Simple Workbench amplifier project

GORDON ROBERTSON said:

Even in this age of digital TV, the audio output stages and speakers of TV still seem to be regarded as an area where compromises are made particularly with lower priced units. I've never heard one of those sound bars, do they sound good?

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I don't know what is going on with sound these days. At one time the sound on TV, while not hifi, was crystal clear and non fatiguing to listen to. I had a 27 inch Sony CRT type which epitimised this. There was a genuine effort to make the sound good. And the limiting factor was the small speaker, so you didn't get extended base.

Then things changed. In general the speaker chassis improved but the electronics got a lot worse- mainly I think because of the adoption of class D. On our TV I was going to put a couple of 4mm terminals on the back to drive some external speakers. But the sound was worse- like severe cross over distortion. I then tried the earphone socket- even worse on HiFi phones. Before anyone pops up and says there must be something wrong with my set, just think first.

I have noticed this disturbing edginess on so called hifi systems too. I don't know if people are immune or what.

My fairly high end laptop sound is the same. it has 'HiFi' speakers but very edgy sound. There is even a significant DC offset- once again the amps are class D.

I was in John Lewis' and overheard a classical pianist reviewing the various systems accompanied by plenty bull from the salesman. One system stood out and sounded similar to a real piano. The rest were quite simply awful. Which system did he chose- one of the awful ones. I couldn't believe it .

Yes, sound bars can sound very good. They input digital and have built-in analogue amps. But the best is separate speakers, either left and right or L&R + bass sub.

I bought a nice pair of bookshelf speakers for £30 and am upgrading my DAC/headphone amp soon so I will used the old DAC to drive a couple of amps in one of the speaker cabs.

spec said:

I don't know what is going on with sound these days. At one time the sound on TV, while not hifi, was crystal clear and non fatiguing to listen to. I had a 27 inch Sony CRT type which epitimised this. There was a genuine effort to make the sound good. And the limiting factor was the small speaker, so you didn't get extended bass.
Then things changed.

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The most important thing on TV or in a movie is to hide the microphones. Far away, under a thick turtleneck sweater or under the desk or table. Then the sound from voices is muffled or full of echoes. The reporter on the street is speaking with the audio set for high fidelity so we hear all the truck and car engines, instead of cutting the very low frequencies.
Music is compressed with a compressor with an attack time so slow that the sound suddenly goes to full blast and is full of distortion before it is compressed. Of course they turn up the gain too high then the compressor pumps the background music level down with the beat of the music.

spec said:

Oh I misunderstood. I thought you were talking about input power protection. That's what my fuse and Zener were all about.

You don't normally have to worry about input protection because it is all built into the chip. That huge 470K resistor will give protection against anything. Note that you can safely reverse bias a PN junction so long as you limit the current to around 500uA. Typically a transistor eb junction goes over at around 7V. Placing zeners on the input will create distortion and noise

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Thanks Spec, that makes sense. Yeah, zeners are quite good noise generators, I understand.

spec said:

I was in John Lewis' and overheard a classical pianist reviewing the various systems accompanied by plenty bull from the salesman. One system stood out and sounded similar to a real piano. The rest were quite simply awful. Which system did he chose- one of the awful ones. I couldn't believe it .

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Some people just don't seem to hear the difference at all. My wife can't really tell the difference between the sound quality of a cheapish all in one " HiFi" and separate components with good speakers, except perhaps for greater volume in the latter case. I'm somewhere in the middle as certain subtle effects go unrecognized by the audio part of my brain. It is perhaps just as well that I don't have the ears of a thoroughbred audiophile as I'm unlikely to ever be able to afford the ultimate reproductive setup!

Nigel Goodwin said:

Getting a bit carried away with the amplifier as well though if you hard wire your Celestion's to the TV amplifier it will sound pretty good then as well.

But unless your speakers are pretty large, they aren't likely to match the bass from a reasonable sub-woofer - although they will certainly be better quality overall.

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I am running a pair of Celestion Ditton 110s (I would call them large bookshelf speakers) - seriously doubt the TV's inbuilt amplifier could handle them, considering the faffy little speakers it has and how quiet it is even on full volume.

We run the 'TV' (we only ever watch netflix or Blurays) or our hifi system through them. Sounds great and did not cost that much. There is more than enough bass in my opinion with the speakers as is.

RichTheDude said:

(we only ever watch netflix or Blurays)

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No off air viewing ever? Don't blame you in some respects, so much crap on most channels. You do get some good stuff on cable and satellite TV at times, but you need to pay for that! My wife enjoys her TV shows which is fine by me as I can fiddle with my electronics or go online and talk about electronics without interruption!

Yes Gordon, I know what you mean. My wife is similar but even she is disturbed by the sound from our TV. It is so bad that every so often I have to go and listen to a nice little transistor radio in the bedroom to make sure my ears aren't distorting.

About this Audiophile thing. Many people think it is crazy spending all the money and effort chasing the last knockings in quality and they are right. But you could say the same thing about any hobby, from golf thru cars, thru photography, thru stamp collecting.

My point about the latest stuff is that there is audible distortion which is well known to be distressing to the listener. This is quite different to loss of resolution or narrowing of the frequency response. To give an example, the TDA2030 chip you have just used in your lab amplifier, although not hi fi, has a very pleasant sound that is not annoying of fatiguing. I have even run it through high end phones, where the slightest problem is multiplied ten fold, and still the same.

I bet you do have Audiophile ears. If you like music that is what you have. As I have said before, being an engineer, I had a 'logical' approach to HiFi: the only thing that could possibly impact the sound quality were loudspeakers (obviously) and pick up cartridges. Amps had such vanishingly small distortion and wide bandwidth that they were just bits of wire with gain. This view turned out to be absolute nonsense. Take the amplifier: a typical spec may be frequency response 10Hz to 30KHz, power 50W. Distortion 0.05% full band. In other words way beyond human ear characteristics, or in summary perfect. And so it is... to the spec. The trouble is that the spec premise is nonsense and does not encompass what is actually going on with real signals or the complex way that the ear/brain works. To illustrate this you can get two amplifiers one with 0.005% distortion and one with 0.5%. The former may sound just awful while the latter sounds superb.

On a practical note, there is absolutely no reason why, these days, anybody should not own a very good hifi system, especially someone like yourself with electronics savvy. I am going to stick my neck out and say it could be done for around the £100 mark at a push, but certainly £200, and I'm not necessarily talking about building much either.

GORDON ROBERTSON said:

No off air viewing ever? Don't blame you in some respects, so much crap on most channels. You do get some good stuff on cable and satellite TV at times, but you need to pay for that! My wife enjoys her TV shows which is fine by me as I can fiddle with my electronics or go online and talk about electronics without interruption!

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High again Gorden,
You do know that FreeSat is er.. free. That will get you a pretty good range of programs.

GORDON ROBERTSON said:

Some people just don't seem to hear the difference at all. My wife can't really tell the difference between the sound quality of a cheapish all in one " HiFi" and separate components with good speakers, except perhaps for greater volume in the latter case. I'm somewhere in the middle as certain subtle effects go unrecognized by the audio part of my brain. It is perhaps just as well that I don't have the ears of a thoroughbred audiophile as I'm unlikely to ever be able to afford the ultimate reproductive setup!

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Back on this topic again.

Even worse than the John Lewis experience was the Curry's experience. I was looking at fridges with the wife and I overheard a couple discussing what minifi system to get. They had narrowed their choice down to 3 systems and were comparing specs: mains power consumption. one had IC technology, while the other had quasy sonic power compensation you know the sort of thing. But what finally clinched the deal was the distortion figures. One was say 1%, the second was 0.9% and the third was only 0.5%. They immediately latched on to this and chose the 1% model because the figure was bigger. I was going to mention something to them, but have learned from bitter experience to keep stum.

spec said:

High again Gorden,
You do know that FreeSat is er.. free. That will get you a pretty good range of programs.

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I would need to check again, but I don't think that the channels my wife and older daughter like are available on freesat.

spec said:

Even worse than the John Lewis experience was the Curry's experience. I was looking at fridges with the wife and I overheard a couple discussing what minifi system to get. They had narrowed their choice down to 3 systems and were comparing specs: mains power consumption. one had IC technology, while the other had quasy sonic power compensation you know the sort of thing. But what finally clinched the deal was the distortion figures. One was say 1%, the second was 0.9% and the third was only 0.5%. They immediately latched on to this and chose the 1% model because the figure was bigger. I was going to mention something to them, but have learned from bitter experience to keep stum.

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He he. The sales staff are often equally clueless too!

RichTheDude said:

I am running a pair of Celestion Ditton 110s (I would call them large bookshelf speakers) - seriously doubt the TV's inbuilt amplifier could handle them, considering the faffy little speakers it has and how quiet it is even on full volume.

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They would work fine, and be louder than the original puny speakers - it's really amazing how much difference a decent pair of speakers makes.

Nigel Goodwin said:

They would work fine, and be louder than the original puny speakers - it's really amazing how much difference a decent pair of speakers makes.

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When I was 15 I had one of those "ghetto blaster" type stereos. Twin cassette and 3 band radio. Fortunately it had detachable speakers which meant that there were speaker outputs. I acquired a pair of old HiFi speakers which I connected instead of the ones that came with the unit. The improvement in sound quality was immense. Even better still when I got a stand alone CD player as a Christmas gift. ( My stereo had stereo line in facility for this )

GORDON ROBERTSON said:

He he. The sales staff are often equally clueless too!

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Have you noticed that the sales staff always connect speakers out-of-phase then crank up the bass tone control to try to fix the cancellation? Probably many customers do the same thing.

audioguru said:

Have you noticed that the sales staff always connect speakers out-of-phase then crank up the bass tone control to try to fix the cancellation? Probably many customers do the same thing.

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Haven't been in a shop like that in a longtime so can't remember that one. I had a friend with a bit of knowledge of HiFi who got a job in one of these consumer electronics stores ( Curry's or Dixon's ) anyway turns out he was giving accurate advice that was resulting in reduced sales. He was asked to leave soon after that, which he didn't really have a problem with at that time. This was just out of high school.

RichTheDude said:

I am running a pair of Celestion Ditton 110s (I would call them large bookshelf speakers) - seriously doubt the TV's inbuilt amplifier could handle them, considering the faffy little speakers it has and how quiet it is even on full volume.

We run the 'TV' (we only ever watch netflix or Blurays) or our hifi system through them. Sounds great and did not cost that much. There is more than enough bass in my opinion with the speakers as is.

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We are spoiled for choice in England: there are so many good speakers, some at amazingly low prices. Celestion are one of my favorites too. I particularly like their solid base and sparking top. I have heard your speakers on a really high end powerful system (not mine) and they sounded superb.

One thing about hifi speakers is that, with a few notable exceptions like Lowther and Jordan Watts for example, they are quite inefficient and also like a load of amp current capability to show their best.

I'm afraid on my TV the distortion is in the electronics rather than the speaker, which sounds not bad if driven from a decent source.

GORDON ROBERTSON said:

Haven't been in a shop like that in a longtime so can't remember that one. I had a friend with a bit of knowledge of HiFi who got a job in one of these consumer electronics stores ( Curry's or Dixon's ) anyway turns out he was giving accurate advice that was resulting in reduced sales. He was asked to leave soon after that, which he didn't really have a problem with at that time. This was just out of high school.

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It is a wicked wicked world

Bridge Connection.

Bridge connection has been mentioned- this is an excellent way to radically increase power while still using components with the same voltage rating. Hoping not to be a kill-joy though, there is a down side to a bridge configuration. An audio amp has a very difficult load in a loudspeaker, especially as extreme accuracy is required to keep the overall distortion below about 0.5%. The amplifier/speaker interface is one of the most critical areas to get right and it is thought that this area greatly contributes to the characteristic sound of an audio power amp.

With this in view the added complexity of a bridge configuration makes a successful design more difficult and on the basis of less is better the phase splitter can only add more distortion and other undesirable characteristics. I would strongly advise simply increasing the voltage supply to 24V. You will be surprised how good your amp will sound. I haven't checked your circuit, but just in case, it is always a good move to put as large as you can capacitor directly across the supply lines as close as possible to the chip supply pins: 1000uF (1mF) upwards would be fine for a TDA2030. This has a number of benefits that would help your amp show its best.

By the way, a bridge connection is standard for very high power audio systems like PA and also for motor control and some welders.

I had a restaurant lunch today and discovered that I have grown up.
Previously, I heard and was bothered by distorted amplifiers and lousy speakers but today I ignored them in the restaurant's background music and instead I listened to the music. I have heard the same music many times at home with low distortion on my good speakers and remembered how it sounded when I heard it playing poorly today.

But I am shocked with the huge difference between a singer on a recording who sounds perfect and the same singer singing the same song live when it sounds like they can't sing worth a damn. Maybe when recording they sing the song 50 times and pick out only the good parts. Also when they frequently sing off-key, on the recording they use electronics to correct it. In the recording the chorus are all singing perfectly together because they are all sung (singed?) by the same singer.

I know exactly what you mean- you are not going to believe this but in 1963 when this up and coming band, the Beatles appeared at our local Odeon (cinema) they were not that good. Of course, they later improved greatly. I have a few musician friends who gig and I sometimes go to see them practice. Often they don't bother to set levels and mic up. Under those conditions and also if the room acoustics are bad they sound amateurish. Not so on an actual performance though. Some singers though sound even better in the flesh than on record: Chuck Berry, Roy Orbison, Johnny Cash, Russel Watson for example.

Apparently Dean Martin was so laid back that he couldn't be bothered to sing in tune or on time, so the session musicians just followed him and the recording engineers sorted it all out electronically.

I forget who the arranger was, but Blondie sounded awful until he took them on. There are some before and after recordings knocking around- you would not believe they were the same source.

Some famous groups/singers just plain can't sing and sometimes are not even present for the recordings- Bay City Rollers for example- which are all done by session musicians- the creme da la creme. The Archies group with their hit Sugar, Sugar didn't even exist- they were an impromptu assemblage of studio men.

Like you, I am always amazed by the difference in sound between not too good reproduction and a hifi. My walk-around earbuds packed in so I have just got some Sennheiser Momentums to replace then. The Momentums are not run in yet but boy do they make my Android phone sound good. They even make the gross distortion on my laptop sound more gross.