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Old 17th March 2006, 11:49 AM   #1
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Default Are my speakers efficient enough for tubes?

Hi, I am a senior in highschool, so I don't run across alot of money, however my pride and joy are my JBL e60s which ran me a good 400 bucks, my HK3480 reciver ran me another 350, however now I want to explore the world of DIY tube amps, preferably Single-Ended. My E60s are rated with an efficientcy rating of 90db at 1watt/1meter, so my question to all of you intelegent, gifted, rolemodels, do you think i can get enough kick out of a 1 or 2 watt tube amp?
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Old 17th March 2006, 01:18 PM   #2
Sherman is offline Sherman  United States
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I guess the answer is "it depends". However I think you will be OK with those speakers if you don't expect ear-splitting volume or listen in a huge room. I listen to a pair of SE monoblocks with 89dB speakers and think they sound great. However my amps do make a good 6-7 watts.

I also listened to an SE EL84 amp (2W) with those same speakers. The sound was very good at "normal" listening levels but that amp just couldn't do "loud" with those speakers.

Do a search for Mikael's SE KT88 amp schematic in this forum. An easy to build SE UL amp, good sound, KT88s look cool and it can easily make 6 watts.

The problem with SE amps is you need hefty output iron which can be both expensive and heavy. For Mikael's schematic a Hammond 1628SE would work and be relatively inexpensive. For about the same price (from Euphonia Audio) I can personally recommend the James 6123HS. For a bunch less cash ($18) people have been reporting good results with the Edcor SE trafo.

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Old 17th March 2006, 02:32 PM   #3
SHiFTY is offline SHiFTY  New Zealand
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Quote:
all of you intelegent, gifted, rolemodels, do you think i can get enough kick out of a 1 or 2 watt tube amp?
In my intelligent and gifted opinion 1-2 Watts will be ok for normal listening, but will run out of puff fairly quickly.

I would recommend 4-5 watts to ensure you have enough headroom.

Also don't discount push-pull amps, some of the best sounding amps you can buy are EL84 PP (IMHO)
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Old 17th March 2006, 02:39 PM   #4
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I have Yamaha NS-10 studio monitors. They are rated for 87db. I have several tube amplifiers, both SE and P-P, from 2 to 40 watts. In a small listening room (10 X 11 feet) the 2 watt SE 45 amp sounds great, but won't do loud very well, and can't play some music (Jimi comes to mind) at any volume. On the other hand the 30 and 40 watt amps will chase you out of the room.

I have recently been experimenting with a SE ultralinear (UL) amp using a $3 TV tube (6AV5) and the previously mentioned $18 Edcor transformers (XSE-15-8-5K).

I applied cathode feedback to the design, and it ROCKS. Even with my 87db speakers I can play Jimi loud! The amp makes about 7 to 9 watts depending on how hard you push the tube. The cathode feedback really tightens up the bass, and allows you to run the amp volume up into the distortion zone without destroying the sound (within reason). This makes for a loud (but good) sounding amp, which can be built for minimum dollars.

I won't have the schematic on my web site until the middle of April due to an impending road trip. In the mean time look at the link below. It has the schematic for a similar design and the theory as to why this design works well.


http://www.lundahl.se/pdfs/claus_byr...ifier_8wse.pdf
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Old 17th March 2006, 11:25 PM   #5
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Personally, I very much doubt if anything less than 10w would be adequate but it depends on your need to allow sufficient headroom to avoid distortion of transients. The type of music you like will dictate this: e.g. symphony orchestras and choirs need plenty of headroom, while pop, rock and most types of jazz are relatively free from large transients.
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Old 18th March 2006, 12:19 AM   #6
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AM,

A useful rule of thumb is that the amp/speaker combo should be capable of 102 dB. peaks. So, 1 W. = 90 dB., 2 W. = 93 dB., ..., and 16 W. = 103 dB. A 15 WPC amp seems indicated. Also, how is the SPL rating of your speakers specified? If they are 4 Ohm nominal and the rating is specified for a 2.83 V. drive, the true efficiency is 87 dB.

You could get the power you need from push/pull EL84s. SE amps above 8 WPC cost big bucks.

An option you might consider is the construction of a tubed line stage. Your H/K receiver has the crucial preamp out/amp in feature that allows you to bypass completely the internal volume and tone control circuitry. By using the recording O/P to drive the tubed line stage, you retain use of the receiver's tuner, phono section, and selector switch.
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Old 18th March 2006, 02:38 AM   #7
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Considering the fact that you are a senior in high school I seriously doubt that you would be satisfied with that little power.
No offense meant. Do to your age I would expect a much higher DB level in the room.
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Old 18th March 2006, 02:49 AM   #8
anatech is offline anatech  Canada
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I think Joe has used sound reasoning there .... or his memory.

I agree 100%.
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Old 18th March 2006, 03:06 AM   #9
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Chris,

I think it might be memory.

Joe
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Old 18th March 2006, 03:10 AM   #10
arnoldc is offline arnoldc  Philippines
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JBL! These rocks!

Seriously, I was in your predicament years ago. I bought an Infinity Kappa 200 (89dB) with SS amplification, but fell in love with my first SET amp - 2A3. My 2A3 can suprisingly drive my Kappa at loud levels for my cube (yeah, I have a square room- 4m x 4m). My low end HT uses a JBL LX2002 and to my delight, it can also be driven by the 2A3. Although I had an Anthem Amp 1 (40W) at that time, I still prefer the tone and speed of the 2A3.

However, when I tried other speakers, i.e., Monitor Audio that's supposed to be higher efficiency by a bit, it was a harder drive. I also tried a modern Klipsch RB-3 and I didn't like it.

My point is I can't rely on the published sensitivity. If you can borrow amplifiers from friends to try it out with your JBL, that would be best.

Having said that, I would say that something like a Dynaco ST-70 power level might just let it rock!
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