has a power bandwidth (into 2 ohms) that extends to at least 50Khz?
I have come across a problem with the Mosfet amp driving my 2 ohm Maggie ribbons. It is 'stable' into 2 ohms - in that it doesn't blow up (although it gets warm) - but recent measurements have shown that the output voltage at 20Khz is only 73% of the output voltage at 6Khz ... and only 40% at 30Khz.
So it is not delivering equal power at all frequencies ... so is useless for my 2 ohms ribbons.
So I was hoping there might be a Pass circuit which has a power envelope up to 50Khz, for a 2 ohm load.
Thanks,
Andy
I have come across a problem with the Mosfet amp driving my 2 ohm Maggie ribbons. It is 'stable' into 2 ohms - in that it doesn't blow up (although it gets warm) - but recent measurements have shown that the output voltage at 20Khz is only 73% of the output voltage at 6Khz ... and only 40% at 30Khz.
So it is not delivering equal power at all frequencies ... so is useless for my 2 ohms ribbons.
So I was hoping there might be a Pass circuit which has a power envelope up to 50Khz, for a 2 ohm load.
Thanks,
Andy
Thanks, mate. Reading the F5 manual - that seems to be the ticket. But I couldn't find any info on the 'Turbo' version?
And are these:
* fully mase up amps
* or kits which you buy from First Watt and solder?
Thanks,
Andy
Great - thank you very much!
Andy
Yes, That is what I will be doing, Ray - my setup has an amp box containing 3 monoblocs, behind each Maggie.
Andy
Good, they'll get pretty hot, you know. Get plenty of air under and around them.
Read up on all the info available here and at FW before starting. Use the current, proven pcbs.
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Thanks - have just ordered a pair of V3 PCBs plus 2 of the Universal PS PCBs.
It will be an interesting project!
Andy
Don't skimp on the power supply, that's where the the power comes from (of course).
Consider a dedicated 30A high current AC line per channel, talk to a local electrician.
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I presume you mean - make sure to use the amount of uF suggested in the manual?
But what about the DC rails ... or, rather, the transformer secondary voltages? I would think 3a through the Maggie ribbons would melt them (the stock fuse is 2.5a, quick blo) ... so if I allow for 3a continuous ... that's 20w into 2 ohms.
Which is 80w into 8 ohms - well within spec, AIUI?
Yes, I have this covered.
30a at your piddling 110v mains supply equates to 15a at our 240v supply. (less, actually).
I already have 30a wiring in place (in our recently built house) - individual circuits to each of 13 ppts.Andy
Yes, max out the supply capacitance. As long as the drivers are properly fused, you should be ok.
Be a little conservative at first, though.
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I presume you mean - make sure to use the amount of uF suggested in the manual?
But what about the DC rails ... or, rather, the transformer secondary voltages? I would think 3a through the Maggie ribbons would melt them (the stock fuse is 2.5a, quick blo) ... so if I allow for 3a continuous ... that's 20w into 2 ohms.
Which is 80w into 8 ohms - well within spec, AIUI?
Yes, I have this covered.
30a at your piddling 110v mains supply equates to 15a at our 240v supply. (less, actually).
Andy
I doubt you will draw more than 10A or 2.4kW from the wall for this amp.
A push pull power amp running on 25Vdc supply rails is able to put out 25W (20Vpk & 2.5Apk) into an 8r0 load.
It could be a ClassA design with a bias of ~1.3A, or a ClassAB design with a bias of 10mA.
When the load changes to 4r0 the current demand has increased to 5Apk and the output is now 50W into 4ohms
Change the load to 2r0 and the current demand goes up to 10Apk and the output is now 100W into 2ohms.
Both of these lower loads will turn any amplifier into a ClassAB amplifier to meet any current demand that exceeds the ClassA current limit.
You must look at the CURRENT demand and find ways to meet that demand.
It could be a ClassA design with a bias of ~1.3A, or a ClassAB design with a bias of 10mA.
When the load changes to 4r0 the current demand has increased to 5Apk and the output is now 50W into 4ohms
Change the load to 2r0 and the current demand goes up to 10Apk and the output is now 100W into 2ohms.
Both of these lower loads will turn any amplifier into a ClassAB amplifier to meet any current demand that exceeds the ClassA current limit.
You must look at the CURRENT demand and find ways to meet that demand.
Thanks, Andrew.
But just to recap ... all I am looking for is an amp that can deliver a flat FR up to, say, 50Khz into my 2 ohm Maggie ribbons.
The amp I am using currently on my ribbons can't do this ... although it is 'stable' into 2 ohms (ie. it doesn't cark itself).
The F5 seems to be stable into a 0.1 ohm load. If so, it should be well within its capabilities to handle my 2 ohm ribbons.
I doubt that I can pump more than 3a continuous into my ribbons (as the stock Magnepan-supplied fuse is 2.5a, quick-blo). 3a x 3a x 2 ohms = 18w ... say 20w.
Converting that back to a power delivery into 8 ohms ... we get 80w.
Which AIUI, is well within the design parameters of the F5 Turbo.
Andy
your 2ohms ribbons are substantially resistive and thus an easy load compared to a 2ohms voice coil driver.
However the crossover could add a significant reactive component to the ribbon's impedance. I don't know how much extra current your ribbons would demand compared to conventional speakers.
But I disagree completely with your assertion that 3A continuous gets anywhere near the tranisent demands of your ribbons.
a 3A fuse will pass 6A for very many seconds without rupturing and would pass 20A for many milliseconds without rupturing.
Have a look at fuse data to get some idea of the way a fuse handles transient currents and continuous currents.
3Apk is only 9W (+9.5dBW)
I don't believe an F5 is stable (does not oscillate?) into a 0r1 load. Where did you see that data? Post a link.
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