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Old 28th January 2011, 08:43 PM   #1
cricha5 is offline cricha5  United States
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Default How much power do I need in the kitchen?

I have finished my research on the theory of SE tube amps and am now looking at parts to build one very similar to boozehound's simple amp. The first thing I need to know is how much power I need. Since this is my first amp, I don't know how power vs. loudness will work out.

The purpose of this first amp will be very simple. I need an amp to listen to audiobooks in the kitchen through my ipod. It needs to be able to be louder than the dishwasher. It is going to be used while the dishwasher is on, the water running, microwave, etc, so it needs to be able to cut through that, but nothing more. It also does not need to be high fidelity at all. There is no need to have any bass under 100Hz. I'll be running it mono to one speaker. I figure this is a good practical application for a first amp that will give me the skills to make bigger, better and more awesome amps in the future.

Can anyone tell me how many watts I should run and how big a speaker?

And since I will be ONLY using the ipod or iphone connection, can I do away with the input capacitor? Also, I heard that the ipod's line out is 1V p-p. Can anyone verify this? Thanks.
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Old 28th January 2011, 09:24 PM   #2
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Given you are going to use it for spoken word listening and assuming even a medium efficiency speaker, one watt is plenty regardless of how loud your dishwasher is...

In reality, you'll end up building something around 2-3w output anyway if you use any of the popular and easy to get tubes.

Unsure of any DC offset on the ipod, but a cap in the front is going to help in rolling off your bass frequencies anyway, so I'd put one in there.
"It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
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Old 28th January 2011, 10:47 PM   #3
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You ought to look around at resale shops and flea markets for an old Bogen or Stromberg Carlson PA amp. Nice chassis, fitting tube protector grid on the top, decent power transformer. Sound like ****. 10 watts for $10 is pretty common. Then you can upgrade the output transformers for better sound, add feedback for lower power better sound, straighten up the input section, test the tubes for idle current to see if they are at proper settings, change from single ended out to push pull, etc etc. No metal punch work until you have install a new tube socket.
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Old 28th January 2011, 11:38 PM   #4
Doz is offline Doz  United Kingdom
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This is how it started for me ... except mine was destined for the bedroom

although mine was stereo ... 2 6bw6's (I just had to walk into the kitchen to look!!) a GZ34 rectifier (total overkill) and an ECC 83 to drive it ... hammond output transformers (125 series) and an unidentified power transformer.

It's still there now. Bass is surprisingly good for such small output iron, and it remains one of my fav amps ... just sits there , being inoffensive.

oh yeah ... has a resonant choke ...

Built it years ago .. still on it's original tubes (although the ECC was regularly "rolled") despite many hours spent idling once I'd fallen asleep to a Moody Blues CD
"To err is human.. to make a real balls-up requires a computer"
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Old 29th January 2011, 06:29 AM   #5
cricha5 is offline cricha5  United States
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Thanks all. I agree that the input cap would roll off the low frequencies which would make things easier for the amp and speaker, but I figured I could get this same effect with the coupling capacitor between stages. Since the driver tube doesn't really push power, I figured it didn't matter if it got the low frequencies. I figure it only really matters for the power tube. Thoughts?
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Old 29th January 2011, 08:40 AM   #6
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Why on earth spend the time, money and effort to building a tube amp for an application where there is absolutely no need for, or added value of such a device? And why, if you decide to do this anyway, which for the learning experience I can sort of understand, begin with a compromised design from the very beginning?

If you want to build a simple valve amplifier in order to learn about the technology, why not undertake a project that is both simple, relatively safe AND will result in at least half-decent sound quality, such as one of the headphone amps on Headwize, or even the one-tube-per-channel Wavebourn headphone amp?

Nah, this one's beyond me. But if you insist, then build anything you like. Start with something existing and upgrade that as indianajo suggests, or pick any schematic of a low-power tube amp and build it. Doesn't matter if it delivers poor performance, since you won't need hifi in any case. Even a low-gain guitar amp circuit would be fine. And practically any circuit out there on the web will provide more than enough power for your needs. Even e.g. a single ended EL84/6BQ5 will blow you away.

I agree that the input cap would roll off the low frequencies which would make things easier for the amp and speaker, but I figured I could get this same effect with the coupling capacitor between stages.
Always be safe and use an input coupling cap. A low-voltage type will do just fine, so it needed be costly. And since sound quality is of no concern in this case anyway, you can even get away with cheap Wima high-voltage ones for like a buck apiece. Costs a buck, but might save the driver tube one day.
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Old 29th January 2011, 08:46 AM   #7
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This is my advice: Go for speakers first. In my sense of audio for speach use a high efficiant full range speaker, ab. 93-96db/w/m. (old fostex, audio nirvana) They are not only very economical in their power consumption but very high end sounding when it about speech only.

Your all in all power consumption will be only slightly above 1w. (though you don't give em deep and sub bass)
I think even a vintage full ranger like greencones are suitable.

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