Moreplay max output voltage

[Bubbatwoa]

I have a pair of 105 dB sensitive speakers and I'm considering purchasing the Quicksilver Horn Mono amps, which were designed specifically for highly sensitive horn speakers.

The amp is said to be dead quiet due to the very low gain of 8.86 from the 8-ohm tap and 5.5 from the 4-ohm tap.

Part of achieving this low gain results in a claimed input sensitivity of 9 volts.  Stereophile's review from 2002 showed a measured sensitivity of a still-high 6.64 V to achieve full output.  https://www.stereophile.com/content/quicksilver-audio-horn-mono-monoblock-power-amplifier-measurements

"the Horn Mono puts out 36.3W into 8 ohms (15.6dBW). However, it takes an input of 6.64V for the amplifier to reach this level, which might be beyond the capabilities of some preamplifiers."

I just ordered the Moreplay kit and am wondering how it will play with the Quicksilver horn monos.  Can it output 6.64V, to drive the amps to full output?  And what about the BeePre2 with the two upgrades?  Maybe I should mention that the preamp (Moreplay, BP2) will be fed 2.1V from the fixed output of a disc player, if it matters.

 

[Paul Birkeland]

Stereophile has definitely been irksome with this kind of information before.  I can remember them writing a review of a Wavelength 300B amp and complaining that it didn't have enough gain, but that amp went to full power with 1.5V of signal (which is totally appropriately designed!).

Let's look at this a different way, if you put 36W into your 105dB sensitive speakers, that's 120dB of output.  One minute of exposure at that SPL will cause permanent hearing damage.  If this is the goal of your system, then you will need that 6.64V of preamp output!

PJ's extra conservative estimate is that reaching 103dB is generally sufficient for most people, most rooms, and most types of music.  You should be able to get there with 1W, which will happen with far less than 1V of output from a linestage preamp.

Having said all that, a Moreplay will put out somewhere around 32V or so RMS of signal at maximum.  Most sources aren't going to be able to drive the preamp hard enough to make that happen, but it's possible. 

 

[Bubbatwoa]

Quite right PB, I have no intention of driving my speakers with 36 watts RMS, but I do need plenty of headroom to handle large-scale orchestral crescendos that last several seconds.  About  a third of my listening is to classical symphonies.

As a point of reference, my current amp driving these speakers is an EL34-based SET capable of putting out 6-7 watts with KT88 tubes.  It requires a 1.25V input to achieve its full output.  I have my digital source (with volume control) connected directly to it, and the amp starts getting severely strained and compressed before it produces enough volume for the loudest passages.  So I figure I need at least 6 dB more headroom that what I have, which starting from 6W means going to 24W occasionally.  So I'm going to need most of what these Quicksilver amps I'm considering can offer, even if only occasionally for a few seconds.

I know the gain of the Moreplay is said to be 9 dB and the BeePre 2 is 6 dB.  But I don't know how those dB figures translate to volts.  Thus my question.

 

[Paul Birkeland]

As always there's a lot to unpack!

I would wonder more about the specifics of the amps.  I have had plenty of single ended EL34 amps on my bench that made 4W but claimed a lot more (typically they are from a certain part of the world if you catch my drift).

There's also the possibility that the sensitivity of the speakers in question is a little lower than specified, which has also been a rather common experience as well. 

 

[Paul Joppa]

6dB is a gain of 2.0; 9dB is a gain of 2.8. Moreplay at max gain, with 2.1v input, outputs 5.9 volts - about 1dB below your 6.64v desired output.

 

[Paul Birkeland]

So he needs some input step-up transformers!

 

[Bubbatwoa]

I have had plenty of single ended EL34 amps on my bench that made 4W but claimed a lot more (typically they are from a certain part of the world if you catch my drift).

There's also the possibility that the sensitivity of the speakers in question is a little lower than specified, which has also been a rather common experience as well.

Indeed, we're at the mercy of manufacturer-supplied specs.  The speakers, which are brand new Klipsch La Scalas, may very well be closer to 100 dB.  But they're definitely way up there, as are all of the Klipsch Heritage lineup.

The amp is designed and manufactured in southern CA by Justin Weber's company ampsandsound.  His published spec is 8W output with KT88 output tubes and a 5AR4 rectifier (I'm using a 5U4G), but in a conversation I had with him he conceded it may be "a little optimistic" .  So I'm guessing that in its current configuration it's putting out 6-7.  I have no way of testing that though.

I definitely want to build the Moreplay no matter what, and I'm not committed to any particular amp choices yet.  I just thought the Horn Monos would be an ideal match with my speakers and was hoping one of the BH preamps would be a good fit as well.  Only one way to find out for sure!

 

[Bubbatwoa]

6dB is a gain of 2.0; 9dB is a gain of 2.8. Moreplay at max gain, with 2.1v input, outputs 5.9 volts - about 1dB below your 6.64v desired output.

Thanks Paul!  5.9V is probably close enough.

 

[Paul Birkeland]

Depending on where you are, you may be able to find someone close by to have a listen to some of these options, and that may be helpful.