All You Need To Know About AMPLIFIERS To Fix Stuff - A Beginners Guide To Audio Amplifier Repair

A couple of points: As a few people noticed I mixed up the terms peak voltage and peak-to-peak voltage a few times in this video. I do know the difference it was just me having a bad day 🤐. If you noticed the mistakes then I hope you can skip over that and relax in the knowledge that you are correct 😉

Another topic that I did not mention, because I was looking at a PA amplifier, but is very relevant to Amplifier repair especially when it comes to the 'home stereo' type amplifiers from the 80s and 90s (but other decades too). If you have one or more these symptoms:
* an amplifier with the voltage rails present but no sound output on one or both channels
* intermittent audio on one channel or both
*it works on some audio sources but not others
* one channel lower volume than the other (or changing volume by itself)
*crackling, popping or other (often intermittent) noise on one channel or both

Then the most likely cause is the input select, mute and/or speaker select switches that are causing the problem. Usually these are multi pole rotary or push button type switches and the internal contact become tarnished with age. In my experience the only way to fix this (reliably) is to remove the switches from the PCB, carefully dismantle them, and clean the contacts. Usually replacements are not an available option and this becomes more a restoration job than a repair job.

Nice video, you explained it very well. At the Class D topic I think it is a little different, it is not PWM (Pulse Width) but PHM (Pulse Height), following the height at a fixed frequency. I my understanding the amplification operation is closer to AM than FM. Amplitude Modulation instead Frequency Modulation. PWM is Frequency Modulation/Modifcation, it changes the time between pulses of the same height to reduce the voltage by reducing the on or off in length of time. That is not what you want if you want to reproduce an audio signal because otherwise it will change the frequency of the audio (or other artifacts). You can compare it with switching, a carrier wave, constant samples taken from the audio at a fixed frequency (for example 260khz, far above hearing limit). Because of the (carrier wave) frequency, the output is not constantly on like 100% and that are the savings. This is not PWM, the width of on/off is constant, this is switching/oscillating at a frequency, like a microcontroller or CPU do with use of a crystal (that is why D is classified by some people as Digital). With use of switching it follows the height and lows of the incomming amplitude like other amps do but only a fixed periods of time. That is the difference. At the end of stage it uses a low pass filter to filter the the switching noise/carrier wave.

Hey bud how you doing I just want to say that's pretty cool to see you work on a real real amplifier that's when they made an amplifier like the one you're working on it is such a pleasure to see something like that thank you

12vp-p not 6v for the class A. Just leaving this here for the hobbiests not to get confused.

How do you not get a stroke just looking at this monstrosity of an amplifier? What a beast that one is.

What Island... Trinidad

I'm just starting to really learn how to diagnose and repair electronics (amplifiers specifically) and I watched everything but I understand roughly half, give or take, of how everything works as described and illustrated. Feels like I missed a class between what I know and this level, any recommendation on where to go for a more basic level to learn before revisiting this?

Thank you so much for this very informative video! I learned more from this video than some classes I've taken.

Hello I have a pioneer vsx-519v and the issue im having is when using it in stereo mode it is working perfectly but when using it on pro logic mode there lot of noise in the front speakers I check all the components on inside all seems in good condition what might caused these noise please

Liquid cooling 😎 would B😮

That toroidal transformer is a monster! I guess it would account for much of the weight.

Thank you for producing this video and series. Excellent presentation of the types of amplifiers.

Very good; except in bridge mode, if you double the voltage you get 4X the power. P= V^2/R.

I’m a retired master automobile mechanic with almost zero knowledge of electronics, all I ever learned was to trace circuits in wiring harnesses, control area network communication faults and sometimes replacing a mini injector driver relay in a engine control module or just patching a shorted printed circuit, I have a decent understanding of how the electrics work in a vehicle from the battery, charging starting system, it’s relays and switches all the way to the lights and of course, the use of a multimeter, plus the use of a scope to look at crank and cam angle sensor patterns, also have enough understanding to wire a whole house AC circuit and calculate loads to use correct wire gauges and to properly wire and balance a breaker panel. Also have a decent understanding of solar system as I wired some of my house circuits with an emergency solar back up system.

What always fascinated me was the electronics inside the modules, specially back in the 80’s when modules were smaller and more (solid state), same with audio gear from 70’s and early 80’s, never understood how they worked, always wanted to know how a PNP and a NPN worked, what was needed to make it work, same thing with resistors, capacitors variable resistors, etc.
At this late age after retiring from working on cars, I now have time to learn about this stuff, always felt I needed to know this before I go, this is just me, I’m in the process of learning to use an oscilloscope, where components go and their role, later I’ll learn the needed values of each component based on the desire output of an equipment in order to build a device.

Thanks you Sir for what you do.

Is the guitar amp repairs the same theory?

I have a belles 150a hotrod that one channel makes the driver exert forward and hold right when turned on. If any one knows what causes this any info would be appreciated

Ended up answering my own question from my comment yesterday, the topology Peavey used in mkiii’s/mkiv’s etc is “quasi-complimentary”, and they did it due to high power NPN’s being better/more reliable at the time. A video on how these work would be a great addition to this series! Thanks for all the amazing videos btw!

Non of the topologies seem to match up with what’s going on in the Peavey mkiii and mkiv schematics, they have the pnp/npn phase splitting arrangement, but the diodes between them have their own transistors, and the all the power transistors are NPN’s?

Very practically oriented video, liked the way you imparted knowledge.

cool video man. thanks for your info.

Wow thank you so much for this content

What a great job you do explaining these things. Thank you! Like I said on one of your other videos is you should try to explain how to build a VFD from single to 3 phase electric for us Americans with only single. I think that video would do great!

Your Bear hands need those Gaint Caps....Phew...

I've said this before but I feel it is worth saying again. I've gotten more from your series in real world electronics than I've gotten from the AOE

Get to the point!!! For God freaking sake stop going around and be specific!!!

Wire a 470R 10W resistor in place of each DC supply fuse before switching on a repair. It'll drop the rail voltage if there's an overlooked problem component, and limit the damaging current. Once in a while this will upset a healthy amp (can use lower resistance values with lower DC voltages than 90V), but better safe than sorry. Even better is to parallel the droppers with fast resettable fuses, so they are only in-circuit if needed. Add an analogue meter in parallel with each one for a quick visual check.

My god look at those electro-caps. By far the biggest Caps ive ever aeen in an audio amplifier. Surprised they're rated at only 100 volts.

That transformer is also quite the beast. It must have a fairly large magnetic field when running

great job in explaining it

Thanks🙏
I have recently found a old Technics amp at my local op shop.
Got it home and it didn’t work.... I opened it up and looked for anything obvious and saw a blown fuse.
Got the new fuse, and soon as I turned it on there was a flash of green light and a newly blown fuse.
Unfortunately I don’t have the skills or the tools to go any further😞
I find it sad that no one fixes audio gear anymore.... certainly no one where I live in W.Australia.
I also have a Cambridge Audio unit....I think called One🤔 anyway that one I was given because it was broken.
I discovered that although it turned on and appeared to function I couldn’t get any sound out the speakers🤔
In a flash of inspiration I connected my headphones and was surprised to find the sound was coming through them just fine.
I’m sure one day I’ll ask someone that can help me get them working😉🙏

❤❤❤

Thanks

What does it mean if your transformer homes

Mean if your transformer homes

Sir, what a great video.
I've learned tremendously from it.
I'm now a subscriber.
Thank you sooo much for sharing your knowledge.

One question. Bulb power in series in power supply versus amp power. Is there any rule saying what bulb watts value for amplifier wattage ?

I have to say I've never got so perfect lesson about amps philosophy in 1,5 hour. This was invaluable. You should write a books - you maybe would be rich person. I am just renovating DENON 525R amp from 80-ies. And this gave me nice basics to understand what I am doing now and for what I should look for. Thanks a lot and now I have listen next movie. Perfect lesson. Thx. Marek/Poland

Man! Great info!

Where can I get Sanken 2SC3858 and the PNP for an amplifier ? where is a good source that wont make fake ones?

Seriously that lamp "tool", what will that help taking off 160w from an 2300 watt outlet? How could that ever protect anything?

What a great channel! I've been repairing kit like this for decades, but this video has reminded me that every day is still a school day - some handy tips there, thankyou! Talking of a belt & braces approach to testing, I like to stick a voltmeter across the speaker outputs of an unknown amp before connecting the speakers, just in case there's a full 70V just waiting to fry my test speaker! ;)

Do the output transistors normally get a short between their legs, or a short to ground?

I watched entarily video like a good movie. You did the great job explaining everything. The light bulb method is simple and genius in the same way. Now I know how to properly diagnose and repair the amplifier. Thank you very much for sharing your knowledge ❤

Thank you sir ...this stuff is GREAT . Certainly helps clear the cobwebs from this old noggin !!!

Ho. I have a Denon poa 2800. Today it started having problems with the right channel: it makes a very low distored sound that sometimes goes low until you can't hear it. I've tried WD-40 made for electric contacts (waited to dry) over all the Board but with no results. Jack is okay, potentiometer seems okay. Any suggestion? It happens on every output (8ohm, 4 ohm, It doesn't matter: completely distorted)... Also the left Board seems to get more warmer than the right Board...

well A amps are well known to give the more realistic signal due to the treatment of the signal, so they´re suposse to be the most quality amps regardless of whether its class identifies the first letter of the alphabet

Thanks a lot...

I used to run a hill dx3000 was an absolute beast!! Hill audio sounded lovely and used old skool mofets. Lovely warm sound 😊