Toshiba SA-220L output power?

[Skywave]

On test: as per thread title: it's what I call a 'tuner-amp.' It's working O.K., but I'm a bit puzzled about the O/P power spec. All O/P power figures that follow relate to one channel and are RMS with 8 Ω load: the other channel figures are same.

From 'Hi-Fi Engine', for the SA-220C, the O/P power is stated as 11-watts. With my item, SA-220L, at the point of 'noticeable clipping' (using a 'scope), I get 15-watts. Presumably, that difference is a matter of what harmonic distortion level the O/P power was measured at: different in those two cases. So I conclude that there is not a problem there.
Moreover, I do not believe that the difference between the 'C' and the 'L' model is relevant here, either. It has been my experience that such a difference merely reflects the part of the world that the item is intended to be used in. The 'C' has no L.W.; the 'L' does.

However, the 'Radio Museum' gives 25-watts for the SA-220L.

And finally, just for reference, the PSU provides +40 v.d.c. w.r.t. 0v. / gnd. At max. O/P. (my SA-220L) that falls to 36 v. I do not believe that that is a matter for concern. The PSU is the usual unregulated type: centre-tapped transformer sec'y.; bi-phase rectifier; 2200 µF capacitor.

So, who has published incorrect data: 'Hi-Fi Engine' or the 'Radio Museum'? Or am I missing something - something, perhaps, that is obvious?

Your thoughts & comments, please; thank you.

Al.

[paulsherwin]

The difference in quoted power is probably a mixture of RMS/PMPO confusion and testing into different impedence loads. Radiomuseum often lists incorrect details in my experience.

You are right, the 'L' suffix on Japanese gear normally indicates a version with LW for use in Europe.

These things are normally referred to as 'receivers'.

http://www.radiomuseum.org/r/toshiba...r_sa_220l.html

[Tom_I]

Well, Hifi Engine is right about the 220C, as there is a spec sheet in the service manual. It's more difficult to tell if Radio Museum is right or wrong about the 220L.

Data for the 220C shows power output of 7 watts per channel, RMS (min) into 8 ohms, from 40 Hz to 20 KHz with no more than 0.8% total harmonic distortion, or continuous output, both channels driven (1 KHz) of 11 + 11 watts into 8 ohms.

Unfortunately I can't find equivalent figures for the 220L.

However, data for the 220C gives the power supply as 120 volts, 47 watts, while on the back of the 220L it says 220/240 volts, 80 watts, so maybe they are different?

[Skywave]

Originally Posted by Tom_I

However, data for the 220C gives the power supply as 120 volts, 47 watts, while on the back of the 220L it says 220/240 volts, 80 watts, so maybe they are different?

Thanks for that: very thought-provoking. I suspect that the only difference is the freq. coverage of the radio: LW + MW and LW only. So, just for fun, I did some sums. (In all that follows, a load of 8Ω is assumed on each a.f. O/P channel)

Case 1.
My 220L produces a max. audio O/P of 15w + 15w = 30w. Neglecting the power consumption of the low-power stages, a PSU input watts to a.f. output watts of 64% gives an a.c. PSU input power of approx. 47w. (N.B. same as per your figure above for the 220C). That's with a d.c. PSU rail of 36v. at that power O/P level. It also means that there is 17w. of heat, mainly in the O/P transistors and the power transformer. The transformer is a substantial affair; the O/P transistors heat-sink (common to both channels) is not particularly large: probably O.K for about 5w. of heat dissipation. So allow about 10w. dissipated in the power transformer; 2w. for the low-power stages. Total = 17w: that completes the power budget.

Case 2.
For a total a.f. power O/P of 50 w. and an overall power conversion efficiency of 63% (as opposed to 64%, as above), the a.c. power input to the PSU will be 80w. (N.B: same as per your figure above). That leaves 30w. of heat to dissipate. Assuming the same transformer and same heat-sink as above, (which to me seems highly likely), that's 30w. of heat dissipation that the heat-sink & transformer have to handle. Allow 15w. for the power transformer; allow 2w. for the low-power stages: that leaves 13w. for the heat-sink: I can't see it doing that; it isn't big enough. I also assume same transformer and consequently same HT rail: 40 → 36 v. For 50-w. total a.f. O/P power to same 8Ω load, the HT rail will need to be at least 40 v.d.c. at max. a.f. out, but looking at the spec. for the O/P transistors, more than 40v. (at the power they will be dissipating) will be pushing them close to their limit. Then there is the requirement for modified driving circuitry to drive the O/P transistors to that higher power level. Hence at least two contradictions. In conclusion, the '220L at 80w. a.c. input power' just doesn't stack up.

And finally, just to put a nail in the coffin, so to speak, at the rear of my 220L, it states: 220/240 volts, 47 watts.

As for the Radio Museum, I am forced to draw the conclusion as per Paul's remark (post #2) above.

Al.

[Diabolical Artificer]

Sounds pretty conclusive Al. BTW what OP transistors does it use? The OP tranny package can give a quick rough approximation of power OP, IE TO225 a few watts, TO220 around 10w, etc . Bigger package more power dissapation, . TO3/TO247 usually being found on higher powered amps 50 - 70w.

Andy.

[paulsherwin]

It was normal for these entry level receivers to have quite modest output powers, so 10-15WPC is perfectly plausible.

[Skywave]

The O/P transistors are of the TO-220 type: NPN-PNP 'totem pole' config. per channel. 2SC790 and 2SA490: 40v. / 3 amp max. rating; 25W power dissipation max. when on a large heat-sink. That heat-sink is an aluminium plate, about 2mm. thick, non-finned, about 6 sq. in. total area, bent through 90° along its longest axis. The ventilation of the sink is not impressive. All four O/P transistors share that sink.

Al.

[Skywave]

Originally Posted by paulsherwin

It was normal for these entry level receivers to have quite modest output powers, so 10-15WPC is perfectly plausible.

Quite: and it must be said that 10 watts RMS to a typical 8Ω 'speaker is going to be quite loud! And that's just one channel!

Al.

[Herald1360]

Originally Posted by Skywave

The O/P transistors are of the TO-220 type: NPN-PNP 'totem pole' config. per channel.

That sounds like "complementary" rather than "totem pole".


"Totem pole" is a transformer driven (isolated secondaries) arrangement with two identical devices stacked one on top of the other. Could be either NPN or PNP but the arrangement was normally found back in Ge days, so usually PNP. It saved the cost of an output transformer.

I suppose with the right driver transformer phasing you could do an output stage with either common collector or common emitter complementary pairs but there wouldn't be much point except as an academic exercise.

[mhennessy]

Of course, it's normal to be conservative about specifications in mass-production.

If you state the exact output power, you're inviting bad publicity from a reviewer who might make a mistake (slightly low mains or dummy loads of lower impedance or scope out of cal, etc).

Take a look in Hi-Fi News, where you'll note that all amplifiers exceed their test specification by at least 10% - sometimes as much as 25%. I can only think of 1 or 2 examples where the amplifier only just met its specification. My own experiences mirror this. The Musical Fidelity B200 is perhaps the most extreme example I know of - rated at 60W per channel, it delivers over 100W per channel. But not for long, as the mains transformer is only rated at 120VA and failures are all too common.

[Skywave]

Originally Posted by Skywave

The O/P transistors are of the TO-220 type: NPN-PNP 'totem pole' config. per channel.

Originally Posted by Herald1360

That sounds like "complementary" rather than "totem pole".

Ah-Ha! Yes, you're right of course: a simple slip of mine. Thanks for the correction.

Al.

[Simon Gittins]

Interesting to see the measurements.

It's 11W per channel in the specifications (attached).

I won't attempt to upload the manual here as it's 19MB. if anyone wants a copy, PM me with your email address.

Simon.

[mhennessy]

That's a much better scan than the one available at Hi-Fi Engine - is it worth offering them a copy? I'll send a PM with my email address in a moment (thank you for the offer)

As I said, specifications have to be conservative. What they say is that 11W per channel, at 0.8% THD, is a guaranteed minimum, from any production sample, even at the lowest mains input voltage. If you measure more than that in practice, then great! On the other hand, hopefully no-one will measure less, as that's bad PR.

The fact that Al is getting 15W per channel with "noticeable clipping" - which would be more than 1% THD if measured - is no surprise at all. The only mystery is the Radio Museum figure, but I'm sure they'd be happy to correct it in light of this thread.

The same situation occurs all the time, especially if it's a key specification that's easy to measure. For example, the specifications of Fluke DMMs are incredibly conservative - even after many years of use...

[Skywave]

Originally Posted by mhennessy

The only mystery is the Radio Museum figure, but I'm sure they'd be happy to correct it in light of this thread.

Yes: it was the discrepancy in the data between Hi-Fi Engine and the Radio Museum which was the essence of this thread - as per the initial post. But I'm content now with what I know to be reliable.

I'm not a 'fully paid-up member' of the R.M., so if someone who is would be kind enough to follow through the above suggestion, I'm sure many will appreciate the corresponding amendment.

Al.

[Cobaltblue]

Originally Posted by Skywave

And finally, just to put a nail in the coffin, so to speak, at the rear of my 220L, it states: 220/240 volts, 47 watts.

Thats interesting the pictures on RM site shows 80W.

Maybe there was more than one version, mind you the heatsink is pretty small.

Do the pictures on RM match your unit Al? or are there noticeable differences.

Cheers

Mike T

[vidjoman]

There has always been controversy over the way specs are presented. The copy of the spec sheet shows the power as 11 watts with both channels driven. Many specs will show it with just one channel operating, and it may well be 15 watts, so add them together and quote 30 watts output. This started when transistor amplifiers became mainstream and 'power' was a selling point. Later we had 'music power' and some figures doubled. Manufacturers would claim that music is not a steady (RMS) output and so the output, for each sound, is actually greater than the RMS value. I'm sure we have all seen a small amp capable of hundreds of watts output and looked to see how it could possibly work.

[mhennessy]

I wonder if mains power consumption has to be reported differently in different territories? Perhaps when power factor is accounted for, the apparent power could be approaching 80W - audio gear tends to have a relatively poor PF. If there was another, more powerful version, I'd expect it to get a different model number - especially as the Japanese were not exactly hesitant to bring new models to market - but naturally anything is possible...

I'll try to see if I can get the spec amended on RM.org, but I'm not a big user, and don't find it an easy site to interact with.

As to power output, it's true that there is great latitude in reporting figures. This unit is quite explicit in explaining how the figures are arrived at, stating both channels driven, and the maximum distortion at that level. It also states 11 watts per channel into 4 ohms, suggesting a supply that "sags" somewhat under load (though allowing that permits savings on heat sinks and output devices).

If values are quoted, but with no qualification about the number of driven channels, then it will be assumed that both/all channels are driven to maximum output - I've never seen an exception to that because if a manufacturer takes that liberty, they will quickly be caught out. If single-channel figures are quoted, it'll be made clear. Though doing so might only serve to suggest that your PSU is not as "stiff" as it could be, so it's often wisest to omit it, frankly. But if you've gone to the expense of a regulated PSU, then Marketing might want to shout about it...

Happily, Toshiba don't use the incorrect label of "Watts RMS", which is marketing-speak at best. I suppose that "continuous average sine wave power" is a bit of a mouthful

[mhennessy]

Originally Posted by mhennessy

I'll try to see if I can get the spec amended on RM.org, but I'm not a big user, and don't find it an easy site to interact with.

The details on RM.org have now been updated: http://www.radiomuseum.org/r/toshiba...r_sa_220l.html

I must say that this is one of the easier things I've done on there, and all credit to the team who replied to my suggestions for their prompt and courteous replies

One thing did come up, however, as a result of this comment:

Originally Posted by Skywave

I'm not a 'fully paid-up member' of the R.M.,

I've been asked to point out that you don't have to pay to be a member. You can choose to pay a nominal up-front fee or build up "credit" by submissions (I did the latter). However, the policy has changed, and now guests can obtain data for free. The folk at Radio Museum feel that it's important to correct mis-information about how the site operates where possible.

Having said that, it's probable that Al was using that phrase as a figure of speech - but it could be interpreted literally, especially if English is not your first language. Either way, I'm just passing the message on.

To the model itself, it's interesting that they have the following data:

Continuous power output 7 watts per channel, min RMS, at 8 ohms, both channels driven with no more than 0.8% harmonic distortion, from 40 Hz to 20,000 Hz.
Continuous power output at 1,000 Hz (both channels driven): 11 watts per channel (8 ohms).

As a result of that, they are classing it as 14 watts (undistorted), clearly adding 7 and 7 together.

The 7W "power bandwidth" figure is in the data from Hi-Fi Engine, but not in the (much better) scan from Simon. It's easy to miss, as the scan from Hi-Fi Engine is quite hard to read.

Anyway, hopefully this encourages others to submit corrections to Radio Museum in future, as it really was very straightforward - much more so than previous experiences had led me to expect

Mark

[Skywave]

Originally Posted by Cobaltblue

Do the pictures on RM match your unit Al? Or are there noticeable differences.

As far as I can detect, they look the same.

Al.

[Skywave]

Originally Posted by mhennessy

One thing did come up, however, as a result of this comment:

I've been asked to point out that you don't have to pay to be a member. You can choose to pay a nominal up-front fee or build up "credit" by submissions (I did the latter). However, the policy has changed, and now guests can obtain data for free. The folk at Radio Museum feel that it's important to correct mis-information about how the site operates where possible.

Having said that, it's probable that Al was using that phrase as a figure of speech.

Yes, in essence, it was a figure of speech. That why I enclosed that remark in inverted commas. But what follows is also relevant . . .

I was not aware that the policy at R.M. had changed: "now guests can obtain data for free." I rarely visit the R.M when I do seek info., (various other sites in the 'Net are available; it's just a matter of what pops up on a Google search) but a few years back I did pay the nominal up-front fee. I then did not access the R.M for about at least one year, but when I then did, it seemed that that payment had 'expired' - or something to that effect.

As for becoming a member by building up "credit" by submissions, it has always seemed to me that I have never had anything to contribute that was not already sufficiently covered at the R.M.

Al.