nicholas9976 Posted August 29, 2017 Share Posted August 29, 2017 I once saw online a device that can increase the impedance of low impedance speakers so that you can drive such speakers with regular amplifiers. It was claimed that the device - installed on the speaker wire between teh amplifier and the speakers - does not affect the sound. I believe the product had a very specific name (not just "resistor" or similar) and I have forgotten the special name of this product/device so I can't find it. Does anyone know what the device is called? Anyone used one? Link to comment Share on other sites More sharing options...
aechmea Posted August 29, 2017 Share Posted August 29, 2017 (edited) "autoformer" is what they are called. Somewhat popular with people with planar and electrostatic speakers that have low impedance. No such thing as a free lunch though, so there will be side effects. I haven't used one. Google "autoformer change impedance" and there is heaps of info. Here is an old thread from here. http://www.stereo.net.au/forums/topic/3461-paul-speltz-autoformer/ I should try one since I run my planars with bridged amps which see about 1 - 2 ohms. Edited August 29, 2017 by aechmea add stuff ... twice 1 Link to comment Share on other sites More sharing options...
nicholas9976 Posted August 29, 2017 Author Share Posted August 29, 2017 6 minutes ago, aechmea said: "autoformer" is what they are called. Somewhat popular with people with planar and electrostatic speakers that have low impedance. No such thing as a free lunch though, so there will be side effects. I haven't used one. Google "autoformer change impedance" and there is heaps of info. Here is an old thread from here. http://www.stereo.net.au/forums/topic/3461-paul-speltz-autoformer/ I should try one since I run my planars with bridged amps which see about 1 - 2 ohms. That's the one! Has anyone used an autoformer, and if so what sort of difference to the sound did you notice it made in A/B testing? I would like to try using a regular (i.e. not high current) amplifier that I'm interested in on my Duntech Sovereign speakers, but the amp would likely be fried without a device like this to increase the speaker's impedance dip in the bass frequencies. Link to comment Share on other sites More sharing options...
Bronal Posted August 29, 2017 Share Posted August 29, 2017 I used them for a few years when I had Ambience speakers with valve amps. They work very well and actually improve the sound as the amp isn't working as hard. I had them measured as flat to beyond 100kHz. Link to comment Share on other sites More sharing options...
nicholas9976 Posted August 29, 2017 Author Share Posted August 29, 2017 Thanks. I have now posted a Wanted To Buy ad looking for a used autoformer: Link to comment Share on other sites More sharing options...
Bronal Posted August 29, 2017 Share Posted August 29, 2017 You do know you need one for each channel, don't you? Link to comment Share on other sites More sharing options...
nicholas9976 Posted August 29, 2017 Author Share Posted August 29, 2017 2 minutes ago, bronal said: You do know you need one for each channel, don't you? Yes, I have updated the WTB ad to be clear I need a pair. Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 29, 2017 Share Posted August 29, 2017 3 hours ago, nicholas9976 said: That's the one! Has anyone used an autoformer, and if so what sort of difference to the sound did you notice it made in A/B testing? I would like to try using a regular (i.e. not high current) amplifier that I'm interested in on my Duntech Sovereign speakers, but the amp would likely be fried without a device like this to increase the speaker's impedance dip in the bass frequencies. Dumb idea. Buy an amplifier that your (superb) speakers deserve. Why, you may ask? For a whole host of good reasons, including: An autoformer is just like a transformer. IOW, it performs the following functions: * Increases current. * Decreases Voltage. * Decreases impedance. Sound good? Nup. Not even remotely close to good. That little 'decreases Voltage' thing is a serious drawback. It means you will seriously limit maximum available power. But wait: It gets worse. ALL transformers introduce some loss. Usually around 10%. Then, more seriously, the secondary of the transformer exhibits a resistance figure. This will further decrease available power. The amount of loss will depend on the secondary resistance. Figure on around 1 Ohm for a VERY, VERY good transformer. This can cause some pretty ordinary frequency response problems with speakers that are not essentially resistive in nature (like Maggies, or Ambience, which are resistive). Then you have the phase shift and frequency response problems that afflict all transformers. And so on. You have an absolutely world class pair of speakers. Buy a decent amplifier for them and stop faffing around with silly crutches. 4 Link to comment Share on other sites More sharing options...
andyr Posted August 29, 2017 Share Posted August 29, 2017 38 minutes ago, Zaphod Beeblebrox said: Dumb idea. Buy an amplifier that your (superb) speakers deserve. You have an absolutely world class pair of speakers. Buy a decent amplifier for them and stop faffing around with silly crutches. +10!! Or, if you can't afford to buy an appropriate amp ... sell the Duntechs and buy yourself ordinary speakers that your existing amp can drive. Andy 1 Link to comment Share on other sites More sharing options...
Keith_W Posted August 29, 2017 Share Posted August 29, 2017 +1. I would have said the same as Zaph but in far less technical terms. Get a new amp. Link to comment Share on other sites More sharing options...
expat Posted August 29, 2017 Share Posted August 29, 2017 Could buy a McIntosh amplifier which come as standard with autoformers. The McIntosh Output Autoformer is a special transformer that is designed and manufactured in-house by McIntosh. This allows any speaker type to be used with a McIntosh amplifier and have all of the power that the amp is designed to deliver. All other amplifier designs will not have even power with differing speaker designs. McIntosh amplifiers with the output autoformer® will deliver ‘All the Power You Pay For’ regardless of speaker type chosen. Never heard a McIntosh amp however. 1 Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 29, 2017 Share Posted August 29, 2017 8 hours ago, expat said: Could buy a McIntosh amplifier which come as standard with autoformers. The McIntosh Output Autoformer is a special transformer that is designed and manufactured in-house by McIntosh. This allows any speaker type to be used with a McIntosh amplifier and have all of the power that the amp is designed to deliver. All other amplifier designs will not have even power with differing speaker designs. McIntosh amplifiers with the output autoformer® will deliver ‘All the Power You Pay For’ regardless of speaker type chosen. Never heard a McIntosh amp however. An autoformer on a (good) SS amplifier is like bolting a fifth wheel to a Ferrari. Not only is it completely unnecessary, but it actually damages performance. Output transformers and autoformers on SS amplifiers made sense in the 1950s and 1960s, when output devices capable of supplying large amounts of current were either not available or were horrendously expensive. Back then, 3 Amp output devices were high current devices. Today, 25 Amp devices are inexpensive and very linear. Link to comment Share on other sites More sharing options...
georgehifi Posted August 29, 2017 Share Posted August 29, 2017 (edited) 10 hours ago, expat said: Could buy a McIntosh amplifier which come as standard with autoformers. Why do this to an amp, that if built right to begin with it shouldn't need it? Auto transformers are a bandaid fix to make an amp that's not suited "work" sort of. Far better of getting the right amp to start with. EG: I have a pair of speakers that are a pig of a load, but it's driven by an amp that has no problem with them. A friend gave me some "highly" regarded Zero auto transformers, just as an experiment I used them on my system, I knew what would happen and it did, the sound took a massive hit for the worse! Cheers George Edited August 29, 2017 by georgehifi Link to comment Share on other sites More sharing options...
expat Posted August 30, 2017 Share Posted August 30, 2017 So why do people fawn over McIntosh stuff? Link to comment Share on other sites More sharing options...
expat Posted August 30, 2017 Share Posted August 30, 2017 So why do people fawn over McIntosh stuff? Link to comment Share on other sites More sharing options...
georgehifi Posted August 30, 2017 Share Posted August 30, 2017 13 minutes ago, expat said: So why do people fawn over McIntosh stuff? Why put an output transformer, on a solid state output stage?? Unless it's rubbish (seriously unstable, prone to going dc or has no drive into low impedance's) or maybe a wish to colour the sound. Don't get me wrong the original Mac 275 was a great amp, even for tube. Cheers George Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 30, 2017 Share Posted August 30, 2017 (edited) 2 hours ago, expat said: So why do people fawn over McIntosh stuff? It's well built, using old fashioned principles, in the main. There's lots of copper and iron (with all those useless transformers, adding to the considerable heft) and old school construction. The stuff is generally pretty reliable, so no downside there. They've retained the same styling for many decades, so that keeps the hipsters happy. In fact, one could argue that McIntosh products are purpose built for hipsters. Sound-wise, of course, some like it and some don't. McIntosh valve equipment, though built in a similar fashion, is a different matter entirely. [EDIT] One more, very important thing about McIntosh: It is (mostly) built in the USA. Hipsters love that stuff. Edited August 30, 2017 by Zaphod Beeblebrox Link to comment Share on other sites More sharing options...
t_mike Posted August 30, 2017 Share Posted August 30, 2017 On Tuesday, August 29, 2017 at 4:48 PM, andyr said: +10!! Or, if you can't afford to buy an appropriate amp ... sell the Duntechs and buy yourself ordinary speakers that your existing amp can drive. Andy To me... 1 Link to comment Share on other sites More sharing options...
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