Guitar amp based on TDA7294

[gamberone]

Hi. I want to built a guitar amplifier based on chip TDA7294. I want to follow the scheme present on datasheet (typical application circuit). I would know if this type of circuit it's OK for a guitar or it need to be modified (it's too "linear"?). I put in out of circuit a speaker (woofer) that has 8 ohm of impedence.
Pleas help me.
Bye.

[teemuk]

The basic drawbacks of doing that are:

- Impedance mismatch due to too low input impedance: Recommendation for magnetic pickups is at least 1 Megaohm and the recommendation for pietzos even higher.

- Too low gain. The nominal output signal from a typical pickup is about few hundred millivolts - likely less. The application note circuits are designed for higher input sensitivity than that.

- Most guitar amplifiers introduce a significant midrange notch at 300 - 1kHz. A linear frequency response may sound unnatural.

- It won't have tone controls.

If you couple the TDA7924 amp with an adequate preamp all those problems are solved.

[gamberone]

Yes, I've supposed that I have to build a guitar preamp to resolve those problem. A preamp based on MOSFET or on OpAmp could be ok?
There's only a "problem": I don't use only the guitar in amp, but I use also some effects that improve the signal leven came from guitar. Also if I use some pedals, I have to introduce a guitar preamp?

Thak you for the answer.

[scaesic]

you could probably get away with using a "booster" pedal as a pre-amp.

infact, im planning on using a mosfet booster pedal design as a pre-amp.

the thing i''d be concerned with is the "voicing". but you can try it and see, and if it sounds crap add a tonestack later.

[oldfatbubba]

I've given this question considerable thought...

I would build a tube preamp similar to a Fender Bassman model 5F6A. The preamp would feed a NPN configured as an emmiter-follower that would drive the Chipamp. I would choose a darker-sounding guitar amp speaker since the Chipamp will be brighter than a tube amp, maybe a Celestion Silver series.

Alternatively, an op-amp could be used to 'bridge' the tube preamp to the chip amp though I'm not sure which would work better.

[scaesic]

Originally posted by oldfatbubba
I would choose a darker-sounding guitar amp speaker since the Chipamp will be brighter than a tube amp, maybe a Celestion Silver series.

Personally, i dont think it'l do much brightening,

if the pre attenuates the highs then there wont be much left to "brighten"

also, i like the idea of brightening up a signal after "warming" it up. means the signal will be well balanced.

its all down to preference though.

on the pedal idea again though - you can buy "booster pedals" with a tube in them, which you could use as a pre.

[gamberone]

I have some experience with construction of effercts for guitar, that are similar to pre amp based on MOSFET. For this, i would to build this preamp and put beforme my amp (TDA7294). Could someone indicate me some great project to solve my problem about preamp? A scheme not too complicate and with a good sound (like tube... ).

Grteeting to all persone that are answred me!

[teemuk]

I believe you can not find a "simple" solid-state preamp design unless it's for clean tones and has very few features. What do you consider simple anyway? - You know there can be complex topologies with low parts count or simple topologies with high parts counts...

For example, I consider a preamp circuit like SansAmp pretty simple if I break it down to parts but initially it may look pretty complex. You shouldn't be scared away by the seeming complexity of circuits: You can always break them into modules and build piece by piece - that makes fixing or modifying things easier as well.

Personally, I would start by browsing the schematics of some of your favourite amplifiers, pedal effects or alike (Internet is full of these) for inspiration of features you like to have and how they are usually put together. If you figure those out you can pretty much design the schematic of a preamp yourself. Maybe someone should start a thread listing schematic sites for this kinds of stuff because this topic seems to come up at least once a month. Do a search at the "musical instruments" section, you'll find a lot of info from there.

[PeteMcK]

try the 'peppermill' FET preamp from Runoffgroove with your chip amp, very simple and to my mind as good as any tube preamp,
has a nice soft distortion.

Of course, if you want Heavy Metal type distortion you"ll have to
add a distortion stage (or use a pedal.... like everybody's hero SRV...)

DON'T use a woofer, most won't have enough highs... use a guitar speaker or a cheap paper cone Hi Q speaker with whizzer in an open backed cabinet.

[gamberone]

Hi. I search a "simple" preamp, with few components and without tone control. It's use is only to solve problems described by TEEMUK in the first reply, only for this. A clean preamp, without any type of distortion; in fact I introduce the distortion and/or other effects with external pedals.

Bye.