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Controlling gain in VA stage

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deicide67

Member
Joined 2008
AikidoAmp3.gif

I built this a while ago, and it sounds pretty nice. The only issue is the gain is crazy high. Is there a way to tame down the gain in the first stage of this preamp?

Thanks for any ideas!

Blair
 
rayma

rayma

Moderator
Joined 2011
deicide67 said:
The only issue is the gain is crazy high.
Is there a way to tame down the gain in the first stage of this preamp?
Click to expand...

Are you using a linear pot at the input? This would make it seem as though you can't easily adjust the gain.
Use a standard audio taper volume control instead.

The circuit only has 20dB of gain, and that's not enough to use global NFB unless you want near unity gain.
 
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Eli Duttman

Member
Joined 2004
deicide67 said:
I can now use about 1/4 of the rotation on the pot. Before, it launched straight to insane just as the wipers started to catch. The amp is an Emotiva and I think the spec is 1.2v to full power.
Click to expand...

Are your speakers fairly sensitive? 1.2 V. for full power is not especially sensitive.

It's easy enough to gain more utility out of the volume control. "Pad" the control by inserting a low noise 47 Kohm resistor in the line between the I/P jack and the "top" of the potentiometer. The "padder" will attenuate the I/P signal by roughly 6 dB.
 
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deicide67

Member
Joined 2008
Hi Eli,

Long time! It may be more sensitive. Have no idea where the paperwork is. I know Mac has .5v to full power along with other manufacturers.

My speakers are not super efficient either, but in a small room which makes it feel a bit more obvious with volume changes.

I will definitely try the padding resistors.

Thanks!
 
Palustris

Palustris

Member
Joined 2006
I would suggest that you map out the gain structure of your amplifying chain from the output of the source to the output tube's driver stage. What is the input sensitivity of your power amp? We know that the source, if it is a CD player, has an output of 2VRMS. If your power amp has a sensitivity of <2 VRMS, you probably don't even need this preamp. If the input sensitivity is <1 VRMS you definitely don't need any more gain in the system. Figure out how much gain you need and add no more than necessary because you will just attenuate it in the volume control.
 
disco

disco

Member
Joined 2006
Palustris said:
I would suggest that you map out the gain structure of your amplifying chain from the output of the source to the output tube's driver stage. What is the input sensitivity of your power amp? We know that the source, if it is a CD player, has an output of 2VRMS. If your power amp has a sensitivity of <2 VRMS, you probably don't even need this preamp. If the input sensitivity is <1 VRMS you definitely don't need any more gain in the system. Figure out how much gain you need and add no more than necessary because you will just attenuate it in the volume control.
Click to expand...

Monitoring CDP output levels of popular music on my scope hardly exceeds 1 to 1,5 Vpp. That would translate to 0,4Vrms. Do I need new glasses or is something else going on?
 
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