What can you run into a power amp?

[betardfoosier]

I am confused about what you can run into a power amp. I know a guy running a RB200 into a Carvin DCM2000, but I thought you could only run preamps into a power amp. Now I'm confused. How does that all work? What kind of power does a preamp output?

[fdeck]

Some bass heads have a "preamp output" or similar connection that lets you use the preamp portion of the head, to feed a power amp. In that case, the speaker output of the bass head is simply not used.

This is done if you really like the controls and tone of the preamp section of a bass head, but find that it doesn't have enough power for your needs.

[bongomania]

^^^ Exactly. The guy with the RB200 is not running the "speaker output" of that amp into the Carvin. He's using another output jack that is just from the preamp section of the RB200. For more details about preamps driving power amps, check out the FAQ in my sig.

[audiomitch]

My new rig consists of a Tech21 VT Pedal straight in to a Crown XLS1000 power amp. So far, so good.

[dincz]

Originally Posted by betardfoosier

What kind of power does a preamp output?

A tiny amount. It's designed as a voltage amplifier rather than a power amplifier.

Think of a water pistol and a fire hose. The water pistol can produce high pressure (voltage) but only a small flow rate (current).

A fire hose produces both high pressure and flow rate.

A power amp produces both high voltage and current - which together make power.

[betardfoosier]

Great, thanks guys! I will check the back of my b2re and see if its set up for this!

[MuzikMan]

Your b2re has a preamp out for this purpose!

[dug dog]

If you send a signal from a head's preamp to a separate power amp, do you need to connect some sort of load to the original head's output jack?

[bassplayerbob]

Originally Posted by dug dog

If you send a signal from a head's preamp to a separate power amp, do you need to connect some sort of load to the original head's output jack?

Depends on the head. My ampeg b5r didn't need a load on the output, but my gk1001rb manual said not to run the head without a speaker attached. Both as heads too.

[bassplayerbob]

Edit: both solid state heads.

[bongomania]

Most solid state heads will not need a load. There are only a very few exceptions.

[Electricblue]

Originally Posted by bongomania

Most solid state heads will not need a load. There are only a very few exceptions.

Put a load of large 8 ohm resistors wired in series/parallel in an enclosure, small pc fan on the top if needed. Wire it with mains cable to a jack. Instant load.

Should cost no more than £20 to make...

[hennessybass]

Originally Posted by audiomitch

My new rig consists of a Tech21 VT Pedal straight in to a Crown XLS1000 power amp. So far, so good.

I have done similar with a SABDDI, and SWR Amplite.

[Zooberwerx]

Originally Posted by bassplayerbob

Depends on the head. My ampeg b5r didn't need a load on the output, but my gk1001rb manual said not to run the head without a speaker attached. Both as heads too.

Why is that? Conventional wisdom holds that a tube power amplifier needs to see a load but a solid-state component does not.

I learn something new every day.

Riis

[bassplayerbob]

Originally Posted by Zooberwerx

Why is that? Conventional wisdom holds that a tube power amplifier needs to see a load but a solid-state component does not.

I learn something new every day.

Riis

I didn't understand that either. What happens when you have a pre/poweramp setup and use only one side, not in bridge mode? No load on the other side then.

[Bass_Pounder]

Originally Posted by bassplayerbob

Depends on the head. My ampeg b5r didn't need a load on the output, but my gk1001rb manual said not to run the head without a speaker attached.

Not correct...............


Did not sound right, so I downloaded the manual and checked for myself.

Unless your manual is different, here is what it says:

Page 7

2) 700W or 480W Amp Only: ¼” speaker output
jacks. Impedances Lower than 4 Ohms should not be
used. Higher impedances such as 8 Ohms, 16 Ohms,
or No Load are acceptable.

AND........

No damage will
result from operating the amplifier with the speakers
disconnected.


http://www.gallien-krueger.com/manua...I_700RB-II.pdf

[Bob Lee (QSC)]

In general, you can run just any line-level (~ 1 volt or so) audio signal voltage into a power amp input. Even though we call them "power" amps, they're just voltage multipliers with enough current capacity to drive low-impedance loads, namely loudspeakers. Voltage in × gain = voltage out.