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PostPosted: 18 Aug 2015, 04:56 
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You're welcome. As you'll insert the value of 27-28K resistor instead 75K as presented you'll notice another values for the components. As I have read on a document there should be respected the values for 318uS, 3180uS and 73-75uS. In this way we can adjust the RIAA passive filter according to the cartridge used (depending on their frequency spectrum) to obtain the best of the best (La Crème de la crème).

I wanted to add those .pdf here but I can't. Any solution?


Last edited by andreidaniel on 18 Aug 2015, 05:11, edited 1 time in total.

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PostPosted: 18 Aug 2015, 05:08 
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Quote:

"3/ Accurate RIAA! The three time constants in the original RIAAspec create four areas in the audio spectrum: under 50Hz, 50Hz to 500Hz, 500 to 2122Hz, and 2122Hz on up. Now normally a 1dB shift is not easy to hear, but such an error in one of these bands can make a whole system become light and bright (or dark and mysterious) because it moves at least two whole octaves of music bandwidth around!
[...]
Surprisingly, few designers suggest precise caps, and none say to match them super tight channel to channel. But Diego splits the network the way I found sounds best: with the 3180 + 318µS first and the 75 µS last… "

Source: Secrets of the phono stage… Allen Wright, Vacuum State Electronics
http://www.pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Wright_Allan/SP-15_Article.pdf


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PostPosted: 25 Nov 2015, 16:56 
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Location: Bristol, UK
Hi there!

I've just finished this amp and tried it (on some old speakers) with terrible results :(
The music sounds sort of chopped up and there is a bad hum/noise.

I've copied the circuit diagram attached and used a 18v wall power supply.

Did continuity checks on all solder joints and triple checked the layout?!

No idea where to start now.


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PostPosted: 27 Nov 2015, 17:10 
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I have built a number of these and never had a problem. Do you have the FETs in the right way?

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PostPosted: 27 Nov 2015, 17:23 
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A similar, mostly the same design on that kind of PCB like yours I made. Also, I get a small hum, I don't know why. If I try to power the entire bloc from a DC source the hum is higher, so I power it from 3 x 9V battery but they don't last so much. I also placed a 220uF/50V capacitor between + and - for reducing a little the hum.

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The boozhound website recommands a unique power supply for eliminating the hum. http://boozhoundlabs.com/collections/all/products/power-supply-kit
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PostPosted: 27 Nov 2015, 18:03 
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If you are getting hum from batteries its not being produced in the preamp. The cct. brd. should be in a metal enclosure. You find the hum would reduce. It may need a ground plane also. I have also tested mine in a metal enclosure.

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PostPosted: 28 Nov 2015, 09:56 
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So, mwhouston, from your point of view the entire preamplifier should be shielded?


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PostPosted: 28 Nov 2015, 17:24 
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Definitely in an earthed metal enclosure. Attatch the negative of the battery system to the metal enclosure to drain any pickup from the enclosure.

Once I placed a phono stage in a plastic enclosure which hummed.

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PostPosted: 28 Nov 2015, 17:32 
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Ok, but the phono TESLA doesn't have an extra ground, has only a 5 pin DIN connector. Is a phono without separately ground.


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PostPosted: 28 Nov 2015, 17:48 
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My Rega has no ground wire and works well with these preamps. It's more about screening he phono cct. brd. than earthing the TT.

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