250w 8ohm amplifier

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#301
AndrewT said:
Not the way I would put it.

100W into 8r0 is equivalent to 28.3Vac into 8r0.
That can be quoted as +29dBV into 8r0.
If you change the load to 4r0, one would expect the voltage to hold up to somewhere near the 8ohms voltage.
for me >= +28.5dBV would be acceptable as indicating a good current ability into 4r0 test load.
Now change to 2r0 test load. This would require a further small drop in voltage to indicate good current delivery.
>=28dBV into 2r0 would be acceptable.

I work with voltages most of the time. They are so telling of performance.

Convert those dBV back to power if you need numbers.
28.5dBV into 4r0 is 26.6Vac is 177W into 4r0
28dBV into 2r0 is 25.1Vac is 315W into 2r0. (not 100W into 2r0, which would indicate a current crippled amplifier)
Cordell specifies at least 180% power into a halving of load resistance as an indicator of adequate performance. You can see that -0.5dBV does not quite meet Cordell's standard.
-0.4dBV for each halving of test load resistance would slightly exceed Cordell's minimum standard indicator.

BTW,
I can exceed Cordell's (180%) standard with transformers of less than 2 times maximum output power into the lower of the test loads.
i.e. a 625VA transformer for a single channel for 311W (+30.95dBV) into 4r0 and 170W (+31.3dBV) into 8r0 using quiescent rails of +-58.5Vdc, shows a loss of -0.34dBV on halving the test load impedance from the nominal rated amplifier capability.
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again more theory, i say build an amp, test it using a dummy load, a signal generator and a scope, only then will you know for sure...
all this talk about power is meaningless unless we know for sure what actual power traffo is used....
 
#303
Johan Potgieter said:
😀😀😀😀!

What about him? If his amplifier is poor (define poor), fully agreed!

But going OT (apology Mods) - I am not a loudspeaker designer, but I have difficulty seeing how a speaker designer necessarily needs to 'compromise sonics' in order to achieve a reasonable impedance-frequency characteristic. Again then: Are you saying that all those excellent loudspeakers on the marketplace with 'good' impedance graphs, are inferior to the few that are unable to return such?

But I must not lure you OT - this is another subject. I am going to stand off for a while now to watch a rugby match (local national sport); success to you doing 'your thing'! ..... night/early morning there?
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Cricket man , Cricket ....... 🙂
 
#304
Ranchu32 said:
AJT, where can I buy a beautiful transformer like yours? All they sell in my part of the world are ugly toroidals that look like big fat donuts.
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Signal Transformer in the states, http://www.signaltransformer.com/sites/all/pdf/capabilities.pdf
or since you are from down under, you can touch bases with Patrick Turner....index

I have never met the man, but when i do i would like to shake his hands and give him thanks for all the things i kearned from him...😀
 
#306
a.wayne said:
There is a big difference in the sonics , he is not driving a pure resistor with a static frequency , yes his amp will work, but his wife will complain ...🙂

Why compromise the Psu , its Diy , if its cost, better to buy use from Ebay look at Rotels you can buy them for 300.00 and get a higher quality amplifier....
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yes, with diy, the diy'er is king, never mind that it costs more...
what i am saying is that it doesn't have to be 250 watts into 8 ohms,
the arguments start when strict lines are drawn, that takes the fun away...

nowadays, i tend to favor amp designs that can do 2 ohms or even 1 ohm....😀
 
#310
a.wayne said:
Low is not distortionless , low is not blameless and the Halcro as well as others have Issues a lot more than looking at thd PPM values, like a weak psu to begin with and what the hell is a "boutique" amplifier ! Something your wife takes with her when getting her hair done ...
May i suggest we pick one amp actually bench tested and then discuss why its blameless or not and why many consider their gray scale sonics poor..
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You are compounding your disagreements on the fly, a.wayne. You know full well what I and others on this forum mean by "boutique" items. It distinguishes the uncommon or exclusive from the mundane, the rhodium plated from chrome and particularly the kind of suit the guy doing the selling is wearing. In DIY audio, it's the difference between buying your parts from Mouser and Parts ConneXion, for example. The less stock or fewer items produced, the higher the prices - I'm sure you understand the retail game.

I might just as bemusedly ask what the hell you mean by "grey scale sonics" which must be a metaphoric term since it obviously borrows from a colour density standard used in photography, graphic artwork etc. It seems audio industry copy writers and reviewers are always inventing new metaphors.

I see no need to repeat the well documented on what is Blameless. Go to Self's sideline business partnership website for the fully bench tested original blameless design model with specs and read one of his standard texts instead of picking arguments with any whom you deem to oppose your views here. This is a DIY forum - it's a PCB, a kit you can buy or have built even! The real deal. 😉

I'm not going to debate your idea of what blameless or distortionless might be or reignite another debate older than DIYaudio about low THD amplifiers versus designs carefully tweaked to produce a musicality in their distortion components, without which, some might even be termed Blameless too.
This has all been done to death here by many others - some with more clues and authority than both of us.
 
#311
I see you missed the sarcasm Ian, must be the beating Australia took the other day, get over it man , ashes is not everything ... 🙂

You do realize your grey scale low distortion amp is considered tweaking ...

🙂
 
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#312
a.wayne said:
I see you missed the sarcasm Ian, must be the beating Australia took the other day, get over it man , ashes is not everything ... 🙂....you do realize your grey scale low distortion amp is considered tweaking ...🙂
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Nothing to get over, I don't follow sports these days - perhaps when I get senile, the moving images will be entertaining again.
'No room for sarcasm in your first reply unless you are poking fun at the grey scale itself.

'Still don't know what you mean by grey scale sonics either. I assume it's a piece of local retail Hi-fi speak but perhaps, with all the Google hits, its really a disease or clinical condition 😀 ?
 
#314
Ok, what sonics are serious stuff and what do you mean by saying high feedback, low distortion amps feature grey scale sonics? Do you mean a certain type of amplifier as a well as a measurement scale?

TBH, I think this is shaping up as just the latest jargon with no actual meaning at all other than to suggest the association that grey is dull and colourless and so an equally dull label for sound quality, i.e there is no reference scale at all, right?

How serious is that compared to saying: All amplifiers that have high feed back (qualify) and low distortion (qualify) sound dull and boring on my scale of 1-5 🙁s or such (add examples). So amplifier x could be said to have the worst grey scale rating of 🙁🙁🙁🙁🙁

That unequivocally means something but dropping in some new term to the forum (I've not seen it used here previously) without actually saying what it means is speaking a foreign language. Maybe I should also visit some other US audio forums where this in-speak is used.
 
#318
"How about 1kW then? "

My rule-of-thumb is 2VA for every watt you expect the amplifier to deliver.

Can you use less?

Sure.

Can you use more?

Sure.

Amplifiers that use my 2VA rule sound good to me. Using less VA sounds poor when driving hard, more and more VA sounds better. Going beyond 2VA seems to be the point of diminishing return. I find a small regulated supply for the voltage gain stages does more for the sound quality, and costs far less than going beyond 2VA.

YMMV
 
#320
Kevin finished his take on the Blameless. I believe he is going to post it on his website. Maybe keep an eye out for that. I'm looking forward to building this amp. I have a few on the schedule ahead of it but I will get there. I already have a trans for it.

Blessings, Terry
 
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