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Hello there, I’m having a few issues after putting together the three-time champ.
the LED won’t turn on.
I was attempting bias the 2n5457s to 5v, but the lowest I can get is 7 ish, and sometimes it can’t that low either
when I can get signal to pass, the volume and gain pots are reversed. Things get louder as I turn them down. Any thoughts on where I messed up? The trim pots are 10k, though I didn’t verify that with a DMM.
I believe the LED anode is the center pad on D1.
As Fig says your LED anode + is soldered to a ground pad if it’s the white wire
I’d say the best thing to do is place your white wire in D1 middle solder pad and run a wire from your LED cathode to the pad you’ve currently got your white wire soldered to
Then solder the black wire removed from your LED cathode to S5 leaving the other end where it is 3PDT lug 5, but snip off the strand of bare wire it looks like it may be touching 3PDT lug 6, S6 can be left empty because you are not using a bi colour LED you already have your current limiting resistor soldered to the main pcb (R10)
Your yellow wire already goes to S5 as it should
Your pots are wired the wrong way around they should go to the underside of the pcb if you look at the left pot solder pads you will see a small 1 for pot lug 1 here’s how the pot lugs are numbered for future reference
If it’s a build for yourself I would just leave them working backwards rather than risk damaging solder pads trying to desolder them pcb mounted pots are tricky to desolder if you are confident with desoldering then have a go but it’s not really a problem having them work backwards imho
If it sounds good to you the FET biasing isn’t written in stone it’s more of a guide
As it says in the build doc you’d want Q1 and 2 biased slightly higher than Q3 if you can do that and it sounds good I wouldn’t worry too much about the voltage
Your trimmers should have a 3 digit value code 10K would be 103 the first 2 digits being the significant numbers and 3rd the amount of zeros = 10 + 3 zeros = 10,000
You can get the desired Bias by adjusting R3, R6 and R9 currently all 1k if you cannot get there with the 10K Trimmer. Do this by increasing resistance to say a 10k or anything close to that. You may want to start with just R3 before you de-solder R6 and R9 and test one Q at a time.
This is caused by tolerance of parts. Most of the time this works out but not always.
Note: You will not be able to test and bias a board that is not fully populated.
The drill template in the Doc shows pots under the board. It is an easy mistake to make. Just remember we have a silkscreen on all boards to indicate lug numbers and thus the orientation. I see why you wanted them to be mounted that way to fit under top mounted jacks.
Wow you folks are amazing, thanks Fig Billy and Barry! I’ll get started on these right away. Definitely can see where my wiring errors were now, and I’ll play a bit with the resistors and take my time this time and feel it out.
So far so good!
LED now works, so that’s problem 1 solved.
Required the pots, so now they turn the correct way. Problem 2 solved.
switched R3 to a 10k and that put the voltage on q1 hovering around 9v. So now it has a 100 ohm in there.with q3, when reading the bias, it changes a lot depending on where the drive control is set. Is there a standard position the drive knob should be set when biasing transistors?
Adding more resistance should allow you to Bias to half the supply voltage. Not reducing it.
Make sure that the board is fully populated before you test.
Well it works great now. I changed R3, R6, R9 down to 100 ohms and that got me right to where I needed, bias wise. I put in three J201s (from here of course) and it sounds really great.
Not sure why the bias went down after lowering the resistors, but I’m happy with the results so far!
I am glad too.
Curious you had 1K + 10K Trim (11,000 ohms) and 7v bias – then 100R +10K Trim (10,100 ohms) then 5v Bias.
So the only actual needed resistance was several hundred ohms using J201s?
Was there some other change or difference you can think of?
I am assuming you tried to turn the trimmer both ways with each change?
The J201 substitution I imagine would have made up some of the difference.
Yeah those were the only changes I made. I found it curious too, because the tone drastically changed as well. Before, it was very much like a brighter fuzz, which I just guessed was because of the bias, I don’t know a lot about different transistors though.
I did try turning trimmers both directions. Initially, the lowest I could get was 7ish, and that was with the trimmers turned all the way clockwise.
is it possible something else was not connecting?
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Small bear sells a full featured meter that you can plug transistors into and measure the HFe. I have noticed a drastic difference between those I’ve bought here and those bought elsewhere, and even drastic differences within a single lot. I’ve transitioned to almost exclusively buying Qs from Barry..and testing every other one I get. Glad you got it working, and you are right – these guys are great!
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