A paradox is something that contradicts intuition.
So for the copper shield not to have any function at all when grounded it was contradicting my experience with such TXs.
After Ricardo explained that it does have an effect in his assortment in box, but not when field is minimized by rotation, I had enough data to know that there is no paradox. Ricardo has reached residual hum in this configuration by rotation and rearrangements, so grounding the shield or not makes no real difference.
So for the copper shield not to have any function at all when grounded it was contradicting my experience with such TXs.
After Ricardo explained that it does have an effect in his assortment in box, but not when field is minimized by rotation, I had enough data to know that there is no paradox. Ricardo has reached residual hum in this configuration by rotation and rearrangements, so grounding the shield or not makes no real difference.
pajonec said:🙂 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.
Nice, tell us how you liked the phono when you listen. Also you made good compact PCBs. Give the full files to the people here if you like.
I read somewhere that placement can reduce hum in order to make shielding irrelevant..... Now I can say I found that just using "hands on approach".
Cool
Cool
My life is changing very fast... I am entering a new business so I am experiencing lack of time...
Back to D1, I am having trouble finding the correct zenners.
I built a zener diode voltage regulator circuit so I could match the zeners and the 3.9v zeners only measures 3.5 volts.
The circuit I am using is this: http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm
Am I doing something wrong ?
I get the following readings with several zeners:
13v measures 13.1v
15v measures 15.1v
4.7v measures 4v
3v measures 2.5v
3.3v measures 2.8v
2.7v measures 2.5v
3.9v measures 3.5v (Two of those measure 6.9v) 😕
Ricardo
Back to D1, I am having trouble finding the correct zenners.
I built a zener diode voltage regulator circuit so I could match the zeners and the 3.9v zeners only measures 3.5 volts.
The circuit I am using is this: http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm
Am I doing something wrong ?
I get the following readings with several zeners:
13v measures 13.1v
15v measures 15.1v
4.7v measures 4v
3v measures 2.5v
3.3v measures 2.8v
2.7v measures 2.5v
3.9v measures 3.5v (Two of those measure 6.9v) 😕
Ricardo
Hi,
at what current are you testing each of the Zeners?
If the test current varies then the measured voltage will vary.
If the test current drops dissipation below 10% of maximum then the voltage varies a lot.
at what current are you testing each of the Zeners?
If the test current varies then the measured voltage will vary.
If the test current drops dissipation below 10% of maximum then the voltage varies a lot.
Test them either on circuit, or out of circuit using a 8-9mA 2SK170 in IDSS mode feeding them, and same V+ as in your Riaa.
I measure 51mA for 7.51v using a 4.7v zener + 3.9v zener on the test layout.
I can not test them on circuit.... the zeners must be tested before implementation.... my pcb is very damaged right now.
About the test circuit:
On the 2sk170 I place +28v on D
G+S go to the zener and this one to GND
right ?
I can not test them on circuit.... the zeners must be tested before implementation.... my pcb is very damaged right now.
About the test circuit:
On the 2sk170 I place +28v on D
G+S go to the zener and this one to GND
right ?
Low voltage zeners take a lot of current to make them wake up - one of their disadvantages. This is reflected in the test current cited in their data sheets. A string of yellow-green LEDs might work better, requiring only 10mA or so. Each LED will drop almost exactly 2V at that bias current.
with a suitable jfet, I am reading 10.2mA fed with 26v (not exactly the 28v on my riaa)
The 4.7v zener reads 3.6v
The 3.9v zener reads 2.94v
So it seems the issue persists... maybe my zeners are poor quality ?
Do I need a load for this test ?
The 4.7v zener reads 3.6v
The 3.9v zener reads 2.94v
So it seems the issue persists... maybe my zeners are poor quality ?
Do I need a load for this test ?
Of course.
I used two different metters to compare.
Current is 10mA and the zeners do not reach the indicated value.
Using the same setup, leds work pefectly... 4 leds = 7.7v
I used two different metters to compare.
Current is 10mA and the zeners do not reach the indicated value.
Using the same setup, leds work pefectly... 4 leds = 7.7v
Low voltage zeners need a huge amount of current to wake them up - at least 20ma - their "knees" are very soft and sloppy. LEDs have much lower incremental impedance. As an alternative to using LEDs, try the reverse base-emitter junction of a transistor like the 2N3904 - it yields an extremely sharp zener of 7.5-8V, and it only requires a ma or two.
Thank you wrenchone
Does the 2N3904 provide less noise than the equivalent led string ?
Ricardo
Does the 2N3904 provide less noise than the equivalent led string ?
Ricardo
My goodness... Thank you so much Salas.
can I expext the zeners to maintain its voltage in time with just 10mA?
If so I will choose the best / lower part count possible.
can I expext the zeners to maintain its voltage in time with just 10mA?
If so I will choose the best / lower part count possible.
Doesn't our 8V2 stay steady with the about 10mA IDSS CCS? Works till now. Why not others? You will tell after putting them in. The goal is to listen if some noise was escaping the bypass or not, bcs unfortunately our needed bias coincides with noisy single Zener nominal voltages. If it is escaping enough, maybe you will get more analysis by a simple move. If not, well we will know not to bother.😉