Jojo
Hi Jojo
My email doen't work at the moment (we have had a majer thunder storm) so I post my email here:
There are something basically wrong if your readings are correct.
Example:
The Voltage across R109 are 22.9 Volts = Supply (35V) -Voltage on Q103 Base
(12.1 Volt)
22.9 Volts across a resistor of 3300 Ohms gives: 22.9V:3300Ohms=6,9 mA
These 6.9 mA have to go somewhere, and the only way is through Q101 and R103
or the base of Q103.
The Voltage of the Base of Q101 are steady and determent by R105 and R107 to
app. 1.1V
This gives app. 0.5V on Q101 Emitter. Output of OpAmp are 0.0V with no input
signal.
This gives 0.5V across R103. The current through R103 will then be 0.5V:1000
Ohms= 0.5mA
Where do the remaining 6.9mA - 0.5mA=6.4mA goes?????????????????????????
If they go through Q103 there are something wrong there, and Q103 should get
very hot.
According to you readings the R111 dissapte 1,5W - Not critical but it is
not right!!!!!
Correct Voltage on Q103 Base should be between +33V and +34 Volt
(on Q104 Base: -33 V to -34V).
As you got symmetry in your readings, I think you should check resistor
values and transistor pins
once again....
Please email voltage readings for Opamp pin 6 (output)
Q101/102 Base and Emitter Voltages.
Does the bias respond to different setting of R114??????
Hi Jojo
My email doen't work at the moment (we have had a majer thunder storm) so I post my email here:
There are something basically wrong if your readings are correct.
Example:
The Voltage across R109 are 22.9 Volts = Supply (35V) -Voltage on Q103 Base
(12.1 Volt)
22.9 Volts across a resistor of 3300 Ohms gives: 22.9V:3300Ohms=6,9 mA
These 6.9 mA have to go somewhere, and the only way is through Q101 and R103
or the base of Q103.
The Voltage of the Base of Q101 are steady and determent by R105 and R107 to
app. 1.1V
This gives app. 0.5V on Q101 Emitter. Output of OpAmp are 0.0V with no input
signal.
This gives 0.5V across R103. The current through R103 will then be 0.5V:1000
Ohms= 0.5mA
Where do the remaining 6.9mA - 0.5mA=6.4mA goes?????????????????????????
If they go through Q103 there are something wrong there, and Q103 should get
very hot.
According to you readings the R111 dissapte 1,5W - Not critical but it is
not right!!!!!
Correct Voltage on Q103 Base should be between +33V and +34 Volt
(on Q104 Base: -33 V to -34V).
As you got symmetry in your readings, I think you should check resistor
values and transistor pins
once again....
Please email voltage readings for Opamp pin 6 (output)
Q101/102 Base and Emitter Voltages.
Does the bias respond to different setting of R114??????
one at a time
Hi Jan,
Indeed my readings are weird 🙄 but that's what the meter shows
. There is something I really still can't find the problem, the voltage of Q101! As measured, it is +3.9V, but theoretically it should be around 1.07V only (kirchoff's law). If I can fix that, find what's causing such a voltage - then I'll move on to the next. Step by step. A good sign will be that I can touch the 330om resistor and Q103 
.
Thank you for being patient. 🙂
JojoD
Hi Jan,
Indeed my readings are weird 🙄 but that's what the meter shows
. There is something I really still can't find the problem, the voltage of Q101! As measured, it is +3.9V, but theoretically it should be around 1.07V only (kirchoff's law). If I can fix that, find what's causing such a voltage - then I'll move on to the next. Step by step. A good sign will be that I can touch the 330om resistor and Q103 .Thank you for being patient. 🙂
JojoD
What are the Vbe of Q101 and Q102?
It should be 0.6V each.
Check the two base resistors for thiese transistors.
It should be 0.6V each.
Check the two base resistors for thiese transistors.
weird
Jan,
After careful study of the schematic and a few Ohm's Law, I believe that there is really something terribly wrong with my amp. So this is what I did.
I removed all transistors except for Q101 and Q102 and Q105. I measured the voltage of Q101=0.9V but Q102=0.5V which is suppose to be equal, right?. So I went to borrow as many testers as I can from friends so that I can monitor what is happening. I connected 5 testers, all referenced to ground and this is what I have.
Q101 base +0.9V
Q102 base -0.5V
Pin 7 (V+)=+14.95
Pin 4 (V-)=-8.5
Pin 6 (Out)=-6.5V
Here's the part I can't understand, when I accidentally touched the pins of the opamp with my fingers, the voltages suddenly shifts!
Shifts meaning;
Q101 base +0.5V
Q102 base -0.9V
Pin 7 (V+)=+8.5
Pin 4 (V-)=-14.95
Pin 6 (Out)=+6.5V
When I touch the pins with my fingers again, it sometimes shifts, sometimes don't but the output of the opamp never stays at 0V only at +6.5V or -6.5V.
To sum it all up,
1. If opamp output goes positive, it's V+ pin decreases and the base voltage of Q101 decreases.
2. If opamp output goes negative, it's V- pin decreases and the base voltage of Q102 decreases.
I have replaced the opamp with a known working OPA134 but the output still shifts. The first OPA134 I used was tested to be working ok.
I am up to this challenge, however, I am fresh out of ideas
.
JojoD
Jan,
After careful study of the schematic and a few Ohm's Law, I believe that there is really something terribly wrong with my amp. So this is what I did.
I removed all transistors except for Q101 and Q102 and Q105. I measured the voltage of Q101=0.9V but Q102=0.5V which is suppose to be equal, right?. So I went to borrow as many testers as I can from friends so that I can monitor what is happening. I connected 5 testers, all referenced to ground and this is what I have.
Q101 base +0.9V
Q102 base -0.5V
Pin 7 (V+)=+14.95
Pin 4 (V-)=-8.5
Pin 6 (Out)=-6.5V
Here's the part I can't understand, when I accidentally touched the pins of the opamp with my fingers, the voltages suddenly shifts!
Shifts meaning;
Q101 base +0.5V
Q102 base -0.9V
Pin 7 (V+)=+8.5
Pin 4 (V-)=-14.95
Pin 6 (Out)=+6.5V
When I touch the pins with my fingers again, it sometimes shifts, sometimes don't but the output of the opamp never stays at 0V only at +6.5V or -6.5V.
To sum it all up,
1. If opamp output goes positive, it's V+ pin decreases and the base voltage of Q101 decreases.
2. If opamp output goes negative, it's V- pin decreases and the base voltage of Q102 decreases.
I have replaced the opamp with a known working OPA134 but the output still shifts. The first OPA134 I used was tested to be working ok.
I am up to this challenge, however, I am fresh out of ideas
.JojoD
It looks that the current of the +/-15V supply is not enough for the opamp you use.
It's possible to increase the current, with decrease the value of R118/119. But be careful with this action, you can loose the zeners, due the overheating.
The difference between the Q101 base, and Q102 base caused by the overload of the opamp's power supply (ZD101, 102) too.
So, try to use another opamp, with smaller quiescent current, or decrease the R118/119.
Sajti
It's possible to increase the current, with decrease the value of R118/119. But be careful with this action, you can loose the zeners, due the overheating.
The difference between the Q101 base, and Q102 base caused by the overload of the opamp's power supply (ZD101, 102) too.
So, try to use another opamp, with smaller quiescent current, or decrease the R118/119.
Sajti
update...
with the voltages above, I removed the input to R101 and the supply became stable and the voltage at the output of the opamp decreased.
I checked the opa134 and quescent current is 4.5 - 5 mA max while a TL071 is only 2.5mA max. I substituted the TL071 and the voltage difference has decreased.
so if I lower R118/119 and increase the wattage of zener, that would mean a big difference right?
JojoD
with the voltages above, I removed the input to R101 and the supply became stable and the voltage at the output of the opamp decreased.
I checked the opa134 and quescent current is 4.5 - 5 mA max while a TL071 is only 2.5mA max. I substituted the TL071 and the voltage difference has decreased.
so if I lower R118/119 and increase the wattage of zener, that would mean a big difference right?
JojoD
Yes! Your +/- 15 VDC MUST be there in order for the amp to work.
As I recall you are running with +/-35V supply rails.
With the 2K7 resistor to the 15V Zener you can draw app. 9 mA
on the +/- 15VDC.
This amp was intented to use 50V+ (norm 55V) on the rails,
which would provide app. 16 mA to Q101/102 and Opamp.
Try change R118/119 to 1K2 (also 2W) or just put an extra 2K7 in parallel with each.
I do not know how sensitive the OPA134 are to it's supply, but
it works very well with older LFxxx Opamps.....
Let us know the new readings
As I recall you are running with +/-35V supply rails.
With the 2K7 resistor to the 15V Zener you can draw app. 9 mA
on the +/- 15VDC.
This amp was intented to use 50V+ (norm 55V) on the rails,
which would provide app. 16 mA to Q101/102 and Opamp.
Try change R118/119 to 1K2 (also 2W) or just put an extra 2K7 in parallel with each.
I do not know how sensitive the OPA134 are to it's supply, but
it works very well with older LFxxx Opamps.....
Let us know the new readings
I'm currently interested in this amp...seems kinda cute actually...didn't know I had a use for so many semi-conductors I still keep at my place...basically what should I look out for when I use all On-Semi parts??
Seems like this amp will take a lot of beating...does the low-pass filter cut out the lows or ???
Yes! This amp provides a powerful bas at high levels 😉
The low-pass filter is to prevent high frequencies entering the amp. The amp WILL amplify DC!!! So if your preamp has DC on the output, you might want to put a 4.7uF cap i series with the input of the power amplifier!
The low-pass filter is to prevent high frequencies entering the amp. The amp WILL amplify DC!!! So if your preamp has DC on the output, you might want to put a 4.7uF cap i series with the input of the power amplifier!
The 4.7uF cap will have no polarity right?? Figures...I can't source one easily here...except for crappy blue phillips mains filtering caps...wonder if they sound good on this...I used them on a gainclone...it sounds horrible...I would rather use it without...oh well...we'll see if I need it...
I have been looking at the datasheets for the MJE340 MJE350...I can't seem to figure out the pinouts....izzit looking at the front or back?? seems like the front...but why the white "plate" ?? In case u guys are not sure what I am talking about...here's a link to the .PDF
http://www.onsemi.com/pub/Collateral/MJE340-D.PDF
Thanks for the help...
http://www.onsemi.com/pub/Collateral/MJE340-D.PDF
Thanks for the help...
On the PCB Silk Screen I have stated pin configuration (B C E) and the direction of all transistors etc.
You will find it all on my website within a day or two😉
You will find it all on my website within a day or two😉
That's great...thanks for your really kind help...btw are u sure all the transistors across all manufacturer's have the same pinouts??I have seen some last time that weren't...so I tend to be more careful now...
You can't be sure of the pin configurations...... That's why I
have added manufacturer names on the part list 🙂
And as earlier mentioned, for those using other components or components from another manufacurer I have added pin names (B, C and E) on the silk print /assembly drawing, to ease the assembly and (hopefully) avoid wrong component placement etc.😉
have added manufacturer names on the part list 🙂
And as earlier mentioned, for those using other components or components from another manufacurer I have added pin names (B, C and E) on the silk print /assembly drawing, to ease the assembly and (hopefully) avoid wrong component placement etc.😉
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