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Need help pairing Martin Logan Sequel II speakers with 4 Watt tube monoblocks

areniers

Member
2011-11-24 7:26 am
Hi,

I'm new here. So here comes my first question. I have a pair of Martin Logan Sequel II electrostatic loudspeakers. In a few weeks I'll also have two tube monoblocks with 4 Watts output power. The tubes used are 1x300B, 1x6SL7 and 1x5U4 (rectifier).

Would it be possible to pair these directly (without preamp) with the Martin Logans, which have a sensitivity of 89dB?

Would adding a preamp (solid state or tube) actually alter the situation in any way, given the monoblocks still only posses 4 watts to hand out? If a preamp is desirable what should I look out for?

So in all, what would be the best solution to pair up these monoblocks with the Martin Logans?

Looking forward to reading your replies!

Alvin from Belgium
 
There are two issues here:

1 - is 4W/ch enough to drive the ML's to realistic levels?
2 - how much signal level do the tube amps require to deliver full power?

As to 1, I doubt it. I own Sequell II's myself and in my experience, 4W/ch is not enough, but it depends also on your room and how loud you like it. So if you already have/get the amps, it can't harm to just give it a try.

As to 2, most sources like CD players give off between 1 and 2 V signal level. You should check the amp specs to see if that is enough to deliver full power.
If they do, then all you'd need is a volume control somewhere in the chain.
If the amps require more signal, or if your source delivers less, you may need a preamp with a little bit of gain, but I doubt it - 1-2V is normally enough to fully drive power amps, although there are exceptions.

Hope this helps,

jan
 

areniers

Member
2011-11-24 7:26 am
Thanks for the reply, Jan.

Actually the monoblocks have volume knobs (which makes me wonder if they're not in fact integrated amps; or am I jumping to conclusions here?). Does a power amp with a volume knob actually exist or is it an oxymoron?

I also have a pair of Acoustic Research Status S40 speakers, which have a sensitivity of 91dB. Maybe they would be a better match for the monoblocks; or should I start looking for some really sensitive speakers?

Thanks,
Alvin

P.S. The monoblocks are a "unique" pair, in that they were self assembled by the seller. I couldn't resist the offer (I will be getting them in a few weeks), but it still remains an issue if I can use them in my current set-up. I would like to find good use for them of course to try them out.
 
Nice speakers, but the listening level will be pretty low.

The ML are rated at 89 dB-meter. That means 1 Watt will drive the volume to 89 dB 1 meter from the transducer.

Every time you double the power to the speaker you get +3dB of volume change. So...

2 Watts means that each speaker produces 92 dB.

4 Watts, your maximum power, gets you 95 dB.

Since you have two speakers, if they were both playing the same signal (mono) you can add another 3 dB for a total of 98 dB. Actually, it will probably be less for a variety of reasons.

Most people are not 1 meter from their speakers. Most likely you are about 3 meters from the speakers.

Sound pressure falls off at the square of the distance, so a 95 dB signal from one speaker at 1 meter drops to 85.5 dB at full power from the amp when you are listening 3 meters away.

The human ear can detect a change in volume as small as about 1 dB.

Let's put this in context to something you may be more familiar with. A vacuum cleaner typically is about 80 dB. So, your stereo will be louder than your vacuum cleaner, but not by a whole lot.

An orchestra is about 100 dB. Speech is about 60 dB.

My point is that you will not get much volume out of this combination and worse is that the more power the amp puts out the higher the distortion level will be, too.

So, you will be able to listen to music, but the volume will not be very high even when you do crank it up and you may have some distortion issues as well.

You have two choices, get a larger amp or more efficient speakers or both. I have about 40 to 50 WPC and 95 dB-Meter speakers, so I have no issues with running the amp even close to its limits.

Since you already have these coming to you I would hook them up and enjoy them until you start craving more power. Then I would borrow someone's amp and see how you really like the ML speakers when driven with enough power. You can buy better and more efficient speakers, but they are going to cost you much more than a really good amp by a fair amount.
 
You will able to enjoy them at moderate listening levels, If you want to crank it up have an aux amp for those occasions. I built a little 25watt PP amp and found that is more than adequate for most of my listening levels, when I want to crank it up I have a 60watt/channel amp. Speakers are 89db efficient....
 
Thanks for the reply, Jan.

Actually the monoblocks have volume knobs (which makes me wonder if they're not in fact integrated amps; or am I jumping to conclusions here?). Does a power amp with a volume knob actually exist or is it an oxymoron?

I also have a pair of Acoustic Research Status S40 speakers, which have a sensitivity of 91dB. Maybe they would be a better match for the monoblocks; or should I start looking for some really sensitive speakers?

Thanks,
Alvin

P.S. The monoblocks are a "unique" pair, in that they were self assembled by the seller. I couldn't resist the offer (I will be getting them in a few weeks), but it still remains an issue if I can use them in my current set-up. I would like to find good use for them of course to try them out.

Don't worry about the marketing terms - an amp with a volume control is a very good idea, whatever someone calls them ;)
BTW a is difference of 2dB between the speakers is just about audible; not much.
The proof is in the eating! Take your decision after having listened to them!

BTW The 4W's would be a killer headphone amp is all else fails!

jan
 

areniers

Member
2011-11-24 7:26 am
Well, the amps finally arrived. I took some pictures (see attachments). In the end I decided not to try them with the Martin Logans and neither with the Acoustic Research speakers.

I found a pair of used Klipsch speakers RF-52 for 200,- euros, which have a sensitivity of 96 dB. And man these 4W tube amps just make them sing. Perfect soundstage and crisp highs. The amps don't even need the full signal fed into them, it would just become to loud.

So, yeah I'm happy with them!

You'll notice in the picture that the tube in the back is different in both amps. It's the rectifier tube (5U4). The one in the right amp should be the same as the one in the left amp, but the seller used it for a repair job so he lent me an RCA black plate, while he's searching for the right replacement.

Anyhow, thanks for all the comments!

Cheers,
Alvin
 

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