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Old 5th April 2013, 06:36 AM   #2371
rjm is offline rjm  Japan
Richard Murdey
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If it was me, I'd go with 220 ohms and 3 nF. I'd also change R3 to 220 ohms. That will 1) set the HF response to RIAA standard, 2) give you an RFI screen on the output, and 3) avoid any "short" conditions at ultra-high frequencies.
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Old 15th April 2013, 02:19 PM   #2372
hajj is offline hajj  Lebanon
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First time posting in the thread.

I received my VSPS 300 kit a couple of days ago, and built the PCBs with included parts, very straightforward (great quality PCBs btw)

Next is the PS part, and this is where things get a bit more complex.
I'll be using an 12-0-12V EI core transformer rated at 3 Amps (which equates to 36 VA)
The transformer (a custom wound unit), unlike most toroidal transformers, does not have separate secondaries, it has a common center tap for the secondaries.
I know I can try to fiddle with it and get to the spot where the secondaries are spliced together, So the questions are:

1- Would it matter if the diode bridges share the center tap instead of each bridge having it's separate connection?
2- Would the EI core perform noticeably worse than an equivalent Toroid? (Toroids in Lebanon are hard to come by)
3- Would adding capacitors on the bridge output help the sound in any way by smoothing the power fluctuations?
4- The diode bridges are rated at 6 amps, and are a no name brand, how critical is this part? what are you guys' impressions on better rectifier options?

I've searched the thread for answers, and found some posts relating to the diode part, with people preferring discrete diode bridges while others found prepackaged bridges to fair better. On the other hand, I couldn't find anything about the transformer part and would prefer to delay the build until I get someone knowledgeable to chime in rather than blow up the transformer or even worse, the VSPS...

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Nick
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Old 15th April 2013, 06:15 PM   #2373
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Hello Hajj,

I've experimented with 2 bridges instead of one, but I could not hear any difference. You're more than ok with one..
No idea on the toroidial/EI. In any case, don't put them too close to your preamp. Adding capacitors might smooth things out even more, however, might be pretty useless. Test it out 6 amps is more than enough At 50hz, any diode is good enough
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Old 15th April 2013, 08:00 PM   #2374
hajj is offline hajj  Lebanon
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Hi Wirehead,
Thanks for the reply!
I guess I should stop obsessing and make do with what's available then
I'll keep the PS and the preamp far from each other (1 meter long XLR umbilical)
But one thing I don't get in your post is the rectifier part.
How could one get +12,0,-12v from one single bridge?
My (limited) understanding says you can either get 12,0 or 24,0 (actually this should be 12xSqrt2 and 24xSqrt2) depending on how you wire the secondaries to the bridge (as said earlier, my transformer has only three wires coming out of the secondaries, 12,0,12)

Thanks

Nick
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Old 15th April 2013, 08:28 PM   #2375
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Center tap is GND, and then +12 and -12
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Old 15th April 2013, 08:38 PM   #2376
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Aha, got it.
Didn't think AC and DC played well together
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Old 17th April 2013, 09:19 AM   #2377
hajj is offline hajj  Lebanon
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A couple more questions:
1- If I am to connect two rectifier bridges with them sharing the center tap, would it work? would it cause problems?
2- Where I live we do not have earth connection in the power outlet, only L and N. Will that influence the way I should build the PS?
Thanks
Nick
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Old 17th April 2013, 09:42 AM   #2378
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Here's a good example:
http://www.elecircuit.com/uploads/al...925495P9-0.gif
J1 and J3 go to transformer line, J2 is connected to the center tap.
Why would you want to use two bridges in this kind of setup?
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Old 17th April 2013, 10:42 AM   #2379
hajj is offline hajj  Lebanon
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Quote:
Originally Posted by Wirehead.be View Post
Why would you want to use two bridges in this kind of setup?
I wanted to stick to the original diagram as much as possible.
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Old 17th April 2013, 01:22 PM   #2380
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The option to use two bridges is only available if you have two secondaries, rather than a single winding with center tap.

You can use an EI transformer, but don't add filter capacitors. The capacitance on the board itself is already sufficient.

The EI transformer output is 12-0-12. "0", the center tap, connects to COM, the top and bottom of the winding connect to the "~" terminals of the bridge, V++ and V-- connect to the "+" and "-" terminals of the bridge.
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