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Old 4th February 2013, 04:58 PM   #1261
Renron is offline Renron  United States
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Quote:
Originally Posted by Marra View Post
I am rubbish with the math
You are not alone.
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Old 7th February 2013, 12:32 PM   #1262
Marra is offline Marra  United Kingdom
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This morning I powered up the front end and adjusted the voltages across R5/6;fortunately no issues doing so.As I am running with +- 38V dc I am only getting 11.3V at the jfets[cascoded] Is there an optimum voltage for the jfets as 11.3 seems a bit low. I thought that if I parraled a second 10k resistor;having used Audiosan's formula on the bom I would then have about 16V;would this be better? Tia.
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Old 7th February 2013, 01:01 PM   #1263
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10V-12v is considered sweet spot, I thkn. You can increase if you like and it will not hurt anything. I am unsure how it might affect clipping at higher power levels. It would be something you haev to test.
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Old 7th February 2013, 01:44 PM   #1264
Marra is offline Marra  United Kingdom
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Thanks Buzz if 10/12V is considered the sweet spot I'll leave it as is and see how things go.Waiting on my alluminium supplier to get in touch then I can get busy with some drilling.
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Old 7th February 2013, 04:19 PM   #1265
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What ever became of the boards the store was going to sell?
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Old 7th February 2013, 04:27 PM   #1266
Nikitas is offline Nikitas  Greece
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I've been waiting for those for months. I got responses "in 2-3 weeks will be ready" when I asked, but those weeks lasted months. Looks like the cad designer disappeared - at least untill the day I was waiting - . Go for tea-bags, their all-in-one and of spectacular quality. Only better option I see, is to etch your own.
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Old 7th February 2013, 05:23 PM   #1267
oiphy is offline oiphy  Norway
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buzzforb. or anyone else for that matter. please keep the English simple

what are the pro and cons of high or low rail voltage.
I'm using same teabag boards as you, fully populated.
yet to decide cooling but might go exotic
yet to decide trafo
my caps are several 100v 47000 so.....
any toughs??

ps building 4 boards so stereo mono ... so on ...
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Old 7th February 2013, 06:15 PM   #1268
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Higher rail voltaage means more power into higher ohmic load. For instance, for 100w into an 8 hom load, you will need about 40-42V rails. For a 4 ohm load, you will need only 32v rails. Large impedance loads need more voltage swing. Low impedance loads need more current capacity If you are wanting higher than 100W into 8 ohm load, then you really need to consider balanced(bridged) topology, as this doubles the power into double the load. For example, an amp that can do 50W into a 4 ohm load will be able to do 100W into an 8ohm load if using a balanced(bridged) topology.

A consideration that is often overlooked is heat. Even if you can dissipate a lot of heat, the fet is still generating a lot of heat,internally, before your cooling system takes it away, so life expectancy becomes an issue.

What is your speakers setup?
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Old 7th February 2013, 06:35 PM   #1269
oiphy is offline oiphy  Norway
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its the one I use as a avatar. will upgrade it to 2x6,5. keep tweeter scan speak 9500. superb parts in 24db filter. active sub is long stoke peerless 10" ( will be other amps). in side of speaker.

https://www.dropbox.com/s/sfri0z1tqn...27221751_n.jpg


edit.

so think I'll go for one 32 and one 42v.. so that one can compare
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Last edited by oiphy; 7th February 2013 at 06:48 PM.
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Old 7th February 2013, 06:47 PM   #1270
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do you have impedance graph?
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