THERMAL COMPENSATION OF Vbe MULTIPLIER

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#61
anatech said:
Hi Fotios,
I strongly agree with Jan here. Just use a good foil / film cap here. The smaller it is, the less trouble it will cause. This is just to say that if you need a 1 uF, don't install a 100 uF to lower the cutoff point.

Hi Nordic,
Again, Jan has steered you along the right road. Look at your circuit to chassis coupling. Using two main supplies will only complicate the grounding. Don't forget that L and R grounds are connected together in the preamplifier.

-Chris
Click to expand...

Hi Chris

Be quiet. I am not to omit the input capacitor. What I wrote before is owed in my vexation at the moment. I can understand absolutely his usefulness now that am calm. BTW according your opinion for 2,2mF input cap how much must be the input resistor for a good roll off down to 5 – 10 Hz? From my calculations a value between 50 to 100Kohms it appears that is good.

Fotios
 
#62
Hi,
I aim for 1 to 2Hz.
I get that by adopting 80 to 90mS RC time constant.

2u2F & 39k land right in the middle of that range.
This achieves -1db <4Hz if the input filter sets the LF roll-off.

But if you have a second DC block elsewhere, you must take that into account.
 
#63
Nordic said:
I hope we get to see your nice pre... DIM (do it myself) is no fun 😀

I am thinking of rebuilding my Preamp too....
Click to expand...

Hi Nordic

If you mean my preamplifier, make patience for few days because one very good friend and very good in microcontrollers, he undertook to program a PIC for me and in particular with additional possibilities apart from relays and LCD display control. It has included an additional optional program part for the handling of PGA 2311 of Burr Brown (stereo audio volume control) or the AD840x (digital potentiometers) of Analog Devices. From that I see in all the preamplifiers of last generation the designers use these chips while the volume knob it is a simple encoder. Make little patience and if you do not have a programmer I send you a ready programmed PIC as well the complete control circuit. BTW have any of you experience about the quality of Burr Brown PGA2311 and Analog Devices AD840x?

Fotios
 
#64
Sorry I don't have knowledge of those chips.... I do have a PIC programmer though
 

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#65
AndrewT said:
Hi,
I aim for 1 to 2Hz.
I get that by adopting 80 to 90mS RC time constant.

2u2F & 39k land right in the middle of that range.
This achieves -1db <4Hz if the input filter sets the LF roll-off.

But if you have a second DC block elsewhere, you must take that into account.
Click to expand...

Andrew you are using the equation: t = 1,1 X R X C ok? I quote bellow the schematic of input for not we make mistake. The output of network connected directly in the base of the input transistor of difference amplifier. Sorry for the enormous size of the schematic

Fotios

An externally hosted image should be here but it was not working when we last tested it.
 
#68
Hi Fotios,
I am trying to learn how to program those PIC chips. Just bought a couple off Eeeekbay. 😀 I'd like to build a remote preamp as you are. I think I'd rather use a motorized volume control.

The Burr Brown PGA2311 is supposed to be good, but I am distrustful of semiconductor signal switching and level control. It is the only way for multichannel it seems.

-Chris
 
#69
anatech said:
Hi Fotios,
I am trying to learn how to program those PIC chips. Just bought a couple off Eeeekbay. 😀 I'd like to build a remote preamp as you are. I think I'd rather use a motorized volume control.

The Burr Brown PGA2311 is supposed to be good, but I am distrustful of semiconductor signal switching and level control. It is the only way for multichannel it seems.

-Chris
Click to expand...

Hey Chris
I don't forget no one of my colleagues 😀, when i get the trial board from my friend and i checked that it operates rightly i will send and to you if you want a programmed PIC (and the code separately in the case you want to make job) and the complette schematic of the whole control. I wish and i like to make gifts in my friends. And you are one of those.
BTW if you have seen photos of X0.2 preamp of Pass Labs, it is obvious the presence of such volume control ICs. I can't distinguish the type but i am sure because there are 6 of these connected directly to MCU. Also it is obvious the presense of the encoder in the volume knob. I am sure that this preamp which costs 9400euros in Greece and considered as a top device uses ICs for volume control.
Fotios
 
#71
AndrewT said:
that looks familiar.
Is that the timing of a 555 chip?

Don't bother with the factor 1.1* just use the R*C.
Click to expand...

Thanks Andrew. One question more. The second resistor 18K does not take place in the input filter? If it is so, then we have a third order filter and the calculations may be revised?
Fotios
 
#72
Hi Fotios,
Thank you!

I am looking at programmers right now, I just wish I had a clue about these things. I'd like to do other things too, so a file with the code should be all I need. That and the target device number. 😉

I should peek into the digital forum and try and learn something. Analog -no problem! uP's = big problem where programming comes in.

I did build a programmer for Dallas chips and program (load code only). I bought an EMP10 programmer for loading Atmel chips and some eproms. I just have no clue how to write the code for them.

-Chris
 
#73
fotios said:
The second resistor 18K does not take place in the input filter? If it is so, then we have a third order filter and the calculations may be revised?
Click to expand...
The second resistor is the high pass filter.
R=18k and C=C If C=2u2F then RC=1.8*10^4*2.2*10^-6=4*10^-2=0.04=40mS F-1db~8Hz.
the first resistor is simply there to attenuate the DC that might appear on the open ended socket if the cable is disconnected. I tend to use >1M The Zin=1M//18k.
If there is a DC blocking capacitor in the source then the 1M forms a high pass filter with that earlier series capacitor.
 
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