So everyone agrees? A solid state amp can be run with NO LO

Jay Ganz · Post by **Jay Ganz** » 27 May 2000 7:33 am

I keep seeing this theory in various posts
with no one contradicting it. Any thoughts?

Bill Llewellyn · Post by **Bill Llewellyn** » 27 May 2000 9:10 am

No load? Yes. I have an Adcom GFA-535II amp in my stereo which sometimes drives only 600 ohm headphones, and that's almost no load (loading is inversely proportional to the ohmage). Also, think of a typical home receiver -- it usually has a selector for speakers A or B or none. None = no load, and it does just fine in that position.

In all of my tinkering with (non-class-D) transistor and tube amplifiers over the last 35 years or so, I can't recall a problem running any of them with no load.

PS: The only exception that I'm familiar with is somewhat obscure and technical.... a class-D amp ("switching amp", sometimes called a "digital amp") needs a Zobel filter on its output which (among other things) prevents nasty resonance in it's low pass output filter when there's no speaker connected to supply damping. Usually the class-D amp maker includes the Zobel filter, however. BTW, the Nashville 1000 and Session 2000 are class-D amplifiers.

------------------
Bill * MSA Classic U12 * email * homepage[This message was edited by Bill Llewellyn on 27 May 2000 at 10:30 AM.]

Don Walters · Post by **Don Walters** » 27 May 2000 9:26 am

A while ago I asked Mike Brown from Peavey if there was any problem unplugging the speaker cable on my Session 500 if I wanted to use headphones only. He said it was no problem on the 500.

------------------
Don Walters
get "listed" at the World Wide Steel Guitarist Directory
www3.sk.sympatico.ca/waltd/
(aka On-Line Steel Guitarists of the World)

Bobby Lee · Post by **Bobby Lee** » 27 May 2000 11:22 am

Running without a load is not a problem. Connecting and disconnecting a load while the amp is ON could cause a problem if, in the process, you momentarily shorted the output to ground.[This message was edited by Bobby Lee on 27 May 2000 at 12:22 PM.]

John Russell · Post by **John Russell** » 27 May 2000 2:16 pm

FWIW:

I asked Mike Brown about running my Peavey XR700 powered mixer with no speakers, just headphones to practise to. This is a mixer with two 125 watt amps. He said wouldn't hurt the amps to run with no spkrs. I was a little surprised (haven't tried it yet).

JR

Rich Paton · Post by **Rich Paton** » 27 May 2000 11:51 pm

That certainly sounds feasible, but I don't think I would run it that way at a really high level, for extended periods. I just get a funny feeling about doing that.

Bill Llewellyn · Post by **Bill Llewellyn** » 28 May 2000 8:09 am

I don't want to advise anyone to do something they're uncomfortable about with their amp, definately. To my knowledge, if there's lots of voltage (loud sound) swinging around at its output terminals with no load connected, it will be fine. The voltages are the same with or without the load, so there is no additional voltage breakdown problem with the load disconnected. And since there is no current flowing when there's no load, the output transistors are actually doing less than if there were a 4 ohm speaker hooked up. Your biggest risk is what b0b mentioned, that you'd inadvertantly make a hookup mistake and short the poor thing out while trying to connect or disconnect a speaker. And a lot of amps (not all, but don't I wish!) do have overcurrent protection circuitry which prevents a momentary short from hurting them.

------------------
Bill * MSA Classic U12 * email * homepage
[This message was edited by Bill Llewellyn on 15 October 2000 at 09:22 AM.]

Jack Stoner · Post by **Jack Stoner** » 28 May 2000 8:18 am

Although most SS amps can tolerate no load, I cringe everytime I see someone do it. I would not do it (intentionally) with one of my amps.

ajm · Post by **ajm** » 30 May 2000 6:47 am

However.....
Solid state and Tube amps are the opposite when it comes to a "no load" condition (no load being when no speaker is connected, NOT when the load equals zero ohms a.k.a. a short).

Tube amps should always have a proper load connected. Operating them in the no load (no speaker connected) condition will destroy them. Some tube amps (some VHTs for example) have safeguards designed in that will enable them to tolerate an open load condition, but for all intents and purposes tube amps should not be operated without a proper load connected.

Bill Llewellyn · Post by **Bill Llewellyn** » 30 May 2000 7:00 am

With tube amps, I guess that probably depends on the particular amp. I know I've run tube amps without loads numerous times, those being assorted PA amps, home stereos, the Fender Showman, Fender Bassman, a Leslie organ speaker amplifier, Hammond L-143 amplifier, and a few others. They never complained. But I'm sure there are some out there which will fry if the output isn't terminated into a reasonable impedance. My guess is that you'd could get resonance (oscillation) associated with the inductance of the output transformer and stray capacitances (coupled with the fact that feedback is taken from the output transformer). For me, if I had an amplifier which wouldn't survive if its speaker wires happened to come loose (which is not unlikely, unfortunately), I'd probably end up blowing it up so I'd have to look for some way to protect it, or maybe even look for another amp.

------------------
Bill * MSA Classic U12 * email * homepage[This message was edited by Bill Llewellyn on 15 October 2000 at 09:25 AM.]

ajm · Post by **ajm** » 30 May 2000 11:42 am

(I'm posting this again, since the first one got lost somewhere)

Solid state amps can be run with no load, meaning with no speaker connected.

However.....

Tube amps are different. If you run a tube amp (tube power output stage) with no load connected you will most surely destroy the amp. Some tube amps (some VHTs) have the innards designed so that running them with no load will not fry the amp, but these are few and far between. The bottom line is: don't run a tube amp without a proper load (speaker) connected.

steve takacs · Post by **steve takacs** » 14 Oct 2000 3:13 pm

Bill, In your post you mention that "a class-D amp
("switching amp", sometimes called a "digital
amp") needs a Zobel filter on its output which
(among other things) prevents nasty resonance
in it's low pass output filter when there's no
speaker connected to supply damping"

Do the Nasvhille1000 and Session 2000 include this Zobel filter? Thanks, Steve

Bill Llewellyn · Post by **Bill Llewellyn** » 14 Oct 2000 6:44 pm

Steve,

Frankly I dunno. :} Sorry. If Mike Brown from Peavey is viewing this, maybe he could respond. But I know Peavey is a good solid amplifier maker, and I'd expect they design their amplifiers to operate under the full range of conditions, from no load (infinite load impedance) to the connection of a few speakers in parallel (perhaps down to 2 or so ohms of loading). So if they need a Zobel filter, it's probably there.

Mike, are you listening? Any comment?

------------------
Bill (steel player impersonator) | MSA Classic U12 | Email | My online music | Forum birthdays[This message was edited by Bill Llewellyn on 14 October 2000 at 07:47 PM.]

Keith Hilton · Post by **Keith Hilton** » 14 Oct 2000 7:18 pm

Who came up with the term Switching Amp Bill? Also, who said a Switching amp was sometimes called a Digital Amp? Are you thinking of a switching power supply, or mixed signal ,switching from analog to digital? What is a mystery to me, is how these new amps could have a switching power supply, when Hartley Peavey told me in a letter he has never used a DC to DC converter and doesn't know anything about them. That really seemed strange to me. I use a little switching power supply inside my pedal that contains a DC to DC converter. When you use a DC to DC conveter it is best to use inductors to form a LC network.

------------------
[This message was edited by Keith Hilton on 14 October 2000 at 08:18 PM.][This message was edited by Keith Hilton on 14 October 2000 at 08:26 PM.]

Lee Baucum · Post by **Lee Baucum** » 14 Oct 2000 8:09 pm

Jay - Are you following all of this?

Lee, from South Texas

Bill Llewellyn · Post by **Bill Llewellyn** » 14 Oct 2000 9:59 pm

Keith (and anyone else interested in techno stuff), have a look at these links for more info on class-D (a.k.a. switching, a.k.a. digital) amplifiers:

www.tripath.com/downloads/an2.pdf
www.tripath.com/downloads/an3.pdf

These are Acrobat documents, so you'll need the Acrobat reader from www.adobe.com (which you likely already have). The documents are also written from the perspctive of a particular manufacturer of switching amplifers, so expect a bit of brand focus, so to speak.

------------------
Bill (steel player impersonator) | MSA Classic U12 | Email | My online music | Forum birthdays

Jay Ganz · Post by **Jay Ganz** » 15 Oct 2000 12:33 pm

Hard to believe this topic of mine is 6 months old!!!

There are some excellent points made though.
Guess it depends on what class of amp you're
talkin' about. What it boils down to is,
if you're pickin' away & you don't see any
SMOKE coming out of the amp, then it's OK.