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Old 11th June 2003, 04:06 AM   #1
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Default Recommend a kit for me!

I just got a pair of Polk Audio Lsi9's and am considering building a tube amp (kit) for them. the speakers are rated at 88db efficiency, and they are a 4ohm nominal speaker. I've heard mixed reviews about using tubes with a low efficiency speaker so I'd like to get some expert opinions/suggestions on whether or not a tube amp is worthwhile or should I just stick with a solid state amp.
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Old 11th June 2003, 10:29 AM   #2
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Hi Frank,

I suppose this is not for your home-cinema setup in you main living room. But rather a second setup for the bedroom/study or whatever.

Personally If I were in the market for an amp kit. I would go for the Welborne Labs DRD 300B/2A3/45 kits...

http://www.welbornelabs.com/drd.htm

With the 300b kit version being the most suited to your speakers (300b=+-8 Watt, 2a3=+-3 Watt, 45= +-1,5Watt). The 88dB sensitivity of your speakers are not neccessarily a problem. So would try to listen with a SE 300b amp first before commiting to a 300b or similar kit.

Good luck!

Cheers,
Bas
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Old 11th June 2003, 11:28 AM   #3
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Frank Z

Not knowing what type of music you listen to or the level you desire it is difficult to predict what you would be happy with in terms of power. Not wanting to start WWIII here but I will give my opinion. With a speaker of only 88db @1W 1M I would surely want a lot more power that a 8 watt or less kit could provide. With 8 watts and the efficiency of your speakers I personally don't think you would be happy. I would recommend purchasing a Dynaco stereo 70 or something along that line that would have ample power to provide adequate listening levels. Keep in mind that these amps can be modified to provide great listening pleasure. I started out with some Quicksilver KT88 amps rated at 60 watts per mono block. These are used with some custom speakers with an efficiency of greater that 100db per watt per meter and they deliver very good sound and have a lot of headroom. I had been using solid state SAE amps such as an X25A that was rated in excess of 200 watts per channel.

The Polk is a very good speaker and I surely am not trying to put it or you down. I would certainly audition your speakers in your listening environment before purchasing any amplifier or kit. I am certain that there are a number of dealers out there that wouldn't have a problem with letting you take home a piece of equipment to try out. Just my .02

Joe
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Old 11th June 2003, 11:42 AM   #4
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Thank you for the help guys,
The amp would be for a seperate 2 channel rig. as for auditioning a kit amp, that would be great, but I'm not aware of any dealers in my area, though I will look into it.

Thanks again for the info!
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Old 11th June 2003, 12:30 PM   #5
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Quote:
but I'm not aware of any dealers in my area, though I will look into it.
Basically you'd want to hear ANY SE 300B amp with your speakers since virtually all of them put out around 8Watts or so.

I have 90dB speakers mission 761 and even 1,5Watt makes them go loud enough to p*ss of the neighbours..that's why I said you don't perse need a PP amp or more powerfull amp.

I believe quite a few people are happy with the PP EL34 - Ella Kit. May also be fitted with KT88..(Would recommend Svetlana KT88)
http://www.diyhifisupply.com/diy_kits/the_ella.html then you'd have 40W. PS I think they have an American importer as well....not sure though...

Cheers,
Bas
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Old 6th October 2003, 01:09 PM   #6
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Talking re my planning kits.

Hi,

this is my palnning kits.

pls give me any advise.

2a3SE

thanks

thomas

www.diyaudiocraft.com


http://www.diyaudiocraft.com/bb/viewtopic.php?t=125
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Old 6th October 2003, 01:18 PM   #7
SY is offline SY  United States
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I'm with Joe: single-ended, low-power, high source Z, high distortion amps are completely unsuitable for your speakers. If you want tubes, think push-pull. An ST-70 is a fine base for a project, and there's lots of kits out there for rebuilds that will give you an amp that will be happy driving your speakers. My personal favorite is the ST-70 input boards and power supply/regulator from Joe Curcio.
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Old 7th October 2003, 11:51 AM   #8
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Have a look at Kat 6550 or Kat34 from World Audio
World Audio Design Amplifier Kits
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Old 7th October 2003, 01:03 PM   #9
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Quote:
Originally posted by SY
My personal favorite is the ST-70 input boards and power supply/regulator from Joe Curcio.
Sy, I did this mod to a cousin's ST70 a number of years ago. I had one major problem, that is that the bias resistor kept burning out until I put in a 5W sandcast. According to Curcio there should have only been a couple of milliwatts dissipation there, but nothing else seemed to work. The amp ran smoothly for a few years, but then my cousin complained that he couldn't get the bias up on the unit. I tested with new output tubes, no change. So I started to poke around inside. Vref measured fine, but the high voltage regulators weren't working. I replaced all of the transistors/opamps, even though they tested fine. Still no change. The amp has been sitting on my shelf for almost a year, unusable. Curcio didn't have any suggestions beyond shipping him the amp (expensive, I'm in Canada). Would you have any suggestions?

Sorry to hijack this thread.

FrankZ, I have the makings of an Assemblage ST40 kit. This is the same amp as an Anthem Amp1, a push pull EL34 amp. I've got the power and output transformers for the Anthem, plus the PCB for either the Anthem or the Assemblage, your choice. Also the large reservoir caps and the manual with schematic and parts list. Everything is brand new, you'd have to build a chassis. I bought this from a friend who was the designer of the amp. Search the net and you'll find more info/reviews. If you're interested, email me at ron.steinberg at sympatico.ca replacing "at" with "@".

Cheers,
RonS
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Old 7th October 2003, 08:50 PM   #10
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Low Z, low eff speakers need some power, and a (rebuilt and modified) ST70 would be the minimum I'd suggest, with an HK Cit II being better. Low power SETs will sound like crap.
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