Many people (including myself) believe in the less is more philosophy. The idea being that every component in the signal path has an effect on the sound. The effect can be good for some equipment and some listeners, but that is up to your ears and your setup.
On the good side, using a retail pre-amp/pre-outs has the benefits that you are unlikely to have impedance matching issues, you probably gain useful functionality like remote volume control and possibly (if it's important), surround decoding.
On the good side, using a retail pre-amp/pre-outs has the benefits that you are unlikely to have impedance matching issues, you probably gain useful functionality like remote volume control and possibly (if it's important), surround decoding.
You may not need either a pre-amp or a passive attenuator. A portable player with a built-in volume control (like an iPod) can be plugged directly into your amp. Pre-amps are more robust and give you more choices than a P.A. A passive attenuator may limit your choices of interconnect cables and of what units can be connected to what amplifiers.
That is the most important question that must be answered before looking at details and options.
Do you need extra gain between your source and your receiver?
Will attenuation and no extra gain be sufficient for all my sources?
If you do not need extra gain then do not provide it.
Use a unity gain active buffer plus attenuator or attenuator alone.
Do you need extra gain between your source and your receiver?
Will attenuation and no extra gain be sufficient for all my sources?
If you do not need extra gain then do not provide it.
Use a unity gain active buffer plus attenuator or attenuator alone.
A lot of people report that the LM3875/3886 type gainclone sounds better with an input buffer following the volume control.
If it's a real observation, it probably has more to do with the source component not having enough oomph to drive a passive setup than a problem with the LM3875/3886 themselves.
If it's a real observation, it probably has more to do with the source component not having enough oomph to drive a passive setup than a problem with the LM3875/3886 themselves.
your last statement is quite definitely true.
No decent power amplifier needs a buffer in front of it.
Most sources that have a poor or bad output stage that is not designed to drive cables can benefit greatly from a buffer on their output.
Volume potentiometers are not designed to drive cables.
If one want a cable between a pot and the amplifier then then it is usual to add a buffer to the pot output to drive the connecting cable.
Hi Andrew
Sorry if this is thread jacking
I am currently busy with a tube preamp for my turntable i would like to give this reamp a "volume control" My plan was to have a 100k pot at the ouput rca's.
why would this be bad?
I would not like to add a opamp buffer to my build. And i don't think it would be possibly to add a Pot to the input straight onto the low output of the turntable? or should I.
because the output impedance varies between 0k and 25k. This is very unlikely to be able to drive a cable with audio signal.
What is the output impedance of your tube/valve amplifier?
Has it got a buffer on it's output designed to drive cables?
Is there a location before the last active stage to insert a volume control without interfering with the operation of the amplifier?
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according to these equations:
Vacuum Tube Amplifier Circuits and Equations
an d3a tubes plate resistance of 1.9K ohm
the output impedance of the preamp is:
1.62k ohm ? can this be correct?
Vacuum Tube Amplifier Circuits and Equations
an d3a tubes plate resistance of 1.9K ohm
the output impedance of the preamp is:
1.62k ohm ? can this be correct?
output impedance = 1k62 is very possible.
50k sounds very unlikely for output impedance.
However 50k could be the recommended input impedance of the next stage.
More than 2Vac maximum output is not very high.
Most CD players have a maximum output >2Vac.
Most solid state pre-amps have a maximum output >>3Vac, 7Vac to 10Vac maximum is common for a SS output voltage.
Tube/valve can often have a maximum output around 30Vac. That is high in SS terms but not very high.
50k sounds very unlikely for output impedance.
However 50k could be the recommended input impedance of the next stage.
More than 2Vac maximum output is not very high.
Most CD players have a maximum output >2Vac.
Most solid state pre-amps have a maximum output >>3Vac, 7Vac to 10Vac maximum is common for a SS output voltage.
Tube/valve can often have a maximum output around 30Vac. That is high in SS terms but not very high.
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that's why I repeatedly recommend that beginners only build AC coupled amplifiers.
Leave DC coupling and all the extra bits till after one has learned to understand the operation of the amplifier.
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