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I just bought an Ampeg B5R head and I'm curious about how to combine this with my Ampeg V4. I want to use both amps to get more volume.

Both amps have the "POWER AMP INPUT" and "PREAMP OUTPUT" features, but do either of these actually allow both amps to be used at the same time? It seems like these features simply substitute one amp's preamp for the other, or one amp's power amp for the other.

The manual for the B5R says that when the PREAMP OUTPUT is in use:

Using this output does not break the connection to the internal power amplifier

It seems like this is the way to use two amps at once if you do not have a stereo output pedal or splitter, but I'm not sure.

Whether I use this method or get a splitter to send a signal to both amps, I'm still not clear on what output configuration to use.

Both amps support two 1/4" outputs, but only the V4 has an impedance switch.

The cabinet (Ampeg SVT-410HLF) I'm using takes two 1/4" inputs but it's not clear what the impedance is for one or both when looking at the back panel.

How do I connect these two amps to the cab without blowing something up?

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Important note: You can't connect both amps to that cab without blowing something up. You need two cabinets.

There are some cabinets that support bi-amping, which is using two amps with one cabinet. Your cabinet does not. Your cabinet has two 1/4" inputs wired together in parallel so you can daisy-chain additional cabinets.

Yes you can drive both power amps from one preamp by connecting the preamp out from one head to the power amp input on the other head. When you do this, the head that you take the preamp out from is the one you should plug your bass into. The gain and EQ controls on that head will be the ones that control the sound, the preamp and its controls on the other head will be bypassed.

Then you can plug the speaker outputs of each head to separate speaker cabinets.

Now let's talk about making your rig louder. In order to make your rig sound twice as loud by buying more amps, you have to increase your total wattage by ten times. That means if you have a 100 Watt head now, you'll have to have a total of 1000 Watts to double the loudness of your current head. Plus you'll have to have speakers that can handle that load.

A much better way to increase loudness is to get a better speaker cabinet that is more efficient and reproduces more high frequencies. Yes, I wrote higher frequencies. If you are pumping lots of Watts but still can't hear your bass, then the problem is more likely EQ than power. Make sure you're not cutting your highs and mids too much and just boosting lows. High mids are very important for making the bass heard with the rest of the band. You mainly want the lows to go with the kick drum.

Try turning that high frequency control on the back of your cabinet all the way up

After looking through all your links and gear, I recommend using the B5R only, buy and use a Speakon cable (because 1/4" speaker cables are bad and dangerous at high levels - dangerous to gear, not people) to connect the B5R to your cabinet, crank that high frequency control on the back of the cabinet all the way up, and work with the Ultramid control on the B5R to make yourself heard. Yes, you'll "only" be pushing 300 Watts RMS into 4 Ohms, but you'll have a good amount of headroom which is worth solid gold for bass and PA amplification.

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  • The calculation to get twice as loud - not too sure about that. Agreed that 200watts is only half as much power again compared with 100 watts. But loudness isn't directly related to number of watts, I don't think. And if it is, then that's only when everything is flat out - a rare occurrence. The speakers themselves will have a very important bearing on actual volume, some being far more efficient than others. So, just using more efficient speakers in itself should give more volume. Would any of this make sense?
    – Tim
    Apr 23, 2018 at 17:48
  • @Tim I wrote in my answer that more efficient speakers are the way. 10 times the power (Wattage) results in a 10 dB increase in output intensity ("SPLs"), assuming there is headroom available for that, which is roughly heard as twice as loud by most listeners. Finding a more efficient speaker cabinet and/or increasing the headroom of the rig to have more dynamic range is a much better option. Actually, with a 2 Ohm cabinet with the same sensitivity and the B5R head, that might be about twice as loud, since the B5R can do 500W RMS into 2 Ohms and probably peaks around 1000W.
    – Todd Wilcox
    Apr 23, 2018 at 17:53
  • That all makes sense. I'm curious about how to know what impedance I'm using. If you look at the back of the B5R, it says "300w @ 4ohms, 500w @ 2ohms". How do you "access" these various impedances?
    – JacobIRR
    Apr 23, 2018 at 18:11
  • @JacobIRR The impedances are the impedances of whatever cabinet you plug the B5R into. The B5R is a solid state head that probably uses BJTs or similar output transistors which have very low output impedances, below 2 Ohms. The only reason why there's a 2 Ohm load minimum is because as you decrease the impedance you increase the operating current and overcurrent will burn out the output transistors, otherwise the amp could run into very low impedances. Tube amps like the V4 are different and should be impedance matched from the output transformer to the speaker cabinet.
    – Todd Wilcox
    Apr 23, 2018 at 18:16
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    @JacobIRR Tube output stages that have impedance switches are allowing you to select from multiple taps on a single output transformer. Transistor driven solid state outputs do not need to have a transformer, since they are inherently low impedance.
    – Todd Wilcox
    Apr 23, 2018 at 18:25

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