Hi Everyone , It might be interesting to see what kind first projects have been built to enter into solid state amplification. I'll get it started with mine. Lab work with amplifiers in college never got past 5 watts. I remember the adjustable bench supplies as being 1.5 A at up to +/- 15 V. So, after graduation , I came across this Calectro / GC project in a 1980s hobby magazine. I built it with the horrid TIP series devices and all, but it worked. I got the DIY bug , days latter I bought the proper Mototrola devices ( MPSU , MJE , and MJ series power transistors) to rework the whole amp into a much upgraded 100 WPC amp. Once the front end was upgraded to a proper current source , I boxed it up into a nice chassis, along with a preamp from an op amp "cook book". I wound my own transformer with laminations salvaged from a TV transformer. Years later, I found out that the Calectro project was a knock off of a better , and more well known build from a 1970s magazine. Can anyone identify it ?
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My first power amplifier used a TO-92. There was no planning, just cobbled together with a hand calculator after coming home one day from college.
My first complete build was a LM1875 stereo circuit built into a bud chassis salvaged from geophysical surplus. I used the single supply circuit from the TI datasheet. +30 transformer which gave 42 v rail. I built it point to point on Nema CE board. Both channels motorboated about 2.5 times a second, so I put it away. I do not etch PCB's because disposal of Ferric chloride is legal only in 55 gal drums you rent from Safety Klean or others for $35 a month and $450 pickup fee. I do not knowingly buy anything from *****.
I have successfully built an Apex AX6 board to replace a damaged PC14 driver board in a dynakit ST-120 chassis. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html I modified the AX6 board, deleting the on-board output transistors and using the ones on the heatsink of the chassis. The published pcb version is too tall to fit in the ST-120 chassis.
Mostly I repair commercial equipment, which does not require new PCB's. Most capacitors and resistors can be bought from non nuclear sources. I had a stock of non nuclearr sourced transistors, but my local unemployed house painter hauled all that stock off to the steel scrapyard for me in 2020. Only To3 transistor can now be bought from a safe source.
I have successfully built an Apex AX6 board to replace a damaged PC14 driver board in a dynakit ST-120 chassis. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html I modified the AX6 board, deleting the on-board output transistors and using the ones on the heatsink of the chassis. The published pcb version is too tall to fit in the ST-120 chassis.
Mostly I repair commercial equipment, which does not require new PCB's. Most capacitors and resistors can be bought from non nuclear sources. I had a stock of non nuclearr sourced transistors, but my local unemployed house painter hauled all that stock off to the steel scrapyard for me in 2020. Only To3 transistor can now be bought from a safe source.
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1. Class D amplifier designed from scratch. Works ok, but suffers from some hiss due to PCB routing issues.
2. 50W BJT Class AB loosely based on Blameless. Powers the speakers in my study and sounds great.
3. An IRFP(9)240-based MOSFET version of #2. Now my main living room amplifier. Sounds amazing if you ask me. 😀
The big question is where I go from here. What should be my next project after designing a good Class AB amplifier?
2. 50W BJT Class AB loosely based on Blameless. Powers the speakers in my study and sounds great.
3. An IRFP(9)240-based MOSFET version of #2. Now my main living room amplifier. Sounds amazing if you ask me. 😀
The big question is where I go from here. What should be my next project after designing a good Class AB amplifier?
Hi @njswede ..Have a look at Elliot sound projects in australia.Project NR 101.This one I've first build almost 10 years ago and I've recently reordered the boards for a complete redo....It's a lateral mosfet amp using Exicon ones specially designed for audio,very reliable and very robust.I did a slight adjustment to the org. layout for this reason(soldering and resoldering a view times) I decided to redo the whole thing again. I was astonished of the smooth and clear sound it got.I also did the Project 97,which is a lovely preamp with tone controls.Both projects can be assembled within days ,if you got the necessary case,heatsinks and so on.Best regards.ps the front panel of the preamp was changed...it looks now a lot neater....
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It’s hard for me to believe it, but my first true power amp build was my DH-220C in the late summer of 2020. I had only played with vintage amps and simple Class D modules before that. I updated that amp further with a stout SMPS and it’s been cycled through my systems many times since then, operating wonderfully. How time and projects fly…
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My first was a single 2SB407 (with the bias current flowing through the speaker) then an LM380, then an STK439. It lasted till the STK module does what they all do - start making lightning and thunder sound and eventually fail altogether.
My first real amplifier was something I called the “KM441” - 150 w/ch at 8, and would bridge all night at disco levels at 4 ohm. I had two. It was sort of a cross between a DC300A, a Phase Linear, and an Adcom. Real heat sinks, 4 pair of D424/B554 in EF3 per side, op amp driving a CFA, inside the global feedback. Had the typical Crown slam but waaaaaay lower crossover distortion.
My first real amplifier was something I called the “KM441” - 150 w/ch at 8, and would bridge all night at disco levels at 4 ohm. I had two. It was sort of a cross between a DC300A, a Phase Linear, and an Adcom. Real heat sinks, 4 pair of D424/B554 in EF3 per side, op amp driving a CFA, inside the global feedback. Had the typical Crown slam but waaaaaay lower crossover distortion.
Thanks! It actually looks similar to my MOSFET design, except that I have active current source and VBE-based biasing. And I'm using plain old IRFP(9)240. Attaching the schematic for giggles. I've been thinking of making a version of it with lateral MOSFETs.
I think a more immediate project is that preamp. I've been looking at it for a while.
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My first DIY power amp was rated 100W into 2R load.
A quasi-complimentary design based on RCA app notes using 4 x BD130 output BJTs.
When finished I did a successful continuous max power test into 2 Ohms dummies that boiled a cup of water.
After one hour this test terminated with a loud bang:
The output capacitor had exploded after being cooked by ac current ripple.
Its innards sprayed all over the table.
My very first encounter with ESR 54 yrs ago.
A quasi-complimentary design based on RCA app notes using 4 x BD130 output BJTs.
When finished I did a successful continuous max power test into 2 Ohms dummies that boiled a cup of water.
After one hour this test terminated with a loud bang:
The output capacitor had exploded after being cooked by ac current ripple.
Its innards sprayed all over the table.
My very first encounter with ESR 54 yrs ago.
i must admit that I was late to the game for building a power amp. I ended up with Pete Millett's 50 watt class D boards. I have to admit that they sound much better than I expected, so for quite a while now, they are in my main system. Just a touch better than the 40 watt class A amp that I had put a bunch of money into for a rebuild.
For me, it was one then two mono amps based on tda7293/4, Ermes kits around the mid-90s.
I learned a lot with these things because there was a defect on the pcb that caused a ground loop, and these amps were very sensitive to the quality of the power supply in terms of restitution.
I also learned that the tda7293/34 could explode without warning.
I learned a lot with these things because there was a defect on the pcb that caused a ground loop, and these amps were very sensitive to the quality of the power supply in terms of restitution.
I also learned that the tda7293/34 could explode without warning.
So it was more like a 4 ohm load test than 2, huh? A lot of those old ancient designs relied on output capacitor ESR as protection for short-duration short circuits. My first experience with that was my first pair of PA speakers. Loud bang and the highs disappeared. At least the confetti was confined to the speaker box. That is the reason you use MKPs. Bipolar “crossover electrolytics” of the day were garbage. Today’s are better - they learned a thing or two making caps for SMPS’s. They still fail today, but if they used the manufacturing techniques of the 70’s your PC would run about 5 minutes and the supply would die. You had to buy “computer grade” caps to get ones that would take the pounding. PA amplifiers used them in the power supplies.
Not counting the odd TBA810 application circuit, my first audio power amplifier was a variant of the Blomley circuit that I designed. Apparently I hadn't done that very well, because the second or third time I turned it on, the emitter resistors of the output transistors went up in flames.
In the meantime, I had learned about the class-AB bias loops that Johan H. Huijsing and Frans Tol invented in 1976. I decided that a variant on their idea would conceptually be more elegant than a Blomley circuit, so I didn't try to figure out what had gone wrong, but designed a whole new amplifier instead. That one is still in daily use and has worked fine for 30 years. Its design is described in "Audio power with a new loop", Electronics World February 1996, pages 140...143, https://worldradiohistory.com/UK/Wireless-World/90s/Electronics-World-1996-02-S-OCR.pdf
In the meantime, I had learned about the class-AB bias loops that Johan H. Huijsing and Frans Tol invented in 1976. I decided that a variant on their idea would conceptually be more elegant than a Blomley circuit, so I didn't try to figure out what had gone wrong, but designed a whole new amplifier instead. That one is still in daily use and has worked fine for 30 years. Its design is described in "Audio power with a new loop", Electronics World February 1996, pages 140...143, https://worldradiohistory.com/UK/Wireless-World/90s/Electronics-World-1996-02-S-OCR.pdf
I remember building quasi-complementary amplifiers in the mid-1970s. I had discovered 2N3055s and silicon transistors. That was a big upgrade from the Radio Shack 100-in-1 project kit. 😉
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It kind of scares me that I forgot all about my real first power amp kit, the 'Tiger .01' supposedly 70 WPC. I'm sure that it used a ton of feedback for those specs. of .01 THD. It was a pretty simple build and along with it, I built that companies preamp as well. Boy, was it ever a piece of crap. They both worked supplying the speakers that I built, but I had a long road ahead of me when it came to audio.