Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => The Newcomer's Forum => Topic started by: saturated on September 03, 2026, 04:05:11 AM

Title: Trying to amplify signal
Post by: saturated on September 03, 2026, 04:05:11 AM
I'm trying to make a simple signal tracer amplifier

So the first thing I did was connect the signal generator leads straight to an 8 ohm speaker 🔇 to prove that there would be no sound because it needed to be amplified  xP

Unfortunately it came through loud and clear  :grr

Alright well my little cobbled up one transistor will just make it LOUDER

Unfortunately it did not.

Now there's probably a million things wrong with my circuit but that's kinda the reason I set out like this without looking up a recipe

So this seems to work but it's not as loud as just a direct connection

Also I made the circuit without looking anything up the resistors were arbitrarily chosen and I remembered seems like the base resistor is always a large value

Also the capacitors were arbitrarily chosen

I do get forward bias on base to emitter

IMG_20260903_024408229 (1).jpg

And obviously yes I'm gonna have to crack open some books and try to see what's up

For instance right now I'm kinda wondering hmm what do I need to make it louder CURRENT GAIN

OR VOLTAGE GAIN

I'm pretty excited to get through this part because next I want to take a look at complimentary pair and then also I want to use some 8 DIP amplifiers

And here's one old lady that's glad the storm is gone  xP

IMG_20260902_152755434.jpg

IMG_20260902_153016713.jpg

Title: Re: Trying to amplify signal
Post by: J M Fahey on September 03, 2026, 06:05:38 AM
Well, good intentions but a couple problems.
1) you are injecting signal on the +V rail.
That may have 10-15V DC on it  but it is Audio ground, so you are shorting your signal.

2) same thing, speaker is connected to same +V Audio grounded rail.
Nothing audio there except maybe some hum or ripple.   

3) get a tutorial on how to design a single transistor gain stage.
Values are not random.

4) even if, an 8 ohm speaker has way too low impedance to be driven by a humble small transistor.
Back in the day, Student circuit examples used a very high impedance crystal headphone (almost unobtanium today) o a 2 k ohm magnetic headphone (same thing)

If you want simple, use a small IC such as LM386

(https://electronics-diy.com/schematics/1047/LM386-Audio-Probe-Amplifier-Circuit.gif)

Full article:
https://electronics-diy.com/electronic_schematic.php?id=1047

My only disagreement is them using a 10k input pot.
Audio 100k would be much better.

It easily drives a small speaker, 2" plastic type is fine, or standard walkman/phone earphones
Title: Re: Trying to amplify signal
Post by: g1 on September 03, 2026, 10:26:40 AM
Like JM said, the input and output are going to wrong places.  Even if the transistor were set up with correct resistor values, the input cap would connect to the other side of that base resistor.  The output cap would connect to the other side of that collector resistor.