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Old 23rd February 2007, 07:40 PM   #1
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Default Amplifier for 1-ohm ribbons?

Recently, I was given a pair of Apogee ribbon tweeters. I have'nt done much - not much of anything, really - with them yet, simply because they only have an impeadance of a little over one ohm!

While I could - in theory - build a Gainclone with 4 LM3886's in parallel, I'm wondering if there's a better way to to this. While the ribbons are only roughly 86db efficient (according to the guy I got them from), this will be a bi-amped setup, so performance below 500hz is moot.

Any tips? I'm new to amp building, and have a budget of "as close to free as possible".
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Old 23rd February 2007, 07:51 PM   #2
mlloyd1 is offline mlloyd1  United States
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do a search for messages from user "linesource"
he has done some interesting things on the topic of driving very low impedance loads

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Old 23rd February 2007, 08:40 PM   #3
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Default Re: Amplifier for 1-ohm ribbons?

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Originally posted by Spasticteapot
Recently, I was given a pair of Apogee ribbon tweeters. I have'nt done much - not much of anything, really - with them yet, simply because they only have an impeadance of a little over one ohm!

Any tips? I'm new to amp building, and have a budget of "as close to free as possible".
The easiest path might be to pick up a Krell KSA100 clone kit from the DIY wiki thread, and consider reducing the voltage on the output supply to about +/- 10V to save heat. The KSA100 will drive 1 ohm loads, and many Krells were sold to drive Scintillas.

I've been working on an amp to drive 0.15 to 0.5 ohm ribbons, but I do not have any extra PCBs, and the parts cost(16 Sanken bipolar outputs) is much higher than a DIY KSA100 clone.

I owned Scintillas, and currently have Full Range Apogees as well as DIY ribbons. Using a direct drive amp instead of step-up transformers is a major sonic improvement. The transformers create phase shift that is easy to measure and hear in an A-B comparison.
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Old 23rd February 2007, 08:45 PM   #4
Magura is offline Magura  Denmark
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Hmm, Firstwatt F1 ??


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Old 23rd February 2007, 08:50 PM   #5
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Do a search for a second hand ME-850 (Modular Electronics) they have bags of current and double all the way down to 1ohm, I picked up two ratty ones that worked from Asia for $450aus each.
In Australia where they are made they sold for around $5000aus new, they love low impedence speakers and sound great to boot, big dynamics yet smooth as, no feedback around the output stage, just a bit of local around the input/driver stage.

These things out Krell a Krell

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Old 23rd February 2007, 09:05 PM   #6
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I specifically built the Mini-A for my ribbons (Magneplanar). Take the schematic I posted in the original thread, add a couple more pairs of output devices, and it'll work just fine.
Current source amps will also do nicely.

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Old 23rd February 2007, 10:29 PM   #7
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One Ohm speaker is ideal - for amplifier you need only cheapest power transistors, designed for lowest rail voltage... isn't problem to find transistors with tenth's A colector current..
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Old 24th February 2007, 10:47 AM   #8
tinitus is offline tinitus  Europe
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I have run a 30watt amp with +/-30Vdc rails into 2ohm with no problem - it has only a single transistor pair, but tough ones, and a big trafo, driven into 1ohm in bass it got pretty hot
With ribbon above 500hz it might be much better still

I am sure Krell 50 or Aleph 5 would be nice, but personally I avoid big ClassA

I wonder if one of these would cut it at low voltage

http://www.aussieamplifiers.com/index3.htm

But a Nakamichi 7AII would stay cool, if sound is ok on ribbon
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Old 24th February 2007, 05:51 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
3pair of MJ15003/4 running off 33Vdc to 34Vdc will go to 270W into 1ohm @ 60degree phase angle. That's equivalent to a max of 110db@1m
Safe into 0r5 @ 350W

No idea how to make it stable.
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Old 24th February 2007, 07:31 PM   #10
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To clarify, I'm not wealthy enough to afford a proper Krell clone. I'm not looking for huge output power, either - 20w should be enough for my normal listening levels, I'd think.

If there were a way to make a lower-power Krell clone using cheaper transistors, that might be nice.
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