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Versatile and comfortable passive pre-amp

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udailey

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Joined 2008
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DC offset through a LDR attenuator should be absolutely the same as the output from your source so if you remove the attenuator and measure that of the source you will see what you should be getting when the attenuator is attached. If your source does not have a DC offset problem AND there is a DC offset problem at the output of your LDR attenuator then something is WRONG and pictures are required. Good pictures.
 
Rudi_Ratlos

Rudi_Ratlos

Member
Joined 2009
Mat: the trim-potentiometer is o.k.
Uriah: I do not know about any situation that would "reset" the processor.
The processor has a reset input, but this input is pulled up to 5VDC according to the datasheet.

Ivan: your music source is connected to the leftmost relay, the standard name of which is "AUX".
So you must have changed the source via your remote control to access this relay.
The standard selection after PowerOn or Reset is the rightmost relay, which is associated with "CDP".
What is your display showing after increasing the volume? Does it still show "AUX"?

Best regards - Rudi
 
voxxonline

voxxonline

Member
Joined 2012
Hi.
It was the same both aux and cdp and after I inrease vol it shows attenuation.
Actually no need to vol increase as this effect kicks in any way.
I remember I still have the other ic (will send it back to you Rudi I promise) and it has the same problem.
Attenation shows as minus 16.
Actually it stays constant. Checked it now and while vol increase numbers remain same. Last time it was similar only dB increase appeared on the very end of turn of the pot.
For instance other ic had 0 dB constantly but I need to put it back again to confirm it.

Update: attenuation numbers change but it happens in the last 1/5 of the turn or even less
 
Last edited:
Rudi_Ratlos

Rudi_Ratlos

Member
Joined 2009
Ivan: the display of the volume attenuation does not work properly, as I have
mentioned many times before.
At low or normal volume level the increase of the volume results in a very, very small increase of current
(in the range of some µA) that flows through the LDRs - LED.
This small current-increase cannot be monitored by the MCP6021 and the µProcessor's internal A/D converter.

Only when you turn the volume very loud and each turn of the potentiometer results in some mA (!) increase
of LED-current, the display shows a change.

Is the display of the volume attenuation the only problem that you have?

Best regards - Rudi
 
N

nertia

Member
Joined 2010
Does the problem happen 30s after power on or 30s after music start? Seems odd that it takes time to occur unless something is happening in the meantime like a capacitor charging.

You could try it in another enclosure, that box looks quite shiny, maybe some sort of charge is building up?

Good luck,
Mat
 
A

Awh

Member
Joined 2011
Hi Voxx, C8 on the bom is a 2.2uF tant bead, the board i have has no polarity markings for that cap, you got it the right way around? looks like neg should go to the outside of the pcb.

With tantalum bead caps the +ve is marked unlike electrolytics (-ve).

Andrew
 
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