# Ruby Guitar Amp

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#### Chaim Handler

##### New Member
Hello -
I'm new here. I came across this site after upgrading my 12 year old from a classic to acoustic amplified guitar. After music his next favorite hobby is electronics, so I suggested that we build an amplifier, at least at first.

I found a pretty straightforward circuit called the Ruby amp:

I have a number of questions and I know there are some electronics wizzes who visit this site and are kind enough to share their knowledge with neophytes like myself.

One question I have is, after insisting that gain is the electronics term for volume, sure enough the above circuit has both a gain and volume control. Can someone explain the difference?

I'm unfamiliar with some of the values shown on the schematic. For instance, there are capacitors marked 47n. I am familiar with pf, and µf. What's n? Also, there are resistors with a numeric suffix, such as 1M5 and 3k9. What do the 9 and the 5 stand for?

Could a computer speaker be used to amplify a guitar?
Can this amp be boosted to deliver more volume?
Are there other more powerful circuits out there?

Any info will be greatly appreciated!

#### Hero999

##### Banned
n stands for nanofarrad which is 1000 pF or 0.001µF so the 47nF capacitor is 0.047:mu:F or 47,000pF.

It's pretty standard practise to replace the decimal point with the prefix. 1M5 is 1.5M, 1.5MegaOhms, 1500,000 Ohms, 3R9 is 3.9 Ohms.

A volume control and gain control do the same time, gain means the amplification factor and adjusting it alters the volume.

This circuit isn't vey loud, it'll sound like a clock radio.

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#### flat5

##### Member
The gain control is adjusting the amplification factor of the circuit.
The volume control is adjusting how much signal is applied to the amplifier to be amplified.

For headphone use, this circuit will be nice. Use Duffy's suggestion for a more practical speaker amp.
Choose a good efficient 8 ohm instrument speaker (not Hi Fi) mounted in an enclosure suited to it. Google for that information or perhaps consult a datasheet for the speaker or one like it.

Good luck with the project and music

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#### Chaim Handler

##### New Member
Guitar amp, cont.

I looked into the 2030 chip. I couldn't find a circuit specifically for an acoustic guitar.

Firstly, I think I would need a pre-amp in addition. The MOSFET section of the Ruby circuit is the pre-amp.

Secondly, the article in runoffgroove.com that presents the Ruby circuit discusses how to adjust the Gain and Volume controls to generate effects such as "overdrive" and "breakup" (the kid knows what these are, even if I don't). It even suggests some modifications to enhance these effects.

Besides, most of the 2030 circuits (I also read that the LM1875 can be substituted for the TDA2030) require a more complicated power supply.

I noticed that there is a 1W and a 3W version of the 386 chip. But you're right, I don't see the point of an amplifier if the guitar strings themselves are louder than the amp.

If anyone happens accross a relatively simple amplifier circuit, designed specifically for acoustic guitars, preferably with some knobs attached, that is more powerful than Ruby, I'd love to hear about it.

Also, if anyone can suggest some modifications to the Ruby design, which would boost it's output, that would be great.

#### Hero999

##### Banned
A TDA2030AV will give you a lot more output, and is only slightly more complicated to use. costs around \$3. Look at the circuit on the spec sheet under "single supply amplifier" -
http://www.st.com/stonline/books/pdf/docs/1459.pdf
The disadvantage is that it has a high quiescent current and won't run properly from below 8V so it won't work for very long from a 9V battery.

#### duffy

##### Well-Known Member
Obviously you aren't going to want to try and drive this off a 9V battery. Quiescent current aside, it's designed for 18 - 35 watts - a 9V just can't supply that current.

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