A passively equalized OpAmp RIAA preamp - Page 2

Razorblade · 9th May 2009, 10:57 PM

Hi all,

Could someone give me a hint on the quality of the usual cheapo LC meters, i want to order all the parts tomorrow. I know you get as much quality as you pay but will a cheapo lc meter be enough for the first projects and matching of the caps?

About the fourth pole: When there is nothing past 50Khz on the record, my amp cuts of at a level of ... hmmm lets say 30khz (ultra optimistic estimation)and my ears at 22Khz ... well, i dont understand whats the point of implementing the 4. pole no matter how much i read about it.

jackinnj · 10th May 2009, 01:19 AM

Quote:

Originally posted by Razorblade

About the fourth pole: When there is nothing past 50Khz on the record, my amp cuts of at a level of ... hmmm lets say 30khz (ultra optimistic estimation)and my ears at 22Khz ... well, i dont understand whats the point of implementing the 4. pole no matter how much i read about it.

It may be hurtful to your dog's ears/

Lots of LC bridge meter schematics on the web.

mlloyd1 · 13th May 2009, 10:05 PM

some years ago, i built and used this one and been pretty happy with it. before being laid off, i had a chance to compare it with a nice (i.e. expensive, well maintained and calibrated

) hp analyzer and was not disappointed. it also has a handy delta function that is great for matching caps.

mlloyd1

Quote:

Originally posted by Razorblade
... Could someone give me a hint on the quality of the usual cheapo LC meters ...

Razorblade · 13th May 2009, 10:25 PM

Since i am running on a very tight budget i cant afford any kind of LC meter at the moment so i decided to go with the 0.3% tolerance silver micas, the values of the schematic above are changed to 10.3nF, 30nf for the caps and 97.6k and 7.87k for the resisors. Load is a little higher but still everything simulates fines, does anyone see a problem with this little change (exept for higher resistor noise) ?

Since i cant afford the equipment to handmatch all the parts i will pay the extra price to get the parts with better tolerances.

But i have another big problem: My AC main is fluctuating like hell, when i plug in my cheapo multimeter in the ac outlet i get a reading of 228V-230V jumping up and down at random. When i exhange the probes in the holes of the AC outlet i get a stable reading of 230V, the same with my LC-Audio low noise reg, when i plug it into to the main outlet i get a DC of 11.8 to 12.1 jumping up an down, when i turn the acplug of the regulator by 180 degress its suddenly stable and when i connect the GND of the regulator to the mains safety GND (Green/Yellow cable here in germany) its stable no matter how the mains plug of the regulator is connected to the main outlet, does anyone have a hint why this could be and what to do against it?

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9th May 2009, 10:57 PM	#11
Razorblade diyAudio Member Join Date: Jun 2008	Hi all, Could someone give me a hint on the quality of the usual cheapo LC meters, i want to order all the parts tomorrow. I know you get as much quality as you pay but will a cheapo lc meter be enough for the first projects and matching of the caps? About the fourth pole: When there is nothing past 50Khz on the record, my amp cuts of at a level of ... hmmm lets say 30khz (ultra optimistic estimation)and my ears at 22Khz ... well, i dont understand whats the point of implementing the 4. pole no matter how much i read about it.

13th May 2009, 10:25 PM	#14
Razorblade diyAudio Member Join Date: Jun 2008	Since i am running on a very tight budget i cant afford any kind of LC meter at the moment so i decided to go with the 0.3% tolerance silver micas, the values of the schematic above are changed to 10.3nF, 30nf for the caps and 97.6k and 7.87k for the resisors. Load is a little higher but still everything simulates fines, does anyone see a problem with this little change (exept for higher resistor noise) ? Since i cant afford the equipment to handmatch all the parts i will pay the extra price to get the parts with better tolerances. But i have another big problem: My AC main is fluctuating like hell, when i plug in my cheapo multimeter in the ac outlet i get a reading of 228V-230V jumping up and down at random. When i exhange the probes in the holes of the AC outlet i get a stable reading of 230V, the same with my LC-Audio low noise reg, when i plug it into to the main outlet i get a DC of 11.8 to 12.1 jumping up an down, when i turn the acplug of the regulator by 180 degress its suddenly stable and when i connect the GND of the regulator to the mains safety GND (Green/Yellow cable here in germany) its stable no matter how the mains plug of the regulator is connected to the main outlet, does anyone have a hint why this could be and what to do against it?

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