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 Post subject: krell kst100 impedance?
PostPosted: Wed Oct 10, 2018 4:10 pm 
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i have a krell kst 100. the manual says it can run down to 1 ohm stereo at 800 watt per side.
and it also can be bridge at 400 watt /8 ohm. but that is it no other lower impedance claim in bridge mode.
my question is, if it can take 1 ohm stereo, this should mean it could take probably 4 ohm bridge or maybe even 2 ohm bridge?
I sent them an email a week ago, with no answer??? they (krell) don t seem to care much giving answer or reply ,for their legacy product!
I need to use it to run a center channel that is 4 ohm, more exactly 3.1 ohm consisting of 4 x 6.5 inches sb acoustic woofer in serie parallel. and a wavecor 30 mm tweeter.


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PostPosted: Wed Oct 10, 2018 4:43 pm 
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It will run in unbalanced mode at 4 ohms. In unbalanced bridged mode, it's output would be 800 watts.

-- 11 Oct 2018 00:43 --

It will run in unbalanced mode at 4 ohms. In unbalanced bridged mode, it's output would be 800 watts.


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PostPosted: Wed Oct 10, 2018 5:29 pm 
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I think it should take it no problem, but why the manual don t states so?
I have been running it for 10 month now. I was very surprise to see it run cold .because it was running normal warm when running stereo 4 ohm . but after 10 month bridge on that center , the amp dyed on me a week ago.
I use my classe c 100 for the time I get it fixe. I did run that classe on a sub that was 4.1 ohm at full power with no problem for over 4 year now it was even running cold. but the classe now on my center 3.1 ohm ,when pushed a bit. it start running hot and eventually go on protection.
I have checked my speaker s and all drivers with no issues at all???
I even bought a analogue meter (already have a good digital one) to check when moving cone if any short happening. not at all 4 woofer seems fine, no coil rubbing??? xover seems ok.


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PostPosted: Wed Oct 10, 2018 5:32 pm 
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It's actually not that easy a question to answer....
When you Bridge an amplifier, you're essentially doubling it's output voltage, which (in an ideal world) means quadrupling it's output power. So your 100 watt amp, ideally becomes a 400 watt amp. There are a couple of gotcha's though. The first is, that while you're doubling the output voltage, there's no guarantee that the amp is capable of delivering double the current. Thats why you see amps advertised as 100 watts per side, and 300 bridged (or some similar, less than 4x increase).

The second part, which you won't find on any spec sheet, is SAP, (Safe Area Protection) or SOC (Safe Operating Conditions), or a few other acronyms. Transistors (and tubes) have maximum current, voltage, and power ratings, but it's not quite that simple. They generally publish a graph, showing what combination of voltage and current the device is safe to operate in. Designers who want a reliable product, pay attention to those curves, and design in protection circuits to keep the amp from self destructing when pushed into an un-intended load. It's these protection circuits that cause designers to be reluctant to spec a bridged amp into lower impedances. You're moving outside of that safe operating area, and their protection circuits are going to start kicking in....

I wouldn't suggest you try and drive a 2 ohm load with your Krell bridged. It will probably drive your 4 ohm speaker, provided you don't try and push more than 400 watts.

Cheers, Dave


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PostPosted: Wed Oct 10, 2018 5:49 pm 
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dcrooks wrote:
It's actually not that easy a question to answer....
When you Bridge an amplifier, you're essentially doubling it's output voltage, which (in an ideal world) means quadrupling it's output power. So your 100 watt amp, ideally becomes a 400 watt amp. There are a couple of gotcha's though. The first is, that while you're doubling the output voltage, there's no guarantee that the amp is capable of delivering double the current. Thats why you see amps advertised as 100 watts per side, and 300 bridged (or some similar, less than 4x increase).

The second part, which you won't find on any spec sheet, is SAP, (Safe Area Protection) or SOC (Safe Operating Conditions), or a few other acronyms. Transistors (and tubes) have maximum current, voltage, and power ratings, but it's not quite that simple. They generally publish a graph, showing what combination of voltage and current the device is safe to operate in. Designers who want a reliable product, pay attention to those curves, and design in protection circuits to keep the amp from self destructing when pushed into an un-intended load. It's these protection circuits that cause designers to be reluctant to spec a bridged amp into lower impedances. You're moving outside of that safe operating area, and their protection circuits are going to start kicking in....

I wouldn't suggest you try and drive a 2 ohm load with your Krell bridged. It will probably drive your 4 ohm speaker, provided you don't try and push more than 400 watts.

Cheers, Dave

specs says it dilliver 800watt per side on a 1 ohm load. why it would not safely drive a 4 ohm load bridge for only 800 watt if it can push 1600watt in stereo x 1 ohm?


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PostPosted: Wed Oct 10, 2018 6:49 pm 
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zon001 wrote:
i have a krell kst 100. the manual says it can run down to 1 ohm stereo at 800 watt per side.
and it also can be bridge at 400 watt /8 ohm. but that is it no other lower impedance claim in bridge mode.
my question is, if it can take 1 ohm stereo, this should mean it could take probably 4 ohm bridge or maybe even 2 ohm bridge?
I sent them an email a week ago, with no answer??? they (krell) don t seem to care much giving answer or reply ,for their legacy product!
I need to use it to run a center channel that is 4 ohm, more exactly 3.1 ohm consisting of 4 x 6.5 inches sb acoustic woofer in serie parallel. and a wavecor 30 mm tweeter.


Why bridge it anyway if you are using it for the centre channel?
Use one channel of the amp and insert a 4 ohm resistor across the terminals of the unused channel.


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PostPosted: Wed Oct 10, 2018 6:59 pm 
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You are good to go, your Krell gives 400w 8 ohms and 800w 4 ohms when used as monoblock.

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PostPosted: Wed Oct 10, 2018 7:16 pm 
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c est ce que je pensait. mais je vien de le sauter les outputs sur l ampli, une semaine passer. mon center channel prend environ 300 watt ??? en asttendant je me sert de mon classe c 100 qui aussi peut prendre 4 ohm bridge. pour 500 watt. et il chauffe et trip autour de 400 watt.
jai driver ces 2 ampli la a planche pendant des annees.il ne chauffais meme pas. le classe sur mon sub de 4.1 dc ohm et le krell ,ca fait un ans sur ce meme center depuis un ans sans probleme. je sait que quand le krell as sauter je le drivait pas mal a planche. je me demande si mon center dessans pas plus bas que 3.1 ohm?
that s what I thought. because after a year with no issue and running cold. it never occur to me that it was under strain? 300 watt speaker , 800 watt power?
I wonder if my speaker is dropping under 3.1 ohm ?
just don t want to blow it again. $400 of repair.


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PostPosted: Wed Oct 10, 2018 7:30 pm 
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Zon, years ago I tried those same Krell with my Infinity RS 8 Kappa 4 ohm (but dip at 1.7 ohms 15khz)
they were hot to touch but they never stopped to work.

Do a sweep freq. test at 2-3 different level with your center speaker, if anything is wrong, you will know it instantly.

Martin Colloms, Stereophile wrote:
Simple removal of the top cover provides access to a mono switch which allows the amplifier to perform
in unbalanced bridge mode, working as a monoblock delivering 400W into 8 ohms and 800W into 4 ohms.

https://www.stereophile.com/content/kre ... -amplifier

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PostPosted: Wed Oct 10, 2018 8:00 pm 
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zon001 wrote:
i have a krell kst 100. the manual says it can run down to 1 ohm stereo at 800 watt per side.
and it also can be bridge at 400 watt /8 ohm. but that is it no other lower impedance claim in bridge mode.
my question is, if it can take 1 ohm stereo, this should mean it could take probably 4 ohm bridge or maybe even 2 ohm bridge?


Are those power specifications for single or both channels operating?
It`s entirely possible that although 800 watts can be generated into a single 1 ohm load, the power supply may not be able to support 2 simultaneous 1 ohm loads hence no mono rating below 8 ohms.


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PostPosted: Thu Oct 11, 2018 5:53 am 
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All those specs are on static point of view.
dynamically speaking, with varying impedance curves, the safe area protection or other sensing devices on output of the amp
are stress enough to go in active and protect the output devices.
With time and wear and tear, transistors goes leaky or intermittent because of this stress.
Hence one or more transistor goes and blows all the rest depending on design of the amplifier.
below 2 ohms is risky, mind you it runs but not without stressing even the beefiest amplifier.


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PostPosted: Fri Oct 12, 2018 12:43 am 
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According to Martin Colloms of Audiophile...

Channel separation was checked, and in single-ended mode was satisfactory at 71dB (1kHz) and 55dB (20kHz). In balanced mode, just 45dB separation was measured at 20Hz, compared with 60dB unbalanced, this "averaged" result being partly to do with the command power-supply arrangements and the input balance circuitry which doubles as a phase splitter for monaural operation.

In monoblock mode, with two KSTs used for stereo, each channel would now deliver a basic 400Wpc into 8 ohms, 800W into 4 (both 26dBW), with the recommendation that speaker loads known to rate lower than 5 ohms be avoided as the peak current limit of this powerful amplifier is approached. In this mode I can see the KST as a worthy choice for studio monitoring, where its more compact package and superior value make sense compared with the bigger Krells. The sound quality of the mono KST amplifier will leave most "professional" amplifiers for dead. A trial short circuit at half-power resulted in a harmless spark and successful protection operation. This is a fine set of results from a well-designed amplifier.—Martin Colloms
Read more at

https://www.stereophile.com/content/krell-kst-100-power-amplifier-measurements#zu950molOkdHq4mj.99

https://www.stereophile.com/content/krell-kst-100-power-amplifier-measurements


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PostPosted: Fri Oct 12, 2018 3:45 am 
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hat s a little conflicting , if they say it can take 4 ohm bridged but to avoid less then 5 ohm load ?
I read that article but did not see the avoid notice.


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PostPosted: Fri Oct 12, 2018 6:06 am 
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The only bridgeable amps I know that are used in series or in parallel are Bryston's 7B mono blocks.
Series connection if I remember well is for 8 ohms mono loading, and parallel for 4 ohms and lower.
Bryston's 7B experts correct me if i'm wrong, but manual did explain it this way.
Bridging any amplifier is using each channel and connect them in series, hence most stereo amp in bridge mode will have to be
connected on the red positive speakers posts and feeding the left or right only mono signal.
Once the amplifier is bridge, so both channels in series with each other, same current passes through them.
so below 4 ohms or 2 ohms, you are already reaching maximum safe operating limits of each amplifier connected in series or bridged.


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PostPosted: Fri Oct 12, 2018 6:42 am 
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revoxb77 wrote:
The only bridgeable amps I know that are used in series or in parallel are Bryston's 7B mono blocks.

Several Crown MacroTech series amplifiers are parallel and series mono capable. Parallel mono configurations are indeed better suited for very low load impedance's.


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