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Old 5th August 2014, 08:42 PM   #1
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Default TNT PreAmble / PreAmbolo problem....!!!!

Hello guys,
I recently finished this preamp taken by TNT TNT PreAmble - DIY solid state stereo preamplifier [English] .... I have a strange problem; start on the preamp connect the source, I rotate the volume pot and does not leave any signal / sound, only after a few minutes (even 3-5 minutes) starts to come out of the sound at a low level and distorted as time passes and the minutes sound comes out regularly and everything works fine ... weird ... Maybe it's a power supply problem? what can I check ??Click the image to open in full size.
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Old 6th August 2014, 07:01 AM   #2
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Quote:
Originally Posted by mprivitera1 View Post
Hello guys,
I recently finished this preamp taken by TNT TNT PreAmble - DIY solid state stereo preamplifier [English] .... I have a strange problem; start on the preamp connect the source, I rotate the volume pot and does not leave any signal / sound, only after a few minutes (even 3-5 minutes) starts to come out of the sound at a low level and distorted as time passes and the minutes sound comes out regularly and everything works fine ... weird ... Maybe it's a power supply problem? what can I check ??
Hi, if you use the power supply as described at the original article, than - I quote from there:

"The time constant of the network at the gate of the MOSFET is in fact higher than 2000sec... that is, the units takes something like 3 hours to reach 95% of the final voltage!!!
...

There is at least one drawback: that is, the unit is best never to be switched off, but must remain on all the time. Given the reduced power consumption, it is not a problem."


So this sort of behavior is normal by design
Switch-on today, start using tomorrow type of an amplifier
Very impractical overkill. Especially taking in account not the best performance of the circuit itself - too much distortion in my opinion.

Cheers,
Valery
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Old 6th August 2014, 10:58 AM   #3
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Quote:
Originally Posted by vzaichenko View Post
Hi, if you use the power supply as described at the original article, than - I quote from there:

"The time constant of the network at the gate of the MOSFET is in fact higher than 2000sec... that is, the units takes something like 3 hours to reach 95% of the final voltage!!!
...

There is at least one drawback: that is, the unit is best never to be switched off, but must remain on all the time. Given the reduced power consumption, it is not a problem."


So this sort of behavior is normal by design
Switch-on today, start using tomorrow type of an amplifier
Very impractical overkill. Especially taking in account not the best performance of the circuit itself - too much distortion in my opinion.

Cheers,
Valery
Thank you, ..... so it is a design problem .... So, it should work well on a regular basis after nearly three hours .... I understand ....

Massimiliano
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Old 6th August 2014, 11:17 AM   #4
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at this point, I have to connect it 24 hours 24 hours in electrical voltage ... to be ready for use ...
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Old 6th August 2014, 11:34 AM   #5
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Quote:
Originally Posted by mprivitera1 View Post
at this point, I have to connect it 24 hours 24 hours in electrical voltage ... to be ready for use ...
Yep.
However, as I mentioned - I think it's an overkill. You don't need such a huge time constant in fact.
Inspiration for perfection should not exceed the sanity threshold
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Old 6th August 2014, 11:50 AM   #6
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Quote:
Originally Posted by vzaichenko View Post
Yep.
However, as I mentioned - I think it's an overkill. You don't need such a huge time constant in fact.
Inspiration for perfection should not exceed the sanity threshold
it is true ...

however, given the modest absorption mA is not a crime to leave under constant voltage
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Old 6th August 2014, 11:57 AM   #7
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Well, actually yes - also possible
Imagine - it's a server in data-center... 24/7 operation
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Old 6th August 2014, 12:05 PM   #8
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OK, made it my signature now
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Old 6th August 2014, 12:45 PM   #9
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the first problem is solved ... now let's go to the second question; the project provides input to the following;

"" First of all, there are a set of trimmers in series to each input: Allows this to Set the sensistivity of each circuit, without modifying too much the overall frequency response: in fact the input impedance is limited by the 47K resistors, and the source Impedance at the jfet gate is limited by the potentiometer. So the bandwidth Should not change too much.

Obviously the 500K trimmers can be left apart, if you do not need them. I thought I could need them for accurate comparison of units with different output levels "" "

I have omitted it, however, so I am a channel with a gain of more than the Grim channel .... I'm undecided whether to insert resistor 47K + 500K trimmers or put the """transistor sockets holdershttp://www.ebay.it/itm/251055413379?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1497.l2649 """
in order to test / change so many JFET by finding two similar sounding ....
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Old 6th August 2014, 02:34 PM   #10
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Quote:
Originally Posted by mprivitera1 View Post
the first problem is solved ... now let's go to the second question; the project provides input to the following;

"" First of all, there are a set of trimmers in series to each input: Allows this to Set the sensistivity of each circuit, without modifying too much the overall frequency response: in fact the input impedance is limited by the 47K resistors, and the source Impedance at the jfet gate is limited by the potentiometer. So the bandwidth Should not change too much.

Obviously the 500K trimmers can be left apart, if you do not need them. I thought I could need them for accurate comparison of units with different output levels "" "

I have omitted it, however, so I am a channel with a gain of more than the Grim channel .... I'm undecided whether to insert resistor 47K + 500K trimmers or put the """transistor sockets holdershttp://www.ebay.it/itm/251055413379?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1497.l2649 """
in order to test / change so many JFET by finding two similar sounding ....
Emmm... I would consider those as two different questions.
Trimmers will allow you aligning the levels for different input sources.
Sockets will allow changing the FETs easily, however I don't think you will hear some difference, as the input FET's source degeneration (read - negative feedback) - R108 = 1k - pretty much eliminates this difference.

Cheers,
Valery
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