DOD fx75b input buffer

[R.G.]

Oh, it'll clean your pipes. Derek Lowe is a professional chemist and in his "Things I won't work with" section he describes chlorine trifluoride:

"The compound also a stronger oxidizing agent than oxygen itself, which also puts it into rare territory. That means that it can potentially go on to "burn" things that you would normally consider already burnt to h*ll and gone, and a practical consequence of that is that it'll start roaring reactions with things like bricks and asbestos tile."

Apparently it will also set fire !! to things like wet sand. Sure to clean off some tarnish...

[Baran Ismen]

Beating my dead horse here with a "what if".

Today I had some free time at work and checked possible CE-2 mods that I've made recently, found some and will apply them ASAP. I've also noticed that it has a quite similar layout to FX-75B, as they both rely on MN chips.

I was just wondering if it would be possible to increase the LFO speed of this pedal. In CE-2, there's a 1M resistor (which is suggested by Mark Hammer to be replaced with a 470K for a faster LFO) that regulates the LFO speed between one of the op-amp's inverting & non-inverting leads. I, however, could not find any similarity in FX-75B's schematic in this regard. Of course, I don't expect them both to be the same, yet I thought maybe I'd find out without asking you guys, but I could not Changing C16/25pf with a higher value on 3101 would give me probably a deeper flanging effect, which I already can somehow get with the internal trim pots.

My best bet would be playing around with the R54, but it's not connected to wiper, anyway.



This the CE-2's Rate section.

[ElectricDruid]

The best bet would be to change C11, the non-polarised 15u cap in the LFO. That'll change the entire LFO range without messing with anything else too much.

Changing things around the 3101 clock will change the frequency range that the flanger's sweep covers (maybe - it's probably maxxed out already) but won't alter the actual *rate* of the sweep.

The only confounder is that C27/4u7 looks like it's applying a bit of filtering to the LFO wave to me, and limiting the depth a bit at higher frequencies, possibly. Depending what you do, you might need to tweak that too. Going slower it probably won't matter. Going faster, it might.

[Baran Ismen]

The best bet would be to change C11, the non-polarised 15u cap in the LFO. That'll change the entire LFO range without messing with anything else too much.

Changing things around the 3101 clock will change the frequency range that the flanger's sweep covers (maybe - it's probably maxxed out already) but won't alter the actual *rate* of the sweep.

The only confounder is that C27/4u7 looks like it's applying a bit of filtering to the LFO wave to me, and limiting the depth a bit at higher frequencies, possibly. Depending what you do, you might need to tweak that too. Going slower it probably won't matter. Going faster, it might.

The second I read the #17 answer in this link, refreshed this page and saw the same reply from you   

https://www.talkbass.com/threads/dod-fx72-flanger-speed.1506922/

So, the LFO speed is in direct proportion to cap value? Bigger = faster or vice versa?

[ElectricDruid]

So, the LFO speed is in direct proportion to cap value? Bigger = faster or vice versa?

Bigger = slower, always. It's an RC time constant, so it's always the product (e.g. multiply them) of the R and C. The R is the 500K speed pot in this case.

[Baran Ismen]

So, the LFO speed is in direct proportion to cap value? Bigger = faster or vice versa?

Bigger = slower, always. It's an RC time constant, so it's always the product (e.g. multiply them) of the R and C. The R is the 500K speed pot in this case.

Cheers much, Tom, appreciated much as always!

[Baran Ismen]

Made the following revisions yesterday, and it's a success!

- Added 33nf cap between pin3 and pin7 of CD4007 to prevent auto-on of the pedal when powered up, now it does not.
- Changed C11 with a 10uf cap, max. LFO speed increased a bit yet it still has a huge spectrum
- Changed C16 with a 33pf cap (clock gen.), depth is a bit better now.