amplifiers and I started by replicating the input/VAS in Sloane Figure 4.10a on a breadboard. I have a Tektronix 2246A scope, an Instek GPE-3323 power supply (channel A common grounded, channel B positive grounded for +/- rail voltage) and an Instek GAG-810 signal generator and a handful of DMM's. All the bench equipment is plugged into the wall grounded.
The figure indicates the scope, signal generator and +/- power grounded, which I assume is the earth ground on the equipment plugs. But where do the circuit grounds (transistor collector, NFB and input) get connected? When I float the rail voltages, all the voltages check with the LTspice readings. However, if I connect the circuit ground to the power supply earth (green plug) things go haywire. If I raise the voltage beyond 10 volts or if I touch the input ground with a DMM lead, the Instek power supply trips to constant current and the voltage drops.
I'd appreciate any help on how to properly set up the test equipment because I have checked and tripled check the connections and they are correct.
The figure indicates the scope, signal generator and +/- power grounded, which I assume is the earth ground on the equipment plugs. But where do the circuit grounds (transistor collector, NFB and input) get connected? When I float the rail voltages, all the voltages check with the LTspice readings. However, if I connect the circuit ground to the power supply earth (green plug) things go haywire. If I raise the voltage beyond 10 volts or if I touch the input ground with a DMM lead, the Instek power supply trips to constant current and the voltage drops.
I'd appreciate any help on how to properly set up the test equipment because I have checked and tripled check the connections and they are correct.
According to the American version the protection earth must be connected to a mains supply earth , I take it you have done this ---before you connect the circuit to the power supply ?
Also the Mode buttons are set correctly for +/- operation ?
Does it trip when you do that ---before connecting the circuit ?
Just trying to eliminate errors.
If ( as you say ) its when you connect the the circuit to an earth it trips the USA version has a "floating earth " in relation to the mains supply that's why the front panel "GND " is provided to connect to the mains earth .
In the UK version there MUST be a direct mains earth connection as 240 Volts AC ---does kill !
Also the Mode buttons are set correctly for +/- operation ?
Does it trip when you do that ---before connecting the circuit ?
Just trying to eliminate errors.
If ( as you say ) its when you connect the the circuit to an earth it trips the USA version has a "floating earth " in relation to the mains supply that's why the front panel "GND " is provided to connect to the mains earth .
In the UK version there MUST be a direct mains earth connection as 240 Volts AC ---does kill !
for me it seems to be like that.
you have +30 V Red and Black, where black is GND
You have -30 V Red and Black and here RED IS GND,
Green for EARTH LEAVE out. thisNC or =No connection
your Circuit GND you can connect to Black GND & RED GND and all with work just fine..
This is Seondary GND. this is for Europe.
Green Yello or Green is usually PRIMARY GND OR EARTH.
Make an easy test:
Switch off PSU remove the Wall outlet of it.
Take a OHM METER set to X1 and Measure +Black GND and -RED GND, then the Needle or the Numbers should read 0.000OHM
If this is like that connect as I wrote. if not then tell us what you read.
you have +30 V Red and Black, where black is GND
You have -30 V Red and Black and here RED IS GND,
Green for EARTH LEAVE out. thisNC or =No connection
your Circuit GND you can connect to Black GND & RED GND and all with work just fine..
This is Seondary GND. this is for Europe.
Green Yello or Green is usually PRIMARY GND OR EARTH.
Make an easy test:
Switch off PSU remove the Wall outlet of it.
Take a OHM METER set to X1 and Measure +Black GND and -RED GND, then the Needle or the Numbers should read 0.000OHM
If this is like that connect as I wrote. if not then tell us what you read.
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With the PSU both plugged and unplugged it measures open circuit from the green ground to any of the positive or negative outputs, which I assume is correct since the PSU supplies are supposed to be floating.
With all the equipment plugged into the wall, there is continuity (short) between the PSU ground (green), the signal generator ground (black) and the scope probe BNC grounds. This is where I have a concern about damaging the scope so I do not use the scope ground clips on any DUT grounds. But since the signal generator and PSU ground terminal are continuous, I was asking if it is a problem connecting both the signal generator ground and PSU ground to the DUT and maybe the reason why I get overloading the PSU when I probe a point on DUT with the DMM.
The problem I have is that the amplifier breadboard circuit draws a lot of current from a collector-grounded transistor (the VAS) whose emitter goes to Vnegative. The reason is I'm supposed to see a negative voltage on the base about -1.2V below the rail negative but am seeing a much lower voltage, causing the transistor to pull excessive current. All the other voltages from the Vpositive rail down are correct so I was thinking the grounding connections to the DUT was the problem. I had the circuit both on breadboard and psb and both had the same problem -- burning the resistor between that transistor emitter and Vneg.
<Quote>With the PSU both plugged and unplugged it measures open circuit from the green ground to any of the positive or negative outputs, which I assume is correct since the PSU supplies are supposed to be floating.</Quote>
It is not floating, it's a SECONDARY Winding, and that's why you can not measure anything, as the Green Yellow is Primary or HOT Side.
<Quote>With all the equipment plugged into the wall, there is continuity (short) between the PSU ground (green), the signal generator ground (black) and the scope probe BNC grounds. This is where I have a concern about damaging the scope so I do not use the scope ground clips on any DUT grounds. But since the signal generator and PSU ground terminal are continuous, I was asking if it is a problem connecting both the signal generator ground and PSU ground to the DUT and maybe the reason why I get overloading the PSU when I probe a point on DUT with the DMM.</Quote>
Nothing will happen..
<Quote> The problem I have is that the amplifier breadboard circuit draws a lot of current from a collector-grounded transistor (the VAS) whose emitter goes to Vnegative. </Quote>
What kind of AMPLIFIER DO YOU HAVE THAT COLLECTOR is grounded? There must be something very wrong.., Have you build that Amplifier by yourself?
The Reason you can read underneath:
So then you have A SHORT CIRCUIT either on the Positive Transistor or Negative,
Take your DMM on X1, pull all the RAIL OUT and every other cable to and from the PCB
Measure Collector to GND for both Transistors, and the heatsink, which in any case also have to be grounded to circuit GND.
If it reads 0.000 then you have a short on it..
Is it possible to place a pic of that Amp?
What kind of Transistors *Numbers* are the Output?
No need to connect nor Measure the GREEN ONE, just leave it alone. I wrote in my earlier Post how to measure between POSITIVE AND NEGATIVE RAIL.
first comes first. If the RE Burns then the TRANSISTOR IS ALREAY HISTORY.!
What kind of AMPLIFIER DO YOU HAVE THAT COLLECTOR is grounded? There must be something very wrong..
It is not floating, it's a SECONDARY Winding, and that's why you can not measure anything, as the Green Yellow is Primary or HOT Side.
<Quote>With all the equipment plugged into the wall, there is continuity (short) between the PSU ground (green), the signal generator ground (black) and the scope probe BNC grounds. This is where I have a concern about damaging the scope so I do not use the scope ground clips on any DUT grounds. But since the signal generator and PSU ground terminal are continuous, I was asking if it is a problem connecting both the signal generator ground and PSU ground to the DUT and maybe the reason why I get overloading the PSU when I probe a point on DUT with the DMM.</Quote>
Nothing will happen..
<Quote> The problem I have is that the amplifier breadboard circuit draws a lot of current from a collector-grounded transistor (the VAS) whose emitter goes to Vnegative. </Quote>
What kind of AMPLIFIER DO YOU HAVE THAT COLLECTOR is grounded? There must be something very wrong.., Have you build that Amplifier by yourself?
The Reason you can read underneath:
So then you have A SHORT CIRCUIT either on the Positive Transistor or Negative,
Take your DMM on X1, pull all the RAIL OUT and every other cable to and from the PCB
Measure Collector to GND for both Transistors, and the heatsink, which in any case also have to be grounded to circuit GND.
If it reads 0.000 then you have a short on it..
Is it possible to place a pic of that Amp?
What kind of Transistors *Numbers* are the Output?
No need to connect nor Measure the GREEN ONE, just leave it alone. I wrote in my earlier Post how to measure between POSITIVE AND NEGATIVE RAIL.
first comes first. If the RE Burns then the TRANSISTOR IS ALREAY HISTORY.!
What kind of AMPLIFIER DO YOU HAVE THAT COLLECTOR is grounded? There must be something very wrong..
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