AR LS17SE Volume Control


I picked up a used AR LS17SE preamp last fall.   In general I’m quite pleased with it.   It is my first exposure to the AR sound.  
What stands out to me is the limited volume control range.   When I was researching a preamp for my needs this seemed to be the exact fit I was looking for.   It is specified as having 102 detents on the volume control which seemed like a good range of sensitivity to me.  
What I find is it is only 6-8 clicks on the volume control from lowest/no volume to maximum tolerable volume which, to me, is quite disappointing for such a garnered piece/brand.  Especially with the 102 detent reference.  
Am I missing something?
Ag insider logo xs@2xmike_ostradick
Yep, you are missing something. Equipment matching most probably. My first guess is that your speakers are very efficient. Next is that your amp is too sensitive. You can cure this by inserting in-line attenuators between your amp and pre-amp. You might be able to get a mod to your pre-amp's gain stage (insertion of resistors - similar to adding the in-line attenuators). Personally I'd buy (and I did) in-line attenuators which are cheap(ish) and see if you can tolerate them and go from there. I used 10db Rothwells. 
Speakers are Dynaudio S1.4LE at 85db sensitivity.  So not the speakers.  

The amp is an Edge M8m at 30,000 ohms input impedance single ended only.  

The LS17SE is 350 ohms output impedance single ended. 

That is an 85:1 ratio.  Impedance matching was a large factor in pursuing the LS17SE.  I had plugged the Edge into my Aesthetix Calypso (single ended 1000 ohms output impedance) and the volume was noticeably low.  Really had to crank up the Calypso to approach a listenable volume which I interpreted as a poor match at 30:1 ratio.  

What usable percentage of the volume range do others experience on their LS17 or LS17SE?


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You need to do some research on the gain of the Edge amp.  The issue is not so much about line stage output impedance and amp's input impedance, but rather the voltage output of the line stage and gain / input-sensitivity of the amp.  What is the input voltage level to take the amp to full power? 

Here's the rated Output spec for the LS17 SE:
2V RMS 1Hz to 100kHz into 200K ohm balanced load (maximum balanced output capability is 15V RMS at less than 0.5% THD at 1kHz).  

BE VERY CAUTIOUS about line attenuators.  I tried Rothwell 10db attenuators and when I inserted them in my system several years ago, oh yes, the level range was much more suitable, but these things resulted in the musicality being sucked out of my system. This was most likely because they dropped the resultant amp's input impedance.  Perhaps the better place for them is between the source and line stage input?  Anyway, they were in and out in less than a minute and have been in their box ever since.  I just found them in my stash of misc. audio parts.  I would be happy to just pass them your way free of charge and see if this works out for you.  This is much better than you spending $50.

John

John,

I shared the same concern as you experienced regarding the sonic signature they would introduce to the system.  Everything has an influence and I can't imagine a simple device such as this being very positive sonically.  

My next step is probably to contact the original designer(s)/maker(s) of the Edge amp and find out the input sensitivity.  I can also plug it into my other system and see how what the volume range is there.  

I was hoping this would be a simple response from other LS17 owners. 

Mike
The gain on the LS17/SE rises very fast. There is a modification that ARC can do to smooth out the gain control to make it a smoother rising rate. Not too expensive. If I remember correctly less than $500.00. It’s a known “issue” with that pre. Just the way it is designed.  If your amp has input sensitivity control you can mitigate it that way as well.
mike_ostradick OP

Mike you already have too much gain, you don’t need an active preamp with even more gain.
Get yourself a good 10ohm passive preamp, this gives an output impedance max of 2.7kohm and into your 30kohm poweramp you still have more that 1:10 impedance ratio so no problems.

Don’t go inserting line attenuators to bring down the gain, fix the problem with out using that band-aid fix.

PM: Second thoughts, just noticed you use a Nad M51 it has a volume control why aren’t you going direct into your power amp with it, again forget the active preamp??


Nelson Pass,

“We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.”


Cheers George
George,

Thanks for the suggestion.  Unfortunately the NAD M51 left last year.  Otherwise that would be a great choice.  

I did consider passive preamps when I found the LS17SE but I wasn't dialed into the gain balance concern. That explains a lot.  

Mike