Hi PP
I followed your instructions to use 100R resistor for R2 and eliminate C18 then I can adjust R8 50 Ohm trim pot to read 0.3V at output. I have made audition for few hours. The sound quality of this pre-amp is wonderful. It beats my Pioneer vintage pre-amp which was one of the top model Japanese made pre-amp in the 70's. I feel very happy of the sounding of this pre-amp but unfortunately one of the channel has some hum noise. I still have to put some efforts to fix this problem. Other than this everything else of this pre-amp makes me very satisfy. It is a good pre-amp that worth to build as it is a simple design with very few parts and components. The cap on the top of the attached image has already been moved.
Thank you again for your kind advice otherwise I will not be able to fix the problem.
I followed your instructions to use 100R resistor for R2 and eliminate C18 then I can adjust R8 50 Ohm trim pot to read 0.3V at output. I have made audition for few hours. The sound quality of this pre-amp is wonderful. It beats my Pioneer vintage pre-amp which was one of the top model Japanese made pre-amp in the 70's. I feel very happy of the sounding of this pre-amp but unfortunately one of the channel has some hum noise. I still have to put some efforts to fix this problem. Other than this everything else of this pre-amp makes me very satisfy. It is a good pre-amp that worth to build as it is a simple design with very few parts and components. The cap on the top of the attached image has already been moved.
Thank you again for your kind advice otherwise I will not be able to fix the problem.
Attachments
Hi guys
Eventually I fixed the hum problem in the other channel by using a 150 Ohm resistor for R2. In other word I am using 100 Ohm for one channel and 150 Ohm of the other channel. The sound of the amp is great.
Hi PP
What problem you have noticed from the PSB layout?
Hi darkfenriz
The error is fixed.
Thanks
Eventually I fixed the hum problem in the other channel by using a 150 Ohm resistor for R2. In other word I am using 100 Ohm for one channel and 150 Ohm of the other channel. The sound of the amp is great.
Hi PP
What problem you have noticed from the PSB layout?
Hi darkfenriz
The error is fixed.
Thanks
The thing that R2 is different in the two channel is normal, It's not normal if the two R2 values are equal. I have written: "....... Infact, for a regular working it's necessary an appropriated selection of Q3 and Q4. ......" . In order to avoid this selection It's possible to add a resistor to R2
The shunt capacitors are not present in the two schematics , but these are important, this is a problem. You should add two 1nF capacitors for channel. One capacitor should be inserted from the op amp's positive voltage supply to the ground. The second capacitor should be inserted from the op amp's negative voltage supply to the ground. The other channel should be modified in the same manner.
Hi PP
Thank you for your kind advice. Actually I have noticed the shunt caps on other pre-amp circuits. I will add these caps to my amp tomorrow but in the meantime would you please tell me what is the purpose and benefits by adding these caps. I would like to know more from practice.
Regards
Chan
PS: I re-positioned the parts and the components on the circuit board to make all the parts look fully matching and balancing and assembled the pre-amp into an aluminum die cast chassis. Please see attached photo.
Thank you for your kind advice. Actually I have noticed the shunt caps on other pre-amp circuits. I will add these caps to my amp tomorrow but in the meantime would you please tell me what is the purpose and benefits by adding these caps. I would like to know more from practice.
Regards
Chan
PS: I re-positioned the parts and the components on the circuit board to make all the parts look fully matching and balancing and assembled the pre-amp into an aluminum die cast chassis. Please see attached photo.
Attachments
Hi Chan,
Could you check what is the voltage drop across below resistors:
R1
R2
R7
R4
R5 & R6 (should be very close)
Did you match the Idss of Jfet before you put into the circuit?
My best guess is the current through R1 is about 2ma, R7 is about 8-10mA and Q5/Q6 about 8-10mA. Then this op-amp should be working properly.
Spencer
Could you check what is the voltage drop across below resistors:
R1
R2
R7
R4
R5 & R6 (should be very close)
Did you match the Idss of Jfet before you put into the circuit?
My best guess is the current through R1 is about 2ma, R7 is about 8-10mA and Q5/Q6 about 8-10mA. Then this op-amp should be working properly.
Spencer
from the analysis of the circuit it's result that if the current through R1 is about 2mA then R7 will be around 6-6.5 mA.
For the current through R7 = 8-10 mA it result that the current through R1 will be 2.5-3.5 mA.
For the current of Q4, Q5, Q6, Q7 the right goal is the values that spencer has written. Fixed these current it's possible to set R2
for R1 current equal to 2.5-3.5 mA.
Regarding to the 1nF capacitors, the opamp sound could be clear, they assure that the op amp it works correctly avoiding vhf oscillations reducing the power supply cable impedance or/and power supply vhf impedance.
For the current through R7 = 8-10 mA it result that the current through R1 will be 2.5-3.5 mA.
For the current of Q4, Q5, Q6, Q7 the right goal is the values that spencer has written. Fixed these current it's possible to set R2
for R1 current equal to 2.5-3.5 mA.
Regarding to the 1nF capacitors, the opamp sound could be clear, they assure that the op amp it works correctly avoiding vhf oscillations reducing the power supply cable impedance or/and power supply vhf impedance.
Hi Spencer
Welcome to joining us. I measured the following figures from the pre-amp:
R1 (1K) = 2V
R2 (100R) = 0.25V
R7 (330R) = 2V
R4 (10R) = 0.1V
R5 (10R) = 0.05V
R6 (10R) = 0.05V
I do not have the instrument to match the Idss of the JFets but I am going to do that for the next version as soon as I know more technical data of this amp.
The followings are current readings I got from the amp:
R1 = 6.5ma
R7 = 6ma
Q5 2SK170 (D & G pins) 6ma & Q6 2SJ74 1.6ma
It seems some of the measurements are too far off from your standard so please advice what action should I do to correct them.
Thanks
Welcome to joining us. I measured the following figures from the pre-amp:
R1 (1K) = 2V
R2 (100R) = 0.25V
R7 (330R) = 2V
R4 (10R) = 0.1V
R5 (10R) = 0.05V
R6 (10R) = 0.05V
I do not have the instrument to match the Idss of the JFets but I am going to do that for the next version as soon as I know more technical data of this amp.
The followings are current readings I got from the amp:
R1 = 6.5ma
R7 = 6ma
Q5 2SK170 (D & G pins) 6ma & Q6 2SJ74 1.6ma
It seems some of the measurements are too far off from your standard so please advice what action should I do to correct them.
Thanks
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