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Conference napalm::guitar

Title:	GUITARnotes - Where Every Note has Emotion
Notice:	Discussion of the finer stringed instruments
Moderator:	KDX200::COOPER

Created:	Thu Aug 14 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	3280
Total number of notes:	61432

375.0. "Loading Problem" by NEDVAX::DPOWELL (Dan Powell/274-6608) Mon Oct 26 1987 10:22

I have a MusicMan 110RD 50 amp that I'm having problems running directly 
into a board.

Rear of the amp:        *           *           *
                        8           8          600 
                   ohm ext spk   ohm spk   ohm line out (unbalanced)

When I run the amp line out into a high impedance line in at the board I get
uncontrollable distortion. I've solved this by placing a lo/hi impedance
transformer in line. The amp line out is unbalanced, and the transformer 
wants a balanced signal, but it seems to function ok. 

As long as there is a load on the amp (speaker connected) I get a normal, 
controllable sound into the board.

The problem is that I need to remove the speaker load at times. When I do 
this I get the same uncontrollable distortion as with improper impedance 
matching. 

My question, how can I go about simulating a speaker load on the amp without
connecting the speaker?

Dan

T.R	Title	User	Personal Name	Date	Lines
375.1	PLUG THAT SPEAKER LOAD BACK IN WHERE IT BELONGS	AISVAX::FABATELLI		`Mon Oct 26 1987 15:55`	30
	WHOA THERE !!!!! Rule no. 1: NEVER, I mean NEVER remove a load from the output of a tube amp !!!! In order to remove the very good possibility of screwing up a tube amp, leave the speaker connected at all times. Solid state amps aren't as critical. Do you have a LOW-Z input on your board ?? If you're getting a distorted signal into a board and are using a high to low-Z converter already, you either can check to see if you're running the amp too hot thereby staturating the input signal, or your gain is too high on the pot of the board input. When I record bass tracks I go into the LOW-Z input of the board otherwise I get a distorted signal on that track. When I record guitar I mike it in front on one track and sometimes go into a LOW-Z input of the board from a 600ohm (unbalanced output) on another track. You can mike the front and open back of your amp so as to get both sides of the speaker. Roy Buchanan used to turn his amp around so as to face the back to the audience and mike the back only. (Note: this was about 10 years ago and I don't know if he still does it anymore). It does sound like you are overdriving the input signal into the board. Check the silly things first and then try it again. Play with the gain and above all..... "PLUG THAT SPEAKER BACK IN !!!". Fred who-always-thought-that-musicman-amps-had-a-tube-pwr-amp
375.2		MTBLUE::BOTTOM_DAVID	Not so famous rock star	`Tue Oct 27 1987 08:05`	19
	Well most Musciman amps have solid state preamps and tube power amps..... You're gonna blow your output transformer running the amp with no speaker. Trust me, they cost plenty, so plug it back in. You can try, not recommended, but you can try....an 8 ohm 50w resistor if you like in place of the speaker. However, you want a non-inductive resistor...good luck they cost big bucks too, and are not easily available....there is one manufacturer I know of and sorry I can't remember the name...somthing like non-inductive componants... Most speakers are rated at 8 ohms, measure about 6 ohms on a meter (dc resistance) the other 2 ohms is reactance (inductance). Matching this exactly (or close enough for tube amps which are picky picky) is hard using a resistor, most power resistors have a high inductance. dave .