Re: DOD - FX51 ( Juice Box )
Postby Bernardduur » 27 Apr 2015, 20:04
I've bought a broken one for dirt cheap........
And I must say the problems with this unit is as many others have descrived in the online fora. It is bright, the controls have sometimes little to change and the overal sound (with a clean amp) is pretty clangy / overly bright. When combined with an already OD'ing amp it works pretty well...........
So I wanted to see what I could change.
The pedal's brightness is part due to the design and part due to the chosen values of the potmeters. All potmeters in this unit are 100k lin and that doesn't work that well for some paramters. The gain (called 'juice') doens't do anything on the first 50%, then suddenly all nice gain structures can be made. Same with the treble (called 'Tang') that does not function between 20 -100%; only the first 20% really change the treble from down and bassy to high and shrill. Time for a change!
I added a 100k resistor parallel to the gain potmeter. Now I can dial in a lot of gain sounds much better.
I added a 1u cap to the 0.22u cap on the opamps feedback loop to get some more lows in the higher gained settings. Works pretty well!!
I added a 47k and a 10k to the treble potmeter (between the lugs); with these changes it now functions from 0 - 75% perfectly!
This made the unit already great, but I wanted more! There is one gyrator for the lows (approx 106.3Hz / Q=1.47) that is tied to a potmeter so the lows can be dialed in. Another gyrator (approx 876.6Hz / Q=1.21) is set to max. I added another 100k lin potmeter to the unit to dial in the mids. This function really makes the pedal shine! In the lower mids setting it becomes a transparant drive pedal, on the higher mids setting it really cuts through the mix (tubescreamer like). Nice!!
One last thing I noticed is the 'clean interference loop' (Q5 - R21) that I put on a switch. I was expecting it to behave like a clean blend and making the pedal sounds fuller and more broad. But I was surprised to find out that switching this circuit in made the sound only worse. It lowers the output and makes the mids stand out more (a more focussed or edgy sound). Switching this circuit off really opened up the pedal and make it more broad sounding with nice lows and highs.
I dunno why this behaves like this. I can only guess a phase interference to make these sounds. I'm glad that I made it switchable!!
there a schematic for that pedal on this page:
http://www.freestompboxes.org/viewtopic ... 7&p=107164