The No32 vs No52 thread

[AudioIdiot]

Dear Forum,
I would like to start my first thread here at AA that compares the Mark Levinson No32 and No52.

In the past, I designed high-end audio equipment for several brands like Sonic Frontiers, Classé audio, Transrotor, (Dutch Siltech owned) Sphinx and some others, but I have always been impressed by what ML did. When the No32 was introduced, I was extremely impressed with the design philosophy and the 32 was immediately a reference for me. I heard the No32 somewhere in 2004 where it sounded better than the design I made.

Now years later I am a new Aficionado. After a DIY speaker project that turned out quite well my stereo set is playing a lot. The sound has never been so good; streaming Tidal, via Roon with MQA files my audio life is good.
The upgrade virus got hold of me again, and the pre-amp is on my list of changes, so why not my all-time favorite a (second hand) No32?
So a few years ago, I noticed the follow-up unit of the 32, the No52 and I was not at all impressed. If I had judged (on paper) what would be the best unit I would have chosen the No32.

So what is there less to like (on paper, and as an engineer) on the structure of the 52?

• The chassis of the 52, although nice is not as impressive as used in the 32. The 32 is based on a single cast aluminum chassis, CNC machined to form this stable structure. The 52 is a more standard housing. I am not religious about a chassis made out of a single piece, but if you are trying to achieve the last bit of resolution all small things help.
• The first stage power-supply of the 52 is switching (nothing against switching if well designed, but often it’s outperformed by linear). The advantage is that it is auto ranging from AC 100V to 240V so no export models and convenience.
• The second power-supply stage of the 52 is a class-D design, nothing wrong either but building a noise free supply, the 32 had a better design.
• The 2nd power supply stage of the 52 runs on a 200Hz oscillator where the 32 uses a 400Hz oscillator. Both are in the audible frequency but 400Hz is used in many more (military) applications than 200Hz. 400Hz is twice as efficient as 200 and still low enough in frequency not to radiate. I would not have abandoned 400Hz.

Moving down to the audio part:

• The audio stage is virtually the same seen from the schematic but some differences are obvious.
• I have not seen the 52 audio chassis local supply stage, but the 32 has a great push/pull local regulated power-supply used to power the whole preamp stages.
• The relay structure looks identical with relays to remove the unused sources but in 2014, I would have ditched the tape output. Who in the world records analog sources nowadays? This would mean a lot less components and contacts in the signal path.
• The input stage of the52 looks identical with a 4 opamp instrumentation amplifier topology, but it uses small SMD parts instead through hole components. I am not sure what is best, SMD or through hole, but the latter allows for smaller designs and shorter tracks. A normal chip SMD resistor is not the best though I would use mini-MELF metal film resistors for all standard functions and high quality thick metal film, or tantalum-nitride in de volume control and gain stages. I am not sure what the 52 uses, but no Mini-MELF. The 32 uses high quality (through-hole) Dale resistors and film SMD resistors in the volume control. So why are resistors important? Well you use a lot in a pre-amp and they are all handling the precious signal.
• Volume control is done identical but in a smaller footprint in the 52. That should be better in the 52. Smaller is better here.
• Then the output stage is not even close to the great design of the 32. The discrete output stage with high class A bias and zero feedback was a revolutionary design. The 52 just has a simple op-amp based output stage. In my opinion an opamp is the device for an input stage and when you need gain. If you want to drive an output, a (long) cable and power-amp you need a discrete output stage with at least 20mA bias. I know no audio opamp with 20mA output stage bias. So the 52 in my opinion will only perform well with high input impedance power-amps.
• The 52 has the advantage of having two independent output stages (that are connected in parallel, so no individual gain). This in theory would be beneficial in a bi-amp situation like I have used in most cases for the last 25 years (Except for one two year when I owned Avalon Eidolon’s who couldn’t be bi-amped)
• But the 32 unbalanced output is just a mediocre opamp, not using the great class A discrete output stage. I think that ML with this decision thought that an unbalanced connection was not serious. If you own an 32 and use the unbalanced outputs because you have a nice (tube) unbalanced power amp try using the XLR connector with only pin 1 (gnd) and 2 (hot).
• On top of that, these 3 stages in the 52 are on boards connected via a fairly simple connector to the main board. Yes they are small but the signals still travel through at least 6 connectors extra.

I expect that the No52 is lower cost to build, lower cost of material and lower cost in labor. So what does this all say? Nothing if the 52 sounds better than the 32 ….. but does it?

Cheers,
Peter