Update: Tests are done, and we had a follow up call with Chris to talk about what we discovered.
THE BACKSTORY
Chris Caruso Guitars recently posted a video walking through swapping out the stock Legacy preamp for an LHZ. The reason for the change wasn’t due to tone: it was sudden battery death during the gig. Concerned that there was practically no warning, he opted to replace the Legacy.
We reached out to Chris and he agreed to send us the Legacy to do stress testing on.
We noted in our Legacy-vs-LHZ video that the Legacy has a much higher current draw (6.62mA) than the LHZ (0.39mA). Yes, you read that right: one Legacy draws the same current as 16 LHZ preamps!
During that video we never asked the question “How well does the Legacy handle a failing battery?” This is something we did on our Preamp Battery Comparison video when we took the LHZ preamp all the way down to 4 volts to understand how long it takes a failing battery to finally die.
We’ve got Chris’s Legacy preamp in the shop and are put it through the same battery of tests to see how well the Legacy performs as the battery drains.
THE OUTCOME
The test results surprised us. We expected the preamp to sound bad at 5 volts as Chris experienced, but it didn’t. The real problem was the internal resistance that increases as a battery is depleted!
As a battery is depleted, it’s internal resistance increases. This is similar to running the battery through a resistor before powering a preamp: that resistor limits how much current the battery can supply.
For a low-current preamp like the LHZ (drawing 0.39mA), the internal resistance has very little impact.
However, the Legacy requires 6.62mA. At this level of current, the internal battery resistance results in a steep cliff where the battery voltage drops significantly after the battery is no longer able to deliver the current.
RECOMMENDATIONS
- Be aware that the Legacy preamp has shorter battery life and is at risk for sudden battery failure due to it’s higher current load.
- Plan on changing batteries for a Legacy preamp after every 5 performances to mitigate battery failure risk.
The Legacy is great preamp! We’re not advising to replace it. The important thing is to understand how it’s different so you can modify your battery replacement schedule to ensure you have trouble-free performances.