simple (?) mod for JOYO Ultimate Drive for BASS?

[jewellworks]

[jewellworks]

The original capacitor had significant impedance, Cx, at most of the instruments fundamental frequencies.
68nF is worth around 4.7kohm at 500Hz! With the Rin at 2.2k making nearly 7k, so with Rf at 19k (! what an odd value !) making the Rf/Rin gain factor a little under x3 (actually x4 total). Below 500Hz, the gain gets reduced from there, but as this is a non-inverting amp, there is always at least x1 gain added to the Rf/Rin value.

So the original design values means the signal is nearly always below the high pass -3dB point, somewhere down the curve and the gain is heavily frequency dependant.

1uF is worth only 300ohm at 500Hz, which is getting down to negligible impedance in the face of the other values.

It definitely changed the basic Rf/Rin gain, making Rin the dominant factor .

The resistor in series with the cap, R3 2k2 in the Ultimate drive scheme, needs increasing. My first instinct would be to try to fit a trimmer pot in it's place 20k to 50k value


===============

i certainly came to the right place... 

i can see my diagram drawing is slightly wrong.  the resistor in series w the 105 cap to ground is 2.2k, not 10k,  (10k was the value on the 1.0 version of the schematic.  i made an assumption it was the same)
so, increase that resistor to...  say, 40k?  50K?  until it calms down and i have control over the gain im looking for?
a trim pot would be nice, but its a trip back to the store...  i probably have resistors at home in this general range already...

[anotherjim]

If you have any kind of pot of at least 20k, you can temporarily wire it in place of the 2k2, adjust it for a cleaner minimum gain sound. Then remove the pot, measure the resistance and fit a fixed resistor close to that.

[jewellworks]

awesome.   
so it wont need to be over 20K?  pretty sure?  ive got 250K guitar pots for sure.  maybe even 100k... 
the gain it has now, when barely cracked open, is about the maximum id want, -not the minimum.  i can play with that with the 100K pot.
awesome.   

[jewellworks]

Well....  with the gain turned up all the way, anything less than a 350k resistor and the output "chokes" up.  Cuts in and out. 
That said, I actually liked the sound of the distortion better when it had a 2.2k and I barely had the knobs cracked open.  So what else could be done?  The overdrive was incredible, I just couldn't turn it down, -or up without fear of destroying the input to my amp.  There must be something inbetween.  Get the fuzz I want with the full range of the bass, and have control over it...  I'm sure it's all a balancing act.
You guys have been very knowledgeable and inspirational.   This is fun.

[jewellworks]

I decided to take a different approach. I put the 2.2 K resistor back in place and instead increased the capacitor from 683 to a 154.  I could have gone to a 224 without it crapping out, but by then the overdrive was just totally ridiculous and I didn't have anything to work with on the low end of the gain knob.  With the 154 in place, I have a useful overdrive at the low end of the gain knob, and stoopid fuzz at the top.
This has been an interesting experiment.   I'm not sure the low end of the bass comes through any better than before, which was my original goal, but it seems that by raising the value of the cap, it allows more low-end to be distorted, therefore,  more fuzz.
I'm sure there is a way to balance it all out better, but this works for me

[DavidRavenMoon]

This is an OCD clone. So it's the same schematic.

What I did to get more useable range out of the gain pot was to solder a resistor across the two putter lugs on the pot to reduce the value. That reduced the gain. Now I can get an almost clean sound on the very low range. But you still can't go much past 11:00 before it's totally saturated. 


Sent from my iPhone using Tapatalk