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
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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
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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
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.
Thanks guys I appreciate it as stated before this is a great place :dbtu:
I'm gonna go back and do an autopsy on this circuit I'm particularly interested in the voltage at the collector
It's a target 🎯 rich environment for me learning xP
I'm essentially trying to build an aircraft with people from NASA looking on :tu:
Ok I went back and constructed the circuit and took some readings
About the V+ value I think I just wanted enough to get the Vbe I needed
Anyhow
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Seems like I remember the emitter and current should be about the same but that doesn't mean the resistors are the same. In fact all those little circuits I made I don't recall that being the case.
Seems like I do need the collector voltage more positive than the base voltage and I'm pleased with that xP
I better do something so maybe I'll increase the value of the collector resistor :grr
And one problem that needs to be worked out and I had noticed this before
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And as the input signal is turned up it gets worse (base gets more negative)
I have the positive terminal of the electrolytic facing the circuit
Probably something simple doh :grr
Ok yeah the signal (at least half of it) thinks the V+ is ground
Anyway I went back and read some stuff here and decided to heed their advice and add a base resistor to ground
Which I did and it helped but I had to accommodate both V+ and the ground resistor thinking about voltage drops.
I saw where there was a threshold where Vbe would hold up then start to decrease to head south and that coincides with the onset of clipping of the output.
That said I don't expect anyone to make heads or tails of this nonsense I'm gonna have to keep working on it for a while.
Thinking out loud I guess the base voltage needs to exceed the input signal voltage so maybe increase the value of the base to ground resistor
xP
So yeah I'm getting my rear end handed to me that's a good thing xP
Try 1M Base to collector and 3k3 collector to +V and get ready to ride.
Inject 100 mV into Base through a 1 or 10 uF cap, positive end towards Base and scope collector.
You´ll have so much gain that probably signal clips, go figure.
Attenuate signal drive and tell us how many mV it takes to reach clipping.
Gain will be HUGE.
This is a basic gain stage around which I built many projects, from signal boosters to 8 channel mixers back in the 80s, published in Music Magazines, Argentine Musicians built tons of those and used them live .
Google says:
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Overview created by AI
"Project Primavera" was a famous electronics and audio project DIY (do it yourself) published by the renowned Argentine technician and manufacturer Juan Manuel Fahey in the pages of the mythical national magazine El Musiquero in the late 80's.
The project consisted of design and step-by-step schemes to build a home or studio audio mixer console.
Project Details
The Author: Juan Manuel Fahey, an eminence in the manufacture of national audio amplifiers (much remembered for equipping bass players like Ricardo Iorio), was part of the staff of the magazine providing their knowledge in technical sections.
The Publication: It was distributed in the form of monthly deliveries or fascicles within El Musiquero, allowing musicians and enthusiasts of the time to buy the components in electronics houses (such as those on Paraná Street in Buenos Aires) to assemble their own console.
The Legacy: Today it is a cult project between vintage audio technicians, music lovers and nostalgic Argentine analog electronics.
Are you looking for the electrical schematics or the list of components of a specific module of the Primavera console, or are you interested in knowing what exact numbers of the magazine was published?
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Yes sir thanks I will definitely be making some changes to the circuit and I believe your suggestions will help tremendously :dbtu:
Meanwhile I tried to see what was wrong with the original circuit by trying to make a load line and Q point and perhaps there is not one correct data item but if it is then I'm drawing a conclusion that my collector current is too low and needs to be increased by increasing base current by decreasing the value of the base resistor
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:grr
Also another resistor will be added from base to ground so there will be a voltage divider
I'm actually pretty excited about this stuff despite being lost in space 🚀 xP
One of many things I wonder about now is why don't amps just use one BIG POWERFUL transistor instead of an array of components xP maybe they have to build up the signal to get it to a minimum level for input on the output transistor xP
Also I want to connect the output of a transistor to the input of another transistor and maybe more so now I'm wondering if they can be the same (NPN +NPN...) or have to be different xP
At the end of the day I really need to find a schematic for a signal tracer type audio amp even battery powered and use that for a template xP
Alright well back on my junk science project
I did get it to work after trying to up the base current then what really made a difference was bypassing the emitter resistor
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When I calculated Hfe I thought that sounded like a good round typical number :dbtu:
But the peak atlas said much different :grr
So idk
Obviously I have much to learn here.
One thing that was cool I managed to get a decent tone out of the output by connecting an 8 ohm speaker 🔊
But... whenever I connected the speaker the nice amplified output on the scope completely collapsed :grr
Also 50mv was about all I could get on the input before clipping
Seems like increasing DC did help obtain more output
So hey I'll take it :lmao:
Hfe of transistor in use is determined by circuit values. The transistor datasheet value, or that shown on your peak atlas, must be at least that much or greater (for circuit to work right).
Kind of like how you have to use a resistor with a wattage value that will accommodate the wattage it will run at in circuit.
The waveform collapse when loaded shows you that you have voltage gain, but lack current drive.
Take your voltage you see unloaded, now calculate that across an 8 ohm load (or other load value). What current do you calculate? How about wattage? Is this particular transistor capable of that? (see datasheet values)
Yes sir thanks I'm definitely aware that some measurements need to be made and I'm actually dreading it because for me the going gets tough with using a multimeter when AC and DC are together.
That's why I like the scope it's kinda like flying VFR on a pretty day and then using the multimeter is like doing an instrument landing in fog :grr xP
But it's all stuff that I want to know how to do for instance I had taken the supply voltage DC reading and written it down but later when I disconnected the input I noticed it had dropped a few volts :loco
But yes thanks for your help :dbtu:
Ok this evening I went and rebuilt this circuit and tried to add a load resistor (a mere 6.2 ohm) which didn't work
Raising the white flag I decided to take output voltage between the collector and collector resistor
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Basically if I add the load the resistor I get about 0.090 v across it
So idk how the heck I got sound out of the speaker
Then I noticed my voltages on the terminals of my transistor all drop a little when the input signal is added :grr
This probably is connected to the DC power supply being a ground for the signal :grr
Also I have some discrepancy between Vpp on the scope and Vrms on the meter despite doing the calibration :grr
So probably not much to be gained here but it's still been a good experience I have another book coming
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So hopefully I can start constructing some proven traditional configurations and attempt to comprehend them xP
Your meter will not perfectly measure the DC once you have signal present, this is why you see change in transistor voltages when signal applied.
8V rms output means in a perfect world, if you transistor could deliver the current, you would have about 10W output into your 6 ohm load. That would be at around 1.3A of current.
The KSC1845 is only good for 50mA, and half a watt. This is why it all falls apart when the load is applied. :) Your gain stage needs a current amplifier.
You still had sound from the speaker because it takes very little power to make sound. A 1W test tone is a lot louder than you would think.
Micro guitar amps that put out only half a watt are generally considered too loud (cranked) for quiet apartment use!