Welcome! Need support, you got it. Or share your ideas and experiences.
In Reply to: RE: Acquired MGIIIA posted by Beardy on December 08, 2023 at 20:54:41
That's great to hear! :-))
Maybe your next step - just because you can, with the IIIAs - is to replace the external XO box with an active XO ... and actively bi-ap them!
Already chewing on that!
What amp are you currently driving your new IIIAs with?
An Emotiva XPA-200.
My plan is to build 2 or 3 Pass F5 clones and biamp/triamp, but I am still chewing on the active crossover. I'd prefer to build rather than buy and this
is the current favored approach. I am working through exactly how to set this up. I have your MUG tweaks page up in a seperate tab.
You keep your Emotiva XPA for the bass panels ... and build an F5 for the mids+ribbons - or an F5 for the mids plus an F5 for the ribbons (ie. 3-way active).
Even then ... you may find (although the only way to do this is to borrow other amps, to compare) that the F5s aren't really powerful enough. :-((
Why do I say this? Because for about a year (before I then got rid of my Frankenpans) I used 2x 40w-into-4-ohms AKSA ' Alpha Nirvana ' Class A
amps on my mids & ribbons. Actively driven. (You can find the AKSA AN thread on DIYaudio.)
Hugh Dean - the designer - came over and had a listen; he knows my system well and admitted he was a little 'underwhelmed'. :-(( Which surprised him - as he knew how good the amps should sound.
Yet when he came over subsequently - to listen to the same amps driving my new 'zero baffle' spkrs - he was amazed at how good the amps sounded.
My conclusion was that ... although my ANs were the "4 ohm" version (to optimise their delivery into 4 ohm spkrs rather than 8 ohm - and they are stable into 2 ohms!), the Maggie mids & ribbons really needed more power.
The Pass XO should be ideal. I myself (nearly 30 years ago) used Rod Elliott's P09 L-R XO circuit (modded to provide 'Maggie' slopes) - which worked well.
Pass F5 is only 40 W into 4 Ohm. That is not enough!
I tend to agree here, but I'm running a ~50W (@8 Ohm) tube amp right now driving the T-IV's full range and it's sounding good/detailed. If he's going to bi-amp with the Pass amps it -might- be enough if the room is on the smaller side.
I say appx. 50W because the amp is designed for KT-120's and I'm using 6550's instead, so it's output is less than the design spec of 75WPC. As I've stated before, I only need about 15WPC (on 8-Ohm meters) for the room to start feeling 'too loud', however.
Output volume is unarguably related to I^2R. With my DVM I measure typical AC voltages of 5-6 volts at speaker terminals when playing loud. However this meter does not have the temporal response to read accurate values for the peaks, so let me get back to you on that once I have a decent analog AC Voltmeter to play with.
My unfounded belief is that much of this preoccupation with massive power is a reflection of the amplifier architecture required by low impedance speakers. A power supply that can readily provide the current required is feature of a better quality amp. The degradation in sound quality that one might hear from lower power amplifiers may be the impact of shortfalls in the power supply dept.
My expectation is that at `my volumes' there are peaks to perhaps +/-20V, and potentially the impedance of planar may be as low as 2.5 Ohms. This suggests an F5 with a power supply that can give 40V/2.5 Ohms (16A) might do the trick.
However, my wife tells me that on occasion I am wrong.
Keep in mind that Magnepans are one of the most capable speakers at producing impulse transients like drum/cymbal percussion. These instantaneous changes in voltage approach infinite wattage/current in the instant they are generated.
The signal path from the source through to the amplifier all have to try to reproduce that signal/current demand, of course at lesser extremes with lower voltages. When it gets to the power amp, that current demand goes way up as it tries to drive the low impedance load (relatively) of the speakers.
So it really depends on the amp, and it's current delivery capabilities to be able to keep those notes sharp/accurate. Magnepans are so revealing that deficiencies of the amp can be heard, where they may not be with a standard speaker that's not 'fast' enough.
Understood - that echoes my thoughts.
There is always the turbo...
As Dennis said: " So it really depends on the amp, and its current delivery capabilities to be able to keep those notes sharp/accurate ."
Maggies are not the only spkrs that sound better when the amp driving them has bags of current-delivery capability. A mate of mine had some stand-mount B&Ws for many years. He first drove them with a very good-sounding Oz-made 40w tube amp. They sounded very nice - if a little bland ... so one day he decided to try a 150wpc ss amp. That made a huuuge difference ... and he thought he was done! Then, a wicked friend brought over his Magtech to try (500w into 8 ohms, 900w into 4 ohms ... and stable into 2!). Russ then bought a Magtech! :-))
Well, with all forms of conversion to mechanical motion from electricity, it's the magnetic field of the permanent magnets interacting with the magnetic field of the voice coil, or in the case of Magnepans, the linear voice wires. The magnetic field of the wire is generated from the current flowing in the wire. Voltage and current are inter-related but the current (flow of electrons) is what generates the magnetic field.
Still I=V/R. As the Magnepans driven active is a pure restive load there is not a lot of currrent running through them. The power amps used by myself will not run out of current but of voltage. They can deliver a maximum peak current of 80 A but that will only be the case with some completely stupid speakers which need to go back to the designing board. With the 4 Ohm basses of a Magnepan peak current may be about 10 A (400 W in 4 Ohm).
I think it depends on the amp, some amps spec'd at high voltage/wattage will fall short on current delivery under load with dynamics, which again will create higher than 'average' instantaneous current/voltage demands. A lower wattage amp that can deliver high current can be OK, if it can keep up with the instantaneous demand (at lower volumes, of course).
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