Pre amp scematic...help

recks · 11th January 2011, 01:07 AM

hi guys
i am new to the world of audio electronics and was wondering if you could shed some light on the following schematic i have been given as part of an assignment. i am roughly confident with the phantom power part ( capacitors used to block dc signals and act as a filter to remove noise right? aswell as the resitors attenuating power/noise right? pretty confused with the pad part as to why the 220resistor has the option to be connected or not, the rest im pretty uncertain on. if any one could take me throught the flow of the circuit and why such components r used i would be eternaly grateful.

part of the brief below if any1 feels like doing any of the math and explainig how i would again be very grateful but the signal flow would very very grateful
thanks a lot
stevie
should produce a report describing, analysing and calculating the provided
circuit to prove theory of operation and design choice. The preamp should be compared to
existing designs and should be described at component level with supporting math and
technical referencing. You can also provide real world measurements and sound clips to aid
your discussion of the provided circuit.

Areas to discuss include:

Phantom Power
Transformer Ratio
Impedance Reflection
Loading - Fixed, Reflected, Variable and Capacitive
Common Mode Rejection
Balanced to Unbalanced Connection
Mic to Pre Source/Load Relationship
Gain Stages – Feedback Control
Frequency Shaping of Gain
Gain (Av) and dB
Gain Bandwidth
Frequency Response
Distortion – Clipping, Headroom (Maximum Operating Levels) and Magnetic Saturation
AC Coupling / DC Blocking

recks · 11th January 2011, 04:01 PM

any help?

DF96 · 11th January 2011, 04:52 PM

If we do this for you do we get the marks instead of you?

recks · 11th January 2011, 05:47 PM

haha sorry i no seems like a bit much. i wasn't expecting any1 to really go in 2 deep. but if any1 could help with with a brief explanation of the components used it would be great, just quite confused about the gain stages and the numerous resistors and capacitors

BobEllis · 06:23 PM

Rs in series with pots limit adjustment range - perhaps to avoid problems.

There are some RC combinations that serve to limit bandwidth, as well as reduce gain at high frequencies.

There are caps to ground that reduces gain to 1 at DC.

A pot+R and other Rs to set the load seen by the input

Caps to block DC seen by the output. Bonus points if you figure out why two of such different values.

There are Rs to limit current and some to set gain.

There are Cs to filter noise

Now you need to figure out which are which.

VictoriaGuy · 11th January 2011, 06:07 PM

Quote:

Originally Posted by recks

haha sorry i no seems like a bit much. i wasn't expecting any1 to really go in 2 deep. but if any1 could help ...............

Well, it seems you are too lazy to type complete words, and too lazy to do your school assignments as well.....
Not very promising......

Mooly · 11th January 2011, 06:35 PM

Quote:

Originally Posted by VictoriaGuy

Well, it seems you are too lazy to type complete words, and too lazy to do your school assignments as well.....
Not very promising......

N1 (ALOL)

Recks

U C THIS ISNT TWTR U NO (BYKTC)

recks · 11th January 2011, 06:47 PM

sorry i thought it was slightly more acceptable on the internet..didn't mean to get any panties in a twist

. thanks for your reply bob the circuit is begining to make a lot more sense. i wasn't aware that it mattered that too much if the capacitors were of different values...only that one removed high frequencys like mains hum and the other outside interference like radio ...im probably wrong about that to.
il refrain from posting anymore, i was only asking for a push in the right direction

Mooly · 11th January 2011, 07:00 PM

Quote:

Originally Posted by recks

il refrain from posting anymore, i was only asking for a push in the right direction

Keep posting

But remember you learn by experience and by doing and measuring... and making mistakes... there are no shortcuts... it all becomes a lifetimes knowledge.

BobEllis · 11th January 2011, 07:31 PM

You'll often see a moderate value film cap in parallel with an electrolytic. The purpose is pretty much as you surmised. Electrolytics are relatively cheap and small, allowing a great deal of capacitance in a small package. The downside is that they often have poor high frequency performance. Place a film cap parallel and you only need a small capacitance to handle the high frequencies. You could do it all with a film cap, but it would be expensive and huge. BTW, mains hum is low frequency.

11th January 2011, 01:07 AM	#1
recks diyAudio Member Join Date: Jan 2011	Pre amp scematic...help hi guys i am new to the world of audio electronics and was wondering if you could shed some light on the following schematic i have been given as part of an assignment. i am roughly confident with the phantom power part ( capacitors used to block dc signals and act as a filter to remove noise right? aswell as the resitors attenuating power/noise right? pretty confused with the pad part as to why the 220resistor has the option to be connected or not, the rest im pretty uncertain on. if any one could take me throught the flow of the circuit and why such components r used i would be eternaly grateful. part of the brief below if any1 feels like doing any of the math and explainig how i would again be very grateful but the signal flow would very very grateful thanks a lot stevie should produce a report describing, analysing and calculating the provided circuit to prove theory of operation and design choice. The preamp should be compared to existing designs and should be described at component level with supporting math and technical referencing. You can also provide real world measurements and sound clips to aid your discussion of the provided circuit. Areas to discuss include: Phantom Power Transformer Ratio Impedance Reflection Loading - Fixed, Reflected, Variable and Capacitive Common Mode Rejection Balanced to Unbalanced Connection Mic to Pre Source/Load Relationship Gain Stages – Feedback Control Frequency Shaping of Gain Gain (Av) and dB Gain Bandwidth Frequency Response Distortion – Clipping, Headroom (Maximum Operating Levels) and Magnetic Saturation AC Coupling / DC Blocking

11th January 2011, 06:04 PM	#5
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	Rs in series with pots limit adjustment range - perhaps to avoid problems. There are some RC combinations that serve to limit bandwidth, as well as reduce gain at high frequencies. There are caps to ground that reduces gain to 1 at DC. A pot+R and other Rs to set the load seen by the input Caps to block DC seen by the output. Bonus points if you figure out why two of such different values. There are Rs to limit current and some to set gain. There are Cs to filter noise Now you need to figure out which are which. Last edited by BobEllis; 11th January 2011 at 06:23 PM.

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11th January 2011, 04:01 PM	#2
recks diyAudio Member Join Date: Jan 2011	any help?

11th January 2011, 04:52 PM	#3
DF96 diyAudio Member Join Date: May 2007	If we do this for you do we get the marks instead of you?

11th January 2011, 05:47 PM	#4
recks diyAudio Member Join Date: Jan 2011	haha sorry i no seems like a bit much. i wasn't expecting any1 to really go in 2 deep. but if any1 could help with with a brief explanation of the components used it would be great, just quite confused about the gain stages and the numerous resistors and capacitors

11th January 2011, 06:47 PM	#8
recks diyAudio Member Join Date: Jan 2011	sorry i thought it was slightly more acceptable on the internet..didn't mean to get any panties in a twist . thanks for your reply bob the circuit is begining to make a lot more sense. i wasn't aware that it mattered that too much if the capacitors were of different values...only that one removed high frequencys like mains hum and the other outside interference like radio ...im probably wrong about that to. il refrain from posting anymore, i was only asking for a push in the right direction

11th January 2011, 07:31 PM	#10
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	You'll often see a moderate value film cap in parallel with an electrolytic. The purpose is pretty much as you surmised. Electrolytics are relatively cheap and small, allowing a great deal of capacitance in a small package. The downside is that they often have poor high frequency performance. Place a film cap parallel and you only need a small capacitance to handle the high frequencies. You could do it all with a film cap, but it would be expensive and huge. BTW, mains hum is low frequency.

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