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Old 6th June 2003, 07:02 AM   #21
Electrons are yellow and more is better!
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Default Re: Re: QSXM3

Quote:
Originally posted by Cobra2
And it also sounds great ! Now, I need to find a home for it (chassi).
A little gain-adjustment 100ohm -> 75ohm was what I needed.
All components are matched, even had to order another 10 of the RIAA caps for getting a match...
Didn't you use 2.5% caps? Is it polyester....green?

Now the picture looks better but how about the class A circuit? FET + resistor only.
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Old 6th June 2003, 07:35 AM   #22
Oscar is offline Oscar  Sweden
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Default Re: Just another RIAA......

Quote:
Originally posted by Chris
This design is a two stage riaa phono preamplifier.
Currently I use BB opa 37 in the first gainstge an BB opa 606 in the second gainstage. The result is shown in the following pictures.
Very nice work Chris! Could you perhaps elaborate a bit on how you made the case? Especially, how did you get that nice finish on the front plate?
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Old 6th June 2003, 08:05 AM   #23
Cobra2 is online now Cobra2  Norway
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Default Re: QSXM3

6800pF + 2,5% = 6970...
And when I do critical matching, I try to go for +/- 0,1%.
Witch "wastes" a lot of components....
Having looked over the schematics & instructions, I think I have removed the surplus components, exept a few, that should be isolated from the circuit anyway (without transistors).

ArneK
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File Type: jpg qsxm3x2.jpg (57.9 KB, 553 views)
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Old 7th June 2003, 12:02 PM   #24
Mad_K is offline Mad_K  Norway
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Default Re: Re: Just another RIAA......

Quote:
Originally posted by Oscar


Very nice work Chris! Could you perhaps elaborate a bit on how you made the case? Especially, how did you get that nice finish on the front plate?
See any family resemblace? http://www.diyaudio.com/forums/showt...448#post115448

Maybe http://www.elfa.se/pdf/50/05025002.pdf



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Old 7th June 2003, 12:25 PM   #25
Electrons are yellow and more is better!
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Default Re: Re: QSXM3

Quote:
Originally posted by Cobra2
6800pF + 2,5% = 6970...
And when I do critical matching, I try to go for +/- 0,1%.
Can you measure down to 0.1%? I have a LCR-bridge at work which takes 0.25% (12500 SEK = 1500 USD).

Some parts are still there which shouldn't but they seems to float, no harm in that.
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Old 7th June 2003, 02:55 PM   #26
Cobra2 is online now Cobra2  Norway
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Default 0,1 %

or not...
I use this : http://www.peakelec.co.uk/
and I have a few referances.
And measuring thru a lot (time-consuming), I sort them, and compare against a referance.
And (after calibration) I expect the instrument to be close on mentioned value, when it is spot on at 1nF(referance).

Arne K

Going for 96% tonight, or maybe a little less...
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Old 8th June 2003, 07:34 PM   #27
krishu is offline krishu  Europe
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Hi to everybody;

i am currently working on a opamp based phono stage as well. I saw the circuit of the 606 data sheet and it is quite the same as mr lehmann uses (black Cube) except the opamps and a dc coupling cap/subsonic filter.

My plan is to do it like shown on the picture, but i did not finish planning yet. I ordered several OPAmps like AD797, SSM2019, INA217, OPA627 and OPA637. The goal is to have a quiet phono stage, which forces to choose from very few opamps for input stage. Apart from the first three of the obove mentioned there are only a few more to mention: LT1028, THAT1510.

The circuit will be working, but i am not sure about the 1K5 cap on +input of second OPAmp (whether it will change RIAA ...?) and about the output resistor and if i should put a further cap in series with that 100R.

Cheers Christian.
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