A good audio amplifier based around 2N3055(s)? - Page 1
Forum section: electronics / projects

author: Vincent
author_rank: Regular Contributor
timestamp: July 04, 2014, 12:32:02 am
content: Here's the thing:This week I found a nice big power supply using four 2N3055s. The circuit boards didn't have much interesting stuff, but I did grab the transistors. Then while searching information about them I saw they apparently used to be among the top-notch transistors for audio amplifiers in the 60s!A few days later I was examining the frame of an old Toshiba projection TV to see if the boards were worth salvaging, then I noticed the 15W speakers. They're not exactly big in terms of physical size, but I'm fairly sure they could provide more powerful bass for my Yamaha NP-31 electronic piano, which has a pair of 6W speakers. They sound just fine, but the bass sounds a little weak. Hence this project LOL.Since connecting anything on my piano's audio output automatically disables internal speakers, I'm going to need an amplifier circuit for another pair of speakers covering full-range. As for the drivers themselves, I already have a pair of 80s Diatones that sound particularly good with higher frequencies.I assume the amplifier for the full-range drivers can be built using parts that are fairly easy to find. For the bass driver(s) however, I'm pretty much stuck to the four 2N3055s I got, if I don't buy anything that is.So, to summarize this, I'm not sure which amplifier circuit(s) I should choose among all the schematics I can find on the net. My project can take the form of multiple circuits (say one circuit per driver, thus 4 circuits), this way I can give both the bass and full-range their own on/off and volume control if necessary. It's almost a full-range amplifier with bass-boost, come to think of it LOL. That may make it suitable for other uses, eventually.As of the power supply, I can easily find an old stereo system and salvage its power supply transformer, from which I can design my own linear supply. Not the most efficient, yes, but it won't be much hassle xD

author: calexanian
author_rank: Super Contributor
timestamp: July 04, 2014, 02:32:32 am
content: 2N3055's were used in audio because they were stable and cheap. Thats about there their virtues end. By the late 70's they had been replaced by higher beta transistors in nearly every audio application. The do work well as audio amplifiers, provided the circuit can provide them with enough drive current and the feedback loop is good. On the Elliott Sound Products site there are several articles about basic Quasi Complementary amplifiers. Quasi Complementary means the final output transistors are on the same configuration. In the case of a 2N3055 NPN type. Look up the El Cheapo if memory serves me correctly to see a typical low cost implementation of that sort of circuit. Not the best performance, but not thermally critical and good for the wattage range you are talking about. +/- 15 or 20 volt type of thing. There are also a number of transformer driven circuits out there that have various performance characteristics. Most of them were used in Musical instrument amplifiers (Rhodes pianos, later Leslie speaker systems, later standel amplifiers, etc etc) where overall low distortion was not required. With the low cost of TO220 NPN and PNP driver transistors in the late 70's and 80's these circuits practically disappeared in all but the cheapest crap from Taiwan. Start with that Elliot Sound products website and look up the original AP note from Motorola on the full complementary amplifier and you will get pointed in the right direction. The Crown DC300 was originally a quasi complementary circuit, and those worked pretty good.

author: theatrus
author_rank: Frequent Contributor
timestamp: July 04, 2014, 02:34:18 am
content: For example, here is one:http://sound.westhost.com/project12a.htm

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 04, 2014, 04:32:34 am
content: 3055s are nothing to write home about, but if you do the rest of the amp well, it might surprise you. Have a read at Doug Self's site-http://www.douglas-self.com/ampins/dipa/dipa.htmThe amp at the bottom of the page is very good and can be morphed into various other designs.

author: calexanian
author_rank: Super Contributor
timestamp: July 04, 2014, 04:49:56 am
content: Sorry about the google link, but its the fastest one that came up. Here is Motorola AN-485. This is the place most people start for design of practical solid state amplifiers. Most AB class amplifiers are based on this design.http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCUQFjAB&url=http%3A%2F%2Fwww.manuallib.com%2Fdownload%2F2647525%2FC6AFF17160972FE127DFCAB70FC3411B%2FMOTOROLA%2520AN485%2520DATA%2520SHEET.pdf&ei=qjG2U6W0GczwoASLtYLQCQ&usg=AFQjCNFrbripHUJUCkdll-iZ3RFfcNF4AQ&sig2=9uPNPmjpHngXdDnezPWlBQ&bvm=bv.70138588,d.cGU

author: Riotpack
author_rank: Regular Contributor
timestamp: July 04, 2014, 05:06:13 am
content: The legendary NAD 3020 used 3055s and its complimentary pair.You will have to use emitted resistors as the old 3055s were an epitaxial type.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 04, 2014, 05:07:55 am
content: Quote from: calexanian on July 04, 2014, 04:49:56 amThat app note is 29 years old! Can you even get those devices anymore? Do you really think there aren't more modern, better-performing, easier to build, more stable, designs avaiable in 2014?!Why do people even make audio power amps with bipolar transistors anymore when there are modern power FETS?

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 04, 2014, 05:43:44 am
content: Why do people even make audio power amps with bipolar transistors anymore when there are modern power FETS?That is the million dollar question.

author: dannyf
author_rank: Super Contributor
timestamp: July 04, 2014, 07:02:20 am
content: Different people have different definitions of "good".To me, you should be looking for an amplifier with wide open loop linearity and low open loop gain.On that, I would recommend JLH1969 - open loop frequency typically to 25Khz and incredibly fast, being a CFB. Up to 10w and class A only.Along the same lines, Hiraga is also very good.For class B amps, 3020 was mentioned earlier, with quasi complementary OPS. Aksa, closer to a more typical audio amplifier, can be built with just npn output devices as well.Unless you are truly gifted, I wouldn't touch the vertical types.If you have to go with MOSFETs, try the lateral types from Toshiba or power Jfets (very difficult to find now).Unless you are truly gifted, I wouldn't touch the vertical types.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 04, 2014, 07:20:08 am
content: Quote from: Riotpack on July 04, 2014, 05:06:13 amI have fond memories of this beautiful BRAUNhttp://www.hifiengine.com/manual_library/braun/csv-1000.shtml, it uses a couple of paired 3055s per channel that break everytime you accidentally pull out a speaker plug.

author: GK
author_rank: Super Contributor
timestamp: July 04, 2014, 10:04:55 am
content: Quote from: dannyf on July 04, 2014, 07:02:20 amPseudo-technical drivel. What is "wide open loop linearity"?The ignorance reveled by your few sentences is profound. Amplifier "speed" is not related to open loop bandwidth. Low feedback and high open loop bandwidth does not make a technically better performing amplifier - it makes a worse one.

author: GK
author_rank: Super Contributor
timestamp: July 04, 2014, 10:14:08 am
content: Quote from: Richard Head on July 04, 2014, 05:43:44 amUmm.... there are only 1 or 2 boutique semiconductor manufacturers actually making complementary MOSFETs specifically for "linear" (as opposed to Class D) audio power amplification these days, and for the most part they are prohibitively expensive (eg Lateral devices from Profusion/Exicon).The most practical power devices currently available are BJT's from On-semi.

author: Psi
author_rank: Super Contributor
timestamp: July 04, 2014, 10:35:22 am
content: You should make a 50W true class A amp out of them using a big ass heatsinkRun them at 150+C, most have a max operating temp of 200CJust for kicks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 04, 2014, 11:24:14 am
content: Quote from: Vincent on July 04, 2014, 12:32:02 amEr, they were certainly...common. But Walmart is common, too. And I don't think anyone would accuse them of being "top-notch". Get my drift?Personally, I would've left the power supply as is (or fixed it), since that's about all 2N3055s are good for.Quote from: Richard Crowley on July 04, 2014, 05:07:55 amThe oddball ones in the datasheet? Probably not, but also plenty of close enough or better substitutes. Transistors aren't picky things, not the way they're generally used. As for 2N3055s, yes, they are still around, though not likely the same fab as the original parts. fT spec is minimum, so you could get anything from a near-germanium-level slacker to a 50MHz+ screamer. Needless to say, the latter will oscillate in a whole lot of circuits!Tim

author: dannyf
author_rank: Super Contributor
timestamp: July 04, 2014, 11:27:16 am
content: With just four 2n3055, you have a chance to dissipate 50w in a class a amp but no chance of outputting 50w in a class a amp.

author: Andreas
author_rank: Super Contributor
timestamp: July 04, 2014, 06:27:54 pm
content: I would build 2 devices of the legendary "Elektor Edwin 40W" amp with 4 2N3055.Its a class A/B device.With best regardsAndreas

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 04, 2014, 06:50:30 pm
content: likely the projection TV had perfectly fine linear audio power chip amps designed by a team of pros, built on a few decades more recent semi process

author: dannyf
author_rank: Super Contributor
timestamp: July 04, 2014, 07:50:23 pm
content: QuoteAnother CFB amp way ahead of its time.

author: nctnico
author_rank: Super Contributor
timestamp: July 04, 2014, 10:04:49 pm
content: Quote from: Richard Crowley on July 04, 2014, 05:07:55 amNot to mention complete chips and class-D amplifiers.

author: c4757p
author_rank: Super Contributor
timestamp: July 04, 2014, 10:39:04 pm
content: Quote from: Richard Crowley on July 04, 2014, 05:07:55 amBecause they work and they're easy to understand.Quote from: nctnico on July 04, 2014, 10:04:49 pmFor fun.

author: dannyf
author_rank: Super Contributor
timestamp: July 04, 2014, 11:10:05 pm
content: More importantly, because those people know what they are doing.(vertical) MOSFETs are incredibly difficult to design in an audio amp, and sometimes practically impossible - try to build a CFB OPS with vertical mosfets, for example.Aside from older Toshiba mosfets and power jfets (no longer available), you don't see many (any?) quality high power mosfet amps - I think if you were to ask Pass, he would tell you to not build Citation 12M today.So far, (vertical) mosfets success in (linear) power amps are mostly in Class A designs by Pass, or JLH1969M, or Zeus. Those are 10w or less power amps.Advocates of MOSFETs in (linear) power amps are either fooled by (audiophile) marketing or not understanding the challenges.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 05, 2014, 12:51:47 am
content: ... or have read Cordell's book,http://www.cordellaudio.com/- looks like he succeeded in building a vertical Mosfet amp 30 years agohttp://www.cordellaudio.com/papers/mosfet_with_error_correction.shtml

author: nctnico
author_rank: Super Contributor
timestamp: July 05, 2014, 01:31:56 am
content: I have seen this circuit used a lot as a basis for PA amplifiers:http://www.electroschematics.com/4/mosfet-audio-amplifier-irf9530-irf530/

author: retrolefty
author_rank: Super Contributor
timestamp: July 05, 2014, 01:41:56 am
content: My favorite site for all things audio is Elliott Sound Products. Tons of schematics, theory, and practical ideas. He has blank PCBs for many of his more popular projects.http://sound.westhost.com/projects-0.htm#pwr

author: AlfBaz
author_rank: Super Contributor
timestamp: July 05, 2014, 04:06:06 am
content: Quote from: wilfred on July 05, 2014, 03:59:53 amLOL that was the very first kit I ever built.Can't remember the 4 channel mixer/preamp kit that was around at the time but I have to tell you I hooked it up to a couple of 12" speakers, plugged my guitar in and if memory serves me well, my friends and I concluded it's crisp punchy sound was on par with the venerable Fender twin reverb!

author: calexanian
author_rank: Super Contributor
timestamp: July 05, 2014, 06:08:34 am
content: Quote from: Richard Crowley on July 04, 2014, 05:07:55 amClearly there are better devices avaliable today, but the basic design for Class AB solid state amplifiers has changed very little. Many of the chip amps are essentially that style of circuit in a single IC. Of course switching type amplifiers are far more economical and effecient these days, its hard to beat the simplicity of these circuits. Yes, all of those devices are avaliable, with the acception of the bias set diodes. All they are is two diodes thermally connected to the driver transistors anyways.As far as complementary MOSFETS. They suck.. Really technical, I know.. Matching them is a real pain and they can get kinda spiky at times. Top shelf designs with maximum robustness focus these days on the MJE15034 and 35 for drivers and MJL4281 and 4302 as outputs. Also MJ21195 and 96 if you need a T03 package. With those devices you pretty much can do anything "Audio" power wise. The SOA on those devices are great, an the beta is stable through a wide range of operating conditions. I have used those driver transistors up into the HF RF range. Good little beasties.

author: free_electron
author_rank: Super Contributor
timestamp: July 05, 2014, 10:26:30 am
content: Quote from: Richard Crowley on July 04, 2014, 05:07:55 amWhy screw areou d with loose transistors. . Slap in a tda2030 or a modern class-t amplifier.I made an amp that delivers 2x25 watt rms from a so-28 package. It doesnt even need a heatsink.

author: Vincent
author_rank: Regular Contributor
timestamp: July 05, 2014, 04:46:21 pm
content: Oh, thanks for all your replies! I'm aware it does look useless to build an amplifier around 2N3055s, but I got them from a power supply, which was in pieces anyway LOL. I guess I can consider this a part of my learning process? I dunno xD It's the first time I mess with audio circuits, we all start somewhere right? LOLNow as of the full-range amp, I looked in my parts and I found a TDA7499 amplifier on a board from a projection TV. It's capable of 6+6W, 4 or 8 ohms. That should drive my pair of 5W, 16 ohms just fine. So I built the circuit given in the datasheet on a breadboard. Didn't work 1st time, but I managed to get it working. Only problem is... the output is weaker than the input xD Everything else seems normal, the chip even trips if I crank the input's volume too high, and then I can crank it all the way to the max and the output is even weaker. I tried a bunch of things with no success, stays the same. Bad chip maybe?I can get all the amplifier chips I want from recycling, if I'm not looking for a specific part and/or can be patient enough, so I can simply try with another chip and see how it goes.

author: calexanian
author_rank: Super Contributor
timestamp: July 05, 2014, 05:00:39 pm
content: Quote from: free_electron on July 05, 2014, 10:26:30 amI agree, however there is a lot of practical knowledge to be learned from building a proper AB amplifier. Long tail pair design for the input. Thermal coupled bias, complementary driver design, output current limiting and short protection, damping factor calculation, on and on. In all of my designs as of late I myself have just been using chip amps. They are great. But you cannot argue against the educational value of doin it yourself.

author: AlanR
author_rank: Regular Contributor
timestamp: July 05, 2014, 05:19:25 pm
content: Quote from: calexanian on July 05, 2014, 05:00:39 pmAlso beyond a certain power level, one must then go to discrete components to build the output driver end. It is why you still see high wattage audio amplifiers still using transistors for output drive. Of course, one could go class D, but class D will never have the low noise and distortion performance of a proper AB design. Even top of the line car amplifiers from Rockford Fosgate or Kicker still use class AB output for this reason.

author: dannyf
author_rank: Super Contributor
timestamp: July 05, 2014, 08:09:13 pm
content: QuoteSpeakers are pretty tough load to drive. Discrete amplifiers can deliver much more current than most chips can. I would not waste time on those chips amps if you want quality audio.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 05, 2014, 08:30:46 pm
content: Quote from: dannyf on July 05, 2014, 08:09:13 pmAgree, most chip amps are good at light/nominal loads, but most speakers are much more than simple resistive loads, there are often some serious phase angles to deal with at various frequencies.

author: calexanian
author_rank: Super Contributor
timestamp: July 06, 2014, 01:33:06 am
content: audio quality aside Chip amps, in particular the National overture series and the ST high power series with their thermal shutdown and other safety measures are very good at not blowing up under bad conditions. Also having everything on one die is very nice for temperature compensation.

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2014, 05:59:12 am
content: Quote from: jaxbird on July 05, 2014, 08:30:46 pmWhat's the behaviour of an ideal amplifier when faced with reactive loads? Delivering output voltage in proportion to the input signal, regardless of current drawn? I sometime wonder what "correct" behaviour means when faced with speakers that are behaving "incorrectly". Btw, I realise it's unreasonable to expect speakers to be purely resistive.Also, earlier on someone mentioned MOSFETs are bad for class AB because modern MOSFETs are "designed for" class D amplifiers. I don't doubt manufacturers have class D in mind, but what specifically goes wrong when trying to press them into service in a class AB topology? Noisy? Crossover distortion?

author: theatrus
author_rank: Frequent Contributor
timestamp: July 06, 2014, 06:08:33 am
content: Many vertical MOSFETs do not have a safe DC or low frequency linear operating range. They are hyper optimized for switching as fast as possible.P channel MOSFETs are also rarer, bigger, and lower rated. There are very few good "pairs". For switching applications, you can simply use an N fet with the gate driven above the power supply rail. While possible in a linear circuit it's a bit trickier and won't fit into your normal amp topology.

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2014, 07:45:49 am
content: Quote from: theatrus on July 06, 2014, 06:08:33 amSo what's the failure mode? In my mind, linear operation is just a mode where the gate is driven to a voltage that's between the drain and ground, so the transistor conducts and raises the source voltage until VGS hits the threshold voltage. They then follow each other around. The linearness just comes from the equilibrium between on and off, just in the way that an op-amp magically finds a sane output voltage even though its gain is 100,000, or in the way that a comparator can be pressed into service as an op-amp in undemanding (read: audio) applications.One thing that comes to mind is how MOSFETs are famously bad in parallel; does the large heat dissipation demanded of an AB transistor cause hotspots and premature failure?Quote from: theatrus on July 06, 2014, 06:08:33 amGiven that we're intending to burn off unneeded voltage as heat, P-FETs having a higher RDSon hardly seems like a deal breaker. Modern P-MOSFETs are remarkable compared to N-MOSFETs x years ago (for some value of x).Your pairing point is interesting, you may be on to something there. I'm almost thinking of trying to building a MOSFET amp just to see where it goes wrong.

author: IanB
author_rank: Super Contributor
timestamp: July 06, 2014, 08:01:04 am
content: Quote from: rs20 on July 06, 2014, 07:45:49 amLocal hotspots, I believe.

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2014, 09:51:16 am
content: Quote from: IanB on July 06, 2014, 08:01:04 amEven if the device is being used within spec w.r.t. power, current, and power * thermal resistance?

author: SeanB
author_rank: Super Contributor
timestamp: July 06, 2014, 10:14:43 am
content: Linear operation is very limited as to the power dissipation allowed, you run in a very small portion of the allowed current and voltage. A device might be capable of 100A and 100V, but in linear operation you might only be capable of less than 1A at under 20V due to the die size. 100V at 100A is 10kW, and a TOwhatever package will make like a small sun at that power level.Most of the power FETs are designed for digital mode of operation, it is hard to get them to run in a linear part of the curve, you need multiple devices and ballasting resistors to keep them all at around the same level of power dissipation.

author: dannyf
author_rank: Super Contributor
timestamp: July 06, 2014, 01:25:07 pm
content: For linear applications, Rds has no meaning. Just as Vce(sat) - the equivalent of Rds for bjt - has no meaning for bjt in linear applications.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 06, 2014, 02:18:47 pm
content: TI makes a single chip audio amplifier (TAS5630B, sometimes called an "HVIC") that can do as much as 300W per channel. For more power than that, use discrete MOSFETs or IGBTs (for a subwoofer application) just like in an inverter. (Technically, an audio amplifier is a very specialized kind of inverter!)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 06, 2014, 03:00:39 pm
content: MOSFETs are fine in parallel, in saturation: Rds(on) has a strong positive tempco, so if any one transistor (or spot of one) heats up, it draws less current, and the others, more, keeping the heat somewhat spread out.(Note that a single MOSFET, or just as well, a group of them in parallel, all together, can suffer from runaway due to Rds(on) tempco. If you don't design to Rds(on)(max) at Tj(max), your circuit might be fine for a long time, but then along comes this unseasonably hot day, and...)In linear mode, BJTs ans MOSFETs both have the same problem: negative input voltage (Vbe or Vgs(th)) tempco. This is more prominent in BJTs, notorious for "2nd breakdown", where the extra power density of high collector voltage operation makes hot-spotting more probable. A hot spot is going to start as a generally warm area (perhaps due to slightly higher doping in the area, or a variation in thickness, or die bonding quality, or just naturally from the heat island effect of a finite die conducting heat into a non-ideal thermal conductor), and if the power density is below a critical value, the gain of the effect will remain low and the hotspot won't grow much (tightening into a narrower area with a higher peak temperature in the middle). As gain of the effect rises (due to temperature or voltage rise), it worsens, until the temperature at the center of the zone rapidly spikes to a temperature where the silicon is fully conductive; which will either damage the silicon by reaching a temperature where diffusion occurs, shorting C-B-E together, or the power density simply blowing out the silicon altogether (it might be possible to avalanche or otherwise physically destroy bulk silicon when given enough current density, I don't know). Either way, it's basically shot through, and if the surrounding circuit isn't happy with a short in that position, it's probably going to dump plenty of fault current to seal the deal. Within microseconds of failure, all leads are shorted together, at any voltage the fault current cares to develop (I once lost a function generator due to a failed MOSFET -- it blew 50-100V out the gate). If electrolytic capacitors or mains current are involved, the subsequent fireball (starting after maybe 100us and growing into the ms to 10s of ms) can blow the package open and vaporize bond wires, potentially resulting in an open circuit once the dust settles -- but three-way shorts are plenty common, and guaranteed to be a part of the failure.As for MOSFETs, much the same applies: there are three main differences. One, Vgs is somewhat less sensitive, because transconductance is lower (size for size, MOSFETs are worse at 'transisting' than BJTs). Two, the area is much larger, and the current density much lower, so the spot heating phenomenon requires much more voltage, if nothing else. Three, back in the days when MOSFETs were lateral, they were great for linear and RF amps, in part because of these factors! Lateral MOS is naturally quite a lot lower density than vertical, and so, within their operating ranges, couldn't suffer from the effect -- it's always been there, physics guarantees it (just like CMOS latchup from driving pins beyond the rails), but as far as being able to set it off, not so easy.Now that structures have been optimized heavily and current densities pushed up higher, they are again sensitive to this failure mode, and old advice about "no 2nd breakdown" is outdated and must be ignored.Best advice: RTFDS. If they don't give a DC SOA curve, don't use it at DC. Don't assume you can linearly extrapolate the 10ms curve (if given -- some aren't even rated for pulses that long!). This is a thermal phenomenon, and every degree temp rise and second of soak counts. (Actually, you can probably extrapolate it, using some generous worst-case estimates, semi-justified by finding what exponent drives the runaway condition. But at that point, you might as well just shop for one that actually says what you need, and then you'll have CYA to boot.) Some companies more often give DC curves; I think I've seen a lot more from AOS, Infineon and IXYS than from others. Some companies also produce families intended for linear operation, such as IXYS' Linear and L2 series; they generally come at a premium.Some parts even come with DC specs, and show just how terrible they are: IIRC, IXYS' PolarHV series are amazingly useless at DC, even to rather low voltages (something like 50 or 100V comes to mind -- out of an 800V, 1000W module!). I don't think I've ever seen a DC SOA for an IGBT, and many of them don't even provide as much as a 1ms or 10ms curve -- needless to say, don't ever use IGBTs for linear applications, they are optimized expressly for switching (being MOSFET-BJT paired structures, the high current density and sensitivity to local heating shouldn't be surprising).Tim

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 06, 2014, 05:00:35 pm
content: Hi group,If you want to read up on thermal instability in MOSFETs this document from NASA is a good place to start:http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100014777.pdfRegards,Jay_Diddy_B

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 06, 2014, 10:33:05 pm
content: http://www.diyaudio.com/forums/solid-state/101745-bob-cordell-interview-bjt-vs-mosfet.htmlis a fine place to take the mosfet discussion - after all the OP has 2n3055it is amusing how ardent people become about audio electronics - willing to spout thoroughly cocked up theory, blanket statements contradicting engineering principle and practice

author: dannyf
author_rank: Super Contributor
timestamp: July 06, 2014, 10:49:20 pm
content: Some of what he said is decidedly untrue, or highly questionable.QuoteThey definetively suffer from 2nd breakdown. albeit less so than bjts.Quoteft has no meaning for mosfetse. And that statement is only true if you can find a godly driver capable of driving a power mosfet at 300Mhz - you can figure its basic spec.QuoteThey suffer from the same cross-over distortion, and given the higher Vgs, I would argue that unbiased, they suffer more severely.QuoteTrue.QuoteTrue.QuoteDecidedly untrue.QuoteTrue, if we are talking about lateral mosfets.Quotetrue / untrue, depending on the type of mosfets he was talking about.In you want to see a better approach to mosfets in power amps, try Randy Sloan's book: High Power Audio Amplifier. Douglas Self's book on generic audio amplifier design considerations.At the risk of oversimplification, you can think of bjts as current driven devices vs. mosfets as voltage driven devices. Current driven devices have an advantage at higher frequencies.(Vertical) Mosfets are largely unused in today's Class B amplifier designs, for a good reason. Lateral mosfets are not used because of their cost and sourcing disadvantages.

author: LukeW
author_rank: Frequent Contributor
timestamp: July 07, 2014, 04:55:20 pm
content: The Silicon Chip SC-480 published in 2003 used a pair of MJ2955s and a pair of 2N3055s in its output stage.http://archive.siliconchip.com.au/static/images/articles/i302/30285_4mg.jpg

author: Vincent
author_rank: Regular Contributor
timestamp: July 10, 2014, 11:49:51 pm
content: Alright, today I found a TDA2009A on a board from a old Sony CRT TV, and I gave it a try, along with my 15W drivers...Wow! Never imagined my computer speakers were that sh***y! Last time I heard crystal clear speakers like that was when my father bought that expensive pair of Klipsch speakers! Yet it's a pair of cheap drivers from a projection TV! Now it'll be interesting to see how that pair of Diatone drivers sound! Speaking of them, I didn't remember I had a pic!I saved them from an 80s TV that was in pieces. Fortunately the speakers were intact. At the time I grabbed them only because they had a Mitsubishi logo on the label xD Turns out Diatone drivers were actually pretty high-quality!

author: dannyf
author_rank: Super Contributor
timestamp: July 10, 2014, 11:54:06 pm
content: -Wow-you are very fortunate that a tda sounds so wonderful to you.the 2003 is actually quite good.

author: Vincent
author_rank: Regular Contributor
timestamp: August 09, 2014, 12:28:18 am
content: Well, I'm used to the sound quality of computer speakers, whose amplifying circuits are often of questionable quality at best. I've taken a few pairs apart and I wasn't impressed...Now, to make a little update, I'm running the TDA2009A with those Diatone drivers I mentionned earlier as I type this. The sound quality is as good, if not better! The amplifier doesn't seem to mind driving 16 ohm speakers. If anything, I even have the impression to get more powerful sound!On my Yamaha keyboard, the higher notes are quite a bit clearer! I expected to lose a bit of power on the bass side, but that's not the case!Now I need to figure out a way to put the amplifier on a board, since the TDA2009A isn't breadboard/protoboard-friendly. Not sure if prototype boards for multi-leaded packages even exist LOL.