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Amps, current, ohms and whatnot.

T

tommyt

pfm Member
I have questions!

Having just purchased a set of used Shaninian Hawks that I understand are difficult to drive so I have started to look at my options, should my Roksan Caspian M2 not be up to the task.

I have started looking at the obvious candidates.. Dynavector, Plinius, Densen and some of the left field choices like Nord Hypex, Devialet.

Looking at specs is all quite confusing.

Q1)
If an Amp gives rating for 8 ohm & 4 ohms and does not mention 2 ohms or lower what does that mean? Does it mean it cant handle going down that low?

Q3)
The creek evolution 100A specs show 8ohm (110watts) and 4ohm (170watts) and continuous current of >8.5 Amps with a max current of +/- 26 Amp burst into 0.5 Ohms. Is there a reason it doesn't provide a 2ohm rating?

Q2)
What level is "high" when referring to a high current amplifier. My Roksan is 8ohm - 85watt / 4ohm 125watt and 60amp peak. It doesnt give a 2ohm rating either.

Q3)
What current do the dynavectors kick out? I cant seem to find any specs for them.

Q4)
Which of the below do you think would suit the Hawks well and are there others I should I consider?

I am a bit limited in space in my cabinet as its depth is max 40cm and I wouldn't want anything that runs too hot.

Discounted:
- Plinius haito - Too deep (45cm deep)
- plinius sa102 - too deep
- VCC AX-Z1010TN - too deep (45cm deep)
- Hegel H360/160 - too deep
- krell 400 - too deep.

Possible options:
- bi-amp with a Caspian M2 poweramp ~£600-700 used
- Creek 100A - new ~£1500 (can reuse my caspian for 2nd system)
- Devialet D200 - used ~£3000 supports 2ohm but no current specs ("")
- Dynavector HX75,100,1.2 - too expensive new - hard to find used.
- Nord one ups - new £1500-1800, 550W 2ohm and "high" current
- Spectron musician (one in classifieds ~£2k) claims to go to 0.1ohm
- Densen b3xx - 8ohm/4ohm, no current specs
- Hegel H300 - 250watt into 8ohm, down to 2ohm.
- Atc sia2-150 2, 150w into 8, 285w into 4. Might get a bit hot
- Perraux eloquence 150i - mosfet design, possible cold/hard sounding
- Teddy pardo mb100s
- Leema tucana II.


Thanks!
 
The Creek is an intriguing and clever design in that its compact and can have an on-board DAC/Tuner module fitted, however I am not sure it would drive a pair of Hawks with ease. As someone mentioned on another thread, Audiojoy, a member here, had a NOS JVC 1010 for sale and I think that should have no trouble driving the Hawks.
 
A 'perfect amp' will double power in watts as impedance halves, e.g. 100W into 8 Ohms, 200 into 4, 400 into 2, 800 into 1. Very, very few can do this, and the ones that can tend to be hugely expensive US battleship class stuff (Krell, Levison etc). The closest an amp gets to this the more likely it is to be able to drive a low impedance reactive load IME, e.g. a KSA 50 that can manage 50W into 8 Ohms and 100W into 4 is always going to be a far better bet with a tough to drive speaker than say a Quad 303 that actually goes the wrong way and basically fails into a low impedance (45W into 8, 28 into 4!). I've no idea at all how modern class D etc technology copes with this.
 
JensenHealey said:
I reckon your Caspian will be just fine. 60A peak is quite a lot!
Click to expand...

Yes thats what I wondered - at least at low/moderate volume.

The issue I can see is that with my relatively sensitive speakers (90db) it starts to fall apart quite badly at volumes above 80db (sitting 2m away). Whilst normally I listen around 70db it's nice to have a good blast now and then. The Hawks have sensitivity of 87db so my guess is the amp is going to start struggling at a lower volume.
 
tommyt said:
Yes thats what I wondered - at least at low/moderate volume.

The issue I can see is that with my relatively sensitive speakers (90db) it starts to fall apart quite badly at volumes above 80db (sitting 2m away). Whilst normally I listen around 70db it's nice to have a good blast now and then. The Hawks have sensitivity of 87db so my guess is the amp is going to start struggling at a lower volume.
Click to expand...

That's about a watt. If your amp is suffering at that level the speakers must be doing something odd. Perhaps a power resistor in series might help? Or something to drag the load into a safe area for the amp. If you listen at this sort of level a regular commercial value resistor should do. Cheaper than a new amp. I'm happy to be corrected.
 
From what I understand the impedance of a speaker is important as if it falls lower than about 4 Ohm the current required to maintain the voltage rises to a point where the amplifier cannot provide the power and distortion occurs.

The current output of an amplifier comes from the capability of the power supply and the output devices to cope with that current. High power power supplies are expensive and high power output devices need to get rid of heat which means large heat sinks and more expense.

Most music doesn't have constant high power requirements so most amps will be fine at lower volumes as the devices have the opportunity to cool between loud parts of the music programme.

Amplifiers may be designed to cope with low impedance speakers by limiting the current available from the power supply which means they will just not output the required current at high volumes. In fact some amplifiers will cut out if the power requirement is above the design capability.

Very low impedance is an electrical short which will destroy some amplifiers. Otherwise lots of money required, good current limiting amps which will distort at high volume. sometimes this distortion is too much for the speaker which may get hot and fry.

Solution - Expensive amplifier, more sensitive loudspeaker, lower volume, sit nearer or smaller room. You could also listen to more violin music and less heavy metal.

Also happy to be shot down.

PS I went active which seemed to help.
 
Ultimately you need to treat amp/cable/speakers as one unit, and trying to work out what works and what doesn't is really down to experience. Continuous output values are rather limited in what they show - what you need is how fast an amp can deliver current peaks, and for how long - the more difficult the speaker, the more this becomes relevant. I used to think large smoothing capacitance per rail was important - but then bought an XTC power amp that had small relative capacitance but a very, very big transformer and could deliver good performance. As a rule of thumb, the heavier the amp, the better...as long as the weight is not just the casework.

Just try the Capsian, I also think it will be fine.
 
mudlark said:
From what I understand the impedance of a speaker is important as if it falls lower than about 4 Ohm the current required to maintain the voltage rises to a point where the amplifier cannot provide the power and distortion occurs.

The current output of an amplifier comes from the capability of the power supply and the output devices to cope with that current. High power power supplies are expensive and high power output devices need to get rid of heat which means large heat sinks and more expense.

Most music doesn't have constant high power requirements so most amps will be fine at lower volumes as the devices have the opportunity to cool between loud parts of the music programme.

Amplifiers may be designed to cope with low impedance speakers by limiting the current available from the power supply which means they will just not output the required current at high volumes. In fact some amplifiers will cut out if the power requirement is above the design capability.

Very low impedance is an electrical short which will destroy some amplifiers. Otherwise lots of money required, good current limiting amps which will distort at high volume. sometimes this distortion is too much for the speaker which may get hot and fry.

Solution - Expensive amplifier, more sensitive loudspeaker, lower volume, sit nearer or smaller room. You could also listen to more violin music and less heavy metal.

Also happy to be shot down.

PS I went active which seemed to help.
Click to expand...

I'm sure there are lots of expensive ones that wouldn't be suitable. So what specs should I look at that would signify capability or are the specs not telling the whole story?
 
tommyt said:
I'm sure there are lots of expensive ones that wouldn't be suitable. So what specs should I look at that would signify capability or are the specs not telling the whole story?
Click to expand...

They are only telling you what marketing want you to see. Check out my comments about power amps in the Obelisk thread as the same holds true but more so with the Hawks and Diapasons.

The bit about phase angle is important since as this increases more power is dissipated in the output transistors/drivers and less into the speaker. At 45 degrees at 10W into the speaker another 40W is wasted as heat in the output devices so the amp has to provide 50W. With 20dB of transients that 10W becomes 1000W or 5000W total dissipation. However its only momentarily and the average is significantly lower. The Diaps and maybe the Hawks are around 2 Ohm in the treble like the Obs and the phase angle does reach 45 degrees around here. And to make matters worse this is where the ear is most sensitive.

Power amps that handle this will be big, heavy and pricey. My own amps can provide >1600Wpc into 4 Ohms continuous and a short term burst of 22.5KW into 1 Ohm. They do weigh in at 42Kg apiece!

Sounds jolly good too. If I had the space I'd go all the way up to the Diaps but as it is I'm limited to the Obs by the shape of the room and SWMBO.

Cheers,

DV
 
If your concern is low speaker impedance and sensitivity then *for music* the peak current available is perhaps the best guide. Chances are very high sustained sinewaves would melt the speaker anyway. 8-]

Having the power double when you halve the impedance may simply tell you a 'stiff' PSU was employed, but again, for real music with peak/mean ratios of over 10dB the power may simply not fall that far from roughly doubling when you halve the impedance *until* you hit a current limiter.

Bottom line: depends how the specs were set and what kind of music you want to play. etc.
 
Build some Hypex nc400 mono blocks, they are better suited to low impedance loads than the nc500.

8 Ohms: 200W
4 Ohms: 400W
2 Ohms: 580W

Have a read of some reviews, they really are fantastic amps and I've never heard of them struggling even with a difficult load.
 
Jim Audiomisc said:
If your concern is low speaker impedance and sensitivity then *for music* the peak current available is perhaps the best guide. Chances are very high sustained sinewaves would melt the speaker anyway. 8-]

Having the power double when you halve the impedance may simply tell you a 'stiff' PSU was employed, but again, for real music with peak/mean ratios of over 10dB the power may simply not fall that far from roughly doubling when you halve the impedance *until* you hit a current limiter.

Bottom line: depends how the specs were set and what kind of music you want to play. etc.
Click to expand...

I listen to broad range. I have LCD soundsystem on at the moment. Metallica yesterday. Kings of convenience on the day before that. Classical piano or Ben Howard when I want to relax.

I haven't actually seen any amps with a higher current rating than my Roksan - mostly because they don't actually specify.
 
Darth Vader said:
They are only telling you what marketing want you to see. Check out my comments about power amps in the Obelisk thread as the same holds true but more so with the Hawks and Diapasons.

The bit about phase angle is important since as this increases more power is dissipated in the output transistors/drivers and less into the speaker. At 45 degrees at 10W into the speaker another 40W is wasted as heat in the output devices so the amp has to provide 50W. With 20dB of transients that 10W becomes 1000W or 5000W total dissipation. However its only momentarily and the average is significantly lower. The Diaps and maybe the Hawks are around 2 Ohm in the treble like the Obs and the phase angle does reach 45 degrees around here. And to make matters worse this is where the ear is most sensitive.

Power amps that handle this will be big, heavy and pricey. My own amps can provide >1600Wpc into 4 Ohms continuous and a short term burst of 22.5KW into 1 Ohm. They do weigh in at 42Kg apiece!

Sounds jolly good too. If I had the space I'd go all the way up to the Diaps but as it is I'm limited to the Obs by the shape of the room and SWMBO.

Cheers,

DV
Click to expand...


Given I probably cant accommodate the 'ideal' amp, whether price or size or size, out of the list above which ones do you think would cope best? Are the Class D Nords likely to outdo the A/B amps or are the power figures misleading? Are the higher wattage A/B amps likely to do any better than my Caspian or are they just going to give a different flavour? Where would the Devialet fit in to the picture?
 
If size is an issue Dynavector HX75 should be around the same size as the Roksan.

Dynavector and Shahinian are a match made in heaven, the mk2 100W version is deceptive as DV amps can deliver a lot more current than equivalent spec amps.
 
tommyt said:
Given I probably cant accommodate the 'ideal' amp, whether price or size or size, out of the list above which ones do you think would cope best? Are the Class D Nords likely to outdo the A/B amps or are the power figures misleading? Are the higher wattage A/B amps likely to do any better than my Caspian or are they just going to give a different flavour? Where would the Devialet fit in to the picture?
Click to expand...

Current matters if your speakers have points of very low impedance. The Nords probably have better current characteristics than most A/B amps, but the Nords use the nc500 - as stated, the Hypex nc400 is even better at hanling low load impedances.
 
thebiglebowski said:
If size is an issue Dynavector HX75 should be around the same size as the Roksan.

Dynavector and Shahinian are a match made in heaven, the mk2 100W version is deceptive as DV amps can deliver a lot more current than equivalent spec amps.
Click to expand...

How many amperes do they deliver?

By mk2 100w do you mean the hx100? Or is there an hx75 mk2? What about the 1.2 mk2?

Thing is there don't appear to be any available used and various "wanted" ads on hifiwigwam.
 
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