Onboard Preamp

[Nick C.]

I want to put a modified Tillman or Stratoblaster preamp in a guitar that has both single coils and humbuckers. My ojectives are a small boost, no loss of highs when lowering volume, and some simple active eq. I want to keep the stock 500k ohm vol and tone pots. No active to passive bypass.

Question: Will there be a benefit to supplying the preamp straight from the pickup selector and putting the volume pot after the preamp?
Would that help with retention of highs? Add noise or reduce noise?

BTW, The tone pot will be part of the preamp.

Thanks

Nick

[Mark Hammer]

The buffering effects of the preamp on the pickups have to be balanced against the buffering effects of the preamp on the first cable.  Where you stick the volume pot or preamp determines which of those is predominating.  If the preamp is the last thing before the output jack, then it is behaving exactly like a booster pedal on the floor, except that the "cord" leading up to it is really really short.

Since there are obviously pedals with 500k output pots that still have "low" output impedances, I'll shut up here, but my own first reflex would be to put the preamp just before the output jack, simply to assure that the cord will have minimal impact on tone.  Finally, I will also add that the very reason many fender products come with lower-value volume pots than Gibson products is because they load down the pickups in a useful way that shaves some of the "brittle" tone some complain about.  Stiocking the volume pot after the preamp loses that role for the volume pot since the pickups will be buffered from the volume pot.

[Paul Marossy]

I like to put the volume pot after the preamp so it doesn't pick up any scratching noises when operating the volume pot.

[Minion]

In my Onboard preamp design I just installed it right before the output jack , works great ....

[Paul Marossy]

In my Onboard preamp design I just installed it right before the output jack , works great ....

Yeah, that's basically what I did, too.

[RedHouse]

I like to put the volume pot after the preamp so it doesn't pick up any scratching noises when operating the volume pot.

+1

[Ripthorn]

For lower output impedance, you could use a 25k pot just like EMG actives do (their preamp is just built into the pickup).

[Nick C.]

Mark say's:

"Since there are obviously pedals with 500k output pots that still have "low" output impedances, I'll shut up here, but my own first reflex would be to put the preamp just before the output jack, simply to assure that the cord will have minimal impact on tone.  Finally, I will also add that the very reason many fender products come with lower-value volume pots than Gibson products is because they load down the pickups in a useful way that shaves some of the "brittle" tone some complain about.  Stiocking the volume pot after the preamp loses that role for the volume pot since the pickups will be buffered from the volume pot."

Funny thing is that this guitar has a dull tone, replacement passive pickups didn't help much, which is why I was thinking an active preamp might help increase high end.

It looks like others like the post preamp pot, so I give it a try. I did forget about the output impedance. I'll try to fake a lower pot value with the parallel resistor trick.

Thanks

[Minion]

Installing an Onboard preamp to my ESP Made a world of differance ...before it sounded weak ,thin , brittle and overly midrangey but once I installed the preamp it was like a totally different guitar Lots of heavey low end and nice clear Highs and it sounded really up front and in yer Face ...
My design was a very simple single opamp Jobbie useing a OPA132 and the PCB was about 1.5in x 0.75in , if yer interested I can post it for you , i think it is posted somewere on this forum but I can re-post it for you....

Cheers

[Nick C.]

Minion, A schematic would be cool. Thanks

[Minion]

Here it is...It is very simple ....




Adjust the 100K resistor in the feedback loop to adjust the gain ...Maybe replace it with a Trim pot or even a real pot if you like ... Ive built several of these for friends of mine for both guitar and bass and they all love them , which is cool from such a simple curcuit...


Cheers

[alanlan]

Funny thing is that this guitar has a dull tone, replacement passive pickups didn't help much, which is why I was thinking an active preamp might help increase high end.

Doesn't happen to be a Jagstang does it?