# 2N5485 Son of Ben



## okstateblues (Jul 30, 2020)

Looking to finish a Benson build and need some assistance. I have 2N5485's and just want to double check that they will work if installed according to the silkscreen on the board. Any feedback would be greatly appreciated.


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## Nostradoomus (Jul 30, 2020)

The pin out is the same as j201, I’d still use sockets though!


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## okstateblues (Jul 30, 2020)

Ok good deal thanks!


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## temol (Jul 30, 2020)

Why are you going to use 2n5485 instead of j201? Pinout is the same but parameters are different.


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## okstateblues (Jul 30, 2020)

It's all I had on hand


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## temol (Jul 31, 2020)

I've created SOB ltspice model. Let's assume J201 with Vp 0.76V and 2N5485 with Vp 2V.
Then we check build document - set Q1 trimmer to 2k and Q2/Q3 drain voltage to 4V.
There's Q1 10k drain resistor + 2k (trimmer) so we have 12k total.

With J201 as a Q1 we have 5.6V on a drain. With 2N5485 there's only 0.77V...
Let's move to Q2/Q3. To get 4V on drain with J201 we need around 18k. But with 2N5485 we won't ble able to set 4V even with trimmer set to zero. In order to set 4V with 2N5485 we need only 3k6 (remember - there's already fixed 10k).  So you'd have to put 1k resistors (or lower value) or even jumper them (btw - with 50k trimmers resistors are superfluous). Back to Q1. To set the same voltage as with J201 - 5.6V we have to lower overall drain resistance to 2k4 (was 12k).
But voltage is not the only factor here. So let's inject a signal into the circuit. 660Hz, 1V p/p.
And now some simulation results. Blue plot - J201, green plot  2N5485, all controls maxed.

Q1




Q2




Q3




Output




Frequency response




In my opinion - if you replace J201 with 2N5485 it's not SOB anymore. 

T


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## okstateblues (Jul 31, 2020)

Fair point. I'm in the process of going the surface mount route with 201s so I may swap in the near future.


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## okstateblues (Sep 5, 2020)

Quick zombie revival are j113's suitable replacements for the j201?


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## temol (Sep 5, 2020)

J201's are available in SMD - MMBFJ201. So why even bother with substitutes?


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## phi1 (Sep 5, 2020)

I gotta agree With temol... getting used to the smd adapter boards makes life so much easier and opens doors to lots of projects with j201s and 2n5457s.


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## Robert (Sep 5, 2020)

These are a regularly stocked item now:








						MMBFJ201 JFET (Pre-Soldered) - PedalPCB.com
					

JFET




					www.pedalpcb.com


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## phi1 (Sep 5, 2020)

Robert said:


> These are a regularly stocked item now:
> 
> 
> 
> ...



cool. Just curious (if you care to share), are you hand soldering these, or ordering them re-flowed from a shop?  I don’tknow the cost for that process, but seems it would save a ton of time if making on a large scale.


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## okstateblues (Sep 5, 2020)

temol said:


> J201's are available in SMD - MMBFJ201. So why even bother with substitutes?



I tried the surface mount way and burned legs off a few of them. Its really frustrating.


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## okstateblues (Sep 5, 2020)

Robert said:


> These are a regularly stocked item now:
> 
> 
> 
> ...



I may go that route. I have the boards and the SMD's but there has the be a trick to getting these miunted and not burn off a leg.


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## benny_profane (Sep 5, 2020)

For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.


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## okstateblues (Sep 5, 2020)

benny_profane said:


> For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.




I will give it another try and report back with my results.


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## Robert (Sep 5, 2020)

phi1 said:


> cool. Just curious (if you care to share), are you hand soldering these, or ordering them re-flowed from a shop?



Previously they were hand soldered, which is why there were about 20 - 40 available every couple months.      


Now they're pick-and-placed, so there's plenty to go around (and better quality soldering).


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## soothsayer86 (Sep 8, 2020)

benny_profane said:


> For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.


This is the method I use, makes it super easy. Also, using blue tack to hold the board in place while soldering is extremely helpful and makes the process much less frustrating.


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## okstateblues (Sep 8, 2020)

I have given it another shot. Hopefully this works for my Benson clone. I think this is what is killing my tone. Here's to hoping!


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