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pre and power matching

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soundbuff

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O ye knowledgeable ones!
Please tell me if the following combo will be suitable
I have the Xindak A600E which can be used as a pure power amplifier. It has one single ended input.
Specs are as follows:
Input impedance 100 Kilo Ohms
SN Ratio >95
Damping Factor 220
THD 0.03
Freq Response 10hz - 100khz
Peak current 68 A
240000 Filtering capcitance
Input sensitivity NOT Indicated
Dual mono Symmetrical current feedback design.

I am planning (seriously!) to drive this with the Luxman C700u. It has the following specs
Input sensitivity/impedance; Unbalanced 250 mv/46 K ohms
Out put /input impedance: unbalanced 1V /90 Ohms., max 11 v.
Freq Response 20 hz to 20 khz
THD unbalanced 0.007
SNR(IHF-A) unbalanced 125 db.

From what I can make out there should not be any issues. The impedance math seems ok, just concerned if the 11 v. output of the pre will not a problem.
I know that this is a very expensive preamp, but if I can swing it, it would be a keeper for me. The Xindak is actually a very lovely amp and selling it will mean big hit simply as it is Chinese. It has also got a very good preamp stage. Better than the Leben and yes, better than the Metrum jade's variable output. So bettering the preamp section will need a pretty high jump

Please do give it a thought.
Thanks
 
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Fantastic

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I am planning (seriously!) to drive this with the Luxman C700u. It has the following specs
Input sensitivity/impedance; Unbalanced 250 mv/46 K ohms
Out put /input impedance: unbalanced 1V /90 Ohms., max 11 v.
Freq Response 20 hz to 20 khz
THD unbalanced 0.007
SNR(IHF-A) unbalanced 125 db.

From what I can make out there should not be any issues. The impedance math seems ok, just concerned if the 11 v. output of the pre will not a problem.
I know that this is a very expensive preamp, but if I can swing it, it would be a keeper for me. The Xindak is actually a very lovely amp and selling it will mean big hit simply as it is Chinese. It has also got a very good preamp stage. Better than the Leben and yes, better than the Metrum jade's variable output. So bettering the preamp section will need a pretty high jump


You should have no problems. The 11V is only the "maximum possible" output before the signal possibly clips. From what I can see, the sensitivity is most likely 250mV input for a 1 volt output. That's a gain of about x 4 which is fine . Most DACs typically give a 2 V output. Your power amp would typically need a 1 to 2 V input for full output ( strangely not mentioned anywhere !). The overall result would be that you need to turn your volume control very little to achieve normal listening levels. Full output would be at some intermediate position of the volume control and not at the physical max position of the volume control. The position of the volume control does not indicate anything except how much of the input signal is going to the power amp. With a 2 volt input it would have a position that's quite low and with a 250mV input ( typical from most stand alone phono preamps ) you would need to turn up the volume quite high to get the same listening level. Nothing good or bad about that.
The output specs are possibly printed wrong. Must be typical 1 V output ( with 0.25 V input ) and output impedance of 90 Ohms which is fine.

However you could drive this power amp directly from a DAC provided the volume control is controllable either at the DAC or at this power amp. Check that. Otherwise the output will be going at full blast if connected to the DAC with no volume control in-between. Will blow some fuses, your ears and your wallet !
The power amp input impedance is a high (!) 100K ohms. This is much higher than the typical range of 10K ~ 47 K we see more often. Good news is that it will work very well even with the high output impedance that several tube preamps have . They could be from a few K ohms to 10's of Kilo ohms. Of course not all tubed preamps are like that . Depends on the negative feed back they use or don't use.

Suggest you first try it with a DAC directly. Make sure there IS a volume control between the DAC and the power amp. MOST times ANY preamp in-between will degrade the sound slightly not necessarily in a bad way but maybe an unacceptable way ( perhaps !) . With tube preamps with high even order harmonic distortion , it will sound 'warm'. Some people like this kind of sound but it's not the original unaltered sound . A really good tube preamp will not colour the sound but could sound cleaner and deeper due to the minimal impedance loading effects of the input stage of the tube preamp. Anything is OK as long as you like the sound !
 

raghupb

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Sep 11, 2015
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Location
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@soundbuff
On paper there seems to be no issues with the matching.
Good impedance match. 100K input impedance at power amp. 90 ohms at pre at nominal levels.

The pre-out of 11V (max) is surprising. Maybe it was designed to be used with low gain power amps.
Low gain amps have the advantage of low noise/distortion at output stage.
Luxman is spec'd at 1V (real world) pre-amp out.
Most power amps have full output range input sensitivity between 1-2V (as someone suggested earlier).
So all is hunky dory spec/matching wise.

In the end, it comes down to your ears. Whether you like the combo or not, is not ours to guess :)

Cheers,
Raghu
 

soundbuff

Active Member
Joined
Dec 26, 2015
Messages
289
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Location
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Raghu and Fantastic, Thanks for your detailed and informative inputs.
Yes,I was mostly concerned about the 11 v output and rather high 100k input. As you have pointed out however it should not matter.

As for playing the amp directly from a variable DAC. I have indeed tried it, first with my Ayon 1sc a number of times and more recently with the Metrum Jade. There is nothing really bad with the digital direct to the power amp inputs. However in both instances, to my ears at least the integrated sounded better than the direct. The preamp of the integrated has more gain than the DAC variable outputs, but more importantly it has the intangible quality of more life and engagement. Although this is hard to explain in words the Digital out into the power direct did not hold my attention as well as the normal input into the amplifier. The Metrum Jade is however still quite new and perhaps it will improve as it breaks in. I would be quite happy if I did not have to buy a new preamp and run it direct for the best sound. The Jade designer claims that the variably output is special kind of design where information is not lost at low volumes.
 
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