Simple Workbench amplifier project

[Gasboss775]

Yesterday I took a break from experimenting with switched mode power supplies ( which I've been doing since the end of October ) and constructed a simple workbench amplifier. This was based around a TDA2030 amplifier module. The module is actually stereo but I used only 1 channel. These modules are widely available on eBay.

This is very similar to the one that I used:

**broken link removed**

I have attached, a rather blurry image of the unit with its lid off and the simple schematic.

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As you may have noticed from the picture. The heatsink on the tda2030 is not the original. This was necessary to accommodate the module inside a fairly small case, with height around 40mm. I also desoldered the 3.5mm stereo input jack to allow for my own connections.
Additionally, I added in 2 phono sockets passively mixed with the main input for the option of listening to music from my 'phone or tablet whilst Iam working. I might add in some sort of input protection on the main input, I was thinking a 1K resistor and a coup!e of zener diodes. Power input is via a coaxial DC socket and is supplied by a spare "wallwart" power supply of 9V / 2A, though 6-700 mA would've been enough.


This was a fun project and took less than a day to complete. The case was recycled from an old air ioniser.

 

[audioguru]

The Chinese amplifier has "an excellent sense of hearing". So watch what you say because this Chinese amplifier can hear you.
The datasheet for the TDA2030A amplifier IC says that its minimum power supply is 12V but you are feeding it only 9VDC? It has a rectifier diode (only one??) that reduces your 9V to maybe 8V. With a 24VDC supply its output into 8 ohms is 6W. With your 8V supply its output power is almost nothing.

 

[Gasboss775]

The Chinese amplifier has "an excellent sense of hearing". So watch what you say because this Chinese amplifier can hear you.
The datasheet for the TDA2030A amplifier IC says that its minimum power supply is 12V but you are feeding it only 9VDC? It has a rectifier diode (only one??) that reduces your 9V to maybe 8V. With a 24VDC supply its output into 8 ohms is 6W. With your 8V supply its output power is almost nothing.

Volume is reasonable for my purposes. Have yet to measure it with signal gen and 'scope. The actual input voltage from the wallwort was actually around 9.8 volts. At moderate listening volume average consumption was around 100mA, so that's roughly 900mW in, so yes as you say output power is pretty low. My speaker must be quite sensitive and is 4 ohms, so that probably helps too.

I spend quite a bit of time on diyaudio.com and have seen amplifiers with as little as 50mW output power that allegedly produce reasonable volume with a suitably sensitive speaker. Volume is on a logarithmic scale so the perceived difference between 1/2 watt and 6W is less than you might think.

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I just noticed the link to the module in post #1 is for a kit, whereas mine was pre assembled. I think that I may have paid an extra £2 ( $3 ) for that convenience!

 

[spec]

Nice job Gordon,

Of course, if required in the future, you can increase the power and audio quality by simply using another, higher voltage & current, wall wart- I'm knee deep in them

 

[RichTheDude]

That looks like a Nintendo Entertainment System (NES) or Super Nintendo Entertainment System (SNES) power lead, the one with the blue moulded plug. If so, be careful as in the UK they outputted AC rather than DC.

Edit: Just read the amp has one rectifier diode

 

[audioguru]

I dislike clipping and dislike audio compression. So my audio systems have plenty of headroom (maybe 10dB which is 10 times the power). Then if the average power is 1W and most peaks are 10W, the amplifier and speakers can produce 100W for some loud peaks.

Reverse the numbers if the amplifier has a rated output of only 50mW. Then the average power is only micro-Watts or the amplifier is clipping most of the time.

 

[Gasboss775]

Iam reluctant to put in more voltage without first putting a better heatsink in place.
The wallwart was from an old broadband router and probably not the cleanest power source for an audio application, but I didn't have HiFi performance in mind with this project. I too have a big box of wallwarts on hand! Higher voltage would not be a problem if desired, but definitely with more heatsinkage and some ventilation holes in the case.

 

[cowboybob]

This was a fun project and took less than a day to complete. The case was recycled from an old air ioniser.

The wallwart was from an old broadband route

Good job. Gordan. I bet it was fun!

I am always impressed with re-purposing efforts... .

 

[spec]

Iam reluctant to put in more voltage without first putting a better heatsink in place.
The wallwart was from an old broadband router and probably not the cleanest power source for an audio application, but I didn't have HiFi performance in mind with this project. I too have a big box of wallwarts on hand! Higher voltage would not be a problem if desired, but definitely with more heatsinkage and some ventilation holes in the case.

Hi Gordon,

You are wise to be cautious, but in the case of the TDA2030, you have no worries, so long as you don't exceed +-14V or 28V supply lines. The chip has both short circuit and thermal protection and is inherently as tough as old boots. My guitar practice combo has a TDA2030 running 24V with a similar sized heat sink to your bench amp. The power content in music is very low, so the only time the chip may shutdown due to over heating is if you are putting a continuous tone through it but, even so, you will not damage the chip.

**broken link removed**

In any case, if you are a purist just bolt some aluminum sheet to the existing heat sink- job done. Ventilation holes would be a good move under any circumstances. Assuming the unit sits on feet so the bottom is clear of the work surface, holes in the bottom and top would be best, as heat lost from the heat sink is mainly by convection and, as no doubt you know, convection currents rise, because hot air is less dense (lighter) than cold air

About protection: the circuit is protected from reverse voltage input. The only thing it is not protected against is over voltage (28V). If you did want to protect for overvoltage, a series 1k resistor would not be good, but a series 1A fuse with 24V (say) zener would do the job nicely.

After reading your post I am going to get that amp to go into a pair of second hand nice bookshelf speakers I have just bought with the aim of eliminating the awful audio on our plasma TV (too mean to buy a sound bar).

 

[Gasboss775]

You are wise to be cautious, but in the case of the TDA2030, you have no worries, so long as you don't exceed +-14V or 28V supply lines. The chip has both short circuit and thermal protection and is inherently as tough as old boots. My guitar practice combo has a TDA2030 running 24V with a similar sized heat sink to your bench amp. The power content in music is very low, so the only time the chip may shutdown due to over heating is if you are putting a continuous tone through it but, even so, you will not damage the chip.

**broken link removed**

In any case, if you are a purist just bolt some aluminum sheet to the existing heat sink- job done. Ventilation holes would be a good move under any circumstances. Assuming the unit sits on feet so the bottom is clear of the work surface, holes in the bottom and top would be best, as heat lost from the heat sink is mainly by convection and, as no doubt you know, convection currents rise, because hot air is less dense (lighter) than cold air

I was aware of the thermal shutdown facility but was keen to avoid having this kicking in if at all possible. Yes I really think now that I probably should make some ventilation holes with or without a bigger heatsink. I need to dig out my hobby drill. I have so much stuff in such a small space it's hard to find things ( partly because I've a terrible memory ) I did spend quite a number of weeks last year carefully organising parts. I've got 4 of those rack towers with the little plastic drawers, countless lidded plastic storage boxes and still got more stuff to organise! Iam very lucky that my wife tolerates this sprawl in the corner of our bedroom, admittedly it's a good sized room, but my corner must take up at least 25% of the space if not more!

About protection: the circuit is protected from reverse voltage input. The only thing it is not protected against is over voltage (28V). If you did want to protect for overvoltage, a series 1k resistor would not be good, but a series 1A fuse with 24V (say) zener would do the job nicely.

I had thought about using a fuse too with a zener. What was your reasoning against the 1K resistor and zener?

After reading your post I am going to get that amp to go into a pair of second hand nice bookshelf speakers I have just bought with the aim of eliminating the awful audio on our plasma TV (too mean to buy a sound bar).

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 am always impressed with re-purposing efforts... .

Thanks!

I have a big box of wallwarts waiting to find some new use. I sometimes buy "junk" on eBay just to salvage the case. Ready made project cases are often so much more expensive than all of the components that go inside them.

 

[Nigel Goodwin]

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?

The output stages are fine, it's the speakers that are crap - there's no space in a modern TV for decent speakers or a 'cabinet' for it

If you hard wire a pair of small HiFi speakers to the TV they sound amazing.

Soundbars are fine, if you want a LOT more bass - it's the sub-woofer that really makes the difference. Great for loud music and explosions in action films!.

 

[tomizett]

About protection: the circuit is protected from reverse voltage input. The only thing it is not protected against is over voltage (28V). If you did want to protect for overvoltage, a series 1k resistor would not be good, but a series 1A fuse with 24V (say) zener would do the job nicely.

I think the OPs reference was with reference to signal input, not DC power, although I can't see exactly where he means.

As you have a stereo module, you could consider bridging to increase your output power.

 

[Gasboss775]

I think the OPs reference was with reference to signal input, not DC power, although I can't see exactly where he means.

For clarification I've attached a quick diagram.

 

[Gasboss775]

The output stages are fine, it's the speakers that are crap - there's no space in a modern TV for decent speakers or a 'cabinet' for it

I expect you're probably right regarding the output stages, though historically some of the TV output stages were horrific.

Soundbars are fine, if you want a LOT more bass - it's the sub-woofer that really makes the difference. Great for loud music and explosions in action films!.

I'm not familiar with sound bar technology. Why can't it be included in the TV itself?

 

[RichTheDude]

The output stages are fine, it's the speakers that are crap - there's no space in a modern TV for decent speakers or a 'cabinet' for it

If you hard wire a pair of small HiFi speakers to the TV they sound amazing.

Totally agree about with this, I have an old Kenwood (TRIO) amplifier and some Celestion Speakers, makes any sound bar I listened to in Currys the other day sound like complete buttocks.

 

[Nigel Goodwin]

I expect you're probably right regarding the output stages, though historically some of the TV output stages were horrific.

I think you'd have to go back MANY decades to find that, I don't recall any 'horrific' ones - although there were 'horrific speakers' even in some CRT sets.

I'm not familiar with sound bar technology. Why can't it be included in the TV itself?

Because there's no room - if there was you could have decent speakers in the TV, and you wouldn't need a sound bar

Basically a soundbar is left and right amplifiers, and left and right speakers - in 'cabinets' somewhat better than a modern TV (but still not much good). The third, and most important, part is a sub-woofer, in a substantial box with a substantial speaker - this handles all the bass notes, and the left/right just get the mids and highs.

 

[Nigel Goodwin]

Totally agree about with this, I have an old Kenwood (TRIO) amplifier and some Celestion Speakers, makes any sound bar I listened to in Currys the other day sound like complete buttocks.

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.

 

[Gasboss775]

I think you'd have to go back MANY decades to find that, I don't recall any 'horrific' ones - although there were 'horrific speakers' even in some CRT sets.

I was thinking of a long time ago tbh. I went through a phase a few years back of studying the technology of yesteryear, from valves to the early years of semiconductors just to get some historical context, plus its easy with so many old electronics books going for as little as 99p on eBay!

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I think the OPs reference was with reference to signal input, not DC power, although I can't see exactly where he means.

As you have a stereo module, you could consider bridging to increase your output power.

That idea crossed my mind too and there should be enough spare room in the case to include a phase splitting circuit. If I switch to an 8R speaker ( the 4R one that I'm using is very poor quality. It belonged to a cheap 'n' nasty mini "HiFi" ) I may go for the bridged option. My only other concern as I mentioned earlier is heat dissipation.

 

[audioguru]

The TV in my computer room has its audio played through a 2.1 stereo system that has a 4.25 inches "subwoofer" and two satellite speakers each with two little 1.5 inches mid-tweeters. It is rated for 150 Whats but is powered from a 9.9W power transformer so it sound power is about 5.5W to 7W.

 

[spec]

For clarification I've attached a quick diagram.View attachment 96743

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