# TDA2030a Amplifier I.C. Specs

#### Frankchie

Nov 14, 2017
149
The spec sheet for the subject IC has two specs for gain, open loop and closed loop. The closed loop gain has a min=25.5 dB, typ=26dB, max=26.5 dB. The open loop gain is 80dB typical, no min or max specified.
I'm confused why the closed loop gain has such a narrow range. I interpret that to mean that you should use it in that ridiculously narrow range. And yet some of the example circuits in that data sheet are outside that range, 13dB for example.

What am I missing?

Thanks for any help,
Frank

data sheet:https://www.st.com/resource/en/datasheet/cd00000129.pdf

#### Audioguru

Sep 24, 2016
3,654
The voltage divider resistor values at pin 2 set the gain but the variable open loop gain might cause the closed-loop gain to be a little more or a little less if "perfect" resistor values are used.
The datasheet fails to tell you the minimum allowed gain. Most other power amp ICs that have an adjustable gain (look at LM386) say the minimum gain before less gain causes oscillation.

#### Frankchie

Nov 14, 2017
149
Audioguru,
Thanks for the response. Yes, I guess it could mean those dB levels are for some type of ideal performance.

But It's puzzling why they would show a typical application (figure 1) with only a 13 dB gain (by my calculations). A quick look at their other applications also have similar much lower dB values.

BTW, UTC also makes a TDA2030a and their data sheet says the same thing.

Thanks, again,
Frank

Moderator
Nov 8, 2019
2,858

#### Frankchie

Nov 14, 2017
149
Bertus,
Good point, I accidentally used a power gain online calculator...Using a voltage gain calculator shows that the typical application (fig 1) has a 30dB gain..Still outside the 26.5 dB max specification.
I checked two other applications in the data sheet and one did fall within the spec at about 26.5dB, but the other was outside the spec at 20dB.

I would think their typical application should fall within that specification, but at 30 dB it does not. That seems odd to me.

Thanks for the good catch,
Frank

#### Audioguru

Sep 24, 2016
3,654
The test circuit in figure 3 has a 13k feedback resistor feeding 680 to ground which is a voltage gain of 1+ (13k/680)= 21.1 which is reduced a little by the non-infinite open-loop gain. Then the voltage gain is about +26dB.

#### Frankchie

Nov 14, 2017
149
The notation on the top of table 4, where the subject gain parameters are, says refer to the test circuit. So I'm thinking the parameters shown are not necessarily the recommended settings, but provide a example of the performance you can expect with that test circuit. Although it probably makes sense to stay close to the test circuit configuration if you have a choice.

IOW, I'm guessing that many of the parameters in table 4 vary significantly under different allowable circumstances and would be difficult to specify without a a ref circuit.

Audioguru's note saying that test circuit falls within the closed loop gain, helped me conclude the above.

Thanks to all for helping. If I got something wrong, feel free to advise me.
Frank

#### WHONOES

May 20, 2017
1,215
For the TDA2030, there is no gain absolute. The datasheet does not recommend or imply any minimum gain requirement. This means that it could be used from unity gain, essentially a voltage follower, to much larger gain values. Its quoted open loop gain is the gain of the amplifier with no applied feedback.
The ability of any amplifier, but particularly for audio, to provide an accurately magnified copy of its input is dependent on its open loop gain. It is a measure of the amplifiers ability to correct for non linearities in its circuit.
A lower closed loop gain circuit i.e. with feedback applied, will result in lower distortion values than a higher gain circuit because more of the open loop gain is available for correction.
Also, using higher gain circuits will result in reduced bandwidth but that is another subject.
The result of all the above is that you can use any gain you like, within reason, that suits your requirements. The representation in the datasheet is there only as an example and is not mandatory.

#### Frankchie

Nov 14, 2017
149
WHONOES,
Agreed...one minor point, I would say the data sheet does imply a minimum gain..or at-least is somewhat confusing for the unwashed like myself.

For example, on that same data sheet page it specifies min and max voltages and they appear to be real limits. OTOH, the closed loop gain appears to be the characteristic of a specific circuit.

Thanks for commenting, It's nice to have a place to get answers.
Frank

#### Audioguru

Sep 24, 2016
3,654
Maybe ST Micro "assumes" that users know than an audio power amplifier is designed to have very low distortion and a wide frequency response requiring it to have a minimum allowed gain (to avoid instability).
Here is what National Semi says about their audio power ICs:

#### Attachments

• amplifier stability.png
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#### dave9

Mar 5, 2017
1,181
Are you intending to use TDA2030a for a specific purpose?

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,792
Foot note #1 to Table 7. Recommended values of components for a typical amplifier says The value of closed loop gain must be higher than 24 dB.

And did anyone notice that the background "watermark" on each page of the datasheet warns that this product is obsolete? It (or its "clones") seems to be readily available on eBay, Amazon, and the usual Asian vendors. Both the IC and the IC integrated on a small PCB with terminals to form a "module" are sold online, but as per usual caveat emptor (buyer beware) applies.

#### Frankchie

Nov 14, 2017
149
Yes, to replace the audio stage for my old shop radio. Seems to work pretty well, my question was more for educational purposes.

#### Frankchie

Nov 14, 2017
149
HEVANS1944,
Good catch, I certainly did not notice that. Actually I am using one of those Asian modules. A few months ago when I bought the module, I was torn between this module and an LM1875 module.. I see now the LM1875 datasheet is not labeled obsolete.

Leave to you young whippersnappers to notice those things.

Frank
P.S. I am 78

#### Audioguru

Sep 24, 2016
3,654
Foot note #1 to Table 7. Recommended values of components for a typical amplifier says The value of closed loop gain must be higher than 24 dB.

And did anyone notice that the background "watermark" on each page of the datasheet warns that this product is obsolete? It (or its "clones") seems to be readily available on eBay, Amazon, and the usual Asian vendors. Both the IC and the IC integrated on a small PCB with terminals to form a "module" are sold online, but as per usual caveat emptor (buyer beware) applies.
The TDA2030A is also obsolete. Its table 2 has a tiny note that the minimum allowed gain is 24dB.
Sure there are fake, defective and used ones sold on ebay.

#### Frankchie

Nov 14, 2017
149
Audioguru,
It seems odd that the warning is for too low gain, I would have assumed higher gain is the more troublesome area. Then again, maybe that's why I am asking questions and not answering them.

BTW, on my TDA2030a datasheet the tiny note is on table 7, not table 2.

Just an FYI - I now notice that the LM1875 mentioned in my last note is also obsolete according to a small note on an addendum to the datasheet.

Frank

#### Audioguru

Sep 24, 2016
3,654
Lower gain requires more negative feedback then the phase shift at high frequencies causes instability and oscillations.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,792
I have never tried to use the "5-lead" IC audio "power" amplifiers, so it is with great sorrow that I feel that I have missed the last sailing of that boat. All that seems left is a discrete component class a-b design, using either power transistors or beam-power vacuum tubes, the latter with audio output transformers in a Williamson design configuration.

I am particularly interested in maybe reproducing, as accurately as possible, the "100 watt ultra-linear amplifier" with separate plate and screen grid power supplies for the 6146 beam-power pentodes, and using rugged and reliable 6SN7 dual triodes as the pre-amp and drivers. These tubes may be impossible to procure at reasonable prices as NOS, but I think suitable replacements are being made in foreign countries. I could also "roll my own" preamps and driver using whatever tubes are currently available.

I think the output transformer may have to be custom made, but fortunately there is a small company in the USA that specializes in this service for amateur radio customers. I recall seeing a schematic many years ago for a similar circuit that used taps on the output transformer, instead of two separate windings, to apply the screen grid voltages to the pair of output tubes from a single B+ supply connected to the primary center-tap, whereas the linked reference above uses two separate windings and separate power supplies for the screen and plate supplies. Both circuits were identified as "Williamson" derivatives, which at that time (circa 1950 - 1960) meant very linear, low harmonic distortion, state-of-the-art audio power amplifiers. Today they would be called boat anchors, but I thought the ones I heard sounded pretty decent, although they were expensive and I could not afford one, much less two for a stereo "hi-fi" setup.

This is not a construction project for the inexperienced or faint of heart. LETHAL high voltages are required. Electrolytic capacitors with appropriate voltage ratings will be almost impossible to acquire. NOS is not suitable for this, but there are work-arounds using lower voltage capacitors connected in series, with voltage dividers to distribute the high voltage equally across each capacitor. Hardly anyone knows what a "swinging choke" is anymore, and they are probably unavailable, but there is probably a work-around for that too... my Novice rig didn't use a swinging choke, but it did have a voltage-regulated B+ supply with a series pass-tube and negative feedback to control the output voltage. That worked "perty gud" and everyone I worked using CW on the 80m Novice band said my signal sounded great... no chirps, no hum, just pure CW RF.

Fortunately, my first amateur Novice transmitter was a homebrew rig built sometime between 1965 and 1966 while I was serving in the U.S. Air Force. It used a single 6146 power pentode as a Class C RF amplifier. I grew up experimenting with 6SN7 vacuum tubes while learning a little bit of electronics along the way, so those are familiar to me. Playing around with electronics was always a lot of fun and I learned a lot too. This is important to you younger whipper-snappers coming of age here in the 21st Century. If it ain't FUN, why are you wasting your time doing it?

#### Audioguru

Sep 24, 2016
3,654
I made a Heathkit tubes amplifier in 1962. It used Williamson output transformer circuits and sounded pretty good when the tubes were new but they wore out and needed replacement every 3 months. I replaced it in 1964 with a Scott solid state stereo receiver that I still use today in addition to modern ones. Over the years I made many discrete transistor circuits but I never made a simple IC amplifier or an amplifier with Mosfet outputs.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,792
...It used Williamson output transformer circuits and sounded pretty good when the tubes were new but they wore out and needed replacement every 3 months. ...
Yikes! That sounds expensive! No wonder solid-state won over "hi-fi" from vacuum tubes. Seriously, though, if you stick with tubes that don't have indirectly heated cathodes, just (perhaps) thoriated tungsten filaments, and they don't become "gassy" with age, IMHO they should last waaaay longer than three months, years even. I ran the 6146 beam-power pentode in my Novice CW transmitter for almost a year with zero problems and at least fifty watts Class C input power... of course, between the "dits" and the "dahs" it wasn't using any power except that which was used to keep the cathode warm.

In the B-52H (heavy) bomber, there were big racks of vacuum tube linear amplifiers used by the Electronic Warfare Officer to transmit jamming signals, just in case the tail gunner seated to his right happened to run out of 20mm Vulcan Gatling Gun ammunition, or was otherwise inconvenienced. I once got a chance to peek inside one of those slide-out racks and saw dozens of forced-air-cooled 4CX250B tetrode vacuum tubes.

There must have been hundreds of those tubes on every B-52 in our wing. But I didn't see the Armament and Electronics (A&E) Electronics Warfare folks changing out tubes every day. Apparently the tubes were not only very rugged but very reliable. They were readily available on flight-line bench stock, but their ceramic sockets were not. So, I never got a chance to "borrow" a couple of pairs to build a kick-butt hi-fi amplifier. They did enjoy some popularity with hams starting in the late 1960s, when the Strategic Air Command was pretty much standing down B- 52s, but today solid-state linear power amplifiers seem to have taken over that market. I wouldn't know about that because, if I couldn't afford to buy the tube socket, I sure as hell couldn't afford to buy a pair of tubes.

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