You've measured a 4 volt drop across the R2, trimmer, etc seems to indicate approx. 6mA thru this part (and same for negative), so pots adjusted in right area - confirmed with the 100/80mA across R1 &R2
(With trimmer pots P1 &P2 set to minimum at startup, this should be zero volts - ie, zero ohms)
There's no indication of any 0.6V drop across the R11 or R12, so no current flow thru o/p devices?
Only thing not mentioned is orientation of the ZTX transistors, as different to the bc's.
(With trimmer pots P1 &P2 set to minimum at startup, this should be zero volts - ie, zero ohms)
There's no indication of any 0.6V drop across the R11 or R12, so no current flow thru o/p devices?
Only thing not mentioned is orientation of the ZTX transistors, as different to the bc's.
It's remarkable that most of the failures I see are blown front ends that have
been connected to somebody's "prototype tube preamp". You might as well
just plug the input into the wall outlet.
However, I have had perfectly good luck using zeners on the inputs, I use
9.1 500mW types, and they see anywhere from 1K to 4.7K input resistors
in series.
ZTX are Eline and they are the same pin out as BC5xx. Both are cbe, when read from the front (label facing the reader) with the leads pointing down.
The set of three +20V show that virtually no current is passing the Pch output.
The set of three -20V show that virtually no current is passing the Nch output.
The +100mV and -80mV indicate that the third VR P3 is slightly maladjusted.
The current through the upper jFET should be the same as the current through the lower jFET. This will result in the Source Resistors (Rs) dropping the same voltage, if the VR P3 is set to mid point
Recheck the resistance of the upper Rs and the lower Rs and adjust P3 until the two resistances match.
The set of three -20V show that virtually no current is passing the Nch output.
The +100mV and -80mV indicate that the third VR P3 is slightly maladjusted.
The current through the upper jFET should be the same as the current through the lower jFET. This will result in the Source Resistors (Rs) dropping the same voltage, if the VR P3 is set to mid point
Recheck the resistance of the upper Rs and the lower Rs and adjust P3 until the two resistances match.
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look again at the test measurements.
You show -80mV at Q2 source and -20V at Q4 drain.
The resistors between are R8 and R6.
These would be passing (20-0.08)V / [100||100)r = 0.3984A continuously. Almost 4W each !!!!!
Are they HOT?
If not, then find the break in the circuit.
If 398.4mA are passing R6&8, where does that current go and where does it come from?
You show -80mV at Q2 source and -20V at Q4 drain.
The resistors between are R8 and R6.
These would be passing (20-0.08)V / [100||100)r = 0.3984A continuously. Almost 4W each !!!!!
Are they HOT?
If not, then find the break in the circuit.
If 398.4mA are passing R6&8, where does that current go and where does it come from?
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Good day everyone,
I'm experiencing an issue with the initial setup procedure.
A managed to get 0.59V drop across R11 and R12 after about 4h of warming. But I measure a 4.1V drop across R2, which is ok, but a 5.3V drop across R3, which is not expected.
Moreover, I measure a DC offset of 150mV on the output. According to the F5 guide, this should not exceed 50mV.
Is my setup ok anyway or should I investigate?
PS : the inputs are grounded, and the outputs are open off course. My multimeter is a metrix M22.
I'm experiencing an issue with the initial setup procedure.
A managed to get 0.59V drop across R11 and R12 after about 4h of warming. But I measure a 4.1V drop across R2, which is ok, but a 5.3V drop across R3, which is not expected.
Moreover, I measure a DC offset of 150mV on the output. According to the F5 guide, this should not exceed 50mV.
Is my setup ok anyway or should I investigate?
PS : the inputs are grounded, and the outputs are open off course. My multimeter is a metrix M22.
Good.
It means the Vgs of your N and P devices are different. Quite normal, no need to change anything.
Things are likely fine.
Would you please determine what the maximum bias you can achieve with zero DC offset? Report back with that number.
Thanks a lot for all the reply you guys posted for my problem. Unfortunately I cannot work very often on this F5 so it will take me a while before I can follow all suggestions.
I summarize here my homework with some questions:
- recheck without bulb tester and with 2A5 fuse. ZenMod, I'm on 230V supply, do you mean to increase the rating of the fuse to 2.5A? Is there any risk to burn some component in this case? shall I limit the time on? If bulb tester is not there the 1.25A fuse blows few seconds after I turn on
- Remeasure all voltages with input grounded. I will also measure both channels as both have the same problem
- recheck the assembly. ZenMod, when you ask for checking solder joints do you mean something in particular? Only thing I can think is to see if some look as cold joints.
- all the active parts come from forum member h_a. Purchased almost 2 years ago. I only checked good operation of the jfets before soldering. Now I realize I should haev checked all of them.
- ZTX are cbe from the label side but label is on the shorter edge so they are ebc when looked at as in the datasheet. Right?
- I will also recheck P3 and the measures in that area. I did not think to check temperature of R6 and R8. But R5 and R7 should also see a similar current so they should also warm up. Right?
I summarize here my homework with some questions:
- recheck without bulb tester and with 2A5 fuse. ZenMod, I'm on 230V supply, do you mean to increase the rating of the fuse to 2.5A? Is there any risk to burn some component in this case? shall I limit the time on? If bulb tester is not there the 1.25A fuse blows few seconds after I turn on
- Remeasure all voltages with input grounded. I will also measure both channels as both have the same problem
- recheck the assembly. ZenMod, when you ask for checking solder joints do you mean something in particular? Only thing I can think is to see if some look as cold joints.
- all the active parts come from forum member h_a. Purchased almost 2 years ago. I only checked good operation of the jfets before soldering. Now I realize I should haev checked all of them.
- ZTX are cbe from the label side but label is on the shorter edge so they are ebc when looked at as in the datasheet. Right?
- I will also recheck P3 and the measures in that area. I did not think to check temperature of R6 and R8. But R5 and R7 should also see a similar current so they should also warm up. Right?
You can adjust the bias by turning either of the 2 potentiometers. If you increase the offset by turning one pot, you can also increase it by turning the other pot the other way. My guess is that this is what you did. You want to fiddle with both potentiometers "at the same time" while maintaining 0 offset.
Hi everyone. Thank you for your answers.
I managed to correctly setup one channel, but not the other one. Actually, I experienced the same issue than the one described on this post : http://www.diyaudio.com/forums/pass-labs/255683-f5-v3-0-psu-bias-help-needed.html#post3914344.
So I found some 1.1k resistors in my stock and put them in series (in that correct english btw?) with R3 and R4 and restarted the setup procedure from the very beginning. Guess what? I managed to get 0.59V on R11 and R12 easily, and about 20mV DC offset on the output.
So, tomorrow, I'll get four 1% 3.3K resistors and solder them correctly on the PCB and try to reach 0 DC offset.
Should I do the same on the other channel? I manage to reach 40mV DC offset, but the trimmer are almost full.
I managed to correctly setup one channel, but not the other one. Actually, I experienced the same issue than the one described on this post : http://www.diyaudio.com/forums/pass-labs/255683-f5-v3-0-psu-bias-help-needed.html#post3914344.
So I found some 1.1k resistors in my stock and put them in series (in that correct english btw?
) with R3 and R4 and restarted the setup procedure from the very beginning. Guess what? I managed to get 0.59V on R11 and R12 easily, and about 20mV DC offset on the output.So, tomorrow, I'll get four 1% 3.3K resistors and solder them correctly on the PCB and try to reach 0 DC offset.
Should I do the same on the other channel? I manage to reach 40mV DC offset, but the trimmer are almost full.
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that datasheet shows cbe in the top right diagram.
It is NOT ebc,
Eline and BC5xx are both cbe.
You read the legs from left to right as in reading an english text, with the legs pointing down and the label facing the reader.
Here's how not to read the ZTX.
The label must face the reader.
A T1.25A fuse on a 230Vac supply can power upto 288VA if there is no big current pulse at start up. This is what you would use if you had a soft start circuit using a 90r resistance as the current limiter during the first few cycles of start up.
If you chose not to use a soft start, then T1.25A will usually start a 100VA transformer started direct on line. It may start a 120VA and even a 150VA if the smoothing capacitance is quite small. But expect the fuse to eventually blow after a few hundred cold starts.
Hello everyone,
I can confirm that my problem has been solved by using 3k3 resistors instead of 2k2 for R3 and R4.
Now I have 0.59V on R11 and R12 on both channels, and 6mV and 15.5mV DC offset on the left and right channels respectively.
I think I'm good now
Thank you very much to everyone who helped.
I can confirm that my problem has been solved by using 3k3 resistors instead of 2k2 for R3 and R4.
Now I have 0.59V on R11 and R12 on both channels, and 6mV and 15.5mV DC offset on the left and right channels respectively.
I think I'm good now
Thank you very much to everyone who helped.