Impedance and dual transformers? - AVS Forum
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post #1 of 9 Old 05-03-2013, 03:59 AM - Thread Starter
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AVS,

The question is in regards to an AVR with single transformer that goes into protect mode when driven by martin logans at high volumes. (from reviews online)

Would stepping up to the dual transformers with 50% more power help a tad? I listen at low volumes so if the protection ceiling improved a little that would be great.

I'm guessing no because the speakers aren't in series so the impedance never changes. So five 6 Ohm speakers would still present 6 Ohms to the receiver?

Thanks in advance
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post #2 of 9 Old 05-03-2013, 12:54 PM
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AVR transformers are used in the AVR's power supplies, not in the AVR's amplifiers themselves. They have nothing directly to do with how well a receiver can handle low impedance speakers. That's determined by the design of the receiver's amplifier circuits. Some receivers with single transformers work fine with low impedance speakers.

You'll have to specify the models of receivers that interest you to get more detailed answers.

In general, though, people who like "difficult" speakers tend to use them with external amplifiers.

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post #3 of 9 Old 05-03-2013, 05:18 PM - Thread Starter
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NAD T777 vs T787 but it was just a general question non brand specific

Thanks for your input
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post #4 of 9 Old 05-11-2013, 08:52 AM - Thread Starter
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Ok what about voltage or current? I hear lots of mixed opinions online. I'm trying to determine whether or not a dual power transformer will handle Martin Logans better than a single. Or at least increase it's protection ceiling, reduce voltage clipping or current clipping etc.
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post #5 of 9 Old 05-11-2013, 09:25 AM
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Quote:
Originally Posted by snyderkv View Post

AVS,

The question is in regards to an AVR with single transformer that goes into protect mode when driven by martin logans at high volumes. (from reviews online)

As Mr. Ball seems to be suggesting, amplifier protection circuits are divorced from power transformers by several layers of circuitry.

Amplifier protection circuits vary from amplifier to amplifier so it is hard to say much more with 100% generalization.

In general they monitor the current being drawn from the amplifier, and take steps to keep certain limitations from being exceeded. Some monitor both voltage and current, but usually the voltage monitoring is used to modify the current limiting, not actually limit just the output voltage of the amplifier. Excess current drain can overheat and damage amplifiers. Amplifiers tend to be self-limiting when it comes to voltage so there is no further need to limiit voltage.
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Would stepping up to the dual transformers with 50% more power help a tad?

No except that amplifiers that can put out more power can generally also put out more current. Whether the extra current supply comes from one larger transformer or two smaller ones matters little.

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I listen at low volumes so if the protection ceiling improved a little that would be great.

Protection circuits tend to be like brick walls. If you stay even just the tinyest distance from them, then for all intents and purposes they might as well not exist.
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I'm guessing no because the speakers aren't in series so the impedance never changes.

It would be parallel connections that could possibly cause a problem. Series connections if anything reduce the maximum current drain.
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So five 6 Ohm speakers would still present 6 Ohms to the receiver?

Yes. The power transformers are so completely divorced from the amplifier speaker terminals that they are practically irrelevant when it comes to listening to music. OK, they have to be there and they need to deliver enough power. However, the amount of power that is needed is often less than it may seem.

The key thing to remember is that power ratings of amplifiers are generally specified based on bench tests with resistive loads and steady pure test signals. In the US this is done for legal reasons dating back to the 1960s and 1970s when we did not understand many things about audio. Music puts a much lighter load on amplifiers than test tones.

As far as Martin Logan speakers go, some of their electrostatic speakers are very unusual loads, and there is little that can be discerned about driving them that can or should be transferred over into expectations related to more typical kinds of speakers.
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post #6 of 9 Old 05-11-2013, 09:39 AM - Thread Starter
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Thanks Arnyk,

One advantage of a torroidal power transformer is:

" •increased voltage/current output capability for its size" --M Code

"dual Holmgren toroidal transformers powering the audio amplifier section, which should supply plenty of headroom for strong performance in the dynamics department" -- Marketing add

Wattage is less of a concern for Martin Logans than is voltage/current unlike typical box speakers as you mentioned. So If one tranformer increase voltage/current, wouldn't two be better given they are the same size? Or are these comments I pasted misleading?
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post #7 of 9 Old 05-11-2013, 11:28 AM
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Quote:
Originally Posted by snyderkv View Post

Thanks Arnyk,

One advantage of a torroidal power transformer is:

" •increased voltage/current output capability for its size" --M Code

"dual Holmgren toroidal transformers powering the audio amplifier section, which should supply plenty of headroom for strong performance in the dynamics department" -- Marketing add

Toroids are smaller for a given power level and radiate a smaller hum field. They are also more susceptible to certain kinds of power line faults.

http://en.wikipedia.org/wiki/Transformer#Toroidal_cores

"Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (see Classification parameters below). Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types."
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Wattage is less of a concern for Martin Logans than is voltage/current unlike typical box speakers as you mentioned. So If one transformer increase voltage/current, wouldn't two be better given they are the same size? Or are these comments I pasted misleading?

The way this works out is that regardless of the type of transformer, the transformer that is used that produces the necessary amount of current and voltage. If a toroid is not used, then a larger, heavier conventional transformer is usually used.
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post #8 of 9 Old 05-11-2013, 03:00 PM
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Quote:
Originally Posted by snyderkv View Post

Thanks Arnyk,

One advantage of a torroidal power transformer is:

" •increased voltage/current output capability for its size" --M Code

"dual Holmgren toroidal transformers powering the audio amplifier section, which should supply plenty of headroom for strong performance in the dynamics department" -- Marketing add

Wattage is less of a concern for Martin Logans than is voltage/current unlike typical box speakers as you mentioned. So If one tranformer increase voltage/current, wouldn't two be better given they are the same size? Or are these comments I pasted misleading?

wattage IS voltage and current. Actually voltage times current. And if voltage goes up into the same impedance then current has to go up. To do otherwise would break Ohm's law. How much current an amp must deliver at a given voltage depends solely on the impedance of the speaker(s). Ohm's law again.
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post #9 of 9 Old 05-11-2013, 09:30 PM - Thread Starter
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