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N9VOC 30th January 2008 07:42 AM

Favorite Practice/small group guitar amp
Attached is a schematic of my favorite DIY guitar "practice" amplifier. I call it the "Classy Lassy" because the enclosure is made from recycled lumber and the speakers harvested out of "junk" equipment.

The 5 Mohm input impedance doesn load my guitar (piezo or inductive pickups) and the amp also makes a portable radio sound GOOD! I did not want high power, but good sound quality for this amp, thus the LM386-4 based designs.

As noted on the schematic, my hat's off to for their "Ruby" design.

Photos of completed amplifier to follow in another post.

N9VOC 31st January 2008 06:16 PM

2 Attachment(s)
somewhere the attached schematic to my last post got lost.
(Sorry about that!)
So, here is the Classy Lassy Schematic!

Nordic 31st January 2008 06:23 PM

got a higher res version? Iassume you have a 14 or 15" monitor... the image is not realy readale on larger screens.

I built a little gem II for a friend. It is also based on two of those chips... made gain switchable to give a bit of grunge on demand.... I realy should get me an electric 6 string again...
Also you may find more interest in this project in the instruments section.

sek 31st January 2008 06:40 PM

How's the fet input contributing to the sound, i.e. what compression and 'warmth' does the circuit give?

N9VOC 31st January 2008 07:22 PM

Better Res Schematic!
2 Attachment(s)
I found out how to put my schematic into PDF format, and attached it to this post.

Nordic - better res?

Sek -
The FET circuit doesn't add any compression or warmth to the circuit - it is simply a transparent impedance match in source follower format. I found that a low impedance input robbed my "highs" and I lost "sparkle" from my sound.

This amplifier is designed to be operated solely in the linear region of all the components - designed to be squeeky clean, and not "shape" the sound in any way. I have a custom guitar setup that does all the shaping I want by series/paralleling pickup elements. I can also use the FET input with a Piezo pickup. (5 Megohm is usually good enough for most piezos).

There is a bit of warmth to the output sound, due to the triple speaker arrangement and speaker source. The 8" speaker and tweeter were harvested out of an old Magnavox tube type console record player. The 6" is a Bogen speaker - also "recycled". I've used this same basic design concept for several low power amplifiers, and found that speakers make an ENORMOUS difference in the output sound.

The buffered output allows me to interface the amplifier to a house system or effects train to a separate amplifier.

N9VOC 1st February 2008 01:42 AM

picdtures of Lassie
2 Attachment(s)
I've attached pic of the Classy Lassie below: (I think she looks as good as she sounds!)

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