If you have plenty gain without the FET installed, and not enough with the FET in place, then you have the threshold problem...
Jakob E.
Jakob E.
All things G1176 - the new "repost" thread.
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@gswan
Ok I checked something, but I don't know if I had understand gswan.
First I measured the following:
Input Signal = 0,775V
Input Level Control = 0,773V
Ouput Level Control = 0,338V
FET Drain = 0,040V
What do you mean with Vgs? The voltage between Gate and Source? I measured it
Q Bias = 0 then Vgs = 0VDC
Q Bias = full then Vgs = 1,946VDC
@Jakob
What can I do to resolve the threshold problem?
I take a look further in this thread.
Thanks
Ok I checked something, but I don't know if I had understand gswan.
First I measured the following:
Input Signal = 0,775V
Input Level Control = 0,773V
Ouput Level Control = 0,338V
FET Drain = 0,040V
What do you mean with Vgs? The voltage between Gate and Source? I measured it
Q Bias = 0 then Vgs = 0VDC
Q Bias = full then Vgs = 1,946VDC
@Jakob
What can I do to resolve the threshold problem?
I take a look further in this thread.
Thanks
[quote author="gyraf"]If you have plenty gain without the FET installed, and not enough with the FET in place, then you have the threshold problem...
Jakob E.[/quote]
Hello Jakob,
I have checked this thread for the treshold problem, but I don't know what I have to do to resolve this problem. Please help me again.
Thanks,
Bryan
Jakob E.[/quote]
Hello Jakob,
I have checked this thread for the treshold problem, but I don't know what I have to do to resolve this problem. Please help me again.
Thanks,
Bryan
gswan
Well-known member
What is probably happening is that your FET is conducting too soon (with too little signal). This can either be due to mis-calibration of the signal path stage or due to a FET that conductes too early.
I plotted the characteristics of 10 FETs of the same type (2N5457). Look at their spread.
You see some devices turn on early (with very little change in Vgs). These devices may give you a 'threshold problem' where the unit appears to start to compress at very low thresholds. Select a better FET or modify the circuit to compensate for this.
To test this, look at the output signal with the FET in place and then agaion with the FET out. If their is a big difference then this is a likely cause (unless there is a circuit construction error).
You can also measure your compression curves to see what is happening. For example, on my unit:
You can see the thresholds and the compression knee for the different ratios. Check out http://www.axtsystems.com/1176clone/ for more details.
I plotted the characteristics of 10 FETs of the same type (2N5457). Look at their spread.
You see some devices turn on early (with very little change in Vgs). These devices may give you a 'threshold problem' where the unit appears to start to compress at very low thresholds. Select a better FET or modify the circuit to compensate for this.
To test this, look at the output signal with the FET in place and then agaion with the FET out. If their is a big difference then this is a likely cause (unless there is a circuit construction error).
You can also measure your compression curves to see what is happening. For example, on my unit:
You can see the thresholds and the compression knee for the different ratios. Check out http://www.axtsystems.com/1176clone/ for more details.
Hi gswan,
thank you for this detailed answer.
But why is the gain of my device without the FET so weak. I understand the problem with diffent FET's, but the gain I measured is with FET inplace and without the FET. It's all the same.
In your second diagram I saw that the gain without the FET is linear (the gain is 1). In my device the gain is lower then 1. I think that isn't normal.
Greetings,
Bryan
thank you for this detailed answer.
But why is the gain of my device without the FET so weak. I understand the problem with diffent FET's, but the gain I measured is with FET inplace and without the FET. It's all the same.
In your second diagram I saw that the gain without the FET is linear (the gain is 1). In my device the gain is lower then 1. I think that isn't normal.
Greetings,
Bryan
gswan
Well-known member
If it's reduced without the FET in then you have a circuit construction error somewhere. The input amplifier measurements look OK, so you need to concentrate on the following stage.
Check your DC operating point for all the transistors in the next stage, which helps isolate where the problem might be.
Check your DC operating point for all the transistors in the next stage, which helps isolate where the problem might be.
ChrioN
Well-known member
I got a pegging vu meter, both in vu mode and gr mode. I can't get it more close to 0 than -10. I've looked through this whole thread and I've seen tons of people having this problem, but didn't find any solutions.
The compressor sounds great, is dead quiet and compresses good too.
The compressor sounds great, is dead quiet and compresses good too.
gswan
Well-known member
If you've got a pegging meter in GR mode then you have a problem with your GR circuit or calibration. It should sit nicely at 0VU and move down (to the left) when compression occurs.
Hi gswan,
I measured again the DC voltage of the transistors in the pre amp and the line amp. Here are the results:
_____B_______C______E
Q2___1,077___1,755___0,524
Q3___1,755___12,10___1,124
Q4___12,10___29,47___11,49
Q5___4,76____27,7____4,29
Q6___27,7____14,07___28,27
Q7___28,27___14,07___28,91
Q8___14,07___29,43___13,45
Q9___12,77___0_______13,35
I measured again the DC voltage of the transistors in the pre amp and the line amp. Here are the results:
_____B_______C______E
Q2___1,077___1,755___0,524
Q3___1,755___12,10___1,124
Q4___12,10___29,47___11,49
Q5___4,76____27,7____4,29
Q6___27,7____14,07___28,27
Q7___28,27___14,07___28,91
Q8___14,07___29,43___13,45
Q9___12,77___0_______13,35
ChrioN
Well-known member
[quote author="gswan"]If you've got a pegging meter in GR mode then you have a problem with your GR circuit or calibration. It should sit nicely at 0VU and move down (to the left) when compression occurs.[/quote]
As I said, the unit compresses nicely and is working flawlessly except the vu meter behavior.
As I said, the unit compresses nicely and is working flawlessly except the vu meter behavior.
gswan
Well-known member
[quote author="RyanB"]Hello,
I will ask again, because I always have the gain problem. I posted my measured DC voltage and I think they seems to be good. But what can I do now :?:
Please help!
Greetings from germany,
RyanB[/quote]
I'd say you need to get a CRO and a signal generator and start probing.
I will ask again, because I always have the gain problem. I posted my measured DC voltage and I think they seems to be good. But what can I do now :?:
Please help!
Greetings from germany,
RyanB[/quote]
I'd say you need to get a CRO and a signal generator and start probing.
I just began testing my 1176 with Lundahl in/out. It's passing signal fine and all controls is working (including trimpots). However, I can't get any compression. I am suspecting an error in the GR amp section. Here are my notes:
* When I adjust input signal there is no changing DC at point 21.
* DC values in the GR Amp section seems fine.
* Meter and gain does change with Q-bias adjustment. Apparently this verifies that the FET's and release circuit is working.
* I measured AC voltage at point 22. It varies between 0-3 V (depending on input level). After C17 (at the Q12 base) I get only a fraction of this AC voltage. Is this correct?
/Greatful for any help
* When I adjust input signal there is no changing DC at point 21.
* DC values in the GR Amp section seems fine.
* Meter and gain does change with Q-bias adjustment. Apparently this verifies that the FET's and release circuit is working.
* I measured AC voltage at point 22. It varies between 0-3 V (depending on input level). After C17 (at the Q12 base) I get only a fraction of this AC voltage. Is this correct?
/Greatful for any help
gswan
Well-known member
[quote author="Flundran"]I just began testing my 1176 with Lundahl in/out. It's passing signal fine and all controls is working (including trimpots). However, I can't get any compression. I am suspecting an error in the GR amp section. Here are my notes:
* When I adjust input signal there is no changing DC at point 21. It's steady at about -2.45 V.
[/quote]
That's correct. You will notice a change here when you change the ratio switch. It's afixed -DC offset that is summed with the GR output prior to rectification.
[quote author="Flundran"]
* DC values in the GR Amp section seems fine.
[/quote]
That's good.
[quote author="Flundran"]
* Meter and gain does change with Q-bias adjustment. Apparently this verifies that the FET's and release circuit is working.
[/quote]
Gain should not change with Qbias setting, only attenuation. I assume that's what you mean. This is good. If it's biased correctly then the FET is already marginally turned on to attenuate by 1dB without compression.
[quote author="Flundran"]
* I measured AC voltage at point 22. It varies between 0-3 V (depending on input level). After C17 (at the Q12 base) I get only a fraction of this AC voltage. Is this correct?
[/quote]
What frequency signal did you use? Check the value of C17. What DC bias voltage did you get on the base of Q12? Is R61 the correct value?
* When I adjust input signal there is no changing DC at point 21. It's steady at about -2.45 V.
[/quote]
That's correct. You will notice a change here when you change the ratio switch. It's afixed -DC offset that is summed with the GR output prior to rectification.
[quote author="Flundran"]
* DC values in the GR Amp section seems fine.
[/quote]
That's good.
[quote author="Flundran"]
* Meter and gain does change with Q-bias adjustment. Apparently this verifies that the FET's and release circuit is working.
[/quote]
Gain should not change with Qbias setting, only attenuation. I assume that's what you mean. This is good. If it's biased correctly then the FET is already marginally turned on to attenuate by 1dB without compression.
[quote author="Flundran"]
* I measured AC voltage at point 22. It varies between 0-3 V (depending on input level). After C17 (at the Q12 base) I get only a fraction of this AC voltage. Is this correct?
[/quote]
What frequency signal did you use? Check the value of C17. What DC bias voltage did you get on the base of Q12? Is R61 the correct value?
[quote author="Flundran"]
What frequency signal did you use? Check the value of C17. What DC bias voltage did you get on the base of Q12? Is R61 the correct value?[/quote]
Frequency is about 1kHz. I have swapped C17 to another one with no result (1.0 uF polyester). On Q12 base I have +4.47V. Collector + 15.76 V Emitter + 2.92 V
Emitter value seems a bit low, doesn't it? R61 is 470kOhm
What frequency signal did you use? Check the value of C17. What DC bias voltage did you get on the base of Q12? Is R61 the correct value?[/quote]
Frequency is about 1kHz. I have swapped C17 to another one with no result (1.0 uF polyester). On Q12 base I have +4.47V. Collector + 15.76 V Emitter + 2.92 V
Emitter value seems a bit low, doesn't it? R61 is 470kOhm
gswan
Well-known member
Yes, it is low. It should be one Vbe lower than Vb, which would be around 4V.
Check the value of R63, R65 and R68. Also check that you have C19 in the correct way around. What voltage do you have on the emitter of Q13?
Check the value of R63, R65 and R68. Also check that you have C19 in the correct way around. What voltage do you have on the emitter of Q13?
[quote author="gswan"]Yes, it is low. It should be one Vbe lower than Vb, which would be around 4V.
Check the value of R63, R65 and R68. Also check that you have C19 in the correct way around. What voltage do you have on the emitter of Q13?[/quote]
The values of R63, R65 and R68 is right (I read off the color codes on the resistors). C19 is turned the right way. Here are voltages around Q13:
Collector 30.23 V
Base 15.76 V
Emitter 15.18 V
Check the value of R63, R65 and R68. Also check that you have C19 in the correct way around. What voltage do you have on the emitter of Q13?[/quote]
The values of R63, R65 and R68 is right (I read off the color codes on the resistors). C19 is turned the right way. Here are voltages around Q13:
Collector 30.23 V
Base 15.76 V
Emitter 15.18 V
gswan
Well-known member
The voltages around Q13 seem OK.
Don't rely on the colour codes, measure the values.
You have a problem around the emitter of Q12. Look for solder shorts and wrong value components in this area. Check the transistor type and orientation as well.
Don't rely on the colour codes, measure the values.
You have a problem around the emitter of Q12. Look for solder shorts and wrong value components in this area. Check the transistor type and orientation as well.
I lifted a couple of resistors around the GR amp, and they all seemed correct. When I powered the 1176 up after this, It suddently worked. Perhaps a bad solder joint then... According to my signal generator it works fine now!
Earlier today I ran a signal thru it from a Digi002's line output. The signal to the 1176 was very weak. I use the transformer balanced input, so my first thought was: Is the digi002's outputs balanced? When I measured the output of the digi002 I could NOT get signal between pin3 and pin1. Only pin2 and pin1. According to the digi002 manual the 1/4" outputs are balanced. Is this what is called "impedance balanced" output?
Earlier today I ran a signal thru it from a Digi002's line output. The signal to the 1176 was very weak. I use the transformer balanced input, so my first thought was: Is the digi002's outputs balanced? When I measured the output of the digi002 I could NOT get signal between pin3 and pin1. Only pin2 and pin1. According to the digi002 manual the 1/4" outputs are balanced. Is this what is called "impedance balanced" output?
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