Preamp

[happy hippy]

Hello there,
Here's the schematic for my new preamp. It will feed an LM3876 amp. According to TI, I can substitute an OPA2132 for the TL072 if I choose to. I'll be breadboarding it an then we'll see what it sound like. All comments, constructive criticisms, etc. are gratefully appreciated, as I'm an amateur at this. Everything on here has bee copied off several sites, so I don't think there will be problems. You can see the power supply on the LM3876 PowerSupply thread I posted in the appropriate sub-forum.

Thanx
The Happy Hippy

[happy hippy]

Here's the schematic.

[nigelwright7557]

Your pin numbers 2 and 3 are marked the wrong way around.
You have 3- and 2+ when it should be 3+ and 2-.

[sgrossklass]

The gain pot looks a little odd, too.

Speaking of which, consider moving that behind the tone control, which will no doubt be relatively noisy. (No need to spoil the LM's good noise performance.) A 10k type will do fine then, it should be low enough to be usable in the amp input and not too low for the modest load driving capabilities of a 072.

[happy hippy]

Originally Posted by sgrossklass

The gain pot looks a little odd, too.

Speaking of which, consider moving that behind the tone control, which will no doubt be relatively noisy. (No need to spoil the LM's good noise performance.) A 10k type will do fine then, it should be low enough to be usable in the amp input and not too low for the modest load driving capabilities of a 072.

You haven't seen the amp schematic yet, 'cause I don't have it up on this thread yet. But there is a 10k pot between the preamp and the amp. It may look odd, but then, so do I All the downloads I did of similar units had both, so that's the way I drew it. Being a novice, I don't really know why both of these are there. So if you can enlighten me it will be appreciated.

Thanx
The Happy Hippy

[AndrewT]

Go to ESP and Decibel Dungeon and do some reading.

[discrete]

Originally Posted by AndrewT

Go to ESP and Decibel Dungeon and do some reading.

...seconded:

100W Guitar Amplifier (Mk II)

[Puffin]

Originally Posted by AndrewT

Go to ESP and Decibel Dungeon and do some reading.

Thirded

[happy hippy]

Originally Posted by AndrewT

Go to ESP and Decibel Dungeon and do some reading.

Why?

[sreten]

Originally Posted by happy hippy

Why?

Hi,

Yuor gain pot doesn't do anything than short the input at its top setting.
your input impedance is far too low for a passive bass guitar and you
will lose all the top end etc .....

Its very wrong and very uninspiring. You'd be far better off finding a
decent bass pre-amp schematic or copying the pre-amp section
from the service manual of a good bass amplifier.

The fact you asking Why ? is why you need to do a lot more learning.

I wouldn't use a chip-amp for anything other than a practice amplifier.

TBH if you like good sound don't even think about building a bass amplifier.
I can design hifi circuits but wouldn't know where to start building
something that sounds like my Peavey MkIII, I've looked at the circuit,
its wild, wacky and not remotely hifi, but sounds to me, excellent.

Checkout the features of the combo's on this page, they have all
the basics you need to include in a flexible good cheap bass combo.

Good Cheap Bass Combo Amps - Budget Bass Combo Amp Guide

Bang for buck and feature set consider trying to
build one of these and how much it would cost :
Behringer Ultrabass BXL900A

rgds, sreten.