To Choose the Correct Stepped Attenuator Value. General Rules and Considerations:
upgrading from a potentiometer, use the same value stepped attenuator.
10K, 25K, 50K, 100K, etc.)
the volume control value to the amplifier/pre-amplifier input impedance
is not as important as some people think, so you typically don't really
have to worry about this. For a 100K
input impedance, use a 100K, 50K, 25K, or even a 10K level control.
This applies to passive preamps, active preamplifiers, and power
amplifiers when the control is to be installed at the input. Check your
owner's manual to find the the rated input impedance of your unit, or contact
the manufacturer directly. Our 25K stepped attenuator usually value replaces replaces 20K potentiometers.
the choice of stepped attenuator values in Goldpoint SA1, SA2,
(25K) and SA1X, SA2X (10K), much
observation and thought has gone into this over many years. We concluded
that the values which we are using for our standard off-the-shelf passive
preamps and precision level controls are the right values and should not
be changed (unless really necessary or preferred for some other reason).
Also, it can be said that plug and play in-line level controls (passive
preamps) are best with "lower value" stepped attenuators - making them
more compatible with a wider range of Input impedances they might encounter
Some say that with the higher
value level controls, such as 50K and 100K, they can hear slightly higher
amounts of (desirable) high frequency harmonics, or even that "it sounds
more open and airy". And that the lower values, such as 10K and 25K sound
slightly "richer" or "more full bodied". The actual truth may depend on
the equipment being listened to and/or which set or ears is doing the listening.
I have found that the stepped attenuator (volume control) value is usually
not critical - and that it does not make as much difference as some people
claim - but that other aspects of the equipment or system can make bigger,
more noticeable sonic differences.
is a common misconception that larger value volume controls such as 50K
or 100K will result in LOUDER sound compared to using 10K or 25K volume
controls. This is not true. 10K controls usually yield exactly the same
loudness as 100K units. (Technically, there are other reasons why different
value controls are used in different places or applications.)
tube equipment often uses 25K, 50K,
or 100K level controls, due to the high input impedance of tubes.
Solid-state gear usually has 10K, 25K,
or 50K level controls.
can begin to have "high frequency roll off" beginning to appear with volume
control values above 100K. If you don't have an engineer handy, or just
25K is a good choice
for both vacuum tube and solid-state equipment, especially for passive
|We use the 25K
stepped attenuator value in our home audio (RCA connector) SA1, SA2, and
SA4 passive preamps. Our balanced (XLR connector) SA1X and SA2X precision
level controls use 10K stepped attenuators
- as this level control value is common in the Pro Audio environment.
|Catch 22: But you
can also get away with using a stepped attenuator value which is HIGHER
than the rated input impedance - this doesn't really hurt anything - so
don't worry about it if that's what you end up with. About all that would
happen is front panel -dB calibration markings, if shown, may be a little
bit less accurate - but the sound quality will typically not be affected
to any real noticeable degree.
Standard stepped attenuators of any value will always sound better
to the transparent sonic quality of the Thin Film Nichrome resistors we
use on them.