Need to drop gain a couple of dB to unity?

[georgehifi]

Hi guys need to drop the gain of this (a couple of dB) to unity, without any effects on performance. Which resistor (s) to change up or down?
I figure it's r10 or r9?

Cheers George

 

[rayma]

You can't do that in the nfb network since it's a non-inverting topology, with a gain of (1+R10/R9).
You might consider R10 = 0 (a short), since it gets rid of capacitor C6 to ground in the nfb network.
The C6 doesn't really seem to be necessary anyway, with such low signal gain.

Or, you could change the input filter to have more loss by decreasing R4 or increasing R5.
Then the value of either C3 or C4 might need adjustment.

 

[scottjoplin]

Unity gain implies 100% feedback. What values are the resistors now for 2dB gain?

 

[georgehifi]

I don't know the values as it's back in the system, and would need to be stripped and then taken apart, all I did before it went in was compare the input to the output on my scope and it had a + a couple of dB gain. When it comes out I will measure R9 and R10.

Rayma, if I short R10 then C7 becomes redundant which is the HF filtering for stablity, isn't it?

Cheers George

 

[rayma]

Yes, but other measures can be taken, such as revising the values of R11, C9, and possibly C8.
I question whether C7 does much to improve stability, if the signal gain is so low (+2dB).
The phase bump would be very small.

If you like the circuit as-is, I'd just rework the input filter to have 2dB more midband attenuation.
It would only take changing the value of one resistor (R4 would be best) by about 20%.

 

[PRR]

Can't work as drawn. Fixed to a plausible plan.

 

[georgehifi]

Got this off the net, there is no others. It's a Musical Fidelity X10-V3 buffer.
If anyone has the real schematic, please post it up thanks.

Cheers George

 

[georgehifi]

If you like the circuit as-is, I'd just rework the input filter to have 2dB more midband attenuation.
It would only take changing the value of one resistor (R4 would be best) by about 20%.

Then the input impedance maybe too low for a passive to work into. And I also need total attenuation.

Cheers George

 

[DF96]

Simplest way of achieving unity gain is to remove all components between input and output, and replace with a piece of wire. This will have lower noise, lower distortion and wider bandwidth than the current circuit.

 

[12E1]

Simplest way of achieving unity gain is to remove all components between input and output, and replace with a piece of wire. This will have lower noise, lower distortion and wider bandwidth than the current circuit.

Lower power consumption and corresponding heating effects too.

 

[lcsaszar]

Is it a hybrid power amplifier?

 

[georgehifi]

Simplest way of achieving unity gain is to remove all components between input and output, and replace with a piece of wire. This will have lower noise, lower distortion and wider bandwidth than the current circuit.

Ha Ha, you just described my product, seriously there is a purpose behind this and I need answers not wise cracks, leave them for your plebs to pay out on.

Cheers George

 

[georgehifi]

Is it a hybrid power amplifier?

I's a MF X10-V3 buffer, uses the Mu-Vista 6112 tubes.

Cheers George

 

[aardvarkash10]

Simplest way of achieving unity gain is to remove all components between input and output, and replace with a piece of wire. This will have lower noise, lower distortion and wider bandwidth than the current circuit.

This. Classic.