Rack vs 500 series

[cpeck]

Can someone with some knowledge speak on this?

How will the same preamp (in this case, Chandler Germanium) differ sound wise when comparing the 19” rack version vs the 500 series module?

[øøøøøøø]

So! The short answer is "usually not that much difference"--at least not much that's attributable to the format itself. But there are a few justifiable points of inquiry.

One thing that does have potential to make a difference: power supply considerations.

API 500-series standard used +/- 16v rails at a given current-handling capacity, so anything that's accustomed to being powered by those voltages (or lower) shouldn't see a massive difference.

Some stuff... thinking Neve 80-series preamps (1073, 1084 etc) call for +/- 24V rails as-designed, which generally speaking will afford more headroom. So the performance of a "Neve-style" pre in 500-series format will depend to some degree on how this discrepancy is resolved.

Higher voltages can be derived from 16v rails through the use of voltage multipliers (provided the current draw remains in range). It is certainly possible to use a voltage doubler to arrive at 24v or 28v rails via a 16 volt supply.

But it's also possible to just make a few tweaks and operate the device with lower headroom. Which did the designer choose? And if they did go the voltage doubler route, are there any considerations/tradeoffs to voltage multiplication if a supply is heavily-loaded? Will it clip differently, etc? These are fair questions to ask.

Other things to consider: since 6-10 devices are being operated from a single set of PSU rails, decoupling of the power supply nodes becomes important to avoid crosstalk, etc. Generally speaking any quality commercial 500-series rack will handle this well enough, but it's a point for academic consideration in any case.

Finally, you have those pressures that stem from the shoehorning of the device into a smaller form factor. Were different part technologies substituted to save space (e.g. capacitor dielectrics)? Does this even matter in the specific application? Good transformers exist in small form factors, but are they exactly the same as what would've been chosen for a 19" rack format? Sometimes "yes," sometimes "no," sometimes "doesn't matter."

How does the small form factor impact heat dissipation/longevity/durability, especially for devices that contain vacuum tubes? Etc etc etc.

So it's really device-specific. For something like an API preamp or compressor, there's likely to be little-or-no practical difference at all. For something like a Neve 1073, there may or may not be a discernable difference in performance compared to the full-sized modules--and one manufacturer might do a great implementation even if another does not. Finally, for something like a Retro Doublewide you start to ask... do the limitations of voltage and current lead to design considerations/tradeoffs? Do the tubes generate enough heat to pose a reliability concern? etc.

[øøøøøøø]

Just did some looking-up re: the Chandler Germanium.

If the information I found is correct (and if I've interpreted it correctly), it runs on ±28V rails.

So it'd be interesting to see how they dealt with this in the 500-series adaptation. Most likely they used a voltage doubler or DC-DC converter (charge pump).

Chandler's web site includes this language:

We use the same transformers and amp blocks to assure the sound is consistent with our rack version. We've updated the power on the MKII so there no known power-up issues with current lunchboxes and rack systems.

All Chandler 500 series units have now been tested and proven to have no power issues in the following racks: API 500V 10-slot with L200 PSU; API 500-6B Lunchbox; API 500-6B HC “new version” Lunchbox; BAE 11-slot with power one supply; BAE 6-slot portable with power one supply; BAE 6-slot with Avedis designed supply; A-Designs 2-slot; Purple Sweet 10; and Empirical Labs 2-slot.

This hints that there's some internal stuff going on to step the voltage up to ±28v. That's good!

It also hints that this was causing problems with some older 500-series racks, so... something to be aware of. An earlier version may have caused a current spike on power up that was frying some PSUs, and the revised version may have addressed that.

I'd expect it to sound substantially the same as the rackmount version.

[cpeck]

This is precisely the kind of info I was looking for — thanks! Missed the local Chandler deal but will keep my eyes open.

I’d read about the Neve/500 series complication and was hoping to find something “genuine” that didn’t set me back $30k. (With that said, I am almost loathe to admit how good the UAD 1073 is…)

[øøøøøøø]

I want to correct something I was mistaken about:

The 80 series Neve modules ran on a +24v supply, not +/-24v as I said

So no DC-DC converter would be necessary.

I was mistaken about this for years and coincidentally learned better just today.

But the larger point remains—different power supply configurations have to be adapted to or derived from the +/-16v API standard