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Transistor equivalent

Discussion in 'General Electronics Chat' started by Nikolai Petrenko, Oct 24, 2015.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My pc is running Windows 10 and takes a long time to stop or close a Falstad sim. I thought my pc was permanently frozen.
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    I think that ther are two broad diode detector topologies: series and shunt. The series is used more oftten than the shunt but I seem too remember that the the shunt type had advantages at microwave frequencies.

    I vaguely remember the microwave men having terrible troubles with temperature effects (mil temp range). We used to go to project meetings and this drift subject was discussed extensively. To us anything higher than 100Mhz was hard to to imagine and we had no idea what they were talking about. Anyway to cut a long story short, the cause of the problem was that the diode bias current was drifting with temperature and that was the root cause of the problem- if only they had said that in the first place. When we told them that we could give them a constant current of even 1% if they wanted, they simply wouldn't belive it. But when one of our team gave them around 0.5% they were most impressed. No more problem.

    After that digression here are the two topologies. I wonder what the shunt detector would be like in the xtal radio. You would have to bias the diode around the knee (sorry Bob) for best results.

    MrAl, the more I think about your sync detector idea the better it seems. It shouldn't be too hard to implement either. Seems like a front end amp, a comparator and two RF FETs woul do it. That would be the best xtal radio ever!​

    ETO_xtal_rad_series_shunt_detectors_2015_11_2015.PNG
     
    Last edited: Nov 14, 2015
  3. spec

    spec Well-Known Member Most Helpful Member

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    Mine too. At first I didn't think it was working so I went off and had a coffee. When I got back it was working fine. (win7)
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    :oops: Forget that Tony- been staring me in the face all the time
     
  6. Mikebits

    Mikebits Well-Known Member

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    Spec, LTSPICE sim is the free package most peeps around here use. I just started using it again, and still learning its user interface. The toughest part I have is setting up my simulation to run the way I need it too. Here is a link for download. There are also many user groups for this software. Models and Q&A can be found at Yahoo LTSpice User group.
    I think I understood you right in that you were asking about a Sim package, if not oops...

    http://www.linear.com/designtools/software/
    https://groups.yahoo.com/neo/groups/LTspice/info
     
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  7. spec

    spec Well-Known Member Most Helpful Member

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    Many thanks for the heads up Mike will look into that. I'm just starting to get the hang of Eagle but only for circuit capture.
     
  8. Mikebits

    Mikebits Well-Known Member

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    I kinda wish I had went with Eagle, but alas I made the mistake of purchasing National Instruments Multisim, which does what I want, but it is not quite as good as I hoped, it is the small things like short-cut keys, scripts, attention to detail when creating the user interface. NI seems to be lacking all the little niceties that make ones life easier and productivity go up. For my next go around on a CAD package purchase, I will be much more careful. I have other expenses at the moment such as test equipment. So many tools one needs to properly work in this arena. Oops, I think I am derailing this thread. Sorry.
     
  9. spec

    spec Well-Known Member Most Helpful Member

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    Not you I am the culprit-as usual :banghead:
     
  10. Mikebits

    Mikebits Well-Known Member

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    I blame my mother, she passed the ADHD gene onto me. It's a curse :) I think all of us doing this stuff suffer from ADHD...
     
  11. spec

    spec Well-Known Member Most Helpful Member

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    ADHD, or attention deficit hyperactivity disorder, is a medical condition that affects how well someone can sit still, focus, and pay attention. http://kidshealth.org/teen/school_jobs/school/adhd.html

    Sit still: don't know
    Focus: quite the reverse
    Not pay attention: quite the reverse again from what I have seen of your posts and the others on ETO. :)

    On a serious note, engineers, not just electronic types, tend to have active enquiring minds. They also tend to be analytical. These characteristics are quite differnent from ADHD. Mind you, some are eccentric. There was a mathamatician at work who was quite brilliant but he was unabe to dress himself properly, he always had a cigarette in his chops with ash all down the front of his jacket, and he would bump into the walls as he walked down the corridor and if you talked to him about anything apart from maths he didn't know what to say.
     
    Last edited: Nov 14, 2015
  12. Nikolai Petrenko

    Nikolai Petrenko Member

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    I will replace C945 with PN2222 has max nf=4db. BC549 "low noise" will become noisier than PN2222, 2N3904, BC337 at higher collector current,while noise figure in datasheet was measure at low current like 100µA. At 10mA BC549 slightly noisier (about 1,4nV/√Hz) than 2n3904 at the same condition. At collector current like 10 miliamps (when use for preamp), BC337 is the lowest noise, lower than most of other common transistor. but I only have 1 Bc337 from old machine so I will buy some PN2222 (2N2222 metal case to-18 is better in many cases but seem be extinct)
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    Nikolai,

    May I suggest that you forget about transistor noise figure for the time being. Just use a transistor which has the noise figure mentioned in the data sheet and has the other parameters that suit your circuit. Normally these are current gain (beta, or hFE) at the collector current you are designing for. Get the circuit working and if it is too noisey it may not be due to the transistor alone. Noise will not stop your circuit from working, unless it is a very specialist application.

    Perhaps post your design so we can see your approach. If there is a problem I'm sure someone on ETO will let you know, and probably solve it for you.

    To illustrate the point about noise, below are circuits for two low level audio amplifiers.

    In practical terms they have identical performance, and they both use the same transistor. There is nothing particularly special about the transistor except that it has low noise and reasonable current gain at low collector currents. You will notice that the transistors are biased with identical collector currents. Although the amplifiers have the same voltage gain and the same input and output impedances, they have quite different noise.

    Amplifier 1 would be fairly noisy and, while quite acceptable, wouldn't sound that good by audiophile standards. It would still sound much better than the terrible audio from most TVs (not TV external sound systems).

    Amplifier 2, by contrast, would be much less noisey and would have a smoother and clearer sound.

    Noise and distortion are quite big subjects but, like most areas, you can do quite well by following a few simple rules. For years I had an application report from National, now Texas Instruments, which gave a good coverage of noise and transistor noise figures. I can't find at the moment but if I do I'll post it.

    In the meantime, here is an introduction operational amplifiers which has a chapter on noise which you may like to have a look at:
    http://123.physics.ucdavis.edu/week_1_files/opamps.pdf

    Here is an explanation of a practical design:
    http://www.janascard.cz/PDF/Design of ultra low noise amplifiers.pdf

    Found it but it is a bit more mathamatical than I remebered:
    http://www.electro.fisica.unlp.edu.ar/temas/pnolo/p1_AN-104.pdf

    A bit more readable:
    http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1989/Designing low-noise audio amplifiers.pdf

    A nice simple introduction to noise:
    http://sound.westhost.com/noise.htm




    01CSEL06_ETO_opamp_noise_crop_Iss03.png

    BC184 datasheet: http://www.farnell.com/datasheets/18953.pdf

    bc184_dataswheet.PNG
     
    Last edited: Nov 17, 2015
  14. Nikolai Petrenko

    Nikolai Petrenko Member

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    Phono preamp need very low noise circuit. I am drawing pcb, try to make copper tracks for signal as short as possible, put the board into a metal box to prevent noise from hums in air. I will try to buy polyester-silver foil capacitors and blue resistors.
     
  15. Nikolai Petrenko

    Nikolai Petrenko Member

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    Tubes have lower noise and distortion than transistors but too expensive about 75-250$ :nailbiting:
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    Morning from UK

    Ah! so you are developing an audiophile low noise phono pre amp. That is very intresting. Ignore what I said in a previous post. Obviously low noise is vital for a phono amp.

    Are you doing it as adesign excercise or because you actually wan't a phono amp to use. Have you got a turntable. If so what cartridge have you got. I would presume moving coil rather than ceramic. (Moving coil is nominally 3mV output at 1KHz).

    Can I just say that if you are making the phono amp just for use, using transistors is a hard way to go. If you like I will post a list of opamps that will blow your socks off in terms or quality and low noise. You could then concentrate on the layout etc, which is essential and difficult. You don't have to spend a fortune. I have not heard of polester silver foil capacitors. Sorry to be so negative, but polyester dialectric is not good for HiFi. Geting the right capacitors is absolutely essential to for the right sound. But be careful You can go overboard and spend a lot of money on capacitors unnecessarily. If you would like to go it alone for the experience that's fine. But if you would like me to advise I would be pleased to help. Go for metal film resistors; that is essential. There are a number of other things I could say but I have been going on enough now.

    You are very wise to pay attention to screening and layout. Best the make the copper as thick as possible. Keeping leads shoft is good but the order of 0V connection and power line connection is vital too.

    I have designed many many phono amps along the way. They are partly engineering and partly black art!
     
    Last edited: Nov 18, 2015
  17. spec

    spec Well-Known Member Most Helpful Member

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    :arghh::arghh::arghh:

    I'm going to start again- hope you don't get me wrong, but here goes:

    Tubes have quite high distortion.

    Tubes are no less noisy than transistors, in fact I would say that transistors, and especially those in the new breed of audiophile opamps, have a lower noise.

    Having said that, it may seem odd that tubes do sound better under certain circumstances; guitar amps for example. And as you know, there is some fabulous tube hi Fi, from phono preamps thru headphone amps to power amps. Fabulously expensive too! I would sum up tubes as nice sounding but technically inferior to solid state. A lot of the tube thing is personal taste- I love them, but I also love good solid-state stuff.

    The way that humans hear is a mystery. For example, loudspeakers have comparatively high distortion, even the best, but they sound ok if well designed. Vynal is the same. But you can get a class A amplifier (no x over distortion) with a fantastic spec; very very low distortion, low noise, wide frequency response and it may sound fine at first but after a while you find something is bothering you about the sound. The reason is the black art side of things.

    My son bought a nice sounding amp. It had a particularly fine moving coil phono input stage, for the time, and made my home-made stuff sound bland, so I copied the design- same components, pretty much the same layout, but it never sounded as good as the original. The smallest thing can mess up the sound, even the wrong solder.

    I will leave you to get on with your good work.

    PS: this is the phono amp I was talking about. The RIAA frquency shaping is done in the next stage. Q1 is a matched pair of transistors in a metal can, rather than plastic:

    ETO_Cyrus_2_MC_phono_amp_2015_11_11.png
     
    Last edited: Nov 17, 2015
  18. spec

    spec Well-Known Member Most Helpful Member

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    Here is a bit more advice: start with the physical layout and power supplies.

    The best approach, I suggest, is to buld the power supply in one die-cast box and the phono amp in another.

    Getting the power supply right is vital and an art in itself. Say go for +-15V rails.

    You will need to use gold plated contacts throughout, and the phono sockets should be the types that are isolated from the chassis.

    That way you will have a good foundation for developing your amp.
     
    Last edited: Nov 19, 2015
  19. Nikolai Petrenko

    Nikolai Petrenko Member

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    thank you a lot. blue resistor I mean metal film resistor because they are coated with blue paint and have 5 color strips. I am quite experiences on make pcb, ground line I allway solder an extra copper wire to the ground and line track to make it thicker many time.
    Might my transistor low quality so they have higher distortion and noise than some tubes made by Sony??? :eek:
    Don't laugh at me but my electronic group made a FUNNY RULE for some months in the end this year : "Avoid to use opamps in your circuit, just use dicretr transistors or tubes" :D
     
    Last edited: Nov 18, 2015
  20. spec

    spec Well-Known Member Most Helpful Member

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    Hi Nikolai,

    Sorry if I was preaching about something you already know and have experience with. That's one of the problems I have on ETO, especially being a newbee. Good that you are generous with copper tracks and earths. I expect you are familiar with skin effect. It happens at surprisingly low frequencies.

    You make me feel guilty; I wouldn't laugh; besides which your friends are right. The very best amplifiers are made with discrete transistors, the Burson discrete opamp is a good example: http://www.bursonaudio.com/products/ss-discrete-opamp-v4/

    The thing about tubes is that they inherently seem have a smooth open sound which many people like, including me. Up until about 2000 what your group said was pretty much true and a good rule. Having said that, the phono stage in my son's amp did sound nice and it used an NE5534 but it did have a a pair of matched discrete transistors at the front. Also, the NE5534 was specially selected.

    So where is all this leading. It's this. Your friends are right but even with the best valves or transistors you, or anyone else would have a real job doing all the development work to realise the potential of them. I would guess in a year's time you would still be working at it. The reason is that every little thing makes a difference that's why the top end gear is built on cast and machined chassis and the circuits have all sorts of little bits here and there to make them work to the last knockings. Don't forget the pro designers have masses of specialist gear to help them too. The other thing is that many amps don't just use components off the shelf. Very often they are custom made or selected .Many of the components simply are not available to the public

    On the other hand, if you went with an audiophile opamp you would have a massive head start along the development path. I would suggest that, in practical terms, you would end up with 99.9% of the perfection you are chasing and you would have an amp that isn't too twitchy either. I hate to say this, but in practical terms I suspect that you would end up with a far better performing amp than one you tried to make with discrete transistors.

    I speak from long experience. I'm just like you always chasing the last knockings. It's a good way to be and I admire your enthusiasm but you need to add a touch of practicality. If you treat it as a development/learning programme without necessarily any end product, that's fine. You may not have anything to show for your efforts but you will learn a lot along the way- I did.

    One thing I haven't mentioned is frequency stability. That's what you will get you unless you are very lucky. The circuits you will be developing will have open loop voltage gains of around a 100K, possibly 1M. So work it out 1uV differential signal on the input of your amp will produce 100mV output or if the open loop gain is 1M, 1V. You may look at the circuit and think, the open loop gain might be high but I have negative feedback which reduces that to say 100. That is sort of true but the trouble is that there is no such thing as an opamp like you see on the schematic, there is no such thing as a resistor, capacitor, or inductor either. In fact, it is so bad that there is no such thing as a simple piece of wire. Even air isn't a perfect insulator. You will see on ETO that myschematics are splattered wit 100nF capacitors. That's partly a prcaution against the parasistcs and strays that you dont see on shematics.

    Just to give you a clue, typical tin oxide resistors become an inductor at 200MHz and capacitors have the weirdest models you could imagine. Many turn into inductors even at relatively low frequencies. This is why often the most wonderful amplifier you design on paper with 0% distortion just oscillates. And it is not simple oscillations either. The amp may sit there at 0V input quite happily, but when it gets a signal it might oscillate say from 2mV and stop again at 3mV (just to illustrate). It will probably sound pretty good but there will always be something not quite right when you listen to it for long periods. There are many many more insipid problems that will catch you out. You could do it, but time is your enemy and with too many problems it stops being fun.

    And if I haven't completely put you off yet, be very careful about connecting you latest wonder amp to your precious and expensive speakers. The tell-tale sign is a puff of smoke from the centre pf the speaker chassis and an acrid smell- more of a danger with power amps, but can happen with preamps also. Always put around 16 Ohm resistor in series with the speaker until you are sure that the output offset is around 0V and the amp is copletely stable (oscillations).

    I will stop now but take my and others advice: go for an op amp. You will have plenty enough problems doing an audiophile amp with those! And all things being equal, you should end up with a pretty good phono amp. Alternatively get a part time job and buy the amp you want. It will be much less effort.
     
    Last edited: Jun 13, 2016
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Phono?? You mean you are still playing with old fashioned vinyl records? I still have a turntable with a high quality Shure magnet cartridge that I haven't used for many years until a couple of weeks ago. Click, pop, click, pop .....
    Vacuum tubes?? You mean those old fashioned hot things that produced tremendous amounts of even-harmonics distortion? Some people think the distortion makes a gEEtar sound better.
    Transistors?? You mean those old fashioned little things that produce all kinds of distortion?

    Opamps have been used for audio for many years and new ones are much better than ones designed 47 years ago. Some opamps are designed to be used in phono, tape or anything preamps and are called "audio opamps" because they have low noise and extremely low distortion.

    A transistor produces a lot of distortion because it is not linear. It needs to have a circuit with very high voltage gain so that a lot of negative feedback can be used to cancel the distortion. An overloaded transistor produces more distortion than a transistor that is not overloaded. Opamps have the very high voltage gain that is needed.
     

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