[dasein]

Hey guys!

I finally broke down and bought a pair of used Usher S-520s from someone on Audiogon. They are on their way here but I was wondering if they would benefit from an amp. I was looking around for some DIY amps out there and I stumbled upon the LM3886 gainclone amp kits at http://www.chipamp.com/lm3886.shtml (more info at: http://diyaudioprojects.com/Chip/LM3886_CA/LM3886_CA.htm). I have some experience soldering stuff together for various headphone projects so I felt like I could build this for fun.

Would these be alright to use with the S-520s? The specs for the S-520 are:
2-way system     tweeter 1" (UA025-10), mid-bass 5" (KSW2-5029B)
Sensitivity    86 dB @ 1 watt / 1m
Nominal impedance    8 ohms
Frequency response (-3 dB)    52 Hz ~ 20 kHz
Power handling    75 watts
Crossover frequencies    2 kHz

I wasn't sure how the impedance and power handling worked in terms of looking for an amp to pair them with. Sorry for the really silly question.

Thanks!

[Scott F.]

Hiya dasein,

Congrats on the new speakers. So did you get a Ferrari Red pair?

Got a question or two for you before we might be able to help. First, how big is your listening room (LxWxH). Second, how loud do you normally listen. If you don't ahve an SPL meter, try to give us an idea if when playing your music loud, could you have a conversation at normal levels, elevate you voice a  bit, talk really loud or the music drowns out conversation completely. It would also be good to know what genre of music sees the most playing time in your system.

[dasein]

Hey Scott!

Thanks so much for the reply.

I got the more conservative black pair. I'm not too flashy of a person haha.

My room that I'm planning to put them in is about 12x14x11 I think. It's about a medium sized room. I guess I play my music at levels where I would have to raise my voice a bit to talking really loud. I generally listen to a wide range of music from classical to alternative rock to electronic music.

Does that help?

[Scott F.]

Hi dasein,

Well, conversation level is about 75db. If your lower listening level is just a bit louder than that, lets guess that it is between 78 and 80db. When you get into it, I'm guessing you are listening at just above 90 to maybe 95db. Let me further guess you are on one side of the room and your speakers are on the other.

I'm not going to get into the math (which I probably should) but your new speakers are rated at 86db sensitive. JA at Stereophile did actual measurements and found they are more like 84.5db sensitive. That is all perfectly OK, you just need to take that into consideration when you chose your amp.

Basically, to produce a sound pressure level of 96db at 1 meter on 84db sensitive speakers, you will need 16 watts of amplifier power. Consider that you are sitting across the room, say 10 feet away (for ease of calculation). With every meter away from the distance you move from the speakers, you drop 3db in sound pressure levels (this doesn't take into account room gain). So, at your seating position, you are down 9db from the 96db produced at the speaker.

Lets assume you want to listen at that 96db level at your seating position. To do that, for each 3db of gain, you will need to double the power of the amplifier you are using. So, still trying not to do math, we go from 16wpc to 32wpc (-6db), to 64wpc (-3db) to 128wpc (-0db).

(PS, for those paying attention, that was purely from memory so if I mis-stated something, please go easy on me, TYVM)

Now, 96db of SPL is pretty darned loud when you experience it up close and personal. Realistically, you probably won't exceed 85-90db in normal, louder  listening sessions. At that level, you will hit peaks that reach 95ish db so your amp should have enough reserve power to handle the peaks cleanly.

the whole point of that exercise was to let you know that the little gainclone you are looking at may be underpowered a bit, assuming you are looking at the 25x25 version. The 50x50 will get you a fair amount closer and will likely suit your needs fairly well. I'm afraid that the smaller amp will clip pretty hard when you start to crank it.

If you are unsure about the gainclone, try to find something with about 100wpc (assuming solid state). That way you know you have ample headroom to play it loud when you feel the urge.

Then again, you could toss in the towel and buy a 30wpc tube integrated (an el84 please) and forget about all of it and just enjoy the heck out of your music

[Bob in St. Louis]

Good advice Scott. The entire time I was reading that, I kept thinking, "Headroom, headroom, the guys needs headroom". But in the end, you covered that. 
Nice job man. Your post should be a sticky somewhere important. Very good information.

By the way dasein, I've used a 5wpc tube amp. It sounded good, but wasn't enough for "slightly" louder than my definition of normal listening levels. Far from home theater level volume.
Now, I've got a 40wpc tube amp, and you can hear it a mile away. The speakers have a 96dB rating.
The amp is a used Jolida 202a for $300. The room is slightly bigger than yours with the exception of your high ceiling height.

Bob

[ooheadsoo]

I did some casual research in the past and found that many classical recordings regardless of age have peaks that range anywhere from 15-20db.  If you listen to it at live volumes AND CARE, better get some more power.

[KenSeger]

Dasein,

Matching an amp to a speaker to a room to music has a lot of wiggle room due to room reflections and how peaky the music is.

The straight forward math ( in the case of the Usher S-520s ) is 1 watt = 86db, 2 watts = 89db, 4 w = 92db, 8 = 95db, 16 = 98db, 32 = 101db, 64w = 104, 128w=107, et cetra until the smoke leaks out. Or 1 watt = 86db, 10 w = 96db, 100w = 106db, ecutslo.

Now since you have two speakers rather than one, add 3db to everything.

But since you are not one meter from speakers subtract ?db.

But since the room reflects the sound, at a certain distance ignore the above distance subtraction.

Then we get into peak versus average power.  On REALLY good recordings this can, as ooheadsoo points out, throw all calculations into a cocked hat.

Then there is the amps ability to pass very short term transient peaks. 20% more than rated RMS? 40% more than RMS?  100% more than RMS (which is still only 3db).

How stable it that amp into that speaker?  Does clipping sound like something is going to burst through the grill cloth, or just not as dynamic?

I'm with Scott F. in that tubed units, when they clip, usually don't sound like the end of the world or a precursor of a dead driver.  My speakers are about 94db/1W @ 1M with 6550s for output tubes and a very healthy power supply.  So unless I can control my volume knob (gain knob really, I've never seen the speakers change size, they are big enough already) from outside the room, I'll hopefully never find out what these antiques sound like when they clip.

Ken