BAJA Mini Juggernaut - Bass Rat with Blend and Boost section

chicago_mike · Post by **chicago_mike** » 15 Nov 2009, 05:40

I pulled the one pot thinking it may be bad..but...everything seems to check but Im just not getting the loop section to work or the fuzz.

The blend control and the master volume work, and if I touch around the jfet, the OD seems to work..im using a J201 and I have it in the correct way.

chicago_mike · Post by **chicago_mike** » 15 Nov 2009, 05:41

iphone pics..I dont know how to take good ones when I need too.

bajaman · Post by **bajaman** » 11 Nov 2012, 05:25

FINALLY found the LONG collar pots for this project on Ebay from hongkongsuperseller - he has the 100k log and 50k linear varieties too.

https://www.ebay.com/itm/290702328357?s ... 1439.l2648
I ordered some of these from him and they arrived in less than two weeks and they fit fine - he even supplies two nuts with each pot (I had to insert 30amp fuse wire through the lugs - no drama though

)
cheers
bajaman

bajaman · Post by **bajaman** » 11 Nov 2012, 23:47

Okay
I was just testing the Juggernaut with the new long collar pots and noticed really nasty asymmetrical clipping on the scope output when feeding a 1KHz sine wave through the circuit.
I checked with my scope probe and discovered that it wasn't in the gain stage or subsequent clamping diodes - it was the source follower buffer FET that was clipping first (well before the diodes

). I measured the DC voltages around the FET ( I used a 2SK117 FET not a 2N5458) and discovered the source voltage to be + 0.26 volts instead of + 3.5 volts (the FET source is fed from + 7 volts DC in this circuit

) which would guarantee the largest signal swing before clipping

Perhaps the specified 2N5458 (also used in the RAT ) biases up properly

but i don't know for sure, because I do not use them.
The solution is very simple though and is well worth considering no matter what FET you decide to use - J201, MPF102, 2N5457, 2SK30A, 2SK117, 2N5458 etc.
Simply replace the 1M gate bias resistor (R15 on Gottfried's diagram, or R18 on Bernard's diagram) with a 2.2M resistor. Then connect another 2.2M resistor from the gate to drain pins of the FET you are using. Now the FET will bias up correctly with + 3.5 volts approximately on it's source pin, AND now the clamping diodes will clip the signal BEFORE the FET clips

Interestingly the RAT uses the same poor biasing 1M resistor to ground - maybe THIS is what gives it it's unique sound perhaps

and not the LM301 op amp

cheers
bajaman

chicago_mike · Post by **chicago_mike** » 26 Nov 2012, 14:48

HMMM

I am using a 2sk170 in mine and will do the 2M2 mod.

and finding long shaft pots is VERY cool Baja! Thanks!!

Tyand · Post by **Tyand** » 21 Dec 2012, 17:38

Dear Bajaman,

first thx for the project and the proposed mod. I've build the juggernaut and everything works fine. As Bassist Im happy for every bass specified effect here on fsb.

Concerning the juggernaut:
Does anyone has an idea how to mod the tone knob? Meaning it should cut the lows from the distortion circuit (before clipping) instead of cutting the highs afterwards. Many bassists, for example me, like the bass and low mid frequencys to be undistorted. Im not advanded in electronics so i'm dependent on circuit layouts.

Thanks and greets from Germany

Tyand