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PostPosted: 18 Mar 2009, 20:45 
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Hi Jeff, welcome to the forum.

The S-5 Electronics K-12G Tube Amplifiers Kits will provide about double the power of the 6T9 amplifier. It would be ok with those speakers and low listening levels. Like the 6T9, it would be a good idea to have a spare set of tubes on hand as the supply will run out on these too.

Cheers,
Gio

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PostPosted: 19 Mar 2009, 00:53 
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Thanks for the recommendation. I'll check out the K-12.

Jeff


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PostPosted: 19 Mar 2009, 03:08 
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Jeff wrote:
I am new to the DIY scene (and tubes for that matter) but have been interested in hifi for many years. I am looking at building something like the 6T9 project, but I think I am going to need more power. I currently have a pair of B&W 685s which have a sensitivity of 88dB. I usually play them at low to medium volume levels, so I don't need a ton of power.

I think the others will agree that 88db efficient is too low for a low wattage amp. Even if you play quiet you will not be satisfied. A chip amp http://www.diyaudioprojects.com/Chip/Synergy-LM3875-Gainclone/ like my Synergy or Bruce's OddWatts http://www.diyaudioprojects.com/Tubes/KT88-Push-Pull-Tube-Amp/ would be much better.

Better still build a pair of Fostex speakers http://diyaudioprojects.blogspot.com/2008/10/fostex-fe167e-bass-reflex-speakers.html then build a 6T9 amp.

See simple.

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PostPosted: 19 Mar 2009, 03:19 
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I like the Oddwatts, but they are a bit too expensive at the moment. Also, I would prefer to use a kit with a pcb since I've never done any p2p soldering before. I'm in no big hurry, so I guess I'll have to ponder it a while...


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PostPosted: 19 Mar 2009, 08:48 
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Of course you could always go with a K-12 and a pair of fostex speakers. I just noticed this thread over in the Speaker Forum, you may want to check it out.

Alan

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PostPosted: 19 Mar 2009, 09:53 
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Thanks for the suggestions on the Fostex speakers. However, even with a crappy amp, the 685s sound AMAZING!. I can't wait to get a decent amp to drive them.


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PostPosted: 19 Mar 2009, 12:26 
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I found this info on the B&W 685 Speakers:
Quote:
B&W Model 685 Speakers
Minimum impedance: 5.7Ω at 195Hz
Nominal impedance: 8Ω
Port tuning: 47Hz (port open)
Effective bass extension (-10dB): 36Hz (port open)
Sensitivity: 87dB/2.83V/m

I could not find an impedance plot, but based on the above the impedance seems fairly well behaved so they should be ok with a tube amp for low listening levels.

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PostPosted: 19 Mar 2009, 17:42 
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Jeff wrote:
Thanks for the suggestions on the Fostex speakers. However, even with a crappy amp, the 685s sound AMAZING!. I can't wait to get a decent amp to drive them.

It not a case of crappiness it is a case of low power. I have a K-12M (very modified) and a 6T9. Niether are crappy but both are low power. Some of the best music you will ever hear will come from low power amps matched to efficient speakers.

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PostPosted: 19 Mar 2009, 18:00 
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Right, I was actually referring to the Logitech amp built into my sub. I'm really looking forward to replacing it.


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PostPosted: 06 Apr 2009, 10:31 
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billnchristy wrote:
People do claim that discrete single diodes do a better job than bridge rectifiers...I have not experimented.

I would think that power supply capacitance would affect sound quality due to transient response ability.

Don't forget that noise floor also affects sound...if you have a hum at a certain decibel level then your amp is working to supply that hum which will not only take away from sound quality but also dynamic range. For example an amp with an 80dB S/N ratio has a 25dB disadvantage to an amp with 105dB S/N.

The rectifier topology you choose will have a direct effect on hum characteristics and the PS filtering required. For a half-wave rectifier the fundamental frequency of the ripple is the line frequency (60Hz in the US), for a full-wave bridge (2 or 4 diode) the fundamental frequency of the ripple is twice the line frequency (120Hz in the US). Using the same filter, the half-wave 60 Hz ripple will be considerably greater then the full-wave 120 Hz ripple. The net result is that the half wave rectifier needs more filtering to get the same ripple level.

One reason that a lot of people say the single diode does better is because of the low end characteristics of the amp their building. If any stage of the amp has a roll off point above 60Hz, the half wave hum is attenuated vs. the full-wave hum. This usually happens when using an output transformer with about a 100Hz roll off. (The 100Hz output transformer roll off is more common then you'd think.) The half-wave rectified PS sounds better, not because it has lower hum, but because its hum is below the cutoff frequency of the amp.

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