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9v Guitar Amp w/out LM386

Audioguru

Sep 24, 2016
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Solderless breadboards cause so many problems on these forums.
 

Don Perry

Apr 26, 2017
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Solderless breadboards cause so many problems on these forums.
Is there an alternative?

Well, the circuit works like a charm now that I've got the bootstrap cap properly wired to the output junction. I've been fiddling with it all morning with various guitars and mics (by re-amping) and the performance is stellar. The bossman came by and proclaimed the circuit fidelity is 'almost too high' for his project.

Thanks a million for the help guys, I'll post my final results when the mail comes in.
 

Audioguru

Sep 24, 2016
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Is there an alternative?
I gave up using solderless breadboard years ago when the many rows of contacts and wires all over the place picked up interference or caused oscillation and the intermittent contacts caused many problems.

I use stripboard instead. The copper strips are cut to length with a drill bit so that a strip can have a few parts of a circuit making the circuit board compact then the strips and a few jumper wires form half of a pcb and the parts form the other half. Everything is soldered. Here is a sound level indicator project I designed and made on stripboard:
 

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Don Perry

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I see. This makes sense as I gather most prototyping takes place in multisim these days.
 

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Multisim is taught by old teachers. Most of us use the modern LTspiceXVII sim program.
All my stripboard prototypes worked perfectly and were sold as the final project.
 

Don Perry

Apr 26, 2017
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Hey again, so I've designed just about all the circuits discussed in this thread and I've landed on this guy:
Power-Amp-Final.jpg

First off, the audio this circuit produces is SO LOUD! It's crazy I love it. However I've a few questions as it works but, barely. It sounds like the input is gated and must reach about 200mV before the amp produces any audio. Second, the audio is very distorted... and gated...

As for '? 2', does this actually belong? When connected, the circuit just hums and the audio just barely squeaks through (distorted). When disconnected, the audio is heavily distorted but works (still gated though), albeit very distorted, it's very loud.

This is by far the loudest circuit I've played around with and will, for sure, be the circuit I want to build.

Heading into the shop now, going to rebuild it and check for mistakes. I'll check back soon.

EDIT: Here's the error in my simulation..
Broken.jpg
 
Last edited:

Audioguru

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The amplifier sounds awful because you forgot what I said in my post #38: "R5 TURNS OFF Q3!". Only very loud inputs turn on Q3 a little on the peaks. If R5 is removed then you do not need the first transistor but without the bootstrap capacitor there will be severe distortion as I showed in my post #56.
 

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Don Perry

Apr 26, 2017
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Understood. This circuit is SO LOUD though! All the other are at least 80% quieter than this one. Let me put that together, add the bootstrap and get back with my results.
Thanks for the input.
 

duke37

Jan 9, 2011
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?2 puts 8Ω across the battery/ It will not last long with a drain this high. Remove the link.

?1, the capacitor should be connected across the battery.
 

davenn

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?2 puts 8Ω across the battery/ It will not last long with a drain this high. Remove the link.

?1, the capacitor should be connected across the battery.

what duke said ... you SHOULDNT have +V going down to C1
 

Audioguru

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I simulated it with the puny little low power 2N2222 and 2N2907 output transistors. The output level is less because the top of the output waveform is squashed causing distortion. I reduced the 160k to 100k for the bias resistor of Q3 and the bottom of the output waveform became clipped causing the output power low.

Here is yours without the short and mine:
 

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tedstruk

Jan 7, 2012
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I know I have heard of diode biasing, and its great if you want to control the system, but this is a raw power amp, the longer it loops....the higher the output.
so use a 9v...wow thats a lot of power man! so if you loop it say... 5 times... thats like 45v! so you want some monsters in there... nothing under 50v will do if you want lots of sound. now about that 8ohm speaker.... even a 7 watt system sounds better with 8ohm speakers, most are only 2ohms. but with 9v... well you get the picture.so take that 10% rule and don't mess with the output. Because.. you aren't system matching, your pumping out the jams. get fets!!! and think 2 phase..
My solution to building amps was to think like an egyptian... they built 4 sided pyramids(the true pyramid has 3 sides) Where you might connect an input with a small cap you really don't need it and at the output, the power must be enough to drive the speaker. not enough power and you won't have an amp you will have a compressor of sorts. The idea is... load a slow cap with a charge, and while its loading, load a transistor with the same charge. When the cap fires, it triggers the transisitor, and drives the combined charge(double the signal) onto the next phase, which loops the current with the help of some resistors.... when the resistors can't resist anymore, they drive the speaker. raw power use is very very shocking sometimes!
 

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Tedstruck, you do not make any electronics sense.
The battery in a car is only about 13.8V so they do not use 8 ohm speakers to get only 1.8W. They use 4 ohm speakers and bridged amplifiers. A bridged amplifier has one amplifier driving one wire of a speaker and another out-of-phase amplifier driving the other wire of the speaker so the voltage swing is almost doubled and the power output is about 14W. My car used bridged amplifiers driving 2 ohm speakers for 22W output. 5 amplifier/speakers produced a total of 110W. This is real low distortion continuous power, not Mickey Mouse very distorted momentary "Music power".
 

PD64

May 12, 2017
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Hello all,
Last week my employer commissioned me to build a small guitar amp that would fit inside a tiny cigar box. The caveat is that I'm not allowed to use an LM386. I'm suddenly finding myself way over my head. I've been crawling these forums like crazy and I've found a lot of good information, but I'm not sure that I've seen anyone actually pull it off.

My target is to run a small speaker, I'm gathering that 64Ω is the norm but I've seen those Smokey amps drive 4/8Ω speakers. How is this possible?

Should I be looking at push-pull circuits? Class A or Class AB? I'm just not even sure where to start. I've some, but very limited, experience with analog circuits.

Any Ideas?
I've made 3 small guitar amps for personal use, ruby, little gem & noisy cricket, all use lm386.
From memory all 3 are freely available & ok to replicate for sale with caveat that originator be credited.
 

BobK

Jan 5, 2010
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PD64,

Perhaps you missed the word "not" in the sentence from the OP about using an LM386.

Bob
 

PD64

May 12, 2017
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PD64,

Perhaps you missed the word "not" in the sentence from the OP about using an LM386.

Bob
Didn't miss not. Curious about not. Existing solutions can be sold, was alerting OP to this.
 

Audioguru

Sep 24, 2016
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The employer asked this "digital" worker to make an analog circuit using discrete parts. Maybe for the worker to learn how to find or ask for a circuit on the internet instead of learning how to design the circuit.
 

Don Perry

Apr 26, 2017
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Hey guys, I know it's been months but summers over, the kids are back in school and it's time to dive back in! All the parts are in (have been for a while) and I'm pretty excited to start this up!
 

Don Perry

Apr 26, 2017
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In all it's glory! I'll edit this post with a video later so you can hear what she sounds like. Thanks for everything you guys!!!!!
 

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