Power amp load resistor...

[zorrow]

Hi there!

I have a Pignose Piggy-in-a-box which has two outputs:

1- "Speaker OUT" (5W power amp)

2- "Pre-amp OUT".

I always use the pre-amp output, but I tried the speaker output recently with a small cabinet and loved the sound I got.

So, I purchased a Hughes & Kettner Red Box Pro, which I intend to use as a cabinet simulator with the Pignose power amp output.

The problem is that this red box needs you to connect a true cabinet or a "load resistor" to its "through" hole, or else your power amp might burn, according to the manual. In other words, the red box doesn't seem to provide the required load to your power amp, so you still have to lead its power elsewhere.

My idea is building a little box with a pair of headphones inside and plug it to the 5w output signal coming from the "through" hole. That would be my "load resistor", but I wonder anyway if there's some risk in doing this.

Is there anyone here able to explain me what would be the right way to proceed?

Thanks a lot in advance!

PS: I'm still using the pre-amp out of the Pignose with my Tech21 Power Engine 60 as a monitor. Both outputs on the Pignose work in parallel; which is great, as I intend to send the red box signal to the PA, while keeping my old configuration for monitoring.

[Steve Haynie]

Headphone impedances vary. Some are 600 ohms.

Because the power output is so low, you might get away with just putting a resistor in place of a speaker. It is even possible to use a small light bulb in conjunction with a resistor. Some higher end PA speakers will have an internal bulb as part of the circuitry.

I have a Piggy-In-A-Box, too. I find that when using it as a preamp the pedal pushes the signal hard because the volume jump is drastic. Using the speaker out gets the classic Pignose tone all right, but the choice of speaker makes a big difference in tone. So far, nothing I have really matches up well with the Pignose tone.

[zorrow]

Thanks for the reply!

I guess with a solid state amp (of only 5W in addition) probably a resistor would just do, yes.

BTW, I'll let you know how the Piggy-In-A-Box works with the cabinet emulators on the red box. The red box has two modes: "combo" and 4x12, but I don't really expect any of them to sound like the original Pignose 7-100 amp.

[3of5]

I do a similar thing with my 5 watt amp (Behringer speaker simulator to a small cheap mixer to headphones) and it sounds very good. I use a Weber Minimass as the resistive load. I think you would toast your headphones.

[Armitage]

Transistor amps seldom care if you have a load or not, unlike tube amps.

[Uncle Thor's Hamer]

I'd just buy a 10W resistor from Radio Shack. 8 ohms. Or, two 16 ohm 5W resistors wired in parallel. Your load should be able to handle about twice the power output of the amp to encourage long life.

You can just solder the resistors to the 1/4" jack and use shrink wrap on the wire leads. Don't shrink wrap the body of the resistors because they need to breathe in order to dissipate the heat.

I'm not sure about the headphone idea. The headphone impedance is so much higher than the 8 ohm load that it isn't "in the circuit". That's assuming that you wire the headphones across the load resistor. The amp will still drive 5W into the load resistor, creating a voltage across it of about 6vrms. You have to be sure that this is in the ballpark for your headphones. If it is too high it will possibly fry the headphones or make you deaf. If it isn't enough it will be too quiet. If your amp sounds good at less than full power you can adjust the volume control so that the headphones are at a good level for you. Or, you can get tricky and wire in a volume pot to the load box, but that's going to take some experimentation.