Battery Guitar Amplifier

[property1]

This is both my first post and attempt at an electronic project; please take it easy on an old man! I am trying to build a battery-operated amp for my daughters’ guitar. I am comparing the little gem MKII from the following links:

http://www.runoffgroove.com/littlegem.html

https://www.electro-tech-online.com/custompdfs/2008/04/lgmk2-pcb.pdf

to the Ruby. From these links

http://www.runoffgroove.com/ruby.html


https://www.electro-tech-online.com/custompdfs/2008/04/ruby-pcb.pdf

and the Mini from

http://www.redcircuits.com/Page96.htm

I am looking for feedback that would help me decide which one to build.

Handy Dave

 

[Nigel Goodwin]

The ruby is the best, as it better matches the output impedance of the guitar.

 

[property1]

Thank you. I read that the FET buffer was better in the info. I am curious about the diference in the LM386 based units and the Red circuit use of the TDA7052.

Handy Dave

 

[property1]

One more specific, can someone speak to the MKII use of 2 bridged LM386?

Handy Dave

 

[Nigel Goodwin]

Thank you. I read that the FET buffer was better in the info. I am curious about the diference in the LM386 based units and the Red circuit use of the TDA7052.

The TDA7052 looks to give more power, as presumably it's bridged.

But all of them are only tiny power, so not a lot in it.

 

[audioguru]

The LM386 is designed to drive an 8 speaker. It drives a 4 ohm speaker poorly.

When bridged, a 4 ohm speaker draws as much current as a 2 ohm speaker which is like a short circuit.
When bridged, it would drive an 8 ohm speaker poorly.

 

[property1]

So, as I understand the LM386 drives 8 ohm speakers correctly and not so good on 4 ohm.

Your description of the bridged LM386, (double LM386 circuit) makes it sound like it would drive neither 4 or 8 ohm speakers?

Handy Dave

 

[audioguru]

The article with two bridged LM386 ICs driving a 4 ohm or 8 ohm speaker is crazy. The datasheet shows a low output power when the current is high.

Bridged LM386s would drive a 16 ohm speaker with a power of 1.1W at clipping when the battery is 9.0V. When the battery drops to 6V then the power will be 0.5W.

Two bridged LM386s would drive an 8 ohm speaker to only 0.38W when the supply is 9V which is nearly half as much power as with only one LM386.
The battery lasts a short amount of time when two LM386s are bridged.

 

[property1]

Expanded 9 volt amp question

Allow me to expand this slightly since the obvious answer is now to build the ruby amplifier for the guitar. I also want to build a stomp box to use as foot percussion to amplify the toe tapping that seems to go along with guitar playing. This might add a drum like accompaniment. I envision a thin cigar box with one of these amps and a microphone, probably a piezo, as the pickup. Would a piezo stand up to the action? Without the guitar electronics ahead of the amp, would the choice be the same or would I select one like the little gem that does not use the input buffer? Instead of mounting the speaker in the stomp box would it make since to output to another box with a just a speaker?

Handy Dave

This is both my first post and attempt at an electronic project; please take it easy on an old man! I am trying to build a battery-operated amp for my daughters’ guitar. I am comparing the little gem MKII from the following links:

http://www.runoffgroove.com/littlegem.html

https://www.electro-tech-online.com/custompdfs/2008/04/lgmk2-pcb-1.pdf

to the Ruby. From these links

http://www.runoffgroove.com/ruby.html


https://www.electro-tech-online.com/custompdfs/2008/04/ruby-pcb-1.pdf

and the Mini from

http://www.redcircuits.com/Page96.htm

I am looking for feedback that would help me decide which one to build.

Handy Dave

 

[audioguru]

You can use a piezo transducer or an electret microphone in a Stomp Box. They would need a preamp and have tha gain turned down to avoid acoustical feedback howling if the microphone can hear the speaker.

If you connect the output of the guitar preamp and the output of the Stomp pream to a simple mixer circuit to feed the Ruby amplifier's LM386 power amp and it can drive a single speaker.