Transformer coupled solid state audio amplifier built on breadboard and tested

[@benhoward3049]

Hi John, just wanted to let you know how helpful your videos have been to me. I've been trying and failing to build little amplifiers for a couple of years without much success. Your content explains things in such a concise, detailed way, without ever being boring or patronising and I have learnt a huge amount from you. All of a sudden my builds are working, everything makes sense. You are a hugely valuable resource to people like me. Best wishes for the future, all the best. Ben.

[@JohnAudioTech]

Thanks for the comment, Ben. This is exactly what I hope my videos do. It is a good feeling when you have helped someone.

[@martinda7446]

In the early days of transistor production high power germanium PNP devices were all that was available for some time. Circuit design was following the valve era and substituting like for like. For audio power amplifiers, they knew transistors would not require an output transformer, and there was great expectation of big performance gains here. The lack of a complementary output pair led to new circuit ideas like the quasi complementary output stage and variations of it. The current 2N3055 and 2N2955 pretty much are the same now as the first silicon high power bipolar complementary devices to arrive. I have a few early 60s 3055s lying around. The 1970s was a great time of innovation in audio design and many Japanese manufacturers started a distortion war, all trying to outdo each other to lower their distortion figures. There were some ridiculous figures released for some models - until the early 80s when quality generally seemed to drop off. Harold Leak introduced the 'Point One' series of amplifiers in the 1950s which offered supreme performance from it's 'ultra linear' output stage allowing pentodes to give 0.1% distortion and good power delivery. QUAD had introduced their electrostatic loudspeakers which again offered a close to ideal performance for the first time. A HiFi at home could produce realistic levels of full frequency sound with imperceptible distortion and full dynamic range at the time when studios had managed to perfect their techniques and equipment to capture the artist with almost total perfection - again for the first time (arguably). We must thank Bing Crosby for bringing us audio perfection - believe it or not - He, being who he was, wanted to have his radio shows recorded so he need not have to be in the studio during the performance. He bankrolled a small company called Ampex to investigate the new plastic tape medium developed by the Nazis during WW2, it turned out to be of enormous quality compared with anything seen before. Bing could sit at home while his radio show went on air. We got great Sinatra, Buddy Holly etc... There are audio idiots, but also some great audio genius' who have advanced the state of the art.

[@JohnAudioTech]

Good post. interesting info about Bing.

[@martinda7446]

The early Point One amps were triode connected KT66. The ultra linear technique was an idea developed by Alan Blumlein who along with E H Armstrong invented everything in audio. (seriously they were extraordinary). The Quad speakers of 1957 promised a level of distortion magnitudes below any moving coil motor on any cone loudspeaker. The German tonschreiber was capable of remarkable quality due in part to the introduction of AC bias. It was a complete gamechanger. It is hard to get your head around the possibility that there would be no resurgence of Frank Sinatra's career and possibly none of the sixties explosion (No Beatles?) etc. without Bing Crosby...

[@SODA-iz8lc]

Hi John, Very nice. It reminds me of my younger days. I still got alot of germanium transistors.

[@brianksiazek4666]

You need more breadboards!!!!

[@JohnAudioTech]

I have several but they're all populated with some sort of circuit!

[@SciPunk215]

Thank you John !!!

[@matthewridgeway9250]

I love its awfulness. Perfect for vocals sounding like a bullhorn.

[@barneymiller844]

John on that pam8403 amp board what is the best speaker to use with it

[@kamtapersad1455]

Where did you get the transformers?

[@freespuddy]

Thanks for the nostalgic explanation. It reminded me of an argument I had with an audio salesman 50 years ago. I said I would like to hear what my transistor radio would sound like connected to a large hi-fi speaker. He said there would be no sound because the little radio could not drive a big speaker. I said lets try it and he agreed. I cut the radio speaker out, ran wires from the output to one of the large speakers in the store. I don't remember exactly how it sounded, but I think it was just as loud or louder than the little speaker, plus I think there was more bass.

[@freespuddy]

I also don't remember what he said or the look on his face, but I'm sure he was silently chagrined and embarrassed.

[@JohnAudioTech]

I love disproving silly beliefs (without being cruel). Unfortunately audio is filled with them and some people choose not to listen.

[@k.rmuzik9897]

​@@JohnAudioTech Hey john, i have a circuit i need your help with! it's a transformer coupled push pull amplifier using germanium transistors!

[@martinda7446]

Odd harmonics are main component of any push pull output, the even order harmonics are cancelled. That little output transformer is nasty. The maximum output assuming peak efficiency could reach near a watt (800mW?) with a decent transformer in this circuit, I guess this was saturating near it's rated output which looks like it is about exactly 100mW...A decent 3W transformer has more iron in it than the average Toyota. (I know you said it was all you had, I'm not complaining). Another great video though, I really like your work. Brilliant. PS It looked like it was much worse than 3% distortion, that waveform was visibly very lop sided and wiggly?

[@HillsWorkbench]

I always thought of these transformer designs as lazy, a hang-over from the tube days.

[@martinda7446]

They were a hang over, but choose the right transformer and they work great, still.

[@MarkTillotson]

Part of the issue was efficiency as germanium transistors cannot be pushed to high temperature (90C is the limit for Ge devices, compared to 175C for Si). Thus class B or AB was always going to be the one to use to maximize the usable power from the thermally fragile devices. The manufacturing methods meant for quite a time PNP and NPN were very different - no complimentary devices really.