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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 3rd January 2018, 08:47 AM   #4201
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Badge View Post
It was bouncing between 00.0 and 00.1 no matter how much I changed the resistance with the multi turn pot. The output devices are two pin old style transistors marked 2N3055. I don't think the amp board is getting any power with the meter in series with the B+ That is why I am not seeing any change.
the metal case of To3 devices is the third pin.
Transistors do not come in 2pin versions. That's what the "2" of 2N3055 tells you.
The "2" = 3 leadouts.
A diode is marked 1Nxxx where the "1" = 2 leadouts.
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Old 3rd January 2018, 08:55 AM   #4202
danieljw is offline danieljw  Australia
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Quote:
Originally Posted by AndrewT View Post
the metal case of To3 devices is the third pin.
Transistors do not come in 2pin versions. That's what the "2" of 2N3055 tells you.
The "2" = 3 leadouts.
A diode is marked 1Nxxx where the "1" = 2 leadouts.
2 = two silicon junctions i.e. bipolar transistor "2N3055"

1 = one silicon junction i.e. diode "1N4007"

- Dan.
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Old 3rd January 2018, 09:06 AM   #4203
huggygood is offline huggygood  France
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you're going to confuse him, he seems to be a beginner.
for him the transistor has only two pins, hence my question about insulation...

I helped a buddy to build a jlh by mail and he ended up with the same problem.
he did not put the pad under the transistor with the same result
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Old 3rd January 2018, 01:50 PM   #4204
Badge is offline Badge  United States
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Quote:
Originally Posted by Mooly View Post
I would test the meter before going any further. Make sure it is set for DC current and not AC.

If you have no suitable resistors to use for a test then try connecting an incandescent mains voltage bulb across the DC supply via the meter. That will pull enough current to get a reading of some sort. A linear halogen bulb would be ideal.
Thanks Mooly. You were right. My Fluke meter is the problem. I dug out another meter and I have amperage output to adjust
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Old 3rd January 2018, 01:53 PM   #4205
Mooly is offline Mooly  United Kingdom
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JLH 10 Watt class A amplifier
If you are lucky it might just have popped a fuse. Always fit the specified type.
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Old 3rd January 2018, 04:06 PM   #4206
nigel pearson is offline nigel pearson  United Kingdom
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At No 4192 I gave a concept idea. It works very well except needs low resistor values. I will play with it as having gain is not to be sniffed at. If you look at the LM317 graphs the drop out voltage is better than it would be at full power. I think this circuit has one advantage in that the 2N3055 is not in the feedback loop of the LM317. As it costs very little it is as makers diagram including 2 x 1N4007 diodes.

Here is my banker idea. It's not great yet. It's getting there. I have a LD1084 which now I've thought it through should do nicely. Ripple is about -55 dB lower at the 2N3055 output. Hiss is a tiny bit better than my bench PSU. Top graph is ripple due to a 1 amp load before the regulator.

Some very good news for me. There was only a 2 mm stump of the broken transformer primary ( less than 2 mm I think ). I took a big risk and pulled on it and got 15 mm, I lost about 1 mm at the last pull which was OK. The Nuvotem RS0500 P1-2-025 with triple heatshrink and new insulation outer looks as good as new. I think it " is " as good as new now. It's quiet also.
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Old 4th January 2018, 09:06 AM   #4207
nigel pearson is offline nigel pearson  United Kingdom
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Here is an idea I saw in the 1980's from a Creek amplifier, thanks Michael. He ran two rectifiers from one transformer. He also it for a quiter circuit, the preamp. 1 x WO2 1 amp rectictifier plus 1 x 2200 uF standard grade ( not high ripple ). I get 15 dB reduction in hum. There are a few harmonics that better layout will solve, that is mostly a better 0 V point. 87 dBV = 45 uV hum at 100( 120 ) Hz at 1.2 amps. Otherwize it is the same PSU as before. The ripple is 230 mV BIG capacitor and 15 mV 2200 uF to LM317. That 23 dB better than before of which we get 15 dB. The 2N3055 working very well. If someone tries I think we can work out the current the LM317 is using. 16 mA at a guess. That might only be 11 mA to drive this 2N3055 to 1.2A. That's rather good. 5 mA is used by the 240R/5K6 of the LM317.

I now can run the variac transformer down to 220 ( 110 ) VAC for only a mild change in hum ( 3 dB ), that's 10 VAC better. If you look the LM317 now has 1.3 VDC more to play with.

The beauty of this PSU is a novice should be able to make it. If a Super Beta transistor ( also fast ) was used I would expect slightly better hum. If the small cap was made 4700 uF and the big cap 22000uF 2N3055 will do fine for 2.5 A stereo. I have built better PSU's than this. None as easy to make. Thick wire mostly. I will sort out fusing later. I think 35 VDC at 40V spec is OK. This PSU is using this series of cap from my recycle box. Remember this 2N3055 must go on the main heatsink, LM317 should be off the heatsink as it is easier. Here are typical parts.

http://cpc.farnell.com/multicomp/lpr...50v/dp/CA04834
http://cpc.farnell.com/unbranded/am1...00v/dp/SC07473
http://cpc.farnell.com/unbranded/cm3...00v/dp/SC07541
http://cpc.farnell.com/unbranded/cm3...00v/dp/SC07541

I did try a Darlington ( MJ3000/1 ). I didn't get it to do anything better. Also a BD135+ 2N3055. Same story.

Someone asked why Douglas Self insists AB needs only a simple power supply. The 2N3055 here is working in the same way as Self's amplifiers. At the collector 230,000 uV of ripple, at the emitter only 44 uV. That's nearly 75 dB reduction if the 2N3055 base is fed a clean referece voltage ( or music ). The LM317 reference is - 93 dBV ( - 87 dBV 2N3055 ) hum and hiss the same as the 2N3055. That means the 2N3055 which isn't in a loop of feedback is doing a great job, it has a form of feedback in itself ( link if you like below ). I could imagine this PSU will add a bit of second harmonic distortion, not the one to worry about, I will measure it and if not good enough will say. The output 1000 uF + 0R33 is to mimic the amplifier decoupling which I found to be important. With class A we have the luxury of having a small resistance to protect the 2N3055 during start up. I can return to a unity gain NPN+PNP pair if distortion is an issue. At unity gain it should equal or better this. A 2N3055+ 2N2955 would be fun. That way the Vce of 2N2955 should be excellent and no chance of blowing up the driver. It might even have better hum.

http://www.edaboard.com/thread324683.html

If you do the maths this PSU wastes least energy whilst being linear. If it is adjsted to 27V it should work with any mains voltage. Note I get 26.6 VAC when the rating is 25V at 230 V. This is because I am not using the full 500VA, a useful thing. If you look at a lower cost transformer of lets say 160 VA I would imagine it to be about the same more or less. As a rough guide the 2N3055 needs about >3V minimum in to out to get a good result. The LM317 at this light load should be fine and is getting 1.3V extra due to the rectifier working less hard. I will look at fusing later.
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Old 4th January 2018, 10:12 AM   #4208
nigel pearson is offline nigel pearson  United Kingdom
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I've put my plus and minus wrong on the LM317. It's plus to LM317 in, please forgive. When I do more testing I will redraw it.
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Old 5th January 2018, 10:40 AM   #4209
nigel pearson is offline nigel pearson  United Kingdom
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Someone said of switch mode PSU's " At least they don't have 50/60 Hz noise" I have some very bad news. They do. If you look in your switch mode power supply ( SMPS ) if lucky you might have a 330 uF 400 V capacitor. Lets pretend the SMPS is 100% efficient. When 25V rms ( AC ) I had 230 mV ripple when 35 VDC. That implies for laziness about 23 mV at 246 Vrms as my house. That was with 10 000 uF. If we now do 10000/330 ( cap sizes ) it's 30:1. That implies ripple of 23 x 30 = 690 mV or 0.7 V. That suggest the SMPS must show some 1 to 1000 Hz noise.

Here are the results of a Meanwell RS 50- 24 at 28.1V into 0R33 + 1000 uF at 1.2A. I will bracket linear PSU.

27.8 V ( 29.3 ) 1.2A

Ripple - 50 dBV 75Hz !!!! - 65 dBV 150 Hz. ( - 87 dBV )
Hiss 1 Hz to 4 kHz - 72 dBV ( - 105 dBV )
Hiss 4kHz to 10 kHz - 83 dBV ( -105 dBV )
Hiss 10 kHz to 20 kHz -65 dBV ( -105 dBV )
Hiss 20 kHz to 16 MHz - 88 dBV ( - 105 to - 107 dBV )

The ripple is a very odd mix of 50 + 100 Hz ( beat ). The load is 50 % max so very fair. If we take - 50 and - 87 that's 47 dB difference. That's 225 : 1 or 10 000 uV : ( 44 uV ). From what I remember of the Meanwell spec that's well inside it. It's respectable, it's not the levels JLH suggested. We use dB's as they are logarithmic. That means vastly big numbers come down to smaller values. We can simply subtract or add. 1 = 10 ( 20 dB ) 2 = 100 ( 40 dB ) 3 = 1000 ( 60 dB ). We use 20 log that number. Thus log 2 = 0.30103 20 log = 6.0206. A handy number in digital work. Log base 10 is used. These are voltage ratios as usually used.

Lets look at the spare heat problem. The Meanwell has none we need think od. My Linear has 2.5 amps at 6V = 15 watts, The amplifier 30 x 2.5 amps = 75 watts. To only have 20% extra heat is a nice happy accident of a 25 Vrms transformer fitting the needs. I will go on to try to get a little more lower voltage usability. As said dropping to 27 V will solve that anyway. One can use Schotkey diodes, I have doubts about them. The rectifier is heat wee need to be careful of. I like the big cheap rectifiers ( 35 or 50 A ) bolted to the chassis.

To sum up SMPS. Big ripple noise of - 50 dBV ( -87 linear ) . Nasty 15 dB hump 10 kHz to 20 kHz ( switching ? ). Comendable > 20 kHz range ( digital interfacing ? ) although nearly 20 dB worse than the Linear ( x 10 ) . I would suspect the a much bigger SMPS " could " reduce this hum if lightly loaded. Ripple " should " also be lower.

The best ever PSU I made was - 103 dBV hum ( 6 uV ? ) and - 111dBV ( 2.5 uV ?) hiss to 16 MHz at 1.5 amps. -87dBV and - 105 dBV are not bad. I seem to remember a standard LM317 claims 20uV hiss. This might get to 500 uV if being lazy. The 5K6 + 47 uF deals with most of the hiss and a lot of ripple. It's 10 pence you must spend. In data sheets it say 10 uF. 47 uF is slightly better. LM317 is vastly better than people think. It is not so good on big complex loads where it can go unstable.The single 2N3055 emitter follower should be much better. A class A amplifier must be a LM317's best possible big load. You can use one per amplifier ( just ) LD1084/85 measure the same when I tested them and have low drop out and higher current. For now I like the LM317 + 2N3055 as it seems logically a nicer solution.

I have graphs if needed.
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Old 7th January 2018, 10:18 AM   #4210
stevec67 is offline stevec67  United Kingdom
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Hello all, I've decided I want to build a JLH Class A from a kit, using a case and heat sink that I have around and 2x 19V SMPS. It's going to be my first DIY amp and I haven't done much electronics since my sixth form days. Nevertheless I can read a schematic and at a push I could make this on Veroboard. However a kit would be easier, I can't find the Hart kits any more, can anyone recommend a decent one? The Chinese Ebay specials seem OK but I'd like to avoid the dodgy 2N3055s of unknown origin if possible and get one with better devices. If this still means a 2N3055 then so be it, but I understand that there are better devices these days, both in TO3 case and whatever they call the flat black ones that are possibly easier to engineer by way of flying leads.

So, does anyone have any recommendations please? There could be a whole £10 at stake!
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