# Benson Preamp - Microphonic J201's?



## BeeSharp (Mar 1, 2021)

Hi,

I just built my second Benson Preamp and it has the same problem as the first.  It has a noisy background (just high noise floor - nothing crazy).  When I touch the Q2 J201 (which is a SMT mounted one from PedalPCB), you can clearly hear my touching it like a microphonic preamp tube.  Any thoughts?

Thanks!


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## BeeSharp (Mar 1, 2021)

After fooling with it a bit more and reflowing some solder, the 100nF input cap and some others also seem microphonic.  You can lightly flick them and here a thump thru the amp


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## BeeSharp (Mar 1, 2021)

Actually, everything seems microphonic - resistors, caps, etc.


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## BeeSharp (Mar 13, 2021)

I tried to fix these again, but no luck.  Does anyone else have background noise with the Benson?


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## giovanni (Mar 13, 2021)

What power supply are you using? I don’t think the components are microphonic, I think when you tap on them something that’s acting like an antenna is shaking and picking up different noise. The question is: where’s the antenna? Power supplies come to mind but other things may be doing the same. Is the circuit in the enclosure?


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## BeeSharp (Mar 17, 2021)

The PS is a Strymon Zuma with an OJai extension.  The other pedals seem fine with it.  It was in the enclosure.  Thanks


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## music6000 (Mar 17, 2021)

Show some detailed Pictures, front & back of PCB.
They are worth a Thousand words!


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## Chuck D. Bones (Mar 18, 2021)

BeeSharp said:


> Hi,
> 
> I just built my second Benson Preamp and it has the same problem as the first.  It has a noisy background (just high noise floor - nothing crazy).  When I touch the Q2 J201 (which is a SMT mounted one from PedalPCB), you can clearly hear my touching it like a microphonic preamp tube.  Any thoughts?
> 
> Thanks!


Don't touch it?  Ha ha ha.  Probably a bad solder joint.  Inspect everything under magnification.  Some amount of noise is normal when you crank the gain.  SMT transistors should not be microphonic.  Ceramic caps can be.

And like Music6K said, pictures please.


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## BeeSharp (Mar 22, 2021)

Sorry for the delay and thanks for the help.  Here are the pics!


https://imgur.com/8ifwgN5




https://imgur.com/xzbNGDD




https://imgur.com/GCYPvED


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## BeeSharp (Mar 22, 2021)

I'm using a Hakko at around 750F


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## Chuck D. Bones (Mar 22, 2021)

I see what you did there with the two 1M resistors and the diode on the back side.  Very clever solution!

Trimpots can be microphonic.  You might try twisting them back & forth a few times, then reset them to their previous positions.  

Are you sure you have clearance between the solder tits and the 1M dual pot?

Check the clearance between the bottom of that huge-ass filter cap and diode's solder tits.  (yes, it's a legit term, I didn't make it up).

The solder joints on the middle JFET might be cold.  You can tell better than we can.  Doesn't look like the solder wetted to all three leads.


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## BeeSharp (Mar 22, 2021)

Chuck D. Bones said:


> I see what you did there with the two 1M resistors and the diode on the back side.  Very clever solution!
> 
> Trimpots can be microphonic.  You might try twisting them back & forth a few times, then reset them to their previous positions.
> 
> ...


Thanks Chuck!  I did see a little "tit" sticking up and potentially touching the dual gang pot.  I plugged it back in, I can't remember if this happened before, but with the pedal back in the enclosure, when I touch the dual gang pot's shaft, I get a buzzy sound...The big electrolytic is not touching the 5817 diode tits. I reflowed the solder on the middle jfet


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## Chuck D. Bones (Mar 22, 2021)

That hum problem is usually caused by the pot case not being properly grounded.  Make sure the pots and jacks are all making metal-to-metal contact with the enclosure and the jacks are grounded to the board. The good news is that your case is bare metal inside, no paint scraping req'd.


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## BeeSharp (Mar 23, 2021)

Chuck D. Bones said:


> That hum problem is usually caused by the pot case not being properly grounded.  Make sure the pots and jacks are all making metal-to-metal contact with the enclosure and the jacks are grounded to the board. The good news is that your case is bare metal inside, no paint scraping req'd.


I made sure all pots are grounded well and touching the enclosure, but it still has the same noise and microphonics that they other I built does.  Here is a short video:


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## Chuck D. Bones (Mar 23, 2021)

Sounds like you have the gain cranked and there might be a loose connection.


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## giovanni (Mar 23, 2021)

Are you sure you don’t have cold solder joints that are sorta rattling and causing what sounds like microphonic components?


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## vittoles (Jul 21, 2022)

Hi, did you find the problem?
got the same on an other pedal.
thanks


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## BeeSharp (Aug 7, 2022)

I built two and had the same problem....Probably my fault, but I haven't found it yet...I moved on and have a few to return to


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