Using the AMZ Mosfet Booster for bass

[dpaul_gtr]

Hello everybody,

A couple days ago I was helping a friend build himself a small headphone amp when one of his friends, a bass player, saw the little thingy and asked if he could use it as a volume boost for his bass. I told him that I wasn't sure, but luckily I had just built one of Mr Orman's mosfet boosters, so I gave it to him to try it out. He liked it and told me to build one for him, albeit in an onboard form, since he "doesn't like the idea of pedals" (blasphemer  ).

The thing is that he told me that the booster lacks a little bit of bass, especially on the 5th string. Now, I know Jack Orman himself says that the circuit has a flat frequency response and I tend to believe him since he, well, designed the whole thing, but I got bored last night so I ran the circit in Multisim and the bode plot shows some bass roll-off with the corner frequency of around 50 hz. When I fiddled with the component values in the simulation, I found that increasing the C5 cap (the one between the source of the transistor to the gain pot) from 100u to 470u flattens out the frequency response.
I tried this on the real thing, but couldn't feel a difference with my strat(well, duh) and I don't have anyone to borrow a bass from here since I live in the country side and my friends live in the city.

So (if you managed to read this far without getting bored :p ) I'm asking: can that cap really make that much of a difference? Are there any other mods I should try? Or I should just say "skrew it" and stick a BMP tone control after the boost so he can dial in all the bass he wants?

P.S.: Sorry if my english doesn't make sense from time to time, it's really not my first language, I'm from the awesome country of Romania 

[Kesh]

I would be very surprised if increasing the 100u changed the response in the audio range, unless you also messed with R4 or something.

Depending on what it is being plugged into (did you simulate the load?) the 0.1u output cap may be a little low for bass. Changing it for 1u (still poly though) will cost pennies at most.

[dpaul_gtr]

Thanks for the answer And yeah, I forgot about the load. Anyway now that I've simulated the loads it seems that increasing the output cap improves the bass response, but only for loads below 100k. Over that value, I get the same results as before, with the 100u -> 470u change being the only thing that flattens the frequency response. Anyway, I'm not very sure that she simulation results duplicate in real life, so I'll change the cap with a larger one. Come to think of it, when I built my first mosfet booster I changed the input cap from 0.001u to 0.1u and it kinda felt just a tiny bit different, so who knows?