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Old 12th November 2012, 05:58 PM   #7701
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Here is a D.Self trick to measure with low impedance.
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Old 12th November 2012, 09:26 PM   #7702
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I'm not too worried about the measurements. I always had this line (60hz and harmonics) related noise with my test setup when measuring phono section. It is caused mainly because the test equipment is not floating. When I measured my LC Audio light supplied head amp section, the measured noise was much lower, mainly because the head amp was not connected to any supply.

I expected better result with an actual cartridge (and much lower resistance than 50ohms, thanks MiiB) and with the actual separate enclosures and shielding. I'll use cases made of steel. My test setup had flying alligator clip jumpers, and the actual pre-reg pcb was close to the preamp.

My measurements indicates I think that the preamp is working nicely. Yes both channels imbalance for the RIAA can be tuned by fine tuning the RIAA capacitors. I'll do it in the assembled cases.

I was pleased to see that both channels have the same gain, at 61.4dB and that the small dc offset at the input was easy to null out. All the Gain Cell matched resistors are within 113 and 115mv, both channels, indicating a very good match. To make sure the matched quads were correct, I installed them on a breadboard outside of the PCB. Once I was sure they were well matched, I soldered them in place.

Here is what I got driving at -60dB the input using a reverse RIAA network (From Hagerman Audio). You can see that the square and triangle are almost perfect, indicating that all their harmonics were correctly amplified by the RIAA curve. For me the reverse RIAA is always the fastest way of testing rapidly for good RIAA correction.
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File Type: jpg Square_RevRIAA.jpg (105.5 KB, 297 views)
File Type: jpg Triangle_RevRIAA.jpg (108.6 KB, 268 views)
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Old 12th November 2012, 09:44 PM   #7703
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Tanks Algar

Briliant work

How abouth phase response is it possible for you to mesure that?
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Old 12th November 2012, 10:11 PM   #7704
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Do you mean phase difference between input and output? Since the RIAA network is a filter, it will cause phase shift vs frequency.

Last edited by Algar_emi; 12th November 2012 at 10:25 PM.
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Old 12th November 2012, 10:30 PM   #7705
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Yes especially phase shift between input and output
I use Hagerman as well as anti RIAA and I am aware of that.
Eventually to go around that I will try to measure up single frequency at correct level direct from Sig Gen but my test rig is quite inadequate and I rely mostly on listening
Which compared to your results sems pretty reliable.
I asked a while ago how to make small changes in gain quite a while ago maybe this make more sense now after your post...

PS do you use same IRC or Welwyn there? and watch out for those gold electrolitics (from Rapid?) leackagge currentis prety baad if same as same I have had in the past

Last edited by Bksabath; 12th November 2012 at 10:41 PM.
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Old 12th November 2012, 10:34 PM   #7706
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So to resume, you want phase shift measurement between input and output, but with the inverse RIAA inline with the input?

And Joachim Gerhard what is even more fun with my Paradise it that the pcb I made were almost perfect. Less than 3 small corrections to make to my first prototype, mostly forgotten ground connections. I'm very happy with the result

Last edited by Algar_emi; 12th November 2012 at 10:39 PM.
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Old 12th November 2012, 10:42 PM   #7707
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Sorry posting at same time obviously not with the contribution from anty RIAA
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Old 13th November 2012, 12:46 AM   #7708
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That is really awesome. You are one of the first that is ready and even made your own PCBs !
Do you use the Neumann pole ?
Hagerman recommends that pole and has implemented it in his anti RIAA.
I do not use that pole. My cartridges have a treble lift anyway.
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Old 13th November 2012, 01:21 AM   #7709
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The Hagtech reverse RIAA looks pretty dodgey to me.

Also check the capacitor values.
The Audio Express article states 6.2n...
...The kit states 6.6n ( 2x 33n )

I thought this was a misprint in the Audio Express article when I first spotted it...
...but it appears not to be...
...the value changed, for the kit.

They could have used 4.7nF + 1.5nF...
...but didn't.

Also worth noteing are the lack of plots in the Audio Express article...
...& in the kit PDF, where there are none at all.

The kit PDF also states :- the unit is for testing 'modern' phono-stages, ie. Neumann pole types.
Then goes on about phase problems you might have with other phono-stages ( ie. non Neumann pole stages ).

Perhaps good for playing white-noise to your phono-stage from a CD or electronic device...
...but for testing........................................... .................?

Cheers

Si.
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Old 13th November 2012, 01:29 AM   #7710
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That is the one i use. The resistor values are a bit unusual because i use Dale resistors that are not according to E24.
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