Son Of Ben Q2 Biasing Issue

Stephenthegun

Stephenthegun

Member
I built the Son of Ben and used what are probably not genuine J201's. I got the biasing close but not quite on Q1, however, Q2 and Q3 were in the low 3v range. The pedal sounded good, but I was hoping I could make it better, so I ordered the surface mount J201's. I installed them today and got Q1 and Q3 bang on at 5.1v and 4v but now I cannot get Q2 to drop below 9v. With the trim pot all the way down Q2 reads 9.10v and with it all the way up it reads 9.15v. What have I done? Help!
 
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benny_profane said:
Check for continuity between the circles and verify that the SMD part is installed and making connections. The only jumper you’ll probably need is the light blue line between R8 (1k) and C5 (10u).
Click to expand...
I actually ruined the SMD part while trying to desolder, so I am going to reuse one of the fake J201's I bought that should go high enough to reach 4v. Sorry, for the confusion.
 
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Stephenthegun said:
Yes, @music6000 the picture was really helpful. The colour-coded picture was probably necessary for my thick skull to understand. With this stuff I really need it spelt out like I am a small child.
Click to expand...
You could use the Blue jumper as drawn & put the J201 to the 3 Resistors all from the back side of PCB.
Just make sure the J201 is oriented the right way !!!!

Son Of Ben J201 BlueTrace - Transistor Fix .jpg
 
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music6000 said:
You could use the Blue jumper as drawn & put the J201 to the 3 Resistors all from the back side of PCB.
Just make sure the J201 is oriented the right way !!!!

View attachment 18266
Click to expand...
I am about to try this method now. I tried the other way, using jumpers, and it is really ugly but I thought it should work. It doesn't. Does anyone see a glaring problem other than my board looks like an absolute dumpster fire at this point?
 

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music6000 said:
Your J201's may be fake???
Try This, It's more user friendly :
Test voltage at D ?
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I think the J201s are fake. They worked previously though (albeit not quite to the voltages I needed). I have tried soldering everything the way you suggested and it still isn't working right. I am really confused as to why this isn't working. I am still unable to get less than 9.1v from the drain of Q2. I plugged in the pedal to my amp just to see what would happen and it was really really sputtery. Perhaps I have wired something wrong? Any ideas?
 

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Stephenthegun said:
I think the J201s are fake. They worked previously though (albeit not quite to the voltages I needed). I have tried soldering everything the way you suggested and it still isn't working right. I am really confused as to why this isn't working. I am still unable to get less than 9.1v from the drain of Q2. I plugged in the pedal to my amp just to see what would happen and it was really really sputtery. Perhaps I have wired something wrong? Any ideas?
Click to expand...
If you got them off Ebay, they are probably fake, Do the other 2 bias to 4.5v?
Where are you on planet Earth?
 
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music6000 said:
If you got them off Ebay, they are probably fake, Do the other 2 bias to 4.5v?
Where are you on planet Earth?
Click to expand...
I got the through-hole ones from Banzai. I purchased the SMD from Musikding. The through-hole parts never made it all the way to full bias. two of them were around 3.1V. on Q2 and Q3 and the other was around 4.6V. at Q1. I got the SMD parts installed and soldered correctly in Q1 and Q3 and they are set at 5.1V for Q1 and 4V. for Q3.

I am in Ireland.
 
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Stephenthegun said:
I got the through-hole ones from Banzai. I purchased the SMD from Musikding. The through-hole parts never made it all the way to full bias. two of them were around 3.1V. on Q2 and Q3 and the other was around 4.6V. at Q1. I got the SMD parts installed and soldered correctly in Q1 and Q3 and they are set at 5.1V for Q1 and 4V. for Q3.

I am in Ireland.
Click to expand...
Have you tried here:

Semiconductor: J201 (J 201) - N-CHANNEL GENERAL PURPOSE AMPLIFIER...

j 201, n-channel general purpose amplifier case: to-92 transistor
www.donberg.ie www.donberg.ie
 
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Sorry it took me so long to get my measurements taken. I wasn't able to get to the pedal the last couple of days.

Yellow is measuring between 9.12-9.17 as the trim pot is turned in either direction
Red is only measuring a few mV and bouncing around inconsistently.
 
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