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I love this overdrive, simply because with the "drive" cranked, it turns into an incredible fuzz. However, the switch and bypass are questionable and the pedal is developing some quirks. Here's a write-up of the circuit that actually came in the box with the pedal, and I was wondering what out there is similar to this thing in design/sound. . .

Could you post the schematic a bit bigger ?

Always interested in good overdrives. In the twilightzone between clean and distortion lie the most interesting sound imho.

It's also the hardest to achieve without tubes.

how work the tone control ?

isn't it odd that the level control is connected to Vbias? wouldn't this put DC on the pot and make it crackle?

This one was getting discussed on HCFX the other day. Got me interested enough in it to want to mess with it on the breadboard. Good to see the schematic here, because I couldn't find it anyplace else online. It definitely has much in common with the Supra Distortion; in fact, they're nearly identical. It would probably be really easy to mod a Supra to be like the Overdrive Plus.
And this is a simple enough circuit, it would be easy to do a true bypass DIY version.

RnFR wrote:isn't it odd that the level control is connected to Vbias? wouldn't this put DC on the pot and make it crackle?

There shouldn't be enough current flowing through it for that to be an issue. The voltage dividing that it does is happening with the AC signal, so the DC is more of a static value with little if any current flow.

devastator wrote:how work the tone control ?

It is interesting. At one extreme it amplified only higher frequencies; and at the other, it amplifies only lower frequencies.

I had an FX50-B Overdrive Plus come in for modding. The owner said he didn't care for the way the tone control worked -- too woofy below 11 o'clock and too shrill above 2 o'clock. He also didn't care for the excessive crunch on the boost end of the drive control. Gotta love when they use a linear taper where a log taper belongs to fool the consumer into thinking there is a boost! That's not a very large range to be confined too, so I did my research. There's a good thread about the FX55-B Supra Distortion (same board, different values) over at DIY ( https://www.diystompboxes.com/smfforum/ ... ic=32262.0 )

I did a lot of tinkering this afternoon, and here's what I ended up with:
D1 & D2 - pair of silicon diodes in series (instead of one)
R3 - 1k (bigger)
C8 - jumper (instead of 0.1uF)
C9 - 100pF (smaller)

Jumpering C8 killed the boost in the tone control stage, but it seemed to make the pedal a lot less obnoxious. The owner was pleased with the result. I would have liked more signal boost lower on the drive control, but that's just me. I think auditioning different values for C8 would likely yield a happy compromise.

RnFR wrote:isn't it odd that the level control is connected to Vbias? wouldn't this put DC on the pot and make it crackle?

It does put DC on the pot, and it's used to bias the op-amp after it. It's a method I frequently use, and doesn't introduce any noise at all, because all the three lugs of the pot are at the same DC potential - there is no current flow. It's DC current, or change in DC voltage that causes the crackle.

The bias voltage is bypassed to ground with a large value electrolytic capacitor (effectively a short to ground for AC) so the bottom of the level pot is at AC ground. The whole pot is "floating" at 4.5V DC. It's just a way of eliminating inter-stage coupling capacitors and the need for additional bias resistors. Consider a few of your favourite circuits, and see how many parts you could eliminate by this method! If you're a Japanese manufacturer and you find a way of saving five parts per item, you're going to do it!

Got a sql server error just then, and the post appeared twice!

I've heard that the DOD FX 50 B is a great 'sleeper" pedal. Does anyone have any experience with it? What is it based on or similar to? Prices seem to be all over the map on 'em.

Thanks!

From diystompboxes.com

http://www.geocities.jp/dgb_studio/circuit/fx50b.png

Here are FX50B and FX80B genuine schematics.

I have owned one DOD FX50B at a time when I wanted to own every dirt pedal ever made. Its voice is nice but the pedal is very noisy. I could really see it being good with better parts tolerances. Its sound is not Tubescreamerish, but more full eq. Its treble is a LOT of white sounding noise. Obviously its positive attributes are on the low gain side.
I finally gave it away @ 10 years ago as a birthday present.
These pedals came out when DOD was not making their best product.

http://www.americaspedal.net/fx50b/