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Old 10th November 2012, 12:24 PM   #2221
disco is offline disco  Netherlands
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Outside winding to the lower impedance?
I assume the choke is highly interleaved for reduction of capacitance, so there won't be much difference to the ears. Perhaps it offers another resonant frequency to the tube with wires swapped?
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Old 10th November 2012, 06:34 PM   #2222
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Originally Posted by disco View Post
Outside winding to the lower impedance?
I assume the choke is highly interleaved for reduction of capacitance, so there won't be much difference to the ears. Perhaps it offers another resonant frequency to the tube with wires swapped?
Depending on the choke of course. Many will simply be a single section wound with a start in the middle and the end up outside in the same manner as on a normal spool.

The lower impedance on the outside gives it a bit of screening effect. This may or may not be a good thing of course, but if the hum levels change when one swaps the leads around then at least it gives on a bit of a clue.

Also the capacitance between windings decreases as one goes in towards the centre as the length of wire per turns decreases. Not hugely but perhaps enough to be audible as an interaction with other things.

If one is using EL mains transformers, particularly where the primary is on a separate section with a split bobbin the neutral should be on the outside, and the live to the centre. That way the neutral gives a bit of screening and also the losses could be a fraction lower.

It's all very much a try it and see game of course, as intuition isn't always right.

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Susan.
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Old 18th November 2012, 05:37 PM   #2223
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Originally Posted by Rod Coleman View Post
With any of my PCB-based Regulators, reducing the ripple to 80-140mV should be enough, even for line amps. So LC with 10mH or more and 10000uF is easily good enough.

Of course, this all has to do with differential mode ripple and noise.

When you use a high-capacitance trafo (eg Toroid) the noise that gets in is common-mode. The regulator will reject this, but not completely. Hence the recommendation for split-bobbin trafos.

The old 2004 Regulator circuit rejects CM and DM noise much less effectively.
For my understanding, can we install the full rectifier board plus necessary capacitors on the supply unit, then connect through long cable to the main chassis and directly to the regulators without further caps?
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Old 18th November 2012, 06:31 PM   #2224
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Yes, that's correct.

Maybe a small film (FKP2 or ECHU series) 100nF at the PCB will be useful.
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Old 18th November 2012, 09:23 PM   #2225
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Yes, that's correct.

Maybe a small film (FKP2 or ECHU series) 100nF at the PCB will be useful.
Super.
Thanks.
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Old 27th November 2012, 02:58 AM   #2226
Magz is offline Magz  United States
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Made an improvement to my battery grid biasing today. Initially I was injecting the -9V through a grid bias resistor, and using a 0.22uF cap before that to block DC. Since I also have an LL1676 transformer at the input I decided to remove the 0.22uF cap and the grid bias resistor and put the battery at the bottom of the input transformer secondary instead, between the transformer and ground. This gives the advantages of no cap in the signal path, and much lower resistance to ground for the grid (more stable bias).

The bass improved considerably, and the entire presentation became clearer and more balanced. The battery is bypassed with a 10nF Multicap RTX polystyrene. The transformer secondary is loaded with an RC network of 2nF+850ohms, and the transformer is run in a 2:1 stepdown with primaries and secondaries in parallel.

I highly recommend this bias arrangement; the preamp loves it and so do I!
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Old 27th November 2012, 12:54 PM   #2227
Magz is offline Magz  United States
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Made an improvement to my battery grid biasing today. Initially I was injecting the -9V through a grid bias resistor, and using a 0.22uF cap before that to block DC. Since I also have an LL1676 transformer at the input I decided to remove the 0.22uF cap and the grid bias resistor and put the battery at the bottom of the input transformer secondary instead, between the transformer and ground. This gives the advantages of no cap in the signal path, and much lower resistance to ground for the grid (more stable bias).

The bass improved considerably, and the entire presentation became clearer and more balanced. The battery is bypassed with a 10nF Multicap RTX polystyrene. The transformer secondary is loaded with an RC network of 2nF+850ohms, and the transformer is run in a 2:1 stepdown with primaries and secondaries in parallel.

I highly recommend this bias arrangement; the preamp loves it and so do I!
Attached is a schematic of the new input and biasing arrangement. It sounds far, far better to my ears than the standard arrangement with cap and resistor.
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File Type: jpg 26 Preamp Input Circuit.jpg (14.6 KB, 447 views)
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Old 27th November 2012, 05:27 PM   #2228
Magz is offline Magz  United States
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Attached is a schematic of the new input and biasing arrangement. It sounds far, far better to my ears than the standard arrangement with cap and resistor.

Not sure why my caps came out looking so off kilter, but I re-drew them in paint. I guess you knew what I meant, though...
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File Type: jpg 26 Preamp Input Circuit.jpg (14.6 KB, 434 views)
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Old 28th November 2012, 03:47 PM   #2229
CFT is offline CFT  United States
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Originally Posted by Magz View Post
Attached is a schematic of the new input and biasing arrangement. It sounds far, far better to my ears than the standard arrangement with cap and resistor.
That's a good idea!
I could try it out on mine too. Thanks Magz!
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Old 28th November 2012, 10:56 PM   #2230
Richard is offline Richard  Australia
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Hi Magz,

Thank you for posting your results and schematic. I was thinking about doing the same thing, but I was a bit worried about damaging the transformer if it is spec'd for 0 current with the 26 drawing a very little grid current.

Does anyone have any thoughts of limiting any potential damage to an input transformer in this setup?

Cheers,

Rich
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