Increasing ESP P3A input impedance

christian.lenci · 3rd February 2009, 11:48 PM

Hi all,
having a tube preamp with an output impedance of 5k or so, I just wanted to ask what do you think about increasing the P3A input impedance (~24K) to ~49K by increasing R2 to 47K. Obviously R5 would become 47K too, and R4 would be raised to 2k2 to mantain the same gain. C2 would be changed accordingly.

Would this be too detrimental for the amp's noise perfomance?

Thank you all,
Christian

AKSA · 3rd February 2009, 11:57 PM

Christian,

Might make 0.5dB difference. All my AKSAs, Lifeforce and Soraya power amps have 47K nominal impedance.

Insignificant in the scheme of things. Try it.

Hugh

martinbls · 6th March 2010, 10:43 AM

Quote:

Originally Posted by christian.lenci

Hi all,
having a tube preamp with an output impedance of 5k or so, I just wanted to ask what do you think about increasing the P3A input impedance (~24K) to ~49K by increasing R2 to 47K. Obviously R5 would become 47K too, and R4 would be raised to 2k2 to mantain the same gain. C2 would be changed accordingly.

Would this be too detrimental for the amp's noise perfomance?

Thank you all,
Christian

Hi!

I would like to do same thing on my P3A, but something isn't clear to me...

To achieve an input impedance of ~49k I would have to:
- increase R2 to 47k
- increase R5 to 47k
- increase R4 to 2,2k

Nothing more than that?

What does "C2 would be changed accordingly" mean?

What is the general disadvantage of a higher input impedance, e.g. why is the input impedance of most power amps around 20k and not around 50k, which would obviously be much better suited for source equipment with BOTH low and high output impedances, and of course it would make the use of passive pre's much easier.

Thanks a lot!!

Martin

AKSA · 6th March 2010, 11:23 AM

Not sure what C2 is; if it's the input cap, you can halve it; if it's the feedback shunt cap, same again......

Hope this helps,

Hugh

martinbls · 6th March 2010, 03:52 PM

Hello Hugh,

thanks for your reply!

C2 is a small ceramic from input to ground (parallel to R2) and it's 100pF in the original schematic.

richie00boy · 6th March 2010, 04:38 PM

C2 should remain untouched, it is C1 and C3 which need attention. However, you may find leaving them untouched is fine as it will just result in lower cut-off.

jaycee · 6th March 2010, 05:45 PM

Personally, i think with it's CFP output, making any change is asking for trouble

AKSA · 6th March 2010, 10:36 PM

Changes on the fb and input side should not affect the CFP output stage operation at all.

Hugh

3rd February 2009, 11:48 PM	#1
christian.lenci diyAudio Member Join Date: Nov 2008	Increasing ESP P3A input impedance Hi all, having a tube preamp with an output impedance of 5k or so, I just wanted to ask what do you think about increasing the P3A input impedance (~24K) to ~49K by increasing R2 to 47K. Obviously R5 would become 47K too, and R4 would be raised to 2k2 to mantain the same gain. C2 would be changed accordingly. Would this be too detrimental for the amp's noise perfomance? Thank you all, Christian

3rd February 2009, 11:57 PM	#2
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Christian, Might make 0.5dB difference. All my AKSAs, Lifeforce and Soraya power amps have 47K nominal impedance. Insignificant in the scheme of things. Try it. Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

6th March 2010, 11:23 AM	#4
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Not sure what C2 is; if it's the input cap, you can halve it; if it's the feedback shunt cap, same again...... Hope this helps, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

6th March 2010, 04:38 PM	#6
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	C2 should remain untouched, it is C1 and C3 which need attention. However, you may find leaving them untouched is fine as it will just result in lower cut-off. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

6th March 2010, 10:36 PM	#8
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Changes on the fb and input side should not affect the CFP output stage operation at all. Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

6th March 2010, 03:52 PM	#5
martinbls diyAudio Member Join Date: Feb 2009	Hello Hugh, thanks for your reply! C2 is a small ceramic from input to ground (parallel to R2) and it's 100pF in the original schematic.

6th March 2010, 05:45 PM	#7
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Personally, i think with it's CFP output, making any change is asking for trouble

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Increasing input Z on Leach amp	WithTarragon	Solid State	5	19th October 2008 04:01 PM
DI guitar direct input box - increasing gain?	bubbamc119	Instruments and Amps	10	30th June 2005 01:22 AM
Increasing inductor impedance.	Tor M	Multi-Way	2	2nd April 2005 07:54 PM
increasing o/p impedance to match IT??	AudioGeek	Tubes / Valves	3	10th July 2004 07:15 PM
Increasing Aleph 3 input impedance	Freddie	Pass Labs	5	29th August 2001 10:52 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read