Preamp

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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
 
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.
 
Pots

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
 

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.
 
OK he made some mistakes, but I don't really understand the point of in a DIY forum telling someone to go and buy a commercial product. If he wanted to do that he wouldn't have posted on DIY Forums.

Since he has said he is going to bread board this he can learn about the problems with some help. Just squashing someones enthusiasm is not "constructive criticism" and just telling someone to go and read something with no pointers to why isn't either.

If you don't want to help people who post noob questions then just move on but don't ruin their enthusiasm.

Having said that the rest of what sreten has said is true (as usual).

If you want help on an instrument amp design you might find a more enthusiastic reception on the Instruments and Amps section.

Andy
 
but I don't really understand the point of in a DIY forum
telling someone to go and buy a commercial product.
Andy

Hi,

I'm all for DIY when it gives you what you actually need, and you won't be
disappointed. If you don't understand the problem it is highly unlikely you
will build something suitable. Chip amps and basic tone controls are fine
for audio, and relatively straightforward.

Music instrument amplifiers are a different kettle of fish if you want a
good one. They are far more complex. The above is a viewpoint to
consider, buy or build, analyse it, what you'll get, make your choice.

rgds, sreten.
 

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Hi the pre-http://sound.westhost.com/project27.htmamplifier stages you have found are not really suitable for guitars. This site has a solid state preamp and power amplifier for a guitar and a good description of the reasons for the design choices.

You could use a chip amp to replace the amplifier design although my experience of chip amplifiers is they have poor saturation characteristics so if you are expecting to use overdrive in the power amplifier for a rock effect it is likely to sound nasty. By looking at it it appears that the pre-amplifier has an overdrive type circuit in it (the diodes in the second stage) but I haven't read it in full or evaluated the circuit.

http://sound.westhost.com/project27.htm

Regards,
Andrew
 
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Hi the pre-amplifier stages you have found are not really suitable for guitars. This site has a solid state preamp and power amplifier for a guitar and a good description of the reasons for the design choices.

You could use a chip amp to replace the amplifier design although my experience of chip amplifiers is they have poor saturation characteristics so if you are expecting to use overdrive in the power amplifier for a rock effect it is likely to sound nasty. By looking at it it appears that the pre-amplifier has an overdrive type circuit in it (the diodes in the second stage) but I haven't read it in full or evaluated the circuit.

100W Guitar Amplifier (Mk II)

Regards,
Andrew


....also see post 7! :)

In general Rod (ESP) has very solid designs.
 
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