The first question is what kind of VU meters? And where. Since you said that you're putting them in a preamp, I am assuming that you want them to reflect the voltage at the preamp output. So you need to do this with a buffer tied to the preamp output with a fairly high input impedance so it doesn't adversely load the line out.
Most needle type VU meters you buy have an internal resistance in the neighborhood of about 600Ω. The "zero" is about 4dBu or 1.23v. This equates to a few milliwatts across the load. So whatever you use to drive them needs to be able to comfortably drive the 600Ω load. Also, the mechanical meters require a specified rectifier to work properly. Good Vu meters have an internal rectifier. Cheap ones may or may not.
The easiest way to drive a VU meter is with a low output impedance buffer. This can be a simple emitter follower transistor stage, or a cathode follower if you're into tubes. I would also recommend some manner of range adjustment so you can match each meter per the 1kHz standard. This can be done with small trimmer pots and a low gain transistor stage.
Do you want to design and build from scratch? If not, there are lots of driver boards available that will handle all the buffering and driving. Something like this one off of Amazon for example:
https://www.amazon.com/dp/B07SFHV85Y/ref=dp_prsubs_1. I've never used this particular board. It's just an example to show what kind of setups are available.
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