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Old 21st August 2009, 11:15 PM   #2171
Salas is offline Salas  Greece
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The last set of RMS you describe, shows a logical signal pass with stage gains and filter attenuation in your expected version's ballpark. It works OK regarding the 1kHz tone you fed. Even your total gain calculates at 41dB normal spec with the numbers you gave. See why you have hum with TT. Can you attenuate down to 4mV input from CD and feed your phono out to your headphones amp? Just play the CD tone track and turn down the pot until you measure 450mV RMS on phono's output. If the 1kHz will sound clear without hum, then your problem isn't in the phono itself. Do you ground the tonearm? In case you can not find what is wrong, don't destroy the built channel. I suggest you build the next one with clear head, and if it works OK, see where the other one has the bug by comparing visually the whole thing.
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Old 22nd August 2009, 02:51 PM   #2172
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Hi Salas,
the ground of my TT was not good.
Now the channel work well. Only a little hum when there isn't music and the volume amplifier is over half. May be that when i put all in the box the hum become inaudible. Now if only put the riaa board onto the floor the hum increase. It is very sensible.
At this time i'm listening with Salas riaa that go into JC-2 clone than into stax head amplifier. I must finish my ux250 amplifier and adjust well the riaa value (my C3 is 16,2nF) and Cload.
Thank you very much for your help.
Luca
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Old 22nd August 2009, 03:11 PM   #2173
Salas is offline Salas  Greece
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No big deal. I am happy you progress. When you make everything and it is together, if having hum problems (takes experience with grounding to see and solve), let me know again so I may be of help. It can be made totally hum free, I know it because it has been done a lot of times. But you must have it in a metal box and better have good distance to the transformer. Tell me about the capacitors you used. What are those big blocky redish ones? Russian film?
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Old 22nd August 2009, 10:29 PM   #2174
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The big blocky redish are Lemco Silver Mica 47nF and 16nF 2% (purchased from a seller from GB on Ebay. They are 47,2nF and 16,2nF) than there is one Ft-2 100nF and the output cap is another Russian cap, K73-16, dry mylar.
About the hum: if the transformer is near or far the board the hum not vary. now the transformer is 1 meter away from the board. I think that the problem is the layout of my board. I have hum also with open input.
http://img29.imageshack.us/img29/1576/spa1282.jpg
if i separe rectifier and shunt from the riaa board may vary ?
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Old 22nd August 2009, 11:15 PM   #2175
Salas is offline Salas  Greece
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Trace me the rectification GND, shunt GND and Riaa GND with yellow, green, and orange, I want to see if there is a loop.

Don't separate, it isn't field inducing, its better they are tight, good for shunt's output impedance and RF. I will see if there is another way to relate the 3 GNDs. Your caps are close enough for now. I don't know the quality of the output capacitor. Have you evaluated it before? I have only read that it can be a bit treble etched at times besides being very good in general, so the 16.2n maybe balances it by shaving off just a tad more treble than intended with a suggested 16-16.1n.
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Old 23rd August 2009, 07:57 AM   #2176
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I compared the output cap with mundorf m-cap PP (white cap) and audyn cap Q4 and i like the sound of K73-16. Open, clean... i must evaluate more, also adding a Ft-2 as bypass. If i got a good working riaa i can spend some extra money for the components. The gnd: i don't see a loop; i did a test, i disconnect in and out gnd from the riaa. In this case don't work, the riaa has a cyclic beat (oscillation?) and the led's flash on-off (riaa's and shunt's leds)
http://img19.imageshack.us/img19/1576/spa1282.jpg
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Old 23rd August 2009, 10:32 AM   #2177
Salas is offline Salas  Greece
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There is local contamination. Try this I attach.
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File Type: jpg spa1282altGnd.jpg (450.9 KB, 370 views)
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Old 23rd August 2009, 09:00 PM   #2178
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Salas you are a genius as well as being a kind person.
Now the hum is gone, only with the volume at max I hear a slight breath (shhhhhhhhh). And I'm listening through headphones.
When i build the second channel i must connect the star ground of the second channel to the star ground of the first ? star ground for me is where rectification GND, shunt GND and Riaa GND are connected together
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Old 23rd August 2009, 10:44 PM   #2179
Salas is offline Salas  Greece
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No, you will have to make a chassis star earth using screw and nut, where you will connect 2 + 2 black lines from the channels. The black earth symbol I draw in other words represents that point. Also the tonearm grounding post with a wire there. The mains earth you will connect near the IEC socket to the chassis. When you will have stereo and will listen more, and play with your TT set up, VTA etc, tell me more about the tone. Maybe you will need just a couple of Shinkoh.
The FT caps start up a bit coarse but after some play become unified, passing essential info, not hyper detail, go down slide again for a while and then come up again for good. Lets see how your parts assortment comes together.
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Old 26th August 2009, 11:41 AM   #2180
RCruz is offline RCruz  Switzerland
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Hi Salas

Here you have the latest layout for the riaa. Could you please comment on the locations ?

Centre cap is a 100n FT-3 and below is a 47n obbligato gold. In the output there is a 4u7 obbligato gold.

I am doing it p2p but maybe I will build a pcb for later use.

Can I use 680uF caps on C5 and C6 ?

Regards

Ricardo
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File Type: pdf ExpressPCB salas riaa v12.pdf (12.3 KB, 124 views)
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