Dyan 400's Huge Transformer vs. New Amps?

[oldflame]

IIRC the old Dyna's power transformer had ~twice the capacity of many new high-end amplifiers of similar ratings. OTOH it's filter caps were small in comparison to newer amps. Yet again, many amplifiers don't double their power into 4 ohms as the Dynaco did (provided adequate ventilation).

Considering operating efficiency, maybe Dyna's 1360 watt transformer was right-sized for continuous output. Are modern solid state amps of 200wpc @ 8 ohms properly powered with 600 watt transformers?

 

[egellings]

If the 600W transformer can deliver its power without excessive voltage sag, then yes.

 

[gadget73]

big caps really don't do anything for power output. They can help with very brief transient peaks but constant power is pretty much entirely the domain of the power transformer. If it cant keep up, no amount of capacitor is going to fix it.

 

[oldflame]

In a message, Buck Rogers suggested that the increased efficiency of modern amps allows smaller transformers to be used.

 

[Blue Shadow]

As well, with the ever-increasing use of SMPS

Yes, this makes a big difference. Amplifier class must be the same, old v new to be able to compare transformer needs to supply the amp

 

[gadget73]

In a message, Buck Rogers suggested that the increased efficiency of modern amps allows smaller transformers to be used.

true, but ultimately all of the power going to the speakers comes out of the power supply so it has to be capable of providing enough power to do that. class AB amps like this old Dynaco with a linear power supply need big iron to get that done. Modern stuff is more efficient in terms of power input vs power output, and a switch mode supply is more efficient at turning wall power into DC without large, heavy components. They are also quite a bit more complex though so like everything else there is a trade-off.

 

[tarior]

Last I checked, a class AB amp is a class AB amp. Theoretical maximum efficiency is something like 78%, though typically more like 60%. It's gonna need a power supply that can deliver the goods. The Dyna in question, along with many, many other vintage amps and receivers, has an overkill power supply, while many new amps have a "just enough" power supply.

 

[gadget73]

if we're talking AB, yes. I was interpreting "modern" to mean things that aren't AB amps. Class D for example is a lot more efficient so less power supply is needed for the same output power.

Even if you did an AB amp with a switch mode supply the transformer would be an awful lot smaller even for the same power supply voltage and current capability. Higher frequency switching needs much less iron.

 

[tarior]

if we're talking AB, yes. I was interpreting "modern" to mean things that aren't AB amps. Class D for example is a lot more efficient so less power supply is needed for the same output power.

Even if you did an AB amp with a switch mode supply the transformer would be an awful lot smaller even for the same power supply voltage and current capability. Higher frequency switching needs much less iron.

I was making the dangerous assumption that OP was comparing the old Dyna with newer class AB amps, and not alternative topologies or SMPS equipped amps. It kinda goes without saying that a class D amp with a SMPS is going to be a heck of a lot smaller and lighter in build than a class AB amp of similar output power.

 

[oldflame]

tarior's posts indicate my suspicions about newer amps sometimes having transformers just large enough for modern power rating methods and that some older amps didn't cut as close to the corners.

 

[gadget73]

Also consider the power rating methods, the old FTC method that had the sustained power output for a while vs the sometimes rather more optimistic power ratings that things employ now. 100 watts isn't necessarily 100 watts

 

[llwhtt]

I recently tried the old FTC methd on an Adcom GFA-7607, thermalled out @ 1/3 power long before 1 hour. I guess that's fairly normal for HT crap.

Craig

 

[tarior]

Do you understand how 1/3 continuous rated sine power corresponds to music or movies?

It's the point at which a class AB amplifier is dissipating the most heat. The old FTC standard was quite the torture test.

 

[tarior]

That's exactly point.

If you listen to massively distorted playback it might have some relevance to how the amp works in your livingroom.

The point of it was to insure that an amplifier could deliver advertised power under real world conditions. It was a good standard, IMO.

 

[tarior]

That's not real world how an amp does music. Exactly why the rule has been relaxed. People came to their senses.

But, yeah, I understand "big iron" traditionalists, for lack of better terms, will never acquiesce.

What sort of a standard would you suggest, then? Just take the manufacturers word for it?
Something highly complex that only an EE would understand?

It has zero to do with being a big iron traditionalist. You shouldn't label people without knowing.

 

[tarior]

No, wrong angle. I'm not suggesting no specifications.

I'm saying the 1/3 conditioning test is not reflective of the use of an amp playing music.

It's actually a fairly good comparison to playing compressed recorded music at a high, say just short of audible distortion, level. As good as you'll get using sine waves anyway.
That standard insured that the amp you were paying your hard earned cash to buy would actually deliver the goods, and do so with a decent expectation of reliability.
I wish modern manufacturers (I'm sure some do) would use that standard as well, in a show of good faith.

 

[tarior]

We have a lot of disagreement, which is fine, and I detect neither of us is going to wiggle much from our views. So, I'm going to leave it at that.

I just fail to understand why you wouldn't want amplifiers rated according to stringent standards.

 

[charles 1973]

More important to me then the power rating and weight of a transformer is the ability to drive a 4 ohm load safely, continuously. That doesn't require a 1/2 kw power amp or a 50 lb transformer. Most vintage receivers, often with 10 - 20 wpc where more then capable of driving a 4 nominal ohm load (Dipping even lower) all day.

Many recent AVR's and some stereo amps/receivers are either not certified to drive 4 ohm speakers, regardless of the power rating, Or they require you to put the amp in low power mode. Also they advertise AVR's like my Yamaha Avantage Rx A770 at 95w x 7. That's hogwash. It's 95w x 2, with all 7 channels operating flat out, it's likely closer to 40 - 45w x 7. It does have a big transformer though. To be fair, even that when using a sub to do the heavy lifting is plenty for most folks.

That said, the A770's 590w input power rating is pretty much what we might expect out of a 75 wpc stereo amp. Assuming when I switch it to the 6 ohm mode they suggest to drive lower the 8 ohm speakers the 95w x 2 power rating drops to about 75 wpc.

Consider this. In a perfect world a 100 wpc amp might produce 200w at 4 ohms. Even with highly compressed music or some clipping it might still only need 200w of continuous power with a class A/B amps at 50% efficiency. Short term power will be much higher when we add capacitors. Of course we want to control voltage sag and not over stess the transformer, so to be safe, a 400w transformer should cover it when combined wth enough storage. We are not building tanks or welders, we want to play music.

 

[tarior]

I categorically reject your characterization of my position on the matter.

I welcome a clarification.

 

[gadget73]

That's not real world how an amp does music. Exactly why the rule has been relaxed. People came to their senses.

Whether its sensible or not isn't the issue, the point is that the test method is not the same, therefore the power ratings are not directly comparable and the construction required to meet those standards also aren't the same. I suspect that if the Dyna 400 had to meet today's test standards rather than what was the practice when it was designed, it wouldn't be quite so chunky.