The problem with a pre amp is that it is many things to many people. You may want an active stage without gain, and three inputs, and a particular make/type of volume control. But there will be lots of people with different requirements.
And given the casework of most hi-fi projects is a major part of the job, and that that is personal preference too, you can probably see that it would not make for a successful business project to try and sell a pre amp kit.
That said, you can buy input selector modules, and kits to make a stepped attenuator. But because it is so much of a mix-and-match thing, you are on your own from there.
nickthevoice said:
Build an unbuffered amplifier and listen to it for a while. Then add a buffer and listen to it for a while. Decide for yourself which sounds better in your system. Adding a buffer is not difficult or costly.
nickthevoice said:
The same reason some people prefer to drive a Toyota instead of a Honda - it all comes down to personal opinion and what one chooses to buy.
This is slightly off topic, but -
Why don't people vary the gain resistors to vary the volume (in a non-inverting setup)?
For instance, I've been thinking about adding a few resistors and spdt switches to the grounding resistor (Ra of the 1 + Rb/Ra formula). That way, I could vary the volume without dumping any of the source or preamp signal. Is there a reason not to do this? I assume someone would have tried it already.
Right now, my gainclone is set with Rb and Ra of 22k and 680 ohm, giving a voltage gain of 33. I could add in series several 110 ohm resistors, and at the bottom of each resistor, a spdt switch connecting it to the next resistor, or ground. If I added 4 of these, I would get voltage gains of 33, 29, 25, 23, 21 (approximately)...
Why don't people vary the gain resistors to vary the volume (in a non-inverting setup)?
For instance, I've been thinking about adding a few resistors and spdt switches to the grounding resistor (Ra of the 1 + Rb/Ra formula). That way, I could vary the volume without dumping any of the source or preamp signal. Is there a reason not to do this? I assume someone would have tried it already.
Right now, my gainclone is set with Rb and Ra of 22k and 680 ohm, giving a voltage gain of 33. I could add in series several 110 ohm resistors, and at the bottom of each resistor, a spdt switch connecting it to the next resistor, or ground. If I added 4 of these, I would get voltage gains of 33, 29, 25, 23, 21 (approximately)...
Hi C,
some/many/most amplifiers, whether power or opamp, are stable over a (very) narrow range of gains.
The reactive load hung on the end of this can exacerbate the stability problem. If the load is always resistive and never changes you may be able to set up a wider range of gain and keep the same gain and phase margins over the whole operating range.
some/many/most amplifiers, whether power or opamp, are stable over a (very) narrow range of gains.
The reactive load hung on the end of this can exacerbate the stability problem. If the load is always resistive and never changes you may be able to set up a wider range of gain and keep the same gain and phase margins over the whole operating range.
i think peter daniel has built an amp where he adjusts the gain to control volume.
here are a couple of the links:
6moons link
image
there is another post with some more photos but i can't find it now.
i am pretty sure that the LM3875 chip is unstable with the gain below 10 so i wonder how low the volume goes?
here are a couple of the links:
6moons link
image
there is another post with some more photos but i can't find it now.
i am pretty sure that the LM3875 chip is unstable with the gain below 10 so i wonder how low the volume goes?
cuibono said:
If those gain values work well for you, I don't see a reason why not to try it.
You should also consider that when changing the amp's gain, it may also affect its sonic signature. The 33 value works well for me, the amp sounds great, so I'm not tempted in anyway to mess with that.
What I did in the amp from okapi's link, was to place fixed 10k series resistor and adjust the shunt resistor values only. So your regular 22k resistor has now values ranging from 5R to 22K allowing volume adjustments. Apart from adding Elma selector switch, nothing else has been changed in the amp, which still preserves sonic purity not compromised by adding a potentiometer.
Gain didn't change, the input impedance changes depending on volume setting but this does not have any practical importance, and most of the time input impedance is still around 18K.
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