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Old 11th October 2005, 01:46 AM   #111
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Richard Murdey
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Figure on 10mA per channel for the phonoclone circuit, 20mA per channel including the three terminal regulators.

A couple of people have now reported that the output noise did not change significantly when they swapped the linear regulated supply for batteries. Yet others have clearly heard a difference between 78xx and 317 regulators. That's hard to reconcile. The first observation indicates that the output noise is mainly generated by the phonoclone circuit not the power supply, the second would appear to confirm the opposite.

A very rough calculation would indicate that the voltage noise of the input op-amp should dominate the noise spectrum at least at low to moderate frequencies, while power supply noise would start to become important at high frequency, possibly well above the audio band.

Thus, although the audible noise background may remain the same the sound may still improve as changes are made to the power supply affacting the amount of HF (and RF) noise being injected into the circuit.

/R
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Old 11th October 2005, 10:54 AM   #112
Franz G is offline Franz G  Switzerland
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Quote:
A couple of people have now reported that the output noise did not change significantly when they swapped the linear regulated supply for batteries.
Again: in my case, the amp is absolutely silent, with open or shorted inputs, with psu or battery.

But some (very very little) noise is injected in my case as soon as the turntable is attached. So, I will have to investigate what I can tweak on the turntable.

In fact, the noise is absolutely no problem: with my nearby 100dB/W setup, I am just listening the noise when I have very high volume level, my ears 10cm nearby the speaker and no disc running.

Franz
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Old 11th October 2005, 01:02 PM   #113
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With the input open circuit, the gain of the phonoclone is much lower than with a cartridge connected. That's why the noise gets louder - nothing to do with your turntable.

You can double-check this by connecting a resistor instead of the cartridge at the input.

Since the cartridge impedance or this dummy load sets the gain of the first stage, and thus determines the output noise to a great extent, you must have at least one of these in place before you measure anything.

Richard
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Old 12th October 2005, 07:06 AM   #114
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Phonoclone Measurements Page

Will be updating as time permits.

/R
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Old 13th October 2005, 02:02 AM   #115
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I figured I'd upload the frequency reponse (deviation from RIAA) to the forum, for posterity.

cuz its pretty good.

Its satisfying to know at last that the calculations actually do match reality. The .2dB bump in the midbass is the result of a couple of the RIAA components being about 1% off the target value.

/R
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Old 15th October 2005, 02:46 PM   #116
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My vsps in the making..the transformers will be an alternative output..I am curious to compare them with the BG'sClick the image to open in full size.
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Old 15th October 2005, 03:14 PM   #117
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Default Output Iron

I hope to drill the cases tonight to build mine. Let me know how iron works instead of the caps. Thought of this myself, just was unsure of how much offset there is. Using a cap with the transformer defeats the purpose.
There is a new pair of S & B 410A in my closet. Figured they would come in handy someday. They can deal with a couple mv offset. The input resistance is 38 ohms.

George
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Old 15th October 2005, 03:19 PM   #118
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Quote:
Let me know how iron works instead of the caps.
Will do.
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Old 18th October 2005, 03:59 AM   #119
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Default Phonoclone PCB grounding issue

Its come to my attention that the phonoclone PCB has a minor problem with the ground layout. Before everyone gets excited, please remember:

1. This does not affect the VSPS at all.
2. This does not affect the Phonoclone either unless you use an uregulated power supply.

Ok, the problem is the length of ground trace between the regulator ground pin and COM that is shared by the ground of the filter capacitors C8-11. The ripple currents (about 100mA peak) going though each trace coupled with the rather high resistance of the PCB traces induces a voltage spike on the regulator gound pin that of course floats the regulator output up accordingly. In other words, extra ripple is added to the op-amp's power pins, and find its way to the output.

This is explained in more detail here.

The solution is to rewire the ground leads of the filter capacitors C8-C11 directly to COM, as shown in the photo. Or switch and use a regulated power supply.

Making the mod did improve the sound, in my case.

/R
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Old 18th October 2005, 07:18 AM   #120
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Default Ground earth on VSPS Ultra.

I am close to completing my battery powered VSPS ultra, but as there is no earth/ground connection from the charger, i was wondering where to put the ground wire from the Arm cable.
Any recommendations?

Regards BT
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