S.s. Preamplifier No Feedback O.c.l.

andythefirst · 11th January 2006, 03:20 PM

Hi!
I'm looking for a schematic of a all solid state preamplifier, with approx the following requirements:

- only B.J.T. (no I.C.)
- approx amplification factor 20 times
- max output around 30 volt at minimum THD possible
- Output and interstage Capacitor Less
- low output impedance (around 10 Ohm or less)
- 100% No feedback

No problems with the power supply and budget.

Any schematic or at least ideas?

Thank you, regards!

Steve Eddy · 11th January 2006, 03:34 PM

A couple questions.

Why do you need a 30 volt output? Most every power amp out there has an input sensitivity of around 1-2 volts. Or are you planning to drive some sort of unity gain power buffer?

Also, how literally do you mean "100% no feedback"? Do you mean not even an emitter follower or do you just mean no loop feedback?

se

andythefirst · 11th January 2006, 04:05 PM

Hi!
Thanks for reply.

1)Yes, I need this preamplifier as a voltage amplifier for a current BJT buffer with gain = 0.95 approx.

2)I meant no global feedback, no interstage feedback, but just (if necessary...) local, device feedback.

Any help?

Regards.

Steve Eddy · 11th January 2006, 06:53 PM

Quote:

Originally posted by andythefirst
1)Yes, I need this preamplifier as a voltage amplifier for a current BJT buffer with gain = 0.95 approx.

Ah, ok. Now that makes sense.

Quote:

2)I meant no global feedback, no interstage feedback, but just (if necessary...) local, device feedback.

Ok, I see where you're coming from now.

Quote:

Any help?

Not sure yet. One more question. Do you have a schematic available for the BJT buffer you're using?

se

andythefirst · 12th January 2006, 07:41 AM

Hi!

The buffer I should drive, could be, approximately, the one I link to this message. It Is a stage found on the Net, I know lack in output protection and, eventually, a servo.

Carefully implemented, It works very well.

Now, we have to options:
- entering at same time on points "input A", in the preamplifier stage has two outputs,
- or entering, for example, on "input B", if the pre stage has only one output (Complementary BJT)

BUT, I don't want to use coupling capacitors.
And not I.C. Only BJT.

Sorry for beeing not so precise, and again thank you for reply!

andythefirst · 12th January 2006, 08:06 AM

Sorry, I don't know why for a 20K gif file the admin says "is too big..."

I'll try again later.

Netlist · 12th January 2006, 08:16 AM

The maximum resolution is 800X600, 100Kb IIRC. This could be your problem.

/Hugo

andythefirst · 12th January 2006, 08:42 AM

Thank You!

Here is the schematic...

rozak · 12th January 2006, 09:47 AM

May be this satisfy you?
Distortion 0.06% according to PSice.

andythefirst · 12th January 2006, 11:44 AM

Hello and thank you!

How much is in db the amount of interstage feedback?

In your proposal I must use, according to my schematic, the "INPUT B", is that right?

Is it possible to implemet the two "INPUT A", linking this to collectors of Q23 and Q27 on your schematic?

Thank you in advance for your kind answers!

Pardon, on more question:
I have got Micro Cap evaluation. Will your schematic work on it? And in this case, could you give me the usable file so I can try to simulate and link to it my buffer?

11th January 2006, 03:20 PM	#1
andythefirst diyAudio Member Join Date: Jan 2006 Location: Rome	S.s. Preamplifier No Feedback O.c.l. Hi! I'm looking for a schematic of a all solid state preamplifier, with approx the following requirements: - only B.J.T. (no I.C.) - approx amplification factor 20 times - max output around 30 volt at minimum THD possible - Output and interstage Capacitor Less - low output impedance (around 10 Ohm or less) - 100% No feedback No problems with the power supply and budget. Any schematic or at least ideas? Thank you, regards!

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11th January 2006, 03:34 PM	#2
Steve Eddy diyAudio Member Join Date: Sep 2002 Location: Sacramento, CA	A couple questions. Why do you need a 30 volt output? Most every power amp out there has an input sensitivity of around 1-2 volts. Or are you planning to drive some sort of unity gain power buffer? Also, how literally do you mean "100% no feedback"? Do you mean not even an emitter follower or do you just mean no loop feedback? se

11th January 2006, 04:05 PM	#3
andythefirst diyAudio Member Join Date: Jan 2006 Location: Rome	Hi! Thanks for reply. 1)Yes, I need this preamplifier as a voltage amplifier for a current BJT buffer with gain = 0.95 approx. 2)I meant no global feedback, no interstage feedback, but just (if necessary...) local, device feedback. Any help? Regards.

12th January 2006, 07:41 AM	#5
andythefirst diyAudio Member Join Date: Jan 2006 Location: Rome	Hi! The buffer I should drive, could be, approximately, the one I link to this message. It Is a stage found on the Net, I know lack in output protection and, eventually, a servo. Carefully implemented, It works very well. Now, we have to options: - entering at same time on points "input A", in the preamplifier stage has two outputs, - or entering, for example, on "input B", if the pre stage has only one output (Complementary BJT) BUT, I don't want to use coupling capacitors. And not I.C. Only BJT. Sorry for beeing not so precise, and again thank you for reply!

12th January 2006, 08:06 AM	#6
andythefirst diyAudio Member Join Date: Jan 2006 Location: Rome	Sorry, I don't know why for a 20K gif file the admin says "is too big..." I'll try again later.

12th January 2006, 08:16 AM	#7
Netlist diyAudio Moderator Join Date: Jan 2003	The maximum resolution is 800X600, 100Kb IIRC. This could be your problem. /Hugo

12th January 2006, 11:44 AM	#10
andythefirst diyAudio Member Join Date: Jan 2006 Location: Rome	Hello and thank you! How much is in db the amount of interstage feedback? In your proposal I must use, according to my schematic, the "INPUT B", is that right? Is it possible to implemet the two "INPUT A", linking this to collectors of Q23 and Q27 on your schematic? Thank you in advance for your kind answers! Pardon, on more question: I have got Micro Cap evaluation. Will your schematic work on it? And in this case, could you give me the usable file so I can try to simulate and link to it my buffer?

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