I have a wonderful SD45 that I love, and I have a question about using an attenuator with it. I often use a THD Hot Plate (8 ohms) between
I have a wonderful SD45 that I love,
and I have a question about using an
attenuator with it. I often use a THD
Hot Plate (8 ohms) between the amp
and my Budda 2x12 cab, which works
fine but gets a little too compressed
at times. Recently I heard somewhere
that you can use your attenuator in
parallel (rather than in series) with
your cab, and I was wondering how to
safely do that with the SD45. Would I
plug the cab into the speaker 1 output,
and plug the hot plate into the speaker
2 output, and then set the impedance
switch to 4 ohms? Have you ever tried
this, and can it be done safely?
Thanks a ton and keep making killer
amps!
–Matt
Hi Matt,
First let me pass on an official “thanks
from the Budda guys” for playing a
Superdrive 45 and 2x12 cab. That is certainly
some monster tone, so I can understand
your need to tame those KT66s
once in a while. The THD Hot Plate is one
of my favorite pieces for this task, but
since your question is dealing with an alternative
use of a THD Hot Plate, I called my
friend Andy Marshall, the man behind THD
(thdelectronics.com), to get the “official”
company policy on such use. Here’s basically
what he had to say.
Yes, the Hot Plate can be used as a parallel
attenuation device, but there is a
recommended way to do this so that the
constant impedance virtue of the device
remains intact. Matt, it turns out that your
hook-up assumption above was correct.
Your speaker cabinet should be plugged
into speaker output 1 of the amp, and the
“input from amp” on the rear of the Hot
Plate should be plugged into speaker output
2 of the amp. Since you’re using an
8-ohm cabinet and an 8-ohm Hot Plate (the
purple version, the perfect Budda compliment),
the impedance selector on the amp
should be set to 4 ohms.
Here is where you’ll see that this type of
setup is theoretically very limiting. The only
setting on the Hot Plate that will, in conjunction
with the speaker cabinet, present
the amp with a constant 4-ohm impedance
in this configuration is the “load” position.
This will give you a total attenuation of
3db, which is half-power, but definitely not
half-volume. If you normally use the Hot
Plate for attenuations greater than its 4db
setting, this setup is theoretically not for
you due to its lack of versatility.
I also personally A/B’d this 3db parallel configuration
against the standard usage 4db
attenuation setting on the Hot Plate. The
result? After a lengthy session culminating
in volume-induced vomiting, heart palpitations
and loss of balance (Okay, it really
wasn’t that loud!), I determined that there
was only a negligible difference in tone
and feel between the two, the result of
which I determined to be the extra speaker
cable length between the Hot Plate and
the speaker cabinet. Bottom line? I really
found no major benefits in using the Hot
Plate as a parallel 3db attenuation device.
I did however, against official company
policy I might add, try the other attenuation
settings on the Hot Plate. My favorite
and most transparent was the 4db setting,
which in this parallel configuration
produced only about 1.5db of attenuation.
With that little attenuation, it’s easy to see
why it sounded so transparent. The other
settings did produce greater than 3db
worth of attenuation, but none came close
to their stated degree of attenuation when
the device is used properly. Keep in mind
that these settings also do not maintain
a constant and proper impedance on the
amp, but no setting will take you below 4
ohms. Since Budda amps don’t seem to
be particularly impedance sensitive with
this small degree of mismatch, you can set
the amp to 4 ohms, give the other settings
a try and judge for yourself.
In conclusion, 3db of attenuation works
pretty well no matter which way it is
incorporated, but the one point that I think
everyone needs to realize is that if you’re
trying to throttle down a high-powered
amp to bedroom levels, no attenuation
device is going to sound “just like the
amp.” That’s the reason we make the
Superdrive 18!
Now go forth and assault the masses.
That’s what rock n’ roll is all about!
Jeff Bober
jeffb@budda.com
www.budda.com
©2007 Jeff Bober