Transistor equivalent

audioguru · Nov 19, 2015

My amplifiers are class-AB and sound fine. I think most people need amplifiers that can produce extra power so that peak levels in music are produced effortlessly without the clipping that does not sound like distortion, instead it just muddies the sounds.
I had a circuit on my amplifier that blinked an LED whenever the peaks were clipped and I was amazed at how often there was clipping but not distortion. When the volume control was turned down a little so there was no clipping then the sounds became much clearer.
I have never made and never heard a class-D amplifier but they should sound fine.

Nikolai Petrenko · Nov 19, 2015

Audiophile most don't like class D. I can see distortion on oscilloscope.
If can make good circuit, class B even make sound slightly better than D.
Damn, unlucky enough, 2N3055 very common but 2N2955 too rare.
TIP41-42 common but I can't find TIP34-35

Nikolai Petrenko · Nov 19, 2015

Oh, I just decided decrease the amp power down to 60-100w to reduce money for electric bill (my family not rich) because some new electric devices will by use such as electric table grill... It also because I can't find a good enough speaker can attach with 75w amp ( 300w is total, 150w subwoofer and 2x75w stereo)
2xLA4440 in btl mode will drive satellite speakers (40W)
Transistors will drive subwoofer (35-40W) (to big?) => total 80W
=> need at least 150w transformer (toroidal of C core?)
I also want 35-40w transistor amp circuit that work with single rail power supply not dual rail because dual rail make circuit more complex.
50w subwoofer speaker 5'' is large enough??

spec · Nov 19, 2015

audioguru said:
My amplifiers are class-AB and sound fine. I think most people need amplifiers that can produce extra power so that peak levels in music are produced effortlessly without the clipping that does not sound like distortion, instead it just muddies the sounds.
I had a circuit on my amplifier that blinked an LED whenever the peaks were clipped and I was amazed at how often there was clipping but not distortion. When the volume control was turned down a little so there was no clipping then the sounds became much clearer.
I have never made and never heard a class-D amplifier but they should sound fine.

Mornin from UK. It's 7am and I'm on taxi duties today; taking wife to a pub in the country for lunch with her mates so I'm having lunch and a beer with a mate from work who lives nearby. He is also into audio etc, and has a massive pair of transmission line speakers of the type our gang were building in the 1980's (rectangular bass driver, squawker, tweeter and super tweeter). I had mine in the front room for a year or two, but just with chipboard and no grill. One day my wife said that either the speakers go or she does. She never did though. In the end I sold off the drive units, which I had spent a year saving up for, and built a smaller closed box design with just woofer and tweeter but the cabinets were veneered and had grill. They didn't have the earth-moving thunder of the TLs but I thought they were pretty good, until I heard my son's Epos ESP14 speakers that is.

Back to topic! At one time, in the UK, clipping was a hot subject and there were numerous projects in the electronics and HiFI mags showing how to build the best clipping detector. I had a similar experience to you about the nature of the audio signal. First time I looked at it on a scope I thought there was a fault with the probe: seemed like grass with these huge spikes shooting up to the sky. The amp was only about 10W so it would clip quite often. I also found the same thing about the sound of clipping: nothing you could put your finger on but not quite right. By coincidence, the LME49810 power amp driver chip that I mentioned in a previous post, not only has a Baker clamp to soften the clipping like valve amps, but also a clipping output- schematic from the data sheet attached.

I also found that if one half of an amps output stage had gone open circuit, music didn't sound as bad as you might expect.

The other thing that amazed me was the sound from tweeters. If listened to in isolation they don't seem to be doing much and sound like a grass-hopper scratching its legs together, and about as loud. But if you disconnect the tweeter though, the music sounds like it is coming from the cellar (basement). This link has a sound file which demonstrates this to a degree.

https://www.harbeth.co.uk/usergroup...-or-soft-dome-tweeter-how-does-Mr-Shaw-decide

I really don't know what is going on at the moment with sound. We have a not bad TV, plasma 3D and all that, but the sound is peaky and full of distortion; it drives me mad. It's so bad that I thought there was a fault so I check another TV and exactly the same. It's pretty bad on laptops too and I can't understand why. You have to work hard to make it so bad. I thought it might be due to class D, but as you say class D should sound OK. Oh well! better go and wash the car (auto).

spec · Nov 19, 2015

Nikolai Petrenko said:
Audiophile most don't like class D. I can see distortion on oscilloscope.
If can make good circuit, class B even make sound slightly better than D.
Damn, unlucky enough, 2N3055 very common but 2N2955 too rare.
TIP41-42 common but I can't find TIP34-35

Oh dear! car washing delayed.

You don't have 2SC5200_FJL4315 (NPN) & 2SA1943_FJL4215 (PNP)? They would have been ideal. There are other suitable complimentary pairs too.

2N2955 MJ2955 etc are all the same.

TIP35C (£1.36 from RS
https://uk.rs-online.com/web/p/bipo...245522677633D424F5448267573743D54495033354326

TIP36C (£1.15 from RS)
https://uk.rs-online.com/web/p/bipo...245522677633D424F5448267573743D54495033364326

I will sort out some transistors for you if you like! There are probably hundreds that would be suitable. But a bit busy at the moment.

Also, I will have another look at TIP41 & TIP42 as you seem to favour them.

spec · Nov 20, 2015

Nikolai Petrenko said:
Oh, I just decided decrease the amp power down to 60-100w to reduce money for electric bill (my family not rich) because some new electric devices will by use such as electric table grill... It also because I can find a good enough speaker can attach with 75w amp ( 300w is total, 150w subwoofer and 2x75w stereo)
2xLA4440 in btl mode will drive satellite speakers (40W)
Transistors will drive subwoofer (35-40W) (to big?) => total 80W
=> need at least 150w transformer (toroidal of C core?)
I also want 35-40w transistor amp circuit that work with single rail power supply not dual rail because dual rail make circuit more complex.
50w subwoofer speaker 5'' is large enough??

Glad to hear that you have lowered the amp power- wise move you won't regret it. Will get back to you, probably in 11 hrs time.

UPDATE (14 Hrs later)

Hi Nikolai

I have found the power transistors that I had in mind for your power amp. They are classics and widely respected and used in the audio field. They tick all the boxes and should be good for 70W (but not checked for sure). Nice big TO264 case, which gives low thermal resitance, case to heatsink. Suprisingly low cost too.

These transistors would also be good for general use: linear PSUs, SMPSUs, etc.

Only buy the ON versions. Multicomp also sell them and, while they may be identical, you can't tell.

MJL3281A
NPN
Manufacturer: ON
Cost £2.45 UK
Supplier: RS

https://uk.rs-online.com/web/p/bipo...677633D424F5448267573743D4D4A4C33323831414726

MJL1302A
PNP
Manufacturer: ON
Cost £2.55 UK
Supplier: RS

https://uk.rs-online.com/web/p/bipo...?searchTerm=MJL1302AG&relevancy-data=636F3D32

KeepItSimpleStupid · Nov 20, 2015

if you want to build an amp, build your own version of the Leach Amp. https://users.ece.gatech.edu/mleach/lowtim/

I did, back in the mid-80's. My customizations included: case, protection, power supply, slow turn on (surge elimination, logarithmic ramping of audio), 1% metal film resistors, 10Turn pot for bias adjust, 4 independent supplies for amp, one for protection circuit, 40,000 uf of filtering, 19" rack, 2RU high, cap voltage ratings increased to 100 V except the main caps and no power switch) The 100 V upgrade was totally necessary. No DC protection except a super fast blow fuse (AGX series) An early version had the 50 V caps that were specified and one blew up causing the amp to be missing one supply rail. That why the shutdown was added. Power switching was handled by a triac timer.

Initial version used a single supply ferroresonant transformer rated at about 20 Amp secondary. Very nice sounding, but it hummed. The later version was four 4x35 Vrms*3A transformer (It should be larger) with an external 500 W AC sine wave voltage regulator.

It was favorably compared with a Macintosh tube amp and Klipsch speakers with horn tweeters. The horns did sound better and louder with the low wattage Mac amplifier. Bass was non existent on the Mac amp. The regulator wasn't used. I like dome tweeters. The amp is supposedly fantastic with electrostatic speakers. Bi-amped (leach for bass, tube amp for horns) would probably be fantastic.

The amp needs to be looked at in terms of what's limiting the power.

The system has a dbx 4bx dynamic range expander with "impact restoration", The latter increases the rise time of the signal source and you can adjust it so you actually hear the hammers on a piano or hammer dulcimer type of music. My friend was into classical and had a CD player with a valve front end.

The frequency response is unheard of: DC to about 800 kHz. Respectively rolled of to 0.5 Hz to 40 kHz. The slew rate is >100 V/uS. DC offset <1 mV.

Plans were to add a clipping indicator and an over-temperature indicator. The protection circuit will prevent damage when the output transistors switched places accidentally. Just one resistor fried which is supposed to fry. The protect circuit could be a little more sophisticated, so the resistor won't pop. If a rail fuse blows the current limiting resistor will pop too. There are space constraints in the design.

The optional power limiter was not used in my version.

I added a stupid headphone jack. Really the voltage gain should change when the jack is used.

I did design a really nice clipping indicator for a piece of work instrumentation though.

Servicing requires a service harness that brings a channel out of the case so you can work on it. It was fantastic in the mid-70's and it's fantastic now.

Nikolai Petrenko · Nov 20, 2015

thank you spec, what are the price of those transistors?
I want to use transistors what have better bass response than than other. Power is 35-40w.

MrAl · Nov 20, 2015

spec said:
Hello MrAl,

This is turning into quite a thread- my fault

The subject in this thread is audio amps but that doesn't matter most of what you say is relevant.

As I see it there are two aspects involving the LF response of an audio amplifier. It's generally assumed that, for design purposes, the human ear can go from 20Hz to 20KHz, so you would imagine that an amp that just covered that frequency range would be fine and it probably would be apart from two practical points at the low end (there are separate issues at the high end).

(1) If the amp is 3dB down at 20Hz it involves a phase change which it can be argued is audible.

(2) It is important that the amp keeps control of the speaker at all frequencies especially around the 20Hz area because that is where the speaker is liable to be resonant. Without putting a transducer on the voice coil and using feed-back from the cone, the best that can be done is to present the speaker with a zero impedance and all the current that is required to do that. Hence the 0.1Hz.

In the original transistor amps the speaker was coupled to the amp via a capacitor, typically 1mF (1000uF). This meant that at the low end the speaker was presented with and ever increasing impedance at the very time it needed most damping, not to mention the distortion and phase changes introduced by the capacitor itself. Later the feedback was derived from the speaker side of the capacitor. This sounds like a neat solution but it introduces other problems.

Split supply amps eliminate all this, and they have become the standard now for high end amps and many ordinary audio power amps too. But this meant that the standard current feedback input stage, with all its advantages, could not be used easily so over to long tail pairs. Not only do these give a small offset they also reduce distortion, but at the expense of more noise.

That's right even an offset of +- 100mv only amounts to 80mW which isn't going to bother the average speaker with a power rating of 20W upwards. You do get a small click when you connect the speaker to a live amp though, which can be a bit off-putting to some people.

Chopper stabilised amps are quite something , and as you say the ultimate in low offset. But opamps have improved so much that they can even better 10uV. The OPA182, for example has an input offset of +-5uV and they are not that expensive.

Back in the germanium transistor days I did a chopper amp using a reed relay. By the standard of the day it was quite good but nothing like your 10uV.

Yes, the LM358 and its quad counterpart, the LM324. When they were introduced they opened up all sorts of possibilities mainly because of their low cost but also because of their characteristics:

(1) IOS 3mV,

(2) IPI 20nA,

(3) Supply current 700uA.

(4) IP range down to negative rail,

(5) Supply range from 2V to 32V.

(6) Output voltage to within 5 mV of the negative supply rail.

Pretty good especially at the time.

Where they are bad is frequency response; they have pretty much had it by10kHz and I suspect that is one reason they have such high cross-over distortion. Also the output drive current isn't that good 20mA up and 10mA down. Inspite of that the the LM358 is still useful today.

Your power supply is interesting. When you say the LM358 is not good for power supplies was the frequency stability the issue or the low output current capability, probably both I expect.

When you mention cost is that because it was a hobby or were you working on a very cost conscious application. I worked on military projects were cost wasn't relevant, within reason that is. Home projects were quite the reverse!

Hi again,

The reason for the "cross over distortion" is because of the output stage, but that can be completely eliminated as i have reported several times in this forum. Biasing can eliminate the cross over distortion because it eliminates the cross over. Once gone, there is no more cross over distortion. There may even be an application note out there now that mentions this. This effectively changes the output stage class.

The response of the device isnt that good for power supplies where we want a fast response to over currents and fast recovery from load step. A unit that is faster by about 10 times is preferred to keep the output at a safe level for all modes of operation. The LM358 is a little slow when used as an error amplifier. Granted it could still fit some applications, but in a better quality power supply we want something faster.

The cost issue is based on the cost of the chip vs the cost of other (better) chips, and is always an issue in commercial units, and sometimes home units. Sometimes for our home units we only have to buy one IC though so sometimes the cost isnt as much of an issue. For my power supply i would have to buy 2 units: 1 for use and 1 for backup repair. That would amount to about 12 dollars USD for the better chip and about 1 dollar for the LM358 chip. So it all depends what we want to spend, 12 dollars vs 1 dollar

audioguru · Nov 20, 2015

Many excellent audio amplifiers and ICs use class-D today. The switching frequency is so high that an LC filter at the output completely removes it. Their distortion is (0.01%) 20 times or more lower than you can see on an oscilloscope or hear (0.2%).
If an audiophile can see any distortion on a scope or hear it then he is an audiophool, not an audiophile. A class-D amplifier can be small because it does not need a huge heatsink.

A subwoofer must produce frequencies down to 20Hz or 30Hz. A 5" speaker cannot do it. An 8" speaker might be able to go low enough if its resonant frequency is very low but then it will not be sensitive enough. Use a 10" or 12"speaker for a subwoofer.
Don't guess if the power will be enough. Look at the sensitivity of the speakers on their datasheets to see how much more power one speaker needs compared to another speaker.

Nikolai Petrenko · Nov 20, 2015

so 5' subwoofer can't make low freq sound because the cone isn't heavy enough (50w with 5,5'' cone will be **** enough to make frog sound) .
With a medium power like 80w, toroidal transformer or EI or "C" transformer will be better? ( I thing toroidal is better for power amp, EI or "C" is better for low power such as preamp )

audioguru · Nov 20, 2015

If a class-AB stereo amplifier produces a maximum of 40W per channel at low distortion then its heating is about 50W so the transformer needs to be rated at 130VA for the amplifier to produce full blast continuously. Maybe a 100VA transformer will be fine for an audio amplifier. Use a toroidal transformer.

spec · Nov 20, 2015

Nikolai Petrenko said:
thank you spec, what are the price of those transistors?
I want to use transistors what have better bass response than than other. Power is 35-40w.

Are you asking about the price of the TIP35C/TIP36C. If so, the price can be seen if you click on the respective links. In case the links are not working for you, I have put the prices in the original post.

If you are asking about the audiophile transistors, they will be about £4 each.

spec · Nov 20, 2015

audioguru said:
If an audiophile can see any distortion on a scope or hear it then he is an audiophool, not an audiophile.

unnecessary and circular, but clever... and funny!

spec · Nov 20, 2015

MrAl said:
Hi again,
The reason for the "cross over distortion" is because of the output stage, but that can be completely eliminated as i have reported several times in this forum. Biasing can eliminate the cross over distortion because it eliminates the cross over. Once gone, there is no more cross over distortion. There may even be an application note out there now that mentions this. This effectively changes the output stage class.

Hi MrAl. I get the feeling that you are getting fed up with telling people about the LM358 corossover didtortion but, sure you can elliminate the gross crosover distortion with a pull-down resistor, but in the chips I had there was still some nasties around what would have been the crosover point. I think something was going on with the drivers. In a conventional AB amp you reduce crossover by biasing the op transistors at typically 20 to 100mA. But another aid to reducing it is by negative feedback but above around 10KHz, in a practical circuit, the LM358 doesn't have any gain so no negative feedback. It is all a matter of degree.

spec · Nov 20, 2015

MrAl said:
Hi again,

The response of the device isnt that good for power supplies where we want a fast response to over currents and fast recovery from load step. A unit that is faster by about 10 times is preferred to keep the output at a safe level for all modes of operation. The LM358 is a little slow when used as an error amplifier. Granted it could still fit some applications, but in a better quality power supply we want something faster.

Are you talking about a power supply or a servo amp. If the first could you not use the normal approach of using a big capacitor to handle the fast surges, while the LM358 handles the low frequency. I don't know your application so not sure if that approach would have been suitable.

spec · Nov 20, 2015

MrAl said:
The cost issue is based on the cost of the chip vs the cost of other (better) chips, and is always an issue in commercial units, and sometimes home units. Sometimes for our home units we only have to buy one IC though so sometimes the cost isnt as much of an issue. For my power supply i would have to buy 2 units: 1 for use and 1 for backup repair. That would amount to about 12 dollars USD for the better chip and about 1 dollar for the LM358 chip. So it all depends what we want to spend, 12 dollars vs 1 dollar

Ah! so you worked in the commercial world- dificult!

spec · Nov 20, 2015

Nikolai Petrenko said:
so 5' subwoofer can't make low freq sound because the cone isn't heavy enough (50w with 5,5'' cone will be **** enough to make frog sound) .
With a medium power like 80w, toroidal transformer or EI or "C" transformer will be better? ( I thing toroidal is better for power amp, EI or "C" is better for low power such as preamp )

Torodial is the best, because the stray magnetic fields are minimised. They also tend to have lower resitance giving less droop on the power lines. They also tend to be smaller for a given power. Traditional EI cores are cheaaper but best to go for toroid throughout. In terms of performance for any application, in audio amps, torroids have the edge. But you could use EI for preamp and driver stage if that is all you have. The preamp lines would be stabilised to a high degree anyway. If you plan to put any transformer in the same case as any of the aplifying stages you really have no option but to use torroids or you will have big problema with hum. Sometimes you need to put a magnetic screen around any transformers to minimise hum pick up.

audioguru · Nov 20, 2015

I designed and make one-of-a-kind audio products and since they were custom-made-to-order, the price of the parts did not matter. Usually my prototype was sold as the final product.

Hee, hee that typo. Can you imagine a speaker that is 5 feet in diameter? I have a subwoofer speaker that is 18" in diameter and it weighs a ton. It is rated at 900W RMS I think. I never made an enclosure for it so it is still brand new.
Here is what American people use for a car subwoofer:

spec · Nov 20, 2015

WOW I have seen it all now

Transistor equivalent

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