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Old 21st May 2012, 02:40 PM   #31
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Originally Posted by dimkasta View Post
I was browsing through some transformers and (instead of going for 18V) I was thinking that I will at some point try to turbo it, so I might as well go for 24V transformers from the start (32V rails as per the pre-V1 version in the Turbo article).

Plus, in the 24V range I am finding some nice 500+ VA from mouser and Hammond with free shipping.
The Antek ones will cost almost the same including shipping....
Plus, the Hammonds go as high as 1KVA (although way too heavy) which is really tempting for tests since they cost only 10 euros more... and I agree with you guys, vibration is my concern too.
I have tried Hammonds before, and they tend to vibrate as you go up in VA on the same Voltage (120VA with 12V rails was nice and silent. 225VA was vibrating like crazy)

External PSU is quickly becoming an attractive choice too...
with +/-32V rails you will need dual outputs(or much lowe bias)
and you might want to cascode the J-fets too
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Old 21st May 2012, 02:51 PM   #32
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maybe go streit for a turbo V1? CVillers boards with dual outputs and cascoding.
2x4-500VA 2x24V transformers and a bias of 1.9A(0.95A pr device)
and volla. you have a turbo v1 2x50W classA in 8ohm
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Old 21st May 2012, 03:09 PM   #33
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Dual outputs is not a requirement, as long as we do not exceed half the max dissipation rating of the mosfets (as per papa's pre-V1 notes).

5W resistors and conservative heatsinking is a requirement though, things that I was already planning anyway.
Oh and removing the current limiter might be an option too.
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Old 21st May 2012, 03:13 PM   #34
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over 40W dissipation pr device is a little on the hot end after my taste.
32x1.3=41.6W
also 32V for the 25V rating J-fets is also a little hi after my taste.
if you only use 1pair of outputs, you also need a thicker baseplate on your sinks.

Last edited by AudioSan; 21st May 2012 at 03:18 PM.
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Old 21st May 2012, 03:38 PM   #35
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Thanks for the input
Well I am planning to use the heatsinks specified for the stereo version to dissipate a mono version, so I guess this will be ok.

The jfets get around 30V which is rather within papa's comfort zone, provided that we either chose a lower idss (~8mA) or use a small heatsink on them.

It s getting a bit "hairy" to be honest...
I think for now I will stick to stock F5 and after I am comfortable (since this is my first build) I will go for a V3.

Fraidy-Cat mode => ON
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Old 21st May 2012, 03:49 PM   #36
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so i output pr side?
then you need to mount the fet's outside the board with gate stopper and source resistor soldered to the fet
also. with a heatsink with 10mm baseplate you will have only 100mm effective raidius around your fets(maybe less). the sinks will not be able to transfer heat over a longer distance. at least not very vel

Last edited by AudioSan; 21st May 2012 at 03:52 PM.
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Old 21st May 2012, 05:30 PM   #37
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Originally Posted by AudioSan View Post
so i output pr side?
For now I will stick to 18V toroid, 23V rails and 1,3A per channel.

Too many things can go wrong and I do not feel confident yet experimenting.

I m still considering the huge toroids though
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Old 21st May 2012, 07:09 PM   #38
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Originally Posted by dimkasta View Post
Guys just a question.
Your suggestions are based on experience between 1KVA and smaller ones, or is it just that you are content with the smaller ones?

The reason why I am asking is that I see you saying that the small ones should be "sufficient" or "enough" or other adjectives that tend to describe something that is just working without problems.

Does anyone have actual experience indicating that the 1KVA has no sonic difference over for example the 300VA?

The results I have so far form my phono indicate that the difference is huge with a bigger transformer.

Please have a look at this blog entry by Richard RJM
http://www.diyaudio.com/forums/blogs...-you-need.html

You will see that the rectifier-diode/filter combination does not need current on a continuous basis, but rather in a spike-like manner. And the spikes can reach easily 10 times the nominal current draw. Which can easily be translated according to Andrew's calculations (minus the cooling compensation) to 2,6x10=26A or and for 2x18 secondaries to 18x2x26=936VA

I have tried/verified Richard's theory on my phono and there is a huge difference in the sound.

I see no reason why the bigger PSU should behave any differently. Especially with the huge filter caps that practically act like shorts
1 Get what you can afford
2 bigher is better
3 what if you want to go balanced tomorow?
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Old 21st May 2012, 07:15 PM   #39
SRMcGee is offline SRMcGee  United States
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Originally Posted by buzzforb View Post
32V and exactly like schematic. That should yield about 6A+ Ipk, good for about 200W Class A into 6 ohms, which is my speaker impedance, and about 300W dissipation per channel. Damn yhats hot. If kept it will drive my woofers in an active system.
buzzforb:

You are apparently going to use Antek's AN-6224. Antek also offers 800VA and 1000VA toroids with 25V secondaries. Can you help me understand why the risks associated with the extra 1 volt are more compelling than the advantages of either of the significantly larger transformer alternatives?

Regards,
Scott
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Old 21st May 2012, 07:25 PM   #40
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No reason. 25x1.41 will yield about 34V rails. I own 8 Antek toroidal and have found them to be very stout. Just decided 1.2kV total was enough for me. I am a little cheap too!
Side note; if this were my final build, I would go for 800VA 25V secondary
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Last edited by buzzforb; 21st May 2012 at 07:27 PM.
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