Stereomour vs. Paramount

[Paul Joppa]

THD should be the average of the two parts. The rest of your post is pretty much the way I see it too.

[Doc B.]

I've been running as as many as four amps this way for 6 years and I find little to fault from a performance standpoint.

[Paul Folbrecht]

Hi Paul,

Well, the 10% sale came at an opportune time and I've ordered my second Stereomour kit today.  Could you please post instructions on how to convert the amp to a series-wired monoblock?  (Assume that I'm really stupid...)

[Paul Folbrecht]

The Paramount has a similar legacy from earlier products. "Afterglow" was the second power amp (released in 1997 when the business was still called Electronic Tonalities, before Bottlehead was adopted). It was a high-end design by John Tucker and had direct coupling between driver and power tube. Variants on that design have been in the product line for many of the succeeding 17 hears. Because the power supply voltage and the output transformer impedance of the 300B Paramount were suitable for this topology, we provided that option. It's too esoteric a design to support a fully separate product, but the Paramount adaptation keeps it available for those who really want it. I don't, incidentally, recommend it unless you are pretty knowledgeable because direct coupling is less reliable and more high-maintenance that capacitive coupling. It is a higher-performing 2A3, with direct coupling, DC filament power, and shunt-regulated driver power distinguishing it from the Stereomour. It also has higher internal voltages, requires regular maintenance of the operating point, and has the potential to damage output tubes if you don't use the latest version and follow the turn-on/turn-off protocol carefully.

Hi again Paul.  I am now actually leaning to building the 2A3 Paramounts.  The Stereomour is so good that an increase in performance is very intriguing.

When you say that the amps "require regular maintenance of the operating point", what do you mean?  What would there be to adjust?

I once had a Fi 2A3 which is direct-coupled and also Fi 45 monos and there was no maintenance required.

Thanks!

[Paul Joppa]

In direct coupled designs the driver plate is directly connected to the power tube grid, so that voltage affects the operating point of both tubes. The driver usually (at least in my designs) has plenty of headroom and can tolerate a range of plate voltages, but the power tube can't if you want to get the best out of it.

For this reason, the current (v1.1) Paramount incorporates the "soft-start" upgrade board, which has and adjustable driver cathode voltage. The optimum adjustment is dependent on your power line voltage so you have to calculate it, and then you must check it and re-balance if the tube drifts too far - IHMO, +/-5% or about +/-10v. In the present design that means taking the amp to the test area, turning it over, connecting a meter, and adjusting a trimpot on the PC board. Inconvenient, but as I said this was not the primary design application. I guess, like reel-to-reel tape, this is a design for geeks!

To my ears, a cap coupled amp with a really excellent coupling capacitor, and operated within its power capabilities, is audibly comparable to direct coupling. These days I am more enamored of a fully shunt regulated power supply for that last bit of nuance. There is no such current product but I AM working on it!