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 Post subject: High Current
PostPosted: Wed Sep 13, 2017 4:21 am 
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Joined: Tue Jul 05, 2005 3:09 pm
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Location: Sherbrooke, QC, CA
Why should a power amp be high current?

Would appreciate the objective/technical POV as well as the esoteric/subjective POV please.

As I seem to recall that years ago, when most here were in diapers, when high current power amps became a thing (maybe THE THING?) I read that it didn't really matter for any practical technical/electrical reason. I also seem to remember that high current power amps were touted as being required for speakers presenting a difficult load.

Only useful info please, oh and keep it civil! :wink:


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 4:43 am 
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Location: Repentigny, QC, CA
this is civil AND useful

http://www.atma-sphere.com/Resources/Co ... _Myths.php


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 4:56 am 
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Location: Hamilton, ON, CA
I think that the 'high current amp' designation is meant to describe amps that are capable of driving low impedance speakers. That need was more common in the 70's with some speakers that were harder to drive drive. Speaker designers tend to avoid that sort of thing nowadays.
"Headroom" was another 'feature' that manufacturers liked to use back then, to describe a lower powered amp's ability to supply much more power for very short bursts

There's a discussion about "high current" on the Audio Asylum several years ago: https://www.audioasylum.com/cgi/t.mpl?f=amp&m=97047 It starts out a little weird with the usual goofy 'opinions', but some people who understand amplifier design and power supplies come-in to explain things.


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 6:25 am 
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Current is needed to prevent voltage sag in the power supply. If the voltage sags, output can no longer follow input, and distortion results.

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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 6:33 am 
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Location: Sooke, BC, CA
ripblade wrote:
Current is needed to prevent voltage sag in the power supply. If the voltage sags, output can no longer follow input, and distortion results.


+1


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 7:21 am 
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Location: Copenhagen, , DK
With a beefcake 6000 VA power supply for each monoblock, it is no problem for Krell Evolution 900 to drive low impedance speakers http://hometheaterreview.com/krell-evolution-900-monaural-power-amplifiers-reviewed/


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 7:45 am 
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The term High Current means many things to many different manufacturers and it would be unwise to purchase one amp over another based solely on the term.

What I would hope but not always see in a "high current" solid state amplifier are
Power supply:
A high VA power transformer backed up by significant capacitance. This will prevent the power supply from sagging when played at louder volume or with heavy base notes. It is common to see a 100wpc into 8ohm amplifier using a 180va transformer and 5000 to 10000uF of capacitance per rail. Would this work and sound fine, simply yes it will at normal listening levels, driving speakers with modest impedance swings using most (not all) programme material. Will this double down into 4 ohms probably not and I would expect the headroom to be about 2db. This same amplifier with a 300va power supply and 20000uF capacitance per rail (some will say that's to little others to much) will proved much stiffer power supply and would have added penny's to the cost.
Output Devices:
Its not surprising to encounter 80/100wpc amplifiers with a low output device count 2 to 4 devices per channel, while this may work well at standard volume on simple loads its a recipe for disaster when driving low impedance at high volume or with challenging programme material. Good BJT output devices cost $8 to $15 for a hobbyist to buy in low volumes, there is no reason for a big name manufacturer to skimp or is there.

An amplifier like other things is usually built with usability and end user price in mind. Big transformers with lots of capacitance and many output devices need real estate, add weight and require massive heat sinks. Amplifiers that need 2 people to carry and are a big as an ottoman are often viewed with distain by significant others. As my wife said "those things are beastly why cant you get with the times".

I am currently building some amplifiers to replace the 4 beastly ones that currently drive my Lx521 speakers. At the start of this project I set out a list of specifications and parameters I wanted to meet, it quickly became apparent that I was on my way to 4 beastly boxes. This project has given me a better insight and understanding of the compromises designers and manufacturers have to make.

So back to "high current" you can add that to the pile of sales terms that are used as sales tools. A well designed, well executed amplifier should (one would hope) have sufficient "current" to do the job it was designed for. I will give you a hint, you wont find this is a 6 or more channel home theater amplifier that measures 17" x 15" x 8" there is just not enough real estate (with one caveat I do not know much if anything about switch mode power supplies used in some newer digital designs)


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 Post subject: Re: High Current
PostPosted: Wed Sep 13, 2017 8:38 am 
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Location: Markham, ON, CA
kvn63 wrote:
The term High Current means many things to many different manufacturers and it would be unwise to purchase one amp over another based solely on the term.

What I would hope but not always see in a "high current" solid state amplifier are
Power supply:
A high VA power transformer backed up by significant capacitance. This will prevent the power supply from sagging when played at louder volume or with heavy base notes. It is common to see a 100wpc into 8ohm amplifier using a 180va transformer and 5000 to 10000uF of capacitance per rail. Would this work and sound fine, simply yes it will at normal listening levels, driving speakers with modest impedance swings using most (not all) programme material. Will this double down into 4 ohms probably not and I would expect the headroom to be about 2db. This same amplifier with a 300va power supply and 20000uF capacitance per rail (some will say that's to little others to much) will proved much stiffer power supply and would have added penny's to the cost.
Output Devices:
Its not surprising to encounter 80/100wpc amplifiers with a low output device count 2 to 4 devices per channel, while this may work well at standard volume on simple loads its a recipe for disaster when driving low impedance at high volume or with challenging programme material. Good BJT output devices cost $8 to $15 for a hobbyist to buy in low volumes, there is no reason for a big name manufacturer to skimp or is there.

An amplifier like other things is usually built with usability and end user price in mind. Big transformers with lots of capacitance and many output devices need real estate, add weight and require massive heat sinks. Amplifiers that need 2 people to carry and are a big as an ottoman are often viewed with distain by significant others. As my wife said "those things are beastly why cant you get with the times".

I am currently building some amplifiers to replace the 4 beastly ones that currently drive my Lx521 speakers. At the start of this project I set out a list of specifications and parameters I wanted to meet, it quickly became apparent that I was on my way to 4 beastly boxes. This project has given me a better insight and understanding of the compromises designers and manufacturers have to make.

So back to "high current" you can add that to the pile of sales terms that are used as sales tools. A well designed, well executed amplifier should (one would hope) have sufficient "current" to do the job it was designed for. I will give you a hint, you wont find this is a 6 or more channel home theater amplifier that measures 17" x 15" x 8" there is just not enough real estate (with one caveat I do not know much if anything about switch mode power supplies used in some newer digital designs)


Well said. Additionally, amplifiers with "high current capabilities" also (typically) have high damping characteristics. This is important when driving large speakers (especially woofers) as voice coils generate current as well as being driven by current. The larger the speaker, the more current generated. Damping can be described as an amplifier's ability to absorb this electrical feedback as the voice coil returns to its rest position after being driven by that amp. Insufficient damping will enable this electrical current to "drive" the other speakers in the system (like tweets) which then causes all sorts of distortion in the speaker system....good damping allows for quick, accurate woofer response while continuing to support clear mid and tweet response. That is why many "big speakers" like high-current amplification. At least that is my story and I'm sticking to it. :P


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 Post subject: Re: High Current
PostPosted: Thu Sep 14, 2017 12:14 am 
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Location: New Westminster, BC, CA
Obvious answer is better control into low impedance but...
Let's take two amps at the same rated power and otherwise similar, say 100 wpc and both class A/B. One weighs 35 lbs and the other weighs 70 lbs (bigger everything) and capable of much more current. Which do you think is capable of more satisfying bass? When I was in diapers, this was clearly demonstrated in a showroom comparing an Accurus to an Aragon, both by the same parent company.


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 Post subject: Re: High Current
PostPosted: Thu Sep 14, 2017 1:04 am 
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Location: Orillia, ON, CA
High current amplifier,..During the early 1980s my first attempt at putting together a decent home system was the purchase of a pair of Magnapan MG 3 speakers which only came to life using a so called high current amplifier which happen to be a used Threshold Stasis 3 .
Prior to the purchase of the Stasis 3 trying other solid state amps of the same watts per channel that weren't marketed / labled as high current just didn't work with the Magnapans however with the Threshold it was literally night and day difference from other amplifiers.


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 Post subject: Re: High Current
PostPosted: Thu Sep 14, 2017 3:59 am 
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http://www.canuckaudiomart.com/forum/viewtopic.php?t=34949
Quote:
The harman/kardon HK 980 integrated amplifier deliver 80 watts into 8 ohms RMS. If you think an equally priced surround receiver delivering 7 x 100 watts is more powerful then think again, because you need to know that HK 980 has a serious current delivery of +/- 80 Amps! , which is much more than what most receivers have to deliver to its five to seven speakers.

And the HK 990 has a serious current delivery of +/- 200 Amps! This means the HK 990 can drive difficult driving speakers better than NAD C375BEE

Translated test review of HK 670 from the swedish Saxat ur HiFi & Musik 12 - 2001 magazine: http://www.canuckaudiomart.com/forum/viewtopic.php?f=9&t=34949&start=15
Quote:
It's exactly three years ago we tested the HK 650 with very good results in HiFi & Music No. 1/99, despite opposition from more expensive amplifiers. It was even chosen as the amplifier of the year 1999. We lived with it long here in the editorial and even played at my house. We could just ascertain that Harman/Kardon for the money with HK 650 had made something out of the extraordinary. The cube saturation showed high current capacity and almost perfect square cube, that is exactly as it should be.
Regardless of the speakers we connected to it, it kept both control and style. It sounded clean, chunky and muscular at the same time and was fun to listen to. It was not surprising that people ran out to buy it when you got all this for just 4500 SEK.
At that time, the HK 650 had the little brother HK 630 and big strong uncle in the family was speaker-wrestler HK 690 which had such current resources that it was possible to weld plates with speaker cables. The new HK 670 replaces both the old HK 630, HK 650 and HK 690 big brother. Stylistically, this new amplifier gotten itself a facelift and is now really nice and are designed to complement hand in glove with Harman/Kardon's new model program.

High current capability
Harman/Kardon have a long tradition for building amplifiers with High current capacity and this ability is certainly not lacking.


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 Post subject: Re: High Current
PostPosted: Thu Sep 14, 2017 7:53 am 
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Joined: Mon Jun 11, 2012 11:25 am
Posts: 169
Location: Toronto, ON, CA
PBB wrote:
Why should a power amp be high current?
I read that it didn't really matter for any practical technical/electrical reason.


As the owner of Apogee speakers, a high current amp is a very practical reality, which is why I power them with a Classe DR-3.


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 Post subject: Re: High Current
PostPosted: Sun Sep 17, 2017 3:28 pm 
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Location: toronto, ON, CA
An amp should be high current so that the dips in a speakers impedance do not cause distortion from the amplifier not being able to deliver the required current at the low impedance.


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