Preamp concept - Page 11

PMA · 3rd November 2006, 03:06 PM

Sorry, you are right. Small capacitors are 100nF ceramics. Electrolytes are 1000 uF (see photo of the preamp).

Pot is 5k or 10k. Do not go higher than 10k.

marsel · 3rd November 2006, 06:27 PM

Thank you

PMA · 3rd November 2006, 06:33 PM

MaxS,

I have made my audiopage working again

.

But I have to apologize to the readers - sometimes I am really not able to respond, being pretty engaged in my professional projects ...

marsel · 8th November 2006, 02:06 AM

Oh one more thing what's the connection for little pots. Which lead is connected to the regulation (trim lead)?

and does it matter if 1 or 3 is first?

PMA · 8th November 2006, 06:07 AM

The small trimpots (R9 and R25, or R2 in "values.gif") are used for fine setting of gain - to match gain of both channels. They work as variable resistors, you do not have to care how to connect the middle pin - left or right end, does not matter.

marsel · 8th November 2006, 06:50 PM

I understand that the value that has to be set by these vresistors is 20 mA as shown in the schematic?

marsel · 8th November 2006, 07:22 PM

I wonder why have you put R42 and R38 together instead of one resistor?

I bet it's because U had such values in stock

.

Or is this value to be realy precise 1K97.

I thought about putting there 1K91 ( I can get this value) and it will be within 1% tolerance.

Am I clever

PMA · 8th November 2006, 08:10 PM

These resistors set DC at Q3 collector. It is easier to do it by 2 in series than by 1, as the value has to be set quite precisely.

marsel · 9th November 2006, 07:22 PM

Pavel

I have another question>

What if I changed in-capacitors and out-cap value.

e.g I would like to put there black gates N but there are no such values.

And does the in cap is not as important as out cap.
According to the picture you have put odinary mkp (wima?)cap at the input.

Wouldn't it be better to put pot instead of one of resistors for DC setting?

PMA · 9th November 2006, 07:31 PM

If you change these values, make them higher, never lower. The choice of cap types is up to you.

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3rd November 2006, 03:06 PM	#101
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Sorry, you are right. Small capacitors are 100nF ceramics. Electrolytes are 1000 uF (see photo of the preamp). Pot is 5k or 10k. Do not go higher than 10k.

3rd November 2006, 06:27 PM	#102
marsel diyAudio Member Join Date: Jan 2006 Location: WORTHING	Thank you

3rd November 2006, 06:33 PM	#103
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	MaxS, I have made my audiopage working again . But I have to apologize to the readers - sometimes I am really not able to respond, being pretty engaged in my professional projects ...

8th November 2006, 02:06 AM	#104
marsel diyAudio Member Join Date: Jan 2006 Location: WORTHING	Oh one more thing what's the connection for little pots. Which lead is connected to the regulation (trim lead)? and does it matter if 1 or 3 is first?

8th November 2006, 06:07 AM	#105
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	The small trimpots (R9 and R25, or R2 in "values.gif") are used for fine setting of gain - to match gain of both channels. They work as variable resistors, you do not have to care how to connect the middle pin - left or right end, does not matter.

8th November 2006, 06:50 PM	#106
marsel diyAudio Member Join Date: Jan 2006 Location: WORTHING	I understand that the value that has to be set by these vresistors is 20 mA as shown in the schematic?

8th November 2006, 07:22 PM	#107
marsel diyAudio Member Join Date: Jan 2006 Location: WORTHING	I wonder why have you put R42 and R38 together instead of one resistor? I bet it's because U had such values in stock . Or is this value to be realy precise 1K97. I thought about putting there 1K91 ( I can get this value) and it will be within 1% tolerance. Am I clever

8th November 2006, 08:10 PM	#108
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	These resistors set DC at Q3 collector. It is easier to do it by 2 in series than by 1, as the value has to be set quite precisely.

9th November 2006, 07:22 PM	#109
marsel diyAudio Member Join Date: Jan 2006 Location: WORTHING	Pavel I have another question> What if I changed in-capacitors and out-cap value. e.g I would like to put there black gates N but there are no such values. And does the in cap is not as important as out cap. According to the picture you have put odinary mkp (wima?)cap at the input. Wouldn't it be better to put pot instead of one of resistors for DC setting?

9th November 2006, 07:31 PM	#110
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	If you change these values, make them higher, never lower. The choice of cap types is up to you.