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-   -   IMPOSSIBLE TO REMOVE HUM IN PHONO PREAMP (http://www.diyaudio.com/forums/analogue-source/213932-impossible-remove-hum-phono-preamp.html)

ALPUY 5th June 2012 05:50 PM

IMPOSSIBLE TO REMOVE HUM IN PHONO PREAMP
 
Friends. I built a phono preamp, based on circuits of Rod Elliott. I used good quality components and OPA2134 operational. The construction was carried out by placing the transformer pre cabinet, using a specific one for him. The interconnection notif them has been done with three wire mesh, where the mesh is connected to the network by a mass and on the other side to mass pre star. The issue is that there is always a hum auque is low. It is never silent. Post diagrams to help me that I was wrong. Greetings Jose.
http://i49.tinypic.com/2uo3m6h.jpg
http://i46.tinypic.com/2cc7mf.jpg
http://i45.tinypic.com/f1kunl.jpg

KatieandDad 5th June 2012 05:58 PM

If your layout is good and your problem is not ground loop then try using heavier gauge wire for your 0V connections.

ALPUY 5th June 2012 06:31 PM

OK. Thanks, I'll try what I advised. Greetings Jose.

Osvaldo de Banfield 5th June 2012 06:35 PM

Which is the AC voltage at the secondary of the trafo?. It says 7VA, but it is power. Perhaps, the voltage at the 4700 micro is few to the 78/79 to regulate (no drop out or too low), and hum goes though power lines. You need almost 12/15V, so have 20VDC at C1/C2, and personally unlike this voltage doubler. Donīt you have a 12+12V /100mA and make a Graetz bridge instead of this doubler?

sesebe 5th June 2012 06:39 PM

Hi,

With input in short-circuit the hum remain?
What is the voltage across C1 and/or C2 in power supply?

KatieandDad 5th June 2012 06:59 PM

The PSU is appauling, it is only half-wave rectified. Try a decent centre-tapped transformer correctly rated at 12-0-12V and using a full bridge rectifier.

12-0-12 will give you the required headroom for the regulators. No-one in their right mind would use a voltage doubler at this voltage.

Osvaldo de Banfield 5th June 2012 07:02 PM

Quote:

Originally Posted by KatieandDad (Post 3049280)
The PSU is appauling, it is only half-wave rectified. Try a decent centre-tapped transformer correctly rated at 12-0-12V and using a full bridge rectifier.

12-0-12 will give you the required headroom for the regulators. No-one in their right mind would use a voltage doubler at this voltage.

This is I trying to say.

sesebe 5th June 2012 07:11 PM

I have the same type of voltage doubler in an amplifier without voltage stabilizer and I do not have any hum.
If it is well calculated a voltage stabilizer can work well.

What is the voltage on filtering capacitors from input of voltage stabilizers?

AND

With input in short-circuit the hum it is present?

KatieandDad 5th June 2012 07:13 PM

Modified PSU with CT transformer
 
1 Attachment(s)
Try a decent PSU.

ALPUY 5th June 2012 07:34 PM

OK. I'm using a transformer with CT. I put a diode bridge for full wave rectification. The voltage on C1 and C2 is + - 20v. And as if you hum with the inputs shorted, not tried. I think I need to change the PCB that is not the original of Rod Elliott. PCB shipping diagram used. I appreciate your information. Jose.
Postscript: If you disconnect the wires from the in put (those coming from the turntable) only blows at max volume.
http://i48.tinypic.com/30rtjxl.jpg


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