ONE MORE P3A QUESTION

sakis · 4th August 2011, 11:31 AM

here is another P3A related question

What can be done to achive an input imp. of about 100K without altering the safety status of the amplifier ?

Idea is that with 100k input the amp is going to be way too friendly for passive preamps and/or make a wonderfull pair with B1 buffer ....

kind regards sakis

ot remind the schematic

lineup · 4th August 2011, 11:38 AM

R2=100k
R5=100k
R4=4.7k
C3=22uF

would keep the dc-offset and gain, but make input impedance 100k

C1 could also be lower ~1uF or 2.2uF

AndrewT · 4th August 2011, 11:53 AM

I recommend similar. Just a few minor adjustments.
C1=1uF & R1=100k.
R5=100k, R4=4k7, C3>=33uF.
C2 & R3 adjust to taste.

sakis · 4th August 2011, 01:14 PM

yeap this was my approach too ...

a) please comment on the idea
b) please comment regarding theissue of safety IE anyone things that this might effect stability of the amp?

thanks for your help

sakis

AndrewT · 4th August 2011, 01:22 PM

I don't recognise any safety issue by substituting any of those component values.

Line2 of post3 shows R1=100k. This must be changed to R2=100k. Sorry.

Just noticed you posted an ESP schematic.
Ask him first.

sakis · 4th August 2011, 01:33 PM

The particular schematic is not protected .... its free in the internet ...

Thanks for your help Andrew .

kind regards sakis

AndrewT · 4th August 2011, 01:41 PM

Go and read ESP site.
One of the conditions of using the information he provides freely, is that you agree to not reproduce his drawings as you have done in your post.

sakis · 4th August 2011, 01:57 PM

i apologize for that probably i have been reading it but dont remember

Moderators please remove my post or schematic .

Thanks Andrew for the notice .

Kind regards sakis

homemodder · 4th August 2011, 02:58 PM

Noise will be considerably worse, some hiss may come about.

Ian Finch · 05:53 PM

Or, to keep the amplifier running as present, you could bootstrap the input as per Self's illustration. Chapter 4 in the current 5th edition of his Audio Power Amp. Design Handbook. I haven't tried it but this should keep internal noise at present level while matching to the higher impedance set by the resistive divider added at the input. ..... BTW, It's also part of the trimodal amplifier, if your edition is earlier.

4th August 2011, 11:31 AM	#1
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	ONE MORE P3A QUESTION here is another P3A related question What can be done to achive an input imp. of about 100K without altering the safety status of the amplifier ? Idea is that with 100k input the amp is going to be way too friendly for passive preamps and/or make a wonderfull pair with B1 buffer .... kind regards sakis ot remind the schematic __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

4th August 2011, 11:38 AM	#2
lineup diyAudio Member Join Date: Dec 2005 Location: the north	R2=100k R5=100k R4=4.7k C3=22uF would keep the dc-offset and gain, but make input impedance 100k C1 could also be lower ~1uF or 2.2uF __________________ lineup

4th August 2011, 11:53 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I recommend similar. Just a few minor adjustments. C1=1uF & R1=100k. R5=100k, R4=4k7, C3>=33uF. C2 & R3 adjust to taste. __________________ regards Andrew T.

4th August 2011, 01:14 PM	#4
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	yeap this was my approach too ... a) please comment on the idea b) please comment regarding theissue of safety IE anyone things that this might effect stability of the amp? thanks for your help sakis __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

4th August 2011, 01:22 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I don't recognise any safety issue by substituting any of those component values. Line2 of post3 shows R1=100k. This must be changed to R2=100k. Sorry. Just noticed you posted an ESP schematic. Ask him first. __________________ regards Andrew T.


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4th August 2011, 01:33 PM	#6
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	The particular schematic is not protected .... its free in the internet ... Thanks for your help Andrew . kind regards sakis __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

4th August 2011, 01:41 PM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Go and read ESP site. One of the conditions of using the information he provides freely, is that you agree to not reproduce his drawings as you have done in your post. __________________ regards Andrew T.

4th August 2011, 01:57 PM	#8
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	i apologize for that probably i have been reading it but dont remember Moderators please remove my post or schematic . Thanks Andrew for the notice . Kind regards sakis __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

4th August 2011, 02:58 PM	#9
homemodder diyAudio Member Join Date: May 2006	Noise will be considerably worse, some hiss may come about.

4th August 2011, 05:29 PM	#10
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	Bootstrap Or, to keep the amplifier running as present, you could bootstrap the input as per Self's illustration. Chapter 4 in the current 5th edition of his Audio Power Amp. Design Handbook. I haven't tried it but this should keep internal noise at present level while matching to the higher impedance set by the resistive divider added at the input. ..... BTW, It's also part of the trimodal amplifier, if your edition is earlier. __________________ regards Last edited by Ian Finch; 4th August 2011 at 05:53 PM. Reason: add ref.

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