Tube Amp Archive

Hi, I've questions regarding rackmount handshaking
between power amplifiers and speaker cabinets. I own:

1) Fender/Eminence Bassman 115 Pro Speaker Cabinet
1x15" Fender Special Design Cast Frame USA Eminence ~ 8 Ohm
Power Handling: 800 watts program, 400 watts continuous at 8ohms

2) Fender/Eminence Bassman 410 Pro Speaker Cabinet
4x10" Special Design Eminence USA Speakers Parallel 8ohms ~ 87.5watts
700 watts programmable power (350 watts continuous) at 8 ohms

a) Rocktron Velocity 120 Rackmount Power Amplifier
65watts/channel in stereo, driving 8ohm load

b) Peavey Classic Series CS200X Rackmount Power Amplifier
Works with any load from 2ohms to 16ohms
85-watts RMS into any speaker load from 4-ohms 8ohms 16-ohms
120-watts RMS per channel into 4-ohms (8-ohm setting)

c) Lee Jackson Metaltronix SP1000 Rackmount Power Amplifier
100watts per channel in stereo
4-8-16 ohm load operation
============================


What I'll be doing is experimenting powering a group of three rackmount
preamps with 12AX7 tubes and a couple of digital echo delay effects.
The key word is "experimenting", nothing serious, yet.

I'll use only one power amp at a time and use one speaker cab at a time.
No stacking here. Looking for the best combinations and will sell off the rest.


My question(s) evolve around the speaker cabinets' power handling:
1x15 = 800 watts programmable power 400 watts continuous at 8ohms
4x10 = 700 watts programmable power 350 watts continuous at 8ohms

If I set all speakers and power amps for 8ohm loads,
can I just blast away with the power amps through the speakers?
Whether Rocktron Velocity 60watts, the Lee Jackson SP1000 100watts
or the Peavey CS200X at 85watts or 120watts???
All the same, just blast away?

Where do the speakers' 800/400watts or 700/350watts
figure into the equation???

Currently have been playing low power with caution ~ lol
Thanks for any input.

How do you program a speaker cabinet? Are there any active components in it?

Might it say "Program power", as in "the amount of power being fed by the power amp"?

If impedance matches and the power handling capacity of the speaker cabinet exceeds that of the amplifier, you should be fine.

That said, heavy clipping by overdriving the power amp may sometimes cause damage to speakers, even if within their ratings.

Zippy wrote: ................

That said, heavy clipping by overdriving the power amp may sometimes cause damage to speakers, even if within their ratings.

Excellent point. As I understand it, it isn't power that usually kills speakers; it's clipping/distortion.

Thanks. The speaker specs state programmable or continuous
power features. Just guessing, if all handshaking is 8ohms,
there should be no problem except for clipping by overpowering
the speakers to get them to break-up towards being distorted.
Hopefully, these speakers should handle that with my playing - lol

All my combo amps ~ speaker break-up is easily achievable.


1x15 = 800 watts programmable power 400 watts continuous at 8ohms
4x10 = 700 watts programmable power 350 watts continuous at 8ohms
Seen these ratings all the time ~ not sure how they apply,
especially towards my 85watt to 120watt power amps.

Power handling capability is an issue that has several factors at play. Continuous power is concerned with heat buildup in the coil. Peak power (my best guess of what program power is) is an issue of mechanical robustness - how far can the cone travel without physical damage.

It would be instructive to find the ratings of the speakers in your cabinets, but given what you've shared here regarding the output power of your amps, I'd say "Turn it up!" and play on.

1x15 = 800 watts programmable power 400 watts continuous at 8ohms
4x10 = 700 watts programmable power 350 watts continuous at 8ohms


Thanks, Zippy. Above are the Fender/Eminence specs.
Guessing, someone could play a 350watt amp
through them, but would need to be cautious
of speaker overload or clipping if/when dime(ing) that amp.
No worry here.

If you drive a power amp too hard, the output will clip. A clipped waveform contains higher order harmonics. This shifts more power into a higher frequency spectrum - sometimes more power than the amp is rated for. This can kill speakers.

One must also be careful of stated amp output specs. Often the wattage/power output spec is qualified by a THD spec (when that spec is NOT listed, there is cause for concern). An amp spec published to put out 300 watts at 0.05% THD, might be capable of putting out 500 watts at 25% THD. The latter spec might be the one that kills your driver(s).