Bass OD – Too much drive.

[MathU41]

So I built a Bass OD, and it seems to work horribly right.
With the drive turned to 0, it cuts out. Whatever, I don’t plan to have it turned on for no effect.
Then I can get to maybe 10% before it turns from ‘hair of drive’ to ‘cranked fuzz’.
Even with the bass volume rolled off, if any volume goes into it, I get sputtery, inarticulate grinding sounds, with notable ‘steps’ between slight drive to broken up and then a point where it sputters to even harsher noise.
I can’t blame the circuit, and apparently can’t blame my work (this time) because it’s definitely doing what it’s supposed to, just too much of it.
Currently it’s 3 J113s adjusted to 5.9v. No notable difference from 5.5v.
Does it work well enough to keep rolling those down under the suggested 5-6v? If not, I know the notes say to try different transistors, but I have no idea where anything stands on a ladder of gain.

[Billy]

Yes it’s definitely worth biasing the bottom drain pin to different voltages to see if you can get a sound you’re happy with I generally start around 4.5v and increase bias voltage

Are your pickups active or passive

Where did you get your transistors although J113s are still available in through hole package there are a lot of fake FETs around

 

[MathU41]

Alright, first order of business: fiddle with the voltage, when I get a chance.

Passive pickups. A stock Ibanez GSRM20 and TMB30. Love these things.

I believe I got these ones here. No one’s immune from some supply chain shenanigans, but I trust this place and figure Barry would have found out if he got a bad batch.
Some things I’m willing to get from eBay or Amazon, but if it seems sketchy and I can’t do my research, I stick with a few known places.

[MathU41]

Okay, seem to be on the right track.
Down to 3.5v and have almost half the drive knob usable. Don’t know how much lower I can go, but I do still have a good bit of distance in the trimpots.
The adjustment is almost more of a blend than an amount. It’s more like ‘how much string sound is making it through the velcro.’ I’m sure some of it is because I don’t have my own proper bass amp; I’m running it through a guitar practice amp, usually with headphones.
And I’ll have to attach a few of my SMD J201s to their boards and try those out to compare.

[Barry]

4.5v should be your optimal voltage for the least amount of overdrive.

My transistors are always genuine as you mentioned.

I’m not entirely sure what you mean by “practice amp with headphones,” but I definitely recommend trying it through a standard bass amplifier. There are two unique demo videos on the shop page, and I was able to dial in a wide range of tones using a small 25-watt Orange Crush combo. That said, keep in mind this pedal is designed as an overdrive. From your description, it sounds like you may be overloading the preamp on your practice amp.

[MathU41]

Yeah, overloading this thing might be a genuine concern.
To be fair it was mostly bought for the space concerns, so I could have it in the work area, and it’s usually an almost respectable headphone passthrough . It actually manages a lot better than expected for guitar… I didn’t expect much.
It already struggles a little on bass, and I assume it’s just not designed for those frequencies.
I’ll be going back to the old 15-watt Fender once I’m done with repairs on that, and I’ve also been poking into the local pawn shops checking for actual bass amps.

Anyway, adjustments have helped, I know this can work, and no components got called out, so I’m going to call the circuit good, box it, and tweak from there. I can always adjust trimpots or swap transistors in situ.

[Author]

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