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K-12G Tube Amp Kit Build Thoughts
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Author:  milsman2 [ 22 Aug 2011, 02:51 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Does anyone have any suggestions as to what drivers to pair with this kit? I want to buy the K-12G but am unsure what to do with it but I am thinking of buying a set of full range speakers and building the box. Specific suggestions would be great and I am open to buying pre-built speakers.

Author:  Gio [ 22 Aug 2011, 15:25 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Hi milsman2, how big a room will they be used in and how loud would you like them to be at the listening position? Also, is there a budget and what type of music do listen to?
Cheers

Author:  milsman2 [ 22 Aug 2011, 16:18 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Probably a relatively small room (i.e. apartment bedroom of 15x15ish) for a "smoky filled drinks and friends" kind of atmosphere. I'm thinking no louder than for everyone to hear at about a normal talking level.

Author:  connemaraguitars [ 22 Aug 2011, 19:39 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

I was surprised to realize I've been using my K-12G for more than 20 months...photos of my build are on page 3 of this thread. These days I think it's ugly but, hey, it sounds great!

In the beginning I was using a pair of Infinity Primus P162 bookshelf speakers, which were great. I then added a subwoofer I built following Gio's excellent project:

http://diyaudioprojects.com/Speakers/MAW-10/MAW-10.htm

I had started out with Uriah's optocoupler-based attenuator but a few months ago switched to Bruce's Forewatt (DIY version in a semi-fancy wood chassis, photos to be submitted). No compelling reason for the change other than, well, change. I like building tube amps and if my efforts are successful, then change happens. Otherwise, the fire department is called.

A month or so back (while my wife was out of the country and I was without adult supervision) I bid on, and, much to my dismay, won a pair of B&W speakers (on eBay), the LM1 series (no longer in production). I have B&Ws for my home theater system's rear and center speakers (VM1 series) and love 'em. When the LM1s arrived, I swapped them with the Infinity pair, and find the B&Ws slightly better. I paid about $170 for the latter and probably close to the same for the former.

The combination speakers/subwoofer fill my office to overflowing, even with the volume at 10-15% (or thereabouts).

The K-12G is a good little amp that puts out lots of power, at lease in my estimation. If you are handy and can build speakers, go for a two-way, efficient unit (>88dB; seek the speaker projects page) AND a subwoofer. Otherwise, keep your eyes peeled for a good pair of bookshelf speakers, which shouldn't set you back more than $200 for a pair. There's another thread on this topic, BTW...I'll let you find it. That's only my opinion. If you have great personal wealth, then I think you should spend at least $2,000.00 on speakers for your $200.00 amp! Please buy American. Or Canadian. Hi, Gio!

I think I have, between the original K-12G kit, tube preamp, speakers, and my subwoofer, not much more that $650 invested in the system. Every person who has heard has been blown away...er, really impressed.

Author:  milsman2 [ 22 Aug 2011, 21:48 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

For now I am not going to worry about an attenuator as I will be primarily playing from an iPod or other line level source, but I'll certainly put that project in my back pocket.

I looked up the Infinity's online and you can buy them for about $170 a pair so you were right on. I was wondering though about being able to power those. The kit puts out about 8 W per channel, but aren't those speakers rated for much more than that? I am pretty new at this so this may be a simple misunderstanding, but I have seen a data sheet rating them at something on the order of 150 W RMS. :/ Help?

Author:  connemaraguitars [ 22 Aug 2011, 22:25 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

The Infinitys should be more than OK. The whole watts per channel thing is extremely deceptive...I encourage you to read up on this!

Author:  milsman2 [ 22 Aug 2011, 22:32 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Can you give me some links for further reading in that case? I just fail to understand how an amp rated at 8 W/channel (and somewhat high distortion at that based on the audioXpress review) can power a system rated for 150 W RMS. I really would like to understand this to further my learning on speaker building.

Author:  Vinny Huynh [ 23 Aug 2011, 12:16 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Hi,

This is my first K-12G tube amp kit build. Please take a look.
best regards,

-vh

Author:  milsman2 [ 23 Aug 2011, 13:12 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

Looks great! After doing some reading I have finally figured out how you can in fact hook up the amp to speakers rated for much higher power. Vinny, as well as everyone else, do you have any suggestions other than the Infinity P162's for higher sensitivity 2 way bookshelf speakers that can be had for under $400?

Author:  Suncalc [ 23 Aug 2011, 13:56 ]
Post subject:  Re: K-12G Tube Amp Kit Build Thoughts

milsman2 wrote:
I just fail to understand how an amp rated at 8 W/channel (and somewhat high distortion at that based on the audioXpress review) can power a system rated for 150 W RMS. I really would like to understand this to further my learning on speaker building.

The thing that you need to keep in mind is that sound pressure levels are measured on a logarithmic scale. This means that a 10W amp only peaks at 10dB higher than a 1W amp. A 150W amp only peaks at 17dB higher than a 10W amp or 27dB higher than a 1W amp.

So lets do a quick little thought experiment. Suppose that you have a 10W amp and a set of speakers with a 92dB efficiency rating. At 1W nominal output (about 1/2 volume) your speakers will produce a SPL of about 92dB at 1 meter (per channel). Both channels together will produce about 95dB. This is pretty good and music peaks that are up to 10dB higher will cleanly produce another 10dB or 105dB total SPL. But now lets up that amplifier to 100W. With the amplifier at half volume (about 10W) it will also produce 105dB. But musical peaks that are 10dB higher now produce 115dB SPL. This is close to the pain threshold. But at 1/4 volume (about 1 W) it will produce the same SPLs as your 10W amp at half volume but will be able to handle musical peaks that are 20dB instead of 10 dB without clipping. So what you've really bought with all that power is more headroom for volume excursions.

Here's a simple table assuming a stereo amplifier and a speaker efficiency of 90dB.
Code:
Amp Power per channel      SPL (dB)
      1 W                          93dB
      5 W                         100dB
     10 W                        103dB
     50 W                        110dB
    100W                        113dB
    200W                        116dB
    400W                        119dB

So clearly there is a point of diminished returns where big power amp really doesn't buy you that much more volume.

Does this make sense?

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