Clandestine Pre Biasing Question / Potential Issue

Idlebeach

Member
Hello! I am fiddling with the Clandestine and was messing with the bias and I have a feeling it's not quite right.

According to another thread it should be biased in the 12v ball part - the only issue is that if I turn the trim pot all the way down it can only make it to 17.2v. I also read a comment about measuring your vref and mine was at 22.9 if that ends up being a question for me. My power supply is putting out 9.1v just for more info..

Is it the the 2n5457? Possibly a wrong resistor? Not sure where to go with this one so I thought I'd ask the fine folks over here.

Hope everyone is staying safe and healthy!

Oh yeah - photos! I remembered to take some this time.
 

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Big Monk

Well-known member
Hello! I am fiddling with the Clandestine and was messing with the bias and I have a feeling it's not quite right.

According to another thread it should be biased in the 12v ball part - the only issue is that if I turn the trim pot all the way down it can only make it to 17.2v. I also read a comment about measuring your vref and mine was at 22.9 if that ends up being a question for me. My power supply is putting out 9.1v just for more info..

Is it the the 2n5457? Possibly a wrong resistor? Not sure where to go with this one so I thought I'd ask the fine folks over here.

Hope everyone is staying safe and healthy!

Oh yeah - photos! I remembered to take some this time.

You may have to tweak the fixed resistor down to get more range.
 
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fig

Village Idiot
Where are you measuring the biased voltage?
The pinout is 1=D, 2=S, 3=G..
Pin one is where you read the biased voltage.
You can probably just adjust to ear...but if you can't find a good setting, maybe Big Monk can help you with that resistor swap. (y)
 
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Barry

Well-known member
Where are you measuring the biased voltage?
The pinout is 1=D, 2=S, 3=G..
Pin one is where you read the biased voltage.
You can probably just adjust to ear...but if you can't find a good setting, maybe Big Monk can help you with that resistor swap. (y)

Looks like it actually has a test point between the trimmer and drain
 
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music6000

Well-known member
Hello! I am fiddling with the Clandestine and was messing with the bias and I have a feeling it's not quite right.

According to another thread it should be biased in the 12v ball part - the only issue is that if I turn the trim pot all the way down it can only make it to 17.2v. I also read a comment about measuring your vref and mine was at 22.9 if that ends up being a question for me. My power supply is putting out 9.1v just for more info..

Is it the the 2n5457? Possibly a wrong resistor? Not sure where to go with this one so I thought I'd ask the fine folks over here.

Hope everyone is staying safe and healthy!

Oh yeah - photos! I remembered to take some this time.
Confirm your trimmer has 503 written on the side = 50K
Confirm R3 -3K3 = Orange, Orange, Black, Brown, Brown
Confirm R4 - 1M =Brown, Black, Black, Yellow, Brown
 

Idlebeach

Member
Alright! Let's answer these.

I am using the pad to bias but just to be sure I checked D as well.

The high end on the trimmer gets me to 20.8v

The trimmer does say 503 on the side. I just double checked the resistors mentioned and they have the correct color bands.

If I have to swap out a resistor which one would it be?
 

music6000

Well-known member
Alright! Let's answer these.

I am using the pad to bias but just to be sure I checked D as well.

The high end on the trimmer gets me to 20.8v

The trimmer does say 503 on the side. I just double checked the resistors mentioned and they have the correct color bands.

If I have to swap out a resistor which one would it be?
The next big question is where did you get your 2N5457, do you have others?
The reason for this issue is out of spec or Fake transistor.
Remove R3 - 3K3 & use a temporary resistor around 10K to see if that solves your issue.
 
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Big Monk

Well-known member
The next big question is where did you get your 2N5457, do you have others?
The reason for this issue is out of spec or Fake transistor.
Remove R3 - 3K3 & use a temporary resistor around 10K to see if that solves your issue.

I’ll have to take a look at mine. Mine is a mashup of Clinch EP Pre and the CT Secret Pre built on the Aion Ares.

I believe the Ares delivers a higher voltage from the power rail than the Clandestine so I had to increase the fixed resistor to 10k or greater to get down to 12 vDC.
 

Idlebeach

Member
Thanks for following up!

I got the 2n5457 at Jameco (I think that's what it's called.) I do have a handful of others I can try to swap out to see if it's just a single dud or if they are all bogus. Is there a way to verify they are legit? I do have one of those LCR-T4 testers but I'm not sure how accurate it is.

I will try another couple transistors and if that doesn't work I will play with R3. I appreciate everyone's help!
 
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