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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 3rd January 2019, 06:15 AM   #5491
Ian Finch is offline Ian Finch  Australia
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I suspect your boss was humouring you, Nigel. As a cadet industrial chemist myself once, my boss would mock me in front of colleagues if I resorted to wafty analogies rather than get down to the facts and let a need to use them create a useful understanding. Loose and amusing analogies can pique someone's interest in the unknown but in my case, it was more an attempt to skip the mathematics and "baffle 'em with BS", as he might have indelicately put it.
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Old 3rd January 2019, 11:13 AM   #5492
martyh is offline martyh  United States
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I apologize if this has already been covered but I can’t find it in the thread.
Has anyone used the original 1969 circuit as a headphone amp for 600 ohm phones? Playing around in spice and using a single 30V rail it looks like it will do 140mw or so into that load which is plenty for my needs. I did notice though that HF extension and phase behavior seem to be changed so I’m wondering about stability and I can’t figure out how to check the phase margin in this circuit.
Thanks,
Marty
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Old 3rd January 2019, 12:01 PM   #5493
nigel pearson is offline nigel pearson  United Kingdom
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I know where you are coming from on that Ian. A boss of old almost always had an army training or whatever, with my dad it was the RAF and he was a Radar engineer and opperator. Dad was never one for analogies but was into new ideas, he loved Quantum stuff. Modern bosses want always to know how to sell a thing, constructive dumbing down. My boss likes analogies because it allows him to answer unusual questions if the analogy is strong. He will be very honest and phone me if he gets stuck in a demonstaton. He will say something like this" I am owner of this company, out of need I sell the product. I like you will not understand what has been a lifetimes work of my team. It was my vission how the product should be so that was my input. If you allow I will use analogy to give an idea. Sometimes the analogy falls apart. When so we improve the analogy". Mostly this is exactly what people want to know.

I remember a RAF guy saying how time domain analysis works better for describing real world hi fi distortion at a N-----t demonstation. I know for a fact I was the only one who could go with the maths. I was convinced the guy had a point. I was thrown out of the room for seemingly "dissing" it all. The RAF guy was able to defend it , science always needs proof and ones Peers do that. The RAF guy looked very upset as I think he felt the talk was going somewhere, he gave me a weak smile as I went. I went happily as I had said enough, I was angry. I did something I am not very proud of. I went to all the technical people and said what had happened. They put their heads together and I suspect put an end to it . As they rightly said if all don't agree then it won't happen. Tim de Paravacini gave me an exact reason why we should not use it. He had done it and was not sure the data was relaible. The mistake N-----t made was pretending to know a very complex science and not using analogies to simplify. The sad bit is what they didn't want to say was a signal is made analogue and then put through a ADC. Then we make a digital domain error null with the original CD. If we turn the graph to show time domain errors we arrive at things which are like what we hear. As Tim said an analogue null is not easy, when digital is added it is hard to say it is a true null.

The RAF guy said making an aircraft less noisy is very hard and often things done to the understood science are wrong. From this NXT speakers were patented. The result of wrong made right. They in the end were not a big deal. They started with trying to make aircraft quieter whilst not adding much weight. The same digital systems used to grow the hi fi test idea. Bob Carver won an analogue battle using nulling. Bob said what it proved was other guys had better ears than him. He could by nulling clone a sound. Bob's amp was more like a car HT system in some ways. I can understand why some experts " dissed " him. They lost and it is famous. I think some money was lost, it got a bit nasty.

One thing I did see on that RAF test was how a nasty table for a world class CD player did meaure worse than when on a nice table. Where that went wrong is I would have liked to try a pillow on the nasty table. I totally believe the RAF guy would not lie. The tests were real real time so looked to be true. There was a reduced error. The company do not sell tables I should add. Never be fooled by ears alone AB testing. Do AA AB ABB. Often AA the second time sounds more open and deeper bass. This is because the brain has something like RAM and looks in more detail if identical. A RAM analogy.

The best example of analogy is the water analogy for ohms law. I was told never to use it as it can not depict capacitors for one. Not true. I won't say how. Electronics is an invented science which can set it's own rules. Other sciences came via Alchemy etc so are less closed in. They remember a time when free thinking made the science. Whilst I detest electronics for it's Theology I can see why that would make it a welcolm home for some. I am the first to say it needs to be that way and only a few would like what I like. I would say I return to the Theological Electronics mostly with a willingness to always question. I used the Theology to stop that other idea.

The boss of old stopped the jet engine being in the WW2. Much as old style bosses are fun to know I have no time for them. My maths teacher built those early jets. What idiot forgot to put ram jets on other planes for emergencies? That would have made all the difference. It was about as simple as a thing can be. A Bomber doing 400 MPH.
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Old 3rd January 2019, 12:17 PM   #5494
nigel pearson is offline nigel pearson  United Kingdom
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Quote:
Originally Posted by martyh View Post
I apologize if this has already been covered but I canít find it in the thread.
Has anyone used the original 1969 circuit as a headphone amp for 600 ohm phones? Playing around in spice and using a single 30V rail it looks like it will do 140mw or so into that load which is plenty for my needs. I did notice though that HF extension and phase behavior seem to be changed so Iím wondering about stability and I canít figure out how to check the phase margin in this circuit.
Thanks,
Marty
Great idea. If like the old Senheisser HD414 mk1 one needs the most voltage swing you can get. Perhaps use BD139/135 outputs. What a great idea. Do have capacitor coupling to protect the phones from DC. I lost a few when I didn't. You might need a regulated PSU to reduce hum. 22uF in pairs ( 44 uF ) 250 V polyester perhaps.
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Old 3rd January 2019, 12:32 PM   #5495
nigel pearson is offline nigel pearson  United Kingdom
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Here is a bit of fun I did. Would make a great preamp that can drive headphones. The green resistor is a bit of Folk Law. The BC337 40 is very high current gain. Even a LM358 will be in class A when so ( don't ). Good example of how high gain modern transistors help a JLH. I tried NE5532, TL072, MC33078. The latter I liked best. I had some OPA2604 also.

These are notes to myself. The BC337 is runing too high really. Look how I won't spend the extra penny on the CCS's. That was for fun really. Doubtlesss some error somewhere. Somethings are from before in another test. The results are real. I always remove one part at a time if simplifying.

I remember in to 600R it would be very good.

Click the image to open in full size.
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Old 3rd January 2019, 01:20 PM   #5496
martyh is offline martyh  United States
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I did plan to keep the output cap, at 22uF it looks to be just a couple of dB down at 20Hz. .03% THD at 1KHz 50mw out according to the sim.
Attached Images
File Type: jpg 1969 SCH.jpg (56.3 KB, 546 views)
File Type: jpg 1969 AC.jpg (48.3 KB, 532 views)
File Type: jpg 1969 HD.jpg (32.8 KB, 523 views)
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Old 3rd January 2019, 01:38 PM   #5497
nigel pearson is offline nigel pearson  United Kingdom
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I said 44uF as it is low cost and as you say gives 10Hz. Some think even for headphones that is good. In theroy 200Hz is the lowest note the ear " really " hears. The other 20 Hz to 200 Hz is ear type devices in the body, often lymphatic area. One should always keep an open mind when so cheap do. The brain seems to synthisise when no ear body ear in use.
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Old 4th January 2019, 03:36 PM   #5498
nigel pearson is offline nigel pearson  United Kingdom
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If you took my headphoneamp and used a NE5534 I would guess a 6 watt + version could be made that should be close to the JLH. You need very high gain transistors and about 0.7 to 1 amp standing current. I t can be argued the transistors can be different and 1N4004 is where you start for the CCS side 1R is about 0.7A. Big heatsink and PSU. Say a NE5534 can give 20 mA and the transistors gain of 100, it looks possible. If class A driver added even better. Not sure if a Darlington to the op amp and single type to CCS could work. If it did it is a very pure design, simplicity would be a better word. At 1 mA the 5534 will be in class A. If you had a MJ3001 and 2N3055 in the junk box it could work. Impressive if that nasty pair sounded nice. Tweak the 5534 comp to your taste. There are better/cheaper choices for transistors. +/- 17 Vrails at a guess.
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Old 4th January 2019, 11:29 PM   #5499
martyh is offline martyh  United States
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Thanks for the replies Nigel. I wasn’t disregarding your advice on the output cap, just happened to arrive at 22uf as something I had on hand that would work when I was playing with the spice model. I think your headphone amp looks interesting too. The JLH as HPA is something I arrived at just so I could play with it more when it is done. I’d like it to work as a main power amp also so some kind of switchable output capacitor is probably in order. I have a relay setup rolling around in my head but who knows if it will ever get built that way. I’m at the age where I think about other people using my stuff when I’m gone but still young enough to be lazy about it so it will probably end up just tacking more C on when I need it or using some jumpers inside the case. Tomorrow is the day of the year when I am most likely to come across some really ancient 3055s (big hamfest) and if I see any old RCAs I am going to buy them all
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Old 5th January 2019, 10:04 AM   #5500
nigel pearson is offline nigel pearson  United Kingdom
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If it is for headphones alone many transistors can be tried. I would set current to 100 mA max for 600R. That means at 40V 2 watts per T03 device. With a mini cheap T03 heatsink you have a design or whatever. A T03 will do 2 watts in free air. A T0247 is a better choice. 2SC5200 and a piece of baked bean can larger than it would work. Neither device must touch the other. If you use T0220 which would be ideal this heat sink looks good value.

https://cpc.farnell.com/wakefield-so...%20heat%20sink

An old respected device.

https://cpc.farnell.com/on-semicondu...220/dp/SC06751

And also as very cheap.

https://cpc.farnell.com/on-semicondu...-92/dp/SC13992

It's a shame I didn't post the 600R results that I no longer have. I seem to remember it was 8Vrms or better.

My headphone amp is different to JLH in that the current source is a high impedance output and the output device low impedance, JLH the opposite. In a way mine is best. Although I dislike ready made Darlingtons for this idea it has a certain correctness about it. If you made a Darlington using BC 337-40 and 2SC5200 it would have unreal gain and ft a bit better than old style 2N3055. This means the op amp will be in class A due to nearly zero current requested. All op amps I know of have slight over bias as it is impossible to adjust them once made. This will be the class A part of class AB. Thought to be typically 1 mA level. Being class A a primitive Darlington without feedforward ( BE snubber ) should be tried.


Try my little amp using 15R current setting for headphones. I think you will be surprised. MC33078 my choice of cheaper ones. Gain less than 5 can be a problem. NE5534 can be compensated if less than 5 . It might need it anyway. A bipolar 35 V cap can be used as protection. They actually sound OK. 100uF perhaps. Non polar caps if kept below 0.4 Vrms measure very well, Above that very OK. Polar ones no matter how good are not as good due to diode like structures formed when polarised. A feedback loop lower leg is ideal use of a non polar. 470 uF 35 V is a typical type I use.

I redid a NAD3020 in non( bi ) polar where correct to repair it. Very good results. It wasn't wanting that result. It's I had them in the shed. I did a Rotel RA935 also. I went a bit far with that one and it now has a gentle switch on thump. Sounds great. Going too far was doubling every value. For an amp to sell it would be a problem. Shame as it is a good trade off. Specifically more musical space. Subsonics do matter even though we don't hear them as notes. Science knows this and is a type of hetrodyne or beat.
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