Natural Progression Stereo 200 and 400 Upgrades.

"The NP400 ultimate upgrade sounds phenomenal. It's the most liquid amp I've heard to date." -- A. Ruhl, Chicago, IL.

"The upgraded (Basic Upgrade) Fidelis amp* arrived last week. And finally I had a chance to compare it to my much more expensive ARC Classic 150 amps. I was quite amazed to learn that the Fidelis was so much more smooth, natural and coherent throught the entire frequency range. A switch back to the ARCs and I felt like I was listening to a system rather than a performance. Wow, thank you so much. And for the money I should get for the ARCs, I should be able to do other improvements to my system." -- J. Fox, Plymouth MN
*Note: The "Fidelis" was a very late version of the NPS400. It had a different front panel, and had what Counterpoint called the "full mod" upgrade, which is part of what the Premium upgrade (below) is based on.

There are three types of upgrade possible with the NPS400 or 200. They consist of circuit topology changes and use a class of parts we could never use in production because the normal multiplier used in manufacturing is much higher than I use in my Custom Shop, which means that the cost of a new amplifier using these parts would have been astronomical.

 

None of the upgrades I describe below were installed at the factory; I've developed them all since then. The "A" and "E" versions of the amplifiers were the same as the non-suffixed version. The suffix only referred to whether the amplifier was to be sold in North America ("A"), or Exported ("E"). A few amps were made with a MK II update. There's more information about that below.

This NPS400 has received the Basic and the Premium Upgrades. Note the rebuilt power supplies and upgraded wiring.

Is your amplifier worth it? You bet. There is nothing in your NPS400 that is outdated; no new power amplifier technologies have been invented. You have the basis of a powerful, dynamic and sonically exciting amplifier in your possession. You'd have to spend three or four times the money to purchase a new amplifier that would outperform the upgraded SA-12/100. This rebuild comes with a 5-year warranty.

The Upgrades:

Basic Upgrade
Premium Upgrade
GOLD Upgrade
Option: Improved Input RCA Connectors
Option: Upgraded Speaker Terminals
Option: High-Sensitivity Upgrade
Option: Circuit Board Damping

Basic Upgrade. This is the place to start before considering the rest of the upgrades. This basic upgrade is incredible. It changes the character of the sound altgether by eliminating several sources of electronic coloration. As the designer of this amplifier I am intimately familiar with how it operates, so I do far, far more to it than simply upgrade the components — I make several changes to the circuitry itself. First, I

Closeup of tube section. (Dynamicap now used in place of Auricap), Caddock Tetrinox and Vishay "Naked" resistors, Mills wirewounds are visible. Each and every one of these components is much better than the original parts, and far too expensive to be used in standard production for new retail products. The large capacitors on the right are part of the Premium Upgrade and not part of the Basic.

completely redesign the way the predriver circuit is balanced, which makes it far sweeter-sounding; second, I eliminate the DC servo altogether (servos never sound good: they are always a huge source of transistory, "hashy" coloration). Third, all of the components in the tube signal path are upgraded to Caddock Tetrinox and Vishay "Naked" resistors, Mills noninductive resistors; the bandwidth-limiting input filters are removed to open the bandwidth and transparency; and the coupling capacitors are upgraded to Dynamicaps (better-sounding, in my estimation than the VTV Ultracaps and Auricaps which I was using in earlier versions); and the tube sockets are upgraded to new ceramic/gold ones. Fourth, the bias source and predriver transistors are upgraded to Zetex Super E-line transistors, which sound warm and smooth; and finally, I rebias the predriver and driver stages for sweeter sound. The amplifier sounds liquid, but not dull or slow. It actually sounds faster without a trace of edginess or harshness. A more refined, warm, smooth, detailed and relaxed sound.

NOTE: This Basic Upgrade is not the same as my simple 1995 MKII conversion where several solid-state parts were removed from the tube circuit. The MKII mod is part of this upgrade, but only a tiny part. Even if your amplifier already had the MKII mod done, I re-do it with new, better parts.

Premium Upgrade. If the Basic Upgrade isn't enough and you're looking for even better sound, this would be your next step.

The new power supplies use the excellent Nichicon KG capacitors, offering deeper soundstaging and more spaciousness. Better rectifiers and separate driver stage power supplies give more punch and tighter bass.

GOLD Upgrade. This upgrade is for serious audiophiles and music lovers only. Before getting this upgrade, you must get the Basic and the Premium Upgrades, which take care of a lot of easy-to-fix problems. This upgrade, which uses the good, expensive parts, transforms the amp into a sonic masterpiece. The purity of the tube’s high-voltage power supply is dramatically improved by upgrading the rectifier tubes, upgrading all the aluminum electrolytic capacitors used in the the tube’s plate and cathode supplies to Black Gate’s exceptional powdered graphite non-polarized caps. More of the signal-carrying components are upgraded, including replacing the tube input resistors with Caddock Tetrinox and Vishay "Naked" parts, and replacing the amplifier's output (emitter) resistors with Mills non-inductive wirewound resistors. The transformer is upgraded to a Plitron toroidal, custom-designed for the NPS amplifiers. I also remove the old RCA jacks and speaker terminals and mount Sound Connections's excellent CM1F-OFC direct gold plating over oxygen-free copper RCA jacks and BP-HEX/OFC speaker terminals. Finally, the internal power supply and speaker wiring is re-done with Van Den Hul "The Wind" Hybrid II wire. (The connectors portion of this upgrade are due to the design work of Bruce Wenger who created the factory's 1996 "Full-Mod" upgrade. Click here to see how to tell if your amp has this upgrade already.)

Options

I am making available some additional modifications for the NPS200 and 400 that either greatly improve the unit's sonics, or make it more "user friendly" in certain situations. Please note that these options have been priced with the assumption that they will be installed concurrently with the Basic upgrade, in other words, while the amplifier is already being worked on. As stand-alone modifications, these options will cost a bit more. If you wish to have any of these installed separately, please contact me to discuss the details.

Option 1. Improved Input RCA Connectors

The old RCA jacks are removed and Cardas GRFA RCA jacks are installed in the chassis.

Pricing for Option 1. Add $90 to upgrade the input RCA jacks connectors.
(add setup fee if not done with the "Basic" upgrade.)

Option 2. Improved Speaker Terminals
I replace the original speaker terminals (two stereo pairs) with Cardas CCGR posts. Some chassis modification required.

Pricing for Option 2. Add $240 to upgrade the speaker terminals.
(add setup fee if not done with the "Basic" upgrade.)

Option 3. High-Sensitivity Version
NPS200 and NPS400 amplifiers which have received the factory MKII upgrade, or my Basic upgrade have 22dB of voltage gain. (The pre-MKII version of the amplifiers had 28dB of voltage gain). The reduced gain of the upgraded versions is not usually a big deal: you simply turn up the volume control on your preamp to compensate. However, for systems where the lowered gain after modification would not be acceptable, we offer the High-Sensitivity option, which uses one 12AX7 tube per channel instead of the original 6DJ8/6922 tube. 12AX7's have higher gain, and in the NPS200 and 400 take the amplifier's gain up to 29dB.

Pricing for Option 3. Add $85 for the High-Sensitivity Option when done with a Basic upgrade,
or $320 when done without the Basic Upgrade.

Option 4. Circuit Board Damping.
Circuit boards are light and stiff -- they are resonant as heck, which causes smearing of the sound. Your audio will be substantially improved when we apply thick wool felt damping pads between the circuit boards and the chassis to damp all resonances. This results in MUCH tighter imaging and spatial resolution, MUCH greater retrieval of low-level details, a surprising reduction in edginess, and a greater weight to the tone, which makes everything sound fuller and more "real." Click here for pricing. (add $150 setup fee if not done with the "Basic" upgrade.)

If I can be of any further assistance, do not hesitate to contact me.

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C O P Y R I G H T ©  1 9 9 8 - 2 0 1 0   A L T A   V I S T A   A U D I O  L.L.C.
1445 NW Portland Ave. · Bend, OR 97701 · USA
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Email: mike@altavistaaudio.com
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Pricing Updated: 1 February 2001