Just rearranged the internal layout of the pcb´s in the Riaa and this further reduced the hum (now inaudible at normal listening levels).
Coating the TX with copper tape helped but the major improvement came from rotating the TX until hum is minimum... in this position grounding the TX shield seems to produce no results.
Shielding is effective but the real improvements came from repositioning of the TX.
Now I am ready to test D1 mod.
Ricardo
Coating the TX with copper tape helped but the major improvement came from rotating the TX until hum is minimum... in this position grounding the TX shield seems to produce no results.
Shielding is effective but the real improvements came from repositioning of the TX.
Now I am ready to test D1 mod.
Ricardo
I believe that now you are practically low enough in hum field from TX. In general, the recommendation for future builders is to use separate box for including a big toroid, rectification and main filter capacitors I guess. Me I use a small 50VA toroid mounted vertically and completely opposite to inputs and Riaa board if in same box. This keeps the 50Hz hum field really low, can't hear it, but I can still see a little in FFT. Shielded coax for input and output is a must if the TX is in the same box. OK waiting for your news about D1 Vref made with Leds.
Hi,
are the layers of copper foil tape insulated from each other?
Try connecting all the layers together with a soldered on shorting wire, maybe three or four shorting wires spread around the circumference.
Now that the transformer is located in the optimum position, try rotating it around it's mounting bolt to see if you can measure a variation in the interference that it creates.
are the layers of copper foil tape insulated from each other?
Try connecting all the layers together with a soldered on shorting wire, maybe three or four shorting wires spread around the circumference.
Now that the transformer is located in the optimum position, try rotating it around it's mounting bolt to see if you can measure a variation in the interference that it creates.
Thank you AndrewT
I have done everything you suggested... the foil is glued with conductive tape and I found the best low hum by rotating the TX.
Also I rose the TX by 4 cm and now It is in the best position ever... (it could be better but I would need a hood scoop or some kind of high rise lid 😀 )
I must refer that after reaching best positioning, the shielding seems redundant. (I get no hum increase by unearthing the shield in this position !)
The benefits from reducing hum are outstanding... I can now hear much more detail and the stereo image is wider with improved focus.
This riaa+shunt design really benefits from a hum free psu.... maybe in the future I will build an external enclosure.
Ricardo
I have done everything you suggested... the foil is glued with conductive tape and I found the best low hum by rotating the TX.
Also I rose the TX by 4 cm and now It is in the best position ever... (it could be better but I would need a hood scoop or some kind of high rise lid 😀 )
I must refer that after reaching best positioning, the shielding seems redundant. (I get no hum increase by unearthing the shield in this position !)
The benefits from reducing hum are outstanding... I can now hear much more detail and the stereo image is wider with improved focus.
This riaa+shunt design really benefits from a hum free psu.... maybe in the future I will build an external enclosure.
Ricardo
Is your toroid contained in a metal can already by any chance? That would explain the problem being mainly the secondary exit.
Nice, compact. What version did you make? Looks like low gain mm or high mc, no buffer. Post or link the particular schematics you used and pcb copper mask for people to use if you like.
Are your sinks enough? How much current did you set on shunts?
Are your sinks enough? How much current did you set on shunts?
🙂 Yesh Salas, 27 line preamp I build it long time ago.
and I user original Thorens TD-165 TT with arm. I think about few month my new TT will comming.
and I user original Thorens TD-165 TT with arm. I think about few month my new TT will comming.
Hi Salas
In my Riaa, the zenner is in a tight space..
Can I use miniature leds for D1 or should I stick to the big round 5mm ones ?
Looking at them, it seems the iside parts are bigger in the bigger leds... but that might be paralax error...
Ricardo
PS:
My TX is encapsulated in a plastic case... I do not know if it has any metal screen inside.
If I rotate it 45º, the hum is very pronounced and earthing the shield helps a lot. In the minimum hum position, earthing is not noticeable.
In my Riaa, the zenner is in a tight space..
Can I use miniature leds for D1 or should I stick to the big round 5mm ones ?
Looking at them, it seems the iside parts are bigger in the bigger leds... but that might be paralax error...
Ricardo
PS:
My TX is encapsulated in a plastic case... I do not know if it has any metal screen inside.
If I rotate it 45º, the hum is very pronounced and earthing the shield helps a lot. In the minimum hum position, earthing is not noticeable.
Hi Ricardo,
1. Miniature or even surface mount LEDs are OK.
2. 2X3.9V Zener in series seems to be good as the LEDs.
Now with what you said about the shield, I don't see a paradox anymore. Thanks.
1. Miniature or even surface mount LEDs are OK.
2. 2X3.9V Zener in series seems to be good as the LEDs.
Now with what you said about the shield, I don't see a paradox anymore. Thanks.