Why Select Highest Z Tap
From detritu–(at)–x.netcom.com Sun Apr 16 00:01:24 CDT 2000
From: Lord Valve
Newsgroups: alt.guitar.amps
Subject: Re: Audible difference in 4 / 8 / 16 ohms?
Date: Sun, 02 Apr 2000 22:40:12 -0600
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Richard wrote:
> I was talking to friend about amps today, and the topic came up about
> whether using the 4 or 8 ohm output of a tube amp offering both makes a
> differences in amp sound.
>
> I didn’t know, and he said he just always used the 8 ohm output.
>
> What’s the scoop, please?
>
> —
> Disclaimer: These are simply some of my personal opinions.
> ObURL: http://home.earthlink.net/~huddler
>
> “Cognitive dissonance is your best friend.”
Lord Valve Speaketh:
Well, here’s my take on it: I always run the highest impedance
the amp is capable of driving. The main reason for doing so is
that the power will be transferred to the load via the *entire*
output transformer secondary winding, rather than just a portion
of it. This allows for even heat distribution in the winding,
with a consequent increase in reliability. The damping factor
will be marginally better at the highest impedance, which may
result in slightly better low-frequency performance. In addition,
the resistance of the speaker cable (and any internal cabinet wiring)
is much smaller when considered as a percentage of the total load
impedance; this means that less power is dissipated by the cable
as heat. If, for instance, the speaker cable and the internal
cabinet wiring added up to 1 ohm (it wouldn’t, but round numbers
will make this a lot easier to understand), the total load seen
by the amplifier when driving a 16-ohm rated cabinet would equal
17 ohms. This means 1/17th of the amp’s output power will be
turned into heat within the cabling. Using the same cabling and
internal wiring, but this time with a 4-ohm cabinet, the total
load seen by the amplifier would be 5 ohms. In this case, 1/5th
of the amp’s output power is now wasted as heat…considerably
more. (Of course, this is a very simplistic model. Factors such
as impedance variations in the speaker voice-coils due to applied
frequency, the complexities of a load which is partially resistive
and partially reactive, etc., have been ignored in this example.)
Is there an audible difference? Probably, but it would be *very*
hard to quantify; the fact that an amp sounds one way driving a
4-ohm cabinet and another way when driving a 16-ohm box would
be more affected by the difference in the speakers themselves
than by anything else. No two speakers are ever exactly the same,
and it would be impossible to find two cabinets that were *identical*
in every respect save the impedance…and that is exactly what you’d
need to make the comparison.
Lord Valve
VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/
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From detritu–(at)–x.netcom.com Sun Apr 16 00:02:20 CDT 2000
From: Lord Valve
Newsgroups: alt.guitar.amps
Subject: Re: Audible difference in 4 / 8 / 16 ohms?
Date: Mon, 03 Apr 2000 11:50:13 -0600
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Cybernalt wrote:
> ” I always run the highest impedance the amp is capable of driving … This
> allows for even heat distribution … [and] increase in reliability. The
> damping factor will be marginally better … which may result in slightly
> better low-frequency performance”
>
> LV: Are you assuming multiple taps on the OT? Do these benefits apply if it
> has only an 8 ohm tap, and you run it at 16?
Lord Valve Speaketh:
Yes, I’m assuming a multiply-tapped OPT. No, there are *no*
benefits to running an incorrect impedance; in fact, loading
an 8-ohm output with a 16-ohm speaker can lead to fried tube
sockets (or worse) from flyback. A tube amp can only deliver
its rated output into the correct impedance; any other load
results in less power.
Lord Valve
VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and join my
SPAM LIST; just put “SPAM ME” in the header and I’ll sign you
up. (If you only want a set of e-mail catalogs, put “CATS ONLY”
in the header.) I specialize in top quality HAND-SELECTED NOS and
current-production vacuum tubes for guitar and bass amps. Good
prices, fast service. TONS of gear and parts in stock…let’s DEAL!
NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:00 PM Denver time at 303-778-1156
NOW ACCEPTING VISA AND MASTERCARD
CHAT WITH LORD VALVE: Log onto any DALnet server and join
channel #CONELRAD. Look for me there most any night after
11:00 PM Denver (Mountain) time. Guitar-amp questions and
what-have-you are welcome.
“I’m not an asshole, but I *play* one on the Internet.” – Lord Valve
