To Choose the Correct Stepped Attenuator Value. General Rules and Considerations:
upgrading from a potentiometer, use the same value stepped attenuator.
10K, 20K, 25K, 50K, 100K, etc.)
the stepped attenuator value to be the same as or less than the input impedance
of what it will be controlling. 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. "Same as or less than"
is the rule of thumb.
the choice of stepped attenuator values in Goldpoint SA1, SA2,
(25K) and SA1X, SA2X (10K),
observation and thought has gone into this over the last 15 years. We have
concluded that the values which we are using for our standard off-the-shelf,
in-line passive preamps and precision level controls are the right values
and should not be changed unless absolutely necessary. (see 2. above) Also,
an in-line unit such as those mentioned above are best with lower value
stepped attenuators - making them compatible with a wider range of Input
impedances over the years.
- 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.
There 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.)
Vacuum 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.
You 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 can't decide,
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.