About dynamic headroom (controversial topic :-)

[3db]

That is what TIM is. It's the amplifier input stages running open loop, because the feedback signal is not back yet due to the amp low bandwidth.

Interestingly, when the war on THD started in the mid-70s (remember the ground-breaking 0.5% THD specs?) the TIM skyrocketed, because manufacturers went after high open loop gain and high feedback with the fewest transistors. THD was good, but amps sounded horrible because of TIM, and the domination of odd-harmonic distortion (which tubes had almost none of)

I noticed that the more transistors an amp has, the lower its open loop gain. It puzzled me at first, then realized that the added transistors act as current sources and pullers for the pushers, making each stage more linear. Hence, less need for feedback.

There is tradeoff between bandwidth and gain. The higher the gain of an amp stage, the less bandwidth an amp can pass. The lower the gain, the higher the bandwidth an amplifier can pass.

However, this is changing the topic of power supplies and how it relates to dynamic headroom.

 

[M Code]

I've already stated that but you failed to mention the side affect of using thinner wire but more of it is reduced current capability of the secondary. Heating of the wire isn't core saturation. Heating of the wire is an I^2 xR loss. Core saturation occurs when the flux of the core cannot contribute to producing any more current.

Many negative things happen when costs are skimped for the construction/materials of a power transformer.

Keep in mind..
Transformers are also constrained in their performance by the magnetic flux limitations of the core. Remember that ferromagnetic materials cannot support infinite magnetic flux densities, as they tend to "saturate" at a certain level (dictated by the material and core dimensions), meaning that further increases in magnetic field force do not result in proportional increases in magnetic field flux.

When a transformer's primary winding is overloaded from excessive voltage, the core flux could reach saturation levels during peak moments of the AC sinewave cycle. When this happens, the voltage induced in the secondary winding will no longer match the wave-shape as the voltage powering the primary coil. In other words, the overloaded transformer will distort the waveshape from primary to secondary windings, causing harmonics within the secondary winding's output.

One other crucial point regarding the power transformer, internally this includes a circuit breaker and if the transformer overheats this likely will open, requiring a costly replacement.

A good stout power supply needs large capacitors and a good transformer. Skimping on either one of these components compromises the design equally.

Large capacitors help essentially the low frequency capability of the amplifier as this is when it is frequently under stress if driving full range, low impedance/sensitivity. Also the amount of regulation is important as well.
For your information in an AVR which has an SRP of $499, dealer cost of $300 the power supply components of the transformer, regulator, diodes and output capacitors will make up about 25% of the components BOM (bill of materials). I actually have the BOM for many of the popular brand AVRs and can give you specific component costs if interested, just PM me rather than taking up forum bandwidth.

I also want to reiterate once more the fact of slew rate as I feel this spec is over looked. If the slew rate is low of the amplifier section, then not even the stoutest of power supplies will rescue its performance. The signal will clip.

As I mentioned in my previous posts both slew rate & rise time are crucial specs as well the speed of the output devices. As more & more sources are capable of delivering high dynamic signals of >100dB, the weaknesses of a inexpensive, marginally designed AVRs are audibly apparent..

Just my $0.02...

 

[3db]

.


Large capacitors help essentially the low frequency capability of the amplifier as this is when it is frequently under stress if driving full range, low impedance/sensitivity. Also the amount of regulation is important as well.
For your information in an AVR which has an SRP of $499, dealer cost of $300 the power supply components of the transformer, regulator, diodes and output capacitors will make up about 25% of the components BOM (bill of materials). I actually have the BOM for many of the popular brand AVRs and can give you specific component costs if interested, just PM me rather than taking up forum bandwidth.



As I mentioned in my previous posts both slew rate & rise time are crucial specs as well the speed of the output devices. As more & more sources are capable of delivering high dynamic signals of >100dB, the weaknesses of a inexpensive, marginally designed AVRs are audibly apparent..

Just my $0.02...

Stop lecturing me about transformers and wasting bandwidth. Everyone missed core saturation until I mentioned it first.

Who said anything about inexpensive entry level receivers? You brought this into the thread. Off course entry level receivers are going to skimp to keep cost down. It ain't rocket science like you try and make it out to be.

 

[PENG]

When a transformer's primary winding is overloaded from excessive voltage, the core flux could reach saturation levels during peak moments of the AC sinewave cycle.

That does not make much sense at all. Did you honestly understand how power transformers work or you just google things up? I did assume you do know the technical side of thing; and I still am certain you are knowledgeable in the commercial side of things, being an "insider". There is nothing wrong to google and learn but there is a danger if you don't have a good foundation in the basic theories in a specialized area such as transformer design and then rely heavily on googled knowledge.

I think I can understand 3 dB's (someone who has an EE degree, I think) point about being lectured.

 

[M Code]

Stop lecturing me about transformers and wasting bandwidth. Everyone missed core saturation until I mentioned it first.

Who said anything about inexpensive entry level receivers? You brought this into the thread. Off course entry level receivers are going to skimp to keep cost down. It ain't rocket science like you try and make it out to be.

Does anyone care who mentioned core saturation 1st...

The purpose of the forum is to present objective information that can help the audience and potential product purchasers to better understand the performance/cost trade-offs in our CE products. Regarding costs, these must included as the majority of electrical performance shortcomings are a result of using cheaper components & materials..

If you have additional comments directed toward me or my responses, send them in a PM..

Just my $0.02...

 

[mtrycrafts]

Does anyone care who mentioned core saturation 1st...

.

Sure, we do. You know, there are only so many '1st' stickers available to post.

 

[mtrycrafts]

That is what TIM is. It's the amplifier input stages running open loop, because the feedback signal is not back yet due to the amp low bandwidth.

....

I wonder what Doug Self has to say about TIM.

http://www.douglas-self.com/ampins/ampins.htm

 

[3db]

The purpose of the forum is to present objective information that can help the audience and potential product purchasers to better understand the performance/cost trade-offs in our CE products. Regarding costs, these must included as the majority of electrical performance shortcomings are a result of using cheaper components & materials..

If you have additional comments directed toward me or my responses, send them in a PM..

Just my $0.02...

Objective information has to be correct in the first place and you made some errors in your post about core saturation. Its not the voltage on the primary at all that drives core saturation but the load on the secondary. I also felt like you were attempting to correct me about my knowldege of power supplies and transformer theory with icorrect informatiion. Make sure its with the right facts.

 

[PENG]

Objective information has to be correct in the first place and you made some errors in your post about core saturation. Its not the voltage on the primary at all that drives core saturation but the load on the secondary. I also felt like you were attempting to correct me about my knowldege of power supplies and transformer theory with icorrect informatiion. Make sure its with the right facts.

I agree the voltage on the primary is not the issue here. Again, googling information is fine but one still needs to have a good basic understanding of transformer design and performance if one wants to make statement of facts in this specialized field, instead of just expressing an opinion.

Yes I would agree there may be applications where you could saturate the core by applying voltage well in excess of the rated voltage for a particular transformer, but here we are talking about the power transformer used in the power supply of an amplifier. In this case, the applied voltage is bascally fixed at around 115/120V in the US and Canada. You just don't get the kind of so call "overloaded with applied voltage" situations unless we are talking about surges due to lightning or something like that, but I doubt that's what he has in mind. You can, however, as you are alluding to, overload such a power transformer not necessarily because of undersized winding, but also "under designed/built" core. It could be either, or both. In fact, that's why I have no doubt you can't have a so called "cheap" and poor quality transformer that can produce the same continuous output power rating yet better "dynamic headroom" than one that is more expensive and of higher quailty. The higher quality and more expensive one will likely have a better core and windings, hence less prone to voltage drop and/or overheating due to winding resistance, core saturation and should also have less core losses (e.g. eddy current and hysterisis losses).

 

[PENG]

Someone asked me about speakers today and I thought of the Axiom M80ti. While browsing their site I stumbled onto something relevant to our discussion here.

http://www.axiomaudio.com/dynamicheadroom.html

"....that power has to come from someplace, and in amplifiers it's supplied by the transformer (which connects to your wall outlet) and by capacitors, which store up the reserve electrical energy from the transformer in "joules." According to Axiom electronics R&D engineer Tom Cumberland, the source of good dynamic headroom in an amplifier "comes from having a transformer with a high-flux core that measures up to 13,000 gauss--if it's any greater, the transformer will buzz--but the higher the flux in the core, the more efficient the transformer is. That will give you lots of sustained current and instantaneous current, which is then dumped into the power-supply capacitors. So the better the transformer and the better and larger the power-supply capacitors, then the better the dynamic headroom is."

"......Another important factor in dynamic headroom is that the output transistors must be very tough, and there have to be enough of them, to handle these instantaneous high-current conditions, because a great deal of heat is generated very quickly. If the transistors aren't of sufficient quality, they'll be pushed outside of the "SOA" (safe operating area) and fail. And that may happen because there isn't enough heat-sinking to keep the output devices cool under these very dynamic conditions."

That makes sense to me, better dynamic headroom comes from better power supply that includes the power transformer (all else being equal), not from worse/cheaper power supply.