"1969" John Linsley Hood Class A Amplifier Clone Build
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- Опубликовано: 18 янв 2020
- In this video, I build and test a JLH 1969 Class A amplifier clone kit I found on eBay. It's output power is purported to be 10W, is it? Let's find out.
Link to the kit: www.ebay.com.au/itm/1pc-JLH-1...
Link to reverse engineered schematic: imgur.com/a/P4w5zHg
(Note: the description of the item says the 2N3055 transistors are second-hand, but "work well")
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Deciphering voltage and current adjustment from instruction manual is awesomely useful.
Many thanks.
Phenomenal sounding amplifiers which I have made 2 stereo amps driving my speakers, also I have the 2003 40 watt version that I have yet to set up. A good video, well documented.
I possibly misunderstood you, but I got the impression you said that cross-over distortion was due to "the way transistors work". As far as I understand, crossover distorsion is not present at all when you run a single transistor ( or a tube ) in pure class A, which is the main beauty of it. The cross-over distorsion arises when you run a pair of transistors in push-pull configuration, and bias for class AB operation, i.e. positive half of wave taken care of by one of transistors, negative by the other, and merge the two halves together. The mismatch between the two non-identical ( or non-symmetrical ) halves , or the timing mismatch, gives crossover distortion.
No, I meant on a Class-AB amplifier on a bipolar supply. Class-B can have severe crossover distortion if it's not designed/biased right. Class-A has none on both bipolar and single ended.
Great little amps.Bought (2) stereo pairs of these assembled off EBAY.Been reliable so far, probably 100 hrs on each amp.Very surprising,very listenable,sweet sound.
Really nice, complete, useful video/tutorial. Keep it going!
32:15 "...sometimes results in the output sounding like it's got clicks, pops, snaps and crackles..." Those sounds are something entirely different, like, maybe a bowl of Rice Bubbles being spilt over the amp!
Crossover distortion seems to be widely misunderstood... It can be helpful to think of crossover distortion as a form of clipping.
Not altogether unlike AC rectification (where signal peaks are momentarily steady-state DC), crossover distortion causes the signal to be momentarily steady-state DC too, though, during 0V signal excursions.
Both clipping (peak rectification) and crossover distortion (0V rectification) result in an increased harmonic spectra. However, unlike clipping, where the generation of harmonic components is primarily additive, crossover distortion appears subtractive in nature, often resulting in an anaemic, fuzzy sound, due to the increased odd-order harmonics and limited energy of the fundamental. The negative effects of crossover distortion become much less pronounced with large amplitude signals.
Some audio effects rely on crossover distortion though, so it's not all bad...
Finally, crossover distortion is related to device operating region, not device technology; valves do equally produce crossover distortion when operated at or near cutoff too.
Very good tutorial, thanks for sharing. Greetings from Perth...
To be fair, John audio tested with a square and sinusoidal signals, and the distortion increased noticeably above 10kHz. In that simple oscilloscope, and only with a 1khz sine signal (or listening) that distortion will not be seen.
It's a matter of slew rate, not crossover; the amp starts to have problems with the "rissing speed" side of the signals, it also showed that the original transistors (probably fake (?)) had HF instability issues (ringing).
Anyway, in a listening situation, the overall distortion will be dominated by dist. generated by the speakers; hardly anyone can identify distortions less than 0.15 - 0.2% with their ears alone , that's the "facto standard" for a lot of studio monitors (amplifiers usually have distortions an order of magnitude smaller (0,01% and lower))
Hello Astro,
I bought a set of JLH 1969, similar to your but it use AC input instead of DC ( board had a rectifier) trouble is how you adjust the quiescent current???
Thank you very much for this video. I'm building one of these right now and you explain everything very well. My tube/valve pre amp kit is coming tomorrow to drive it. Solder time!
Can You please check the values for the resistors R4 and R5 in the reverse-engineered schematic? I think they are permuted?
it is strange to me that the class A JLH amp does not have a way to prevent thermal run-away. Is the quiescent current anyway stable?
Thanks
On the eBay listing they say the Motorola transistors are used but good condition and original
Love the video, planning to assemble one too. I bought some bare pcb's, to populate with quality components. I was studying your reversed schematic. Is R4, and R5 around the wrong way in your diagram?
Dude, Thanks for doing this man. Not all of us are circuit wizards. Data and networking sure... But audio circuits, Nope!
Anyways, I might try the build now. But I really want to do a class A tube type thing in a car. Just for the tweeters and mid range. Midbass is simply going to have to be a Class A/B. It seems like this has more then enough output for a tweeter with high sensitivity, but my tweets may not be ideal. I was thinking of building my own ribbion drivers, but I think I will just leave that up to Joesoh Pelon (DIY Ribbon speaker fame)
Again, thanks for this. If possible, would be really cool if you could make another video about mods to this ebay amp, and maybe get more clean power out of it.
Have a good one Astro!
iMickey503
Tubes? In a car? That's waiting for them to fail.....Better use trannies......
Hello, please advise which of those three 220uf capacitors is the Feedback capacitor? I want to try upgrading it with a dissent one . Thanks
bump. i would also like to know
I'm interested in this amp, so when corona over I get a couple.
Cross over distortion? On a class A, class B most definitely but A.
Class A amplifiers do not produce crossover distortion.
The John Audio review shows the use of test gear and why " upgrading " transistors could be a bad idea if not able to do the tests. The power suppy used ( PSU ) is important and has to be of better quality than is unsual. A lab PSU as here would be good.
Great video, just wondering, is a 24 volt (24- 24+) 160 va transformer ok to use for two boards (stereo). Cheers.
Should be. As long as each secondary can handle 2A continuous.
"install the correct success rate to almost 100%". i'm on it
Very nice thank you very much👍👍🇩🇿
It gets VERY hot!
sir yourJLH modified circuit was in Paul Kemble web page for a very long time!
28:40 is it okay that your sine wave is so shifted? 11.15v to -7.5v so average is 3.65/2 volts but it should be zero.
That's just because I never centered it on the screen. The voltage measurements are still the same.
Для 4 Ом. колонок выходной конденсатор нужно увеличить до 6000 мкФ для выравнивания амплитудно частотной характеристики.
English, please.
The original article on this amplifier recommended a 5000uF coupling capacitor for a 3Ω speaker with a 10000uF smoothing capacitor in the supply psu.
I have bought this very kit. It will be my first attempt to adjust a transistor. for that I will be referring to this video. Also I have never installed a transistor on to a heat sink. Can anyone tell me where I put thermal paste for this one if at all. Thank you for any help.
He didn't use thermal paste (the insulator pad works reasonably well for that). What you can do to improve things is where the Aluminum bracket joins the bigger heat sink, use thermal paste there to improve the thermal conductance.
@@Anchor2012 Thank you for the reply. I can now continue with confidence. I am a beginner and my kit came with no instructions. I may have more questions hopefully someone can answer. I am mostly getting into chassis fabrication.
Good advice about thermal transfer between bracket and heatsink
what is the wattage of the speaker...???
The one I was using, or the output wattage? The speaker I think was using was around 10W. The output of the amp won't get any higher than around 5W.
Hi.....first of all congratulations for the video...i'm also building the same jlh1969 amplifier but i didn't understand how to adjust the quiescent current....bad english/chinese...can you tell me exactly where i have to put the two multimeter leads to regular i think about 1.2A??? Thank you ... good evening!
Federico
Sorry for late reply, the leads go in series with the positive supply lead.
@@AstrosElectronicsLab ok many thanks....but you have used a multimiter scale V (volt).....you are sure?? The right scale shouldn't it be the ampere scale or rather milliampere?? 🤔🤔🤔
@@gabrielomar1970 You can masure the voltage drop across a resistor in series with supply lead, say 1 ohm 10W on the voltage scale. Ohms law says for a current of 1.2A, the voltage drop should read 1.2V (V=I x R = 1.2 x 1 = 1.2V)
What (dummy)load did you use? Ohms wise...
8 ohms
30:27 What is a "sinoidal" waveform?
I meant sinusoidal lol.
Hi, which point is test point one exactly. Your help would be much appreciated.
Your calculation of output power ~30min in wrong. It should be about 5.4Watt instead of 10.8Watt. Actually, to use Vpp to calculate average output power, the formula should be Vpp²/8/Load/. So if Vpp=18.65V, Load = 8Ω, the output is 18.65²/8/8=5.43W. So, now the problem, can you get the rated output of 10W by increasing the supply voltage? Or will the amp hitting some problem when the supply voltage is increased. I would like see this included in the video.
You're probably right, I may have forgot to halve it before squaring it. And the max voltage is 25V for the supply.
@@AstrosElectronicsLab I'd say anyone contemplating this build should first read the published articles in Wireless World.
From memory JLHood specified 10 watts into 8 ohms needed 30volt supply at 1.1 amps, higher current/ lower voltages for 4 ohms etc.
Best throw the junk transistors away, use good outputs and if not matched then the higher gain one to the lower poisition in the circuit. Stick to the original design, outputs mounted on BIG heatsinks, not on the bracket. Usual 4 inch wires to the outputs can aid stability. This was a very wideband amp.
The Chinese kits are only usefull for the PCB and not all of those are great.
Built right, this amp is sublime, I built my first in 1972.
I built mine (stereo) at about the same time, worked faultlessly for over 40 years. I introduced a diode into the quiescent current circuit, and glued it to the driver transistor's can, to limit thermal runaway which could happen to these amplifiers. I haven't been able to find the reference to the diode modification though. Good, clear video. Thanks.
When did you measure the distortion properly ? your "scope" cant do that, you are only going by your ears which is very subjective, JAT did point out that the mounting method was less than ideal and that mechanically its not great and his issue with the pot was down to a wiring error on his part, perhaps you should label your DIY power supply properly to avoid confusion between ground and 0v and yeah I remember my folks having similar speakers in the seventies, thank goodness they went out of fashion !...cheers.
Those isolators should go on the base and emitter holes to avoid shorting. The collector to board is shorted by the screw so makes no sense what you did.
Did you watch the video? There is a reason it was done that way. Thanks.
It's not called '1969' at all. It's called 'The John Linsley-Hood Class A amplifier'.
That's what the person who designed the kit called it.
Hi Astro i m from india Mumbai, Plz make a 5A 5v Li ion battery charger with auto cut, thanks
Why do you have to criticize their english? How is your chinese?
his chinglish is about as good as my engrish
hahaha, okay, but let's accept that at least a decent translation is needed in a product manual/description, that shows some care and consideration about it (obviously it's just copy and paste from a translator, no one bothered to check it )
This is what you got from the video? Why even comment? Just leave. No one cares.
If it bothers you so much make your own video.
@@jlev505 bro make your own video if you care so much