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Old 28th June 2003, 03:58 AM   #1
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Default More Output

I was wondering what was involved in modding my 18 watt tube amp to have a greater watt output?

I really want a 100 watt amp, but I would be happy with 60 or so...

Is this a hard project or could someone with moderate experiance do it?

How much do you think it would cost for me to have it done by a pro?
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Old 28th June 2003, 04:18 AM   #2
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Modding an 18W amp to 100W... LOL

Sorry, but you need new iron, new tubes, probably a new driver circuit, basically, new everything. Might as well keep the 18W-er and build a new amp...

Tim
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Old 28th June 2003, 06:17 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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What you could try is bi-amping.

Get a big honking solid state amp to do all frequencies below 100Hz and use the tube amp for above 100Hz.

You could use an active crossover which simply splits the frequencies.

You need heaps of power for bass, but not much at all for high frequencies.
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Old 28th June 2003, 01:37 PM   #4
316a is offline 316a  England
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Default Spot on !

Shifty is correct here , if you use an active crossover there will also be more power transferred to the speakers (as speakers internal crossover can be eliminated) plus intermodulation distortion will be reduced . I used to use a 4w a side PP triode amp with 100w a side mosfet amp for >120Hz . Whatever , remember a doubling of power only provides an extra 3dB so you won't realisticly have that much more clout available with a bigger amp

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Old 28th June 2003, 08:52 PM   #5
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Default Re: Spot on !

Quote:
Originally posted by 316a
remember a doubling of power only provides an extra 3dB so you won't realisticly have that much more clout available with a bigger amp
Biamping can provide an effective 4 x power benefit... if the dividing frequency is approx at the point where the energy above & below the XO point is equal (and the speakers above & below are of equal efficiency), 2 10 W amps provide essentially the same effective power as a single 40 W amp.

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Old 28th June 2003, 09:29 PM   #6
Ilianh is offline Ilianh  Canada
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Quote:
Biamping can provide an effective 4 x power benefit...
Quote:
2 10 W amps provide essentially the same effective power as a single 40 W amp.
Did you want to mean 80 watts?

Did I miss something?
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Old 28th June 2003, 09:33 PM   #7
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Quote:
Originally posted by Ilianh
Did you want to mean 80 watts?
I guess that could get confusing... i meant 4 x the power of a single 10 W amp... but you need 2 of them to bi-amp, so i guess you are getting only 3 dB extra.

But the other benefits (ie driving a less reactive load once the passive XO is removed) and the trend for smaller amps to sound better are what really makes the difference.

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Old 28th June 2003, 11:57 PM   #8
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Hi,

Quote:
But the other benefits (ie driving a less reactive load once the passive XO is removed) and the trend for smaller amps to sound better are what really makes the difference.
When chosing to go for biamping it's not xtra power your after but the other benefits as Dave correctly points out.

IME it's another step into the FR direction...but not quite.
Nonetheless highly recommended but not without caveats.

Cheers,
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Old 29th June 2003, 07:45 AM   #9
EC8010 is offline EC8010  United Kingdom
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Default I don't understand this power gain from bi-amping

If I have an ideal crossover (infinite slope), then if the drivers are of equal sensitivity, I must need equal power amplifiers to achieve the same (undistorted) level slightly above and slightly below the crossover frequency.

Yes, it's true that tweeters don't absorb much power - most are rated at <8W continuous. But they need lots of voltage - it's just that the voltage peaks are of short duration, so the power averaged over the thermal time-constant of the tweeter is low.

Where you can get a gain is by noting that many tweeters are 3dB more sensitive than their associated bass/mid, which means you can use an amplifier of half the power for the tweeter.

I agree with all the other statements people have made about active crossover benefits.
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Old 29th June 2003, 07:50 AM   #10
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Default Re: I don't understand this power gain from bi-amping

Quote:
Originally posted by EC8010
If I have an ideal crossover (infinite slope), then if the drivers are of equal sensitivity, I must need equal power amplifiers to achieve the same (undistorted) level slightly above and slightly below the crossover frequency.
Yeah, it would be rather interesting to hook up a signal generator to each, a transformer in place of the speakers, with the amps powered by said transformers..........

I recall Pat Turner saying on rec.audio.tubes that, though it takes less average power (from the narrower bandwidth), it still takes as much *peak* power, because the music peaks are the same, whatever the bandwidth. (Or something like that. Had something to do with white noise too. )

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