D3a Phonostage reloaded Assistance required

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Mike H
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#46 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

Buxton Spring water, only the best eh? :D

Big roll of solder too.
 
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#47 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Nick wrote:
And what was the attenuation of the inverse RIAA?

Ah. Considerable.

I was wondering how to be more specific without impenetrable maths, which, for me, is most maths….

Umm I thought about comparing the 1.8v on the display looped-through-the-Millett box, which fortunately produces a straight line at all frequencies along the top (green);
... with the 1.8v looped through my inverse riaa, which produces that nice staggered, stepped line in the middle (blue). At around the 1kHz mark, the difference between the two lines green/blue looks to be about -50dB. So I was rather hoping that may be the attenuation of the inverse riaa (at that frequency). Or something. Help!
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thomas
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#48 Re: D3a Phonostage reloaded Assistance required

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Mike H wrote:Buxton Spring water, only the best eh? :D

Big roll of solder too.

Aksherly that's refilled with Kent's finest tap water to dampen my solder sponge, or in this case, my solder flannel……

And the solder is full fat leaded too….
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#49 Re: D3a Phonostage reloaded Assistance required

Post by Nick »

Ok, so if it is 50dB amd 1.8v in, then thats about 5.7mv into the phono. I would aim for about 1mv input at 1kHz to get a representative view of noise floor and distortion levels.
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#50 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

thomas wrote:
Mike H wrote:Buxton Spring water, only the best eh? :D

Big roll of solder too.

Aksherly that's refilled with Kent's finest tap water to dampen my solder sponge, or in this case, my solder flannel……

And the solder is full fat leaded too….
AH!! All is not as it appears.

Ah well yes bit extravagant using Buxton Spring for your solder sponge.
 
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#51 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

OOh, that's classy electronics, I hadn't though that spring water could improve my solder joints and reduce noise-floor.

So if you feed 1mV in, then your second-harmonic will be at eg. 70dB down ( good ) but the noise floor will come up ( bad ) .
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#52 Re: D3a Phonostage reloaded Assistance required

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IslandPink wrote:OOh, that's classy electronics, I hadn't though that spring water could improve my solder joints and reduce noise-floor.

So if you feed 1mV in, then your second-harmonic will be at eg. 70dB down ( good ) but the noise floor will come up ( bad ) .
As I say, there is a lot of fun to be had with a phono stage :-)
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#53 Re: D3a Phonostage reloaded Assistance required

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Nick wrote:Ok, so if it is 50dB amd 1.8v in, then thats about 5.7mv into the phono. I would aim for about 1mv input at 1kHz to get a representative view of noise floor and distortion levels.

Aha. There's some maths coming up now, isn't there?!

I will try and work out what setting in dB on the audio tester I need, and what that voltage will be on the Millett box display, for 1mV through the phonostage. Later, obviously……

I know this is good for me, thanks Nick!
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#54 Re: D3a Phonostage reloaded Assistance required

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IslandPink wrote:OOh, that's classy electronics, I hadn't though that spring water could improve my solder joints and reduce noise-floor.

.

….but I thought that's what all hi end audio electronics used?!
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#55 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

thomas wrote: Aha. There's some maths coming up now, isn't there?!

Image
 
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#56 Re: D3a Phonostage reloaded Assistance required

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Mike H wrote:
thomas wrote: Aha. There's some maths coming up now, isn't there?!

Image
Eeeek!! :shock: :shock: :shock: :shock:

(dusts off a book of log tables last opened in 1978)

But the internet is my friend!

I found an online dB to voltage converter. Ha! It seems a matter of just plugging in numbers….

1.8v attenuated by -50dB gives 5.7mv

If I want 1mv then 1.8v needs to be attenuated by; 0.001 divided by 1.8; which gives -65dB (it says here…). I know my inverse riaa already attenuates by -50dB, and apparently dBs add/subtract, so…

…I reckon I set my audiotester output to the difference, ie -15dB

And that should give a reading of 32mv on the Millett display……

Or have I got this all horribly wrong? One way to find out, once my brain has recuperated…...
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#57 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

Ah yes 20dB = X10 Voltage ratio.

/ 10 = 20 dB

/ 100 (/ 10 twice) = 40 dB

/ 1000 = 60 dB

Plus, er, a bit more, so yes looks about right.
 
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#58 Re: D3a Phonostage reloaded Assistance required

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Yep, thats about right
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#59 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

The master concurs.....

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#60 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Nick wrote:Yep, thats about right

Ta Nick and Mike!

I hope to test this later….
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