Lowered Expectations - bass OD

[bobhill]

As promised yesterday, here is the bass version of the overdrive pedal I posted yesterday. http://www.ssguitar.com/index.php?topic=2679.0

A few notes on the differences between these pedals. The bass version uses green 3mm led's instead of the reds I used in the guitar version, just for the slightly higher forward voltage of the greens. With the higher output from bass pups, I just figured it would keep things from being too harshly clipped. I also went to the 4558 op-amp instead of the LM1458 I used in the guitar version because while the 1458 produced the smooth grind I was looking for in my guitars, the 4558 has a bit more harshness on the guitar, but adds that nice bit of grit to the bass.

When I was first asked to do a bass version of the pedal, I took the easy way and just recalced the filters to drop them an octave. This, while somewhat pleasing, had the same problem as most bass OD pedals on the market, as you drop down the neck, the grind disappears on the lower register. So I went back and re- did things to drop two octaves, and when I saw on the scope that clipping started at 17 hz, I plugged in the Squire P-bass and liked what I heard. Boxed it up, demoed it and had to build 10 more. :cheesy: One of my bass friends described it (Aguilar SS bass head) as giving him back the sound of an Ampeg SVT that is severely ticked off. Both it and the guitar version are in a pair of local recording studios, so I think the sound came out ok.

The PNP is the same for both versions, I've never made a layout sheet for the bass version, just scribbled the values next to the guitar layout. I've never made an off board wiring guide for either, after making close to 30 OD's of these the wiring becomes automatic, so I need to take the time to throw one together. Promises, promises. Enjoy...

Bob

[bobhill]

And a shot of the finished product...

[Roly]

Nice job Bob.   :dbtu:

[J M Fahey]

Real cool.
Congratulations.

Hey Guys, let's give Bob a few chip points by clicking "informative", that's the way to "like" here.  :dbtu:

[bobhill]

Thank you gentlemen. Coming from you, that means a lot.

[phatt]

Hi Bob,  Neat box :tu:

Just a point,
The hidden gotcha is there is a SNR penalty for dropping off the buffer at the front end of those TS type circuits.

Used alone, The noise may not be an issue but chain a few pedals and it starts to add up.

I'm no teck freak,,  just a hobby guy and it took quite a few builds and gnashing of teeth (reading lotsa books helped) before I saw the hidden issue.

Cheers, Phil.

[bobhill]

Hi Phil,

I think you will find that SNR problems tend to creep up more when the entire signal chain suffers from the "True Bypass" marketing bit. I know that people use pedals now a lot differently than we did back in the late 60's through the 70's before anyone decided a 1/4" piece of wire was worth many dollars retail, but I tend to use a fairly small signal chain that includes one buffered pedal at the end of the chain, so I don't get a lot of noise issues. Depending on just how many devices are chained together, it doesn't seem to get very severe. And if I have that many, it is time for subchains with a looper.

And for the record, back in the day my chain was only 5 effects, and I was considered unusual. Of those 5, only one (Craig Anderton's Fresh Fuzz) was true bypass, all the rest (Morley Power Fuzz Wa, Phase 90, Ibanez FL303 flanger and Echoplex) are all buffered or always on. Of course, all these fed into a Marshall Superlead full stack, so I may not have noticed any noise I wasn't making on purpose. Hey, isn't rock supposed to be loud (he said with his tinnitus in both ears). No, we didn't pay any attention to hearing protection back then either. So between the Navy, 15 years of playing verrrry loud music and over three decades on a major freight railroad, well let's just say that I don't tune pianos anymore.

That is in a large part why I started building pedals, to try and recapture that sound at more reasonable levels. About the only thing I occasionally miss is being able to feel the music in the thoracic cavity as well as hear it, but I would just as soon keep the hearing I have left.

Bob