A CFB BJT preamp - any comments?

PMA · 21st June 2006, 07:58 AM

Here it goes:

peranders · 21st June 2006, 08:04 AM

First: 100 ohms input impedance? A bit low, don't you think?

Second: As amp it will work but you must consider different transistors (not 100% alike) and establish working conditions.

Your design is pretty much alike mine and it works splendidly. As pointed out earlier, the power supply must be clean due to poor PSRR.

You must have 22-47 pF at least from the Q11, Q12 collectors down to ground in order to get a nice step response.

PMA · 21st June 2006, 08:06 AM

Per,

an experienced designer like you knows that there is a high impedance input (+IN) at emmiters of Q1-Q2.

peranders · 21st June 2006, 08:10 AM

Since it's an inverting amp R2 is more or less the input impedance, yes

Q1, Q2 is grounded, yes?

PMA · 21st June 2006, 08:17 AM

Any problem to ground R2 and have input at Q2-Q3 emitters, resulting in non-inverting amp??

The circuit is a hint, not a cookbook.

PMA · 21st June 2006, 08:23 AM

is here:

peranders · 21st June 2006, 08:27 AM

That's better if you really ment "non-inverting" but what sort of comments did you want?

PMA · 21st June 2006, 08:34 AM

There is a difference in behaviour of non-inverting and inverting circuit of this kind. For gain like 10x it does not matter, for 1x the inverting behaves much better. We could increase input impedance of the inverting to some 1k and FB to 10k and still having excellent parameters. Buffer at the input would be needed. Not a case for non-inverting.

What kind of comments? This is a "PIM-free" topology

peranders · 21st June 2006, 09:07 AM

10k is probably too much if you want max speed out of the amp.

PMA · 21st June 2006, 03:39 PM

10k would result in >200kHz BW, not SR limited. You may stay non-inverting with 1k FB resistor and BW >>2MHz.

21st June 2006, 08:04 AM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	First: 100 ohms input impedance? A bit low, don't you think? Second: As amp it will work but you must consider different transistors (not 100% alike) and establish working conditions. Your design is pretty much alike mine and it works splendidly. As pointed out earlier, the power supply must be clean due to poor PSRR. You must have 22-47 pF at least from the Q11, Q12 collectors down to ground in order to get a nice step response. __________________ /Per-Anders (my first name) or P-A as my friends call me

21st June 2006, 08:10 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Since it's an inverting amp R2 is more or less the input impedance, yes Q1, Q2 is grounded, yes? __________________ /Per-Anders (my first name) or P-A as my friends call me

21st June 2006, 08:27 AM	#7
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	That's better if you really ment "non-inverting" but what sort of comments did you want? __________________ /Per-Anders (my first name) or P-A as my friends call me

21st June 2006, 09:07 AM	#9
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	10k is probably too much if you want max speed out of the amp. __________________ /Per-Anders (my first name) or P-A as my friends call me

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


	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

21st June 2006, 08:06 AM	#3
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Per, an experienced designer like you knows that there is a high impedance input (+IN) at emmiters of Q1-Q2.

21st June 2006, 08:17 AM	#5
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Any problem to ground R2 and have input at Q2-Q3 emitters, resulting in non-inverting amp?? The circuit is a hint, not a cookbook.

21st June 2006, 08:34 AM	#8
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	There is a difference in behaviour of non-inverting and inverting circuit of this kind. For gain like 10x it does not matter, for 1x the inverting behaves much better. We could increase input impedance of the inverting to some 1k and FB to 10k and still having excellent parameters. Buffer at the input would be needed. Not a case for non-inverting. What kind of comments? This is a "PIM-free" topology

21st June 2006, 03:39 PM	#10
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	10k would result in >200kHz BW, not SR limited. You may stay non-inverting with 1k FB resistor and BW >>2MHz.

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

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Good supply for preamp, Comments?	Algar_emi	Solid State	229	26th July 2003 07:16 PM
Gainclone as a preamp & power amp - comments please.	UncleJessie	Chip Amps	1	13th July 2003 03:13 AM
Comments on a preamp design	mpeg7	Tubes / Valves	9	17th September 2002 10:46 AM

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