onboard MM bass transistor preamp idea

invader_lex · Post by **invader_lex** » 07 Dec 2022, 17:25

Hi, I found a cheap passive stingray bass copy and I build a simple pre amp with spare part I already own, I could have build the OG pre but I do not own a low current opamp and in my country is not easy to get reverse log pots. So I put a Tillman in the input, followed by a scaled james tonestack and a lpb1 boost as recovery, it sound pretty good for a fast and simple point to point build. Some problem, flat is not in the 50%, 50% position is more like in the 50%, 60%.

What do you think?, what do you suggest, what would you change. I want some input and ideas, thanks for your time.

mauman · Post by **mauman** » 07 Dec 2022, 20:20

Welcome, and thanks for sharing this! How about some pictures? It's always interesting to see how onboard devices are fitted into the instrument.

If it works and you like it, then it's right, there's no objective standard beyond that. I see the gain is fixed after the bass volume pot. If you do need to reduce the level, you can add a volume pot after the Tillman (after C1) or after the LPB (after C10).

If you want to set your pot for unity gain, just loosen the knob, turn it where you want it and re-tighten it. You'll have more adjustment available on one side than the other, but it will point where you want it at unity.

invader_lex · Post by **invader_lex** » 08 Dec 2022, 02:35

Point to point. I'm happy with the results. I put the vol there, because I was thinking as if this was meant to be pedal there would be a vol in the bass, So the onboard is my vol. all my guitars have a Tillman after the tone and vol. This pre amp gives +6db when the 2 band is in flat. and it can boost the bass and treble up to +15db.

As you can see I would need to redo all the wiring if I wanted to change the vol position, the Tillman is connected to the vol pot floating there, is a very tight cavity, unlike a jazz bass. That big capacitor is a high voltage 3.3nf, I could not find a smaller capacitor. is not pretty but it is functional and the ugliness will be hidden behind the plate so is ok.

bmxguitarsbmx · Post by **bmxguitarsbmx** » 08 Dec 2022, 13:31

Could you solder a resistor across two lugs of the pot to put that 60% flat position down to 50%? Maybe some alligator clips could help decide the final value.

invader_lex · Post by **invader_lex** » 08 Dec 2022, 16:40

bmxguitarsbmx wrote: ↑08 Dec 2022, 13:31 Could you solder a resistor across two lugs of the pot to put that 60% flat position down to 50%? Maybe some alligator clips could help decide the final value.

is flat enough I was using the default RIN of 38k of the calculator but the output impedance of the input pre is 6k so is flatter. Thanks.

jeepe · Post by **jeepe** » 01 Mar 2023, 22:15

you have misunderstood bmxguitarsbmx's suggestion...