NP220 Rebuild

Seventh Run of these Upgrades
Now Shipping
Click here to see Production Run #7's availability

Now in its 7th Production Run!
Used SA-20's and SA-220's are not that difficult to find. I can convert them to 200-watt stereo amps with remarkable sound and power. If you have a pair of them, I can make them into triode-driven mono bridged monsters with over 600 watts of power.

Natural Progression Rebuilds for the Counterpoint SA-20 and SA-220 Power Amplifiers -- Now with Octal Tubes

"I have now been running the new converted SA-220s with the Premium Gold upgrades (and other custom bits you did for me) for more than 100 hrs with my new preamp, the Hovland HP-100. I love them. "

"It’s a whole new amp! (You told me it would be, Michael.) Bigger in every way - dynamics, detail, sound stage. In fact, the NP220 makes my system sound HUGE! And real. . . Worth every penny!"

"I think this amp rivals the considerably more expensive Pass Aleph 2S in many respects which is no mean feat. The NP220 highs are just about perfect and have a certain presence I think. The mid range is very neutral with just a touch of added warmth to sound very realistic."

"Amazing...the air, sweetness, naturalness I was missing, and even more impact. Playing Strength In Numbers as I of my favorites, and never before as fulfilling. I'm there. I'm drinking the kool aid. I'm convinced. This is what I was hoping for from this amp."
"When I hooked up the NP220 (premium upgrade) that I just received and put on an LP, that rare feeling came over me. know, the one where you kick back in that comfortable old armchair with a feeling of contentment and say, "oh yeah, now THAT sounds GOOD." I could go on and on about how the soundstage blossomed and became huge; how details sprung out of the background; how complex passages became intriguing music instead of incoherent mush; and how effortlessly the music poured out of the speakers. But instead of heaping on the cliches about how wonderful this amp is, I will simply place my order for ANOTHER one, just like this one (premium upgrade/high sensitivity). So, enclosed please find my order and deposit. I will ship the SA220 to be upgraded to you in about 2 weeks."

Read more about this and other upgrades on the testimonials page.
    NP220 Rebuild. Entirely new double-sided circuit boards. Note dual 6SN7's at rear and tube rectifier at front center. Basic Version. Choke filter is located directly behind rectifier.

Product Background. I designed the tube/MOSFET SA-20 in 1985. In 1988 an updated version -- called the SA-220 -- was released. It has output stage protection and a copper-plated steel chassis, but is otherwise identical to the SA-220. This amplifier represented cutting-edge hybrid technology at the time. They used MOSFETs in the output stage, devices which had initially attained a high level of popularity due to their soft and musical sonic characteristic. Critical listening has shown, however, that MOSFETs soften the sound perhaps too much, and add their own coloration - a kind of fine-grained mist - to the sound. Also, due to high internal losses and occasional flaws in manufacturing, MOSFETs have not proven to be as reliable as bipolar transistors. Unfortunately, repairing these amplifiers with new MOSFETs is now impossible because these special parts are no longer available. If you are visiting this page because you have an SA-20 or SA-220 with a blown output stage, click here to read about your repair options.

18 years have passed since I designed those amplifiers.

  • In 1994 Counterpoint released a new class of power amplifiers of my design, the Natural Progression Stereos (NPS). These amplifiers took hybrid design to a new level with a simpler, more direct triode front-end and a unique new output stage that uses rugged bipolar transistors instead of MOSFETs for greatly enhanced reliability. This technology provided fast, clean sound and extremely reliable operation.
  • In spring of 1998, in response to the unavailability of replacement MOSFETs for repair, I created an upgrade for Alta Vista Audio, based on an enhanced version of my 1994 technology to convert the SA-20 or SA-220 into a wholly new power amplifier, the NP220. The upgrade consisted of wholly new output stages, and used the original SA-20/220 motherboard. By March of 1999 I installed this upgrade in over one hundred SA-20's and SA-220's.
  • In fall of 1998, due to popular demand, I introduced a similiar upgrade for the smaller SA-12 and SA-100 amplifiers. But instead of modifying the original circuit board (and living with some of its limitations) the smaller NP100 used a completely new circuit board, with regulated power supplies and other improvements. Less an upgrade, this was a total rebuild. I had not been able to incorporate many of the improvements into the NP220 due to my having to use the original board as its basis. I was aware that the improvements in the NP100 enabled it to sound better than the NP220.
  • In winter 1999, I decided that I would no longer manufacture the 1998 version of the NP220 upgrade and began to create a new rebuild for it based on all that I had learned in the NP100, plus several performance-enhancing features, including:
      • 6SN7 (ECC32) octal tubes. (The SA-20, SA-220, SA-12, SA-100, 1998 NP220 and NP100 use 6DJ8/6922 tubes),
      • Choke-input power supply filtering,
      • Tube rectifier,
      • Switchable from stereo to mono bridge operation (over 600W of power!)

The 6SN7 NP220 is more costly than the 1998 version, but kicks its butt in every aspect of performance. The tube's power supply choke is located right in the center of the large blank area. This large area is reserved for the optional upgrade toroidal choke, described toward the bottom of this document. Basic Version shown. Note: The 1998 NP220 can be improved. Click here for details.
Above: NP220 Basic Upgrade motherboard.
Below: A Platinum NP220.

This is a Platinum-level NP220 upgraded in 2010 for Mr. S. Smith. Click on the image for a larger view (opens in a new browser window).
The original fragile output devices -- MOSFETs -- are replaced with rugged Motorola transistors. New double-sided output boards -- two per channel -- with fat 2oz copper traces, can easily carry hundreds of amperes. You get the power, transparency and reliability of a solid-state power amplifier, without a trace of transistor sound, without a trace of the original MOSFET "mist" and without the hassles of big output tubes.
NP220's new Output Boards

Warranty: This rebuild comes with a 5-year warranty.

What does it sound like? Compared to the original SA-20/220, the 1998 NP220 offered more defined highs, more detail and a more lifelike presentation of the sound. The bass is cleaned up noteably, there's no more of the thick "muddy" sound of the MOSFETs: the whole bottom end sounds cleaner, with more transparency, deeper, more detailed, more impactful bass. The 6SN7 version has a deeper soundstage, velvet quiet background, with sweeter highs and lusher midrange. But most important, the sound is incredibly involving, delivering a strong sense of the performer and the emotion the performer was feeling.

Is my amplifier worth it? You bet. There is nothing in your SA-20/220 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. There is nothing available on the retail level for even three or four times the money that outperforms the NP220. Read about the economics of upgrading versus buying retail here.

The Upgrades:

Basic Rebuild
Premium Rebuild
Premium "Gold" Rebuild

Premium "PLATINUM" Rebuild

Kit Version (please read this separate web page before contacting me)
Option: Mighty, Mighty Plitron Choke

Option: Upgraded Input RCA Connectors
Option: Upgraded Speaker Terminals

Option: Balanced Inputs
Option: High-Sensitivity Version
Option: Monoblock Version
Option: Circuit Board Damping
Tube Options

NP220 "Basic" Rebuild

The fast and powerful driver transistors on the NP220 are more powerful than what most amplifiers use for output transistors, and are one of the many design elements responsible for the amplifier's transparent sound and extreme ruggedness. Click on the picture for an enlarged view. (Amplifier courtesy S. Smith.)

The entire circuit board and the old output MOSFETs are replaced. A new circuit board with a clean, simple differential 6SN7/ECC32 triode driver stage is installed. New output transistors -- rugged Motorola MJ21193 and MJ21194 bipolar devices -- are mounted to the heatsinks on daughterboards. All components are top high-quality. The upgrade boards are double-sided with heavy copper cladding. The finished product is called the NP220. Gone is 26dB of feedback, gone is the thick, closed-in MOSFET sound, gone is the fragility of the MOSFET output stage. Three cloudy-sounding polypropylene coupling caps have been reduced to a single transparent-sounding Dynamicap, the tubes have been upgraded to two 6SN7 (ECC32), regulated power supplies with a Hammond choke input filter replace unregulated supplies for greater dynamics. The signal path is cleaner, simpler. The rebuilt amplifier retains the basic liquidity of the old design (same designer, after all), but with greater liveliness; deeper, wider soundstaging with precise localization; deeper, more powerful bass; broader dynamic nuances; and sweeter, more transparent treble. The amplifier sounds luscious and rich, the music seems to emerge from a silent background with hair-raising snap.

Pricing for the NP220 "Basic" Rebuild: $2,800
Please specify High or Low Sensitivity when ordering.

The Premium, Premium Gold, and Premium PLATINUM. The amps below use parts that are simply not found on products on the retail market. You have probably never experienced anything that sounds this good. These amplifiers have huge dynamics, like real music. Having grown up in a family of jazz musicians, I know what brass and woodwinds are meant to sound like, and how loud they need to be to sound real. These amps beg to be turned up: the music becomes uncannily lifelike without a wisp of strain. Percussion instruments snap out of the speaker with amazing speed and weight, horns have bite and the kind of body that you only hear with the real thing. I've never before experienced this with a hi-fi system until I developed the NP220 family of Premiums.

NP220 Premium Rebuild

The NP220 Premium is the Basic rebuild, but adds several parts enhancements.The circuitry is the same, but the parts upgrade is extensive:

  • Mills, Caddock Tetrinox, and Vishay "Naked" bulk metal-foil resistors are used in critical locations (the eight essential voicing resistors are upgraded to TX2575 naked Z-foil resistors -- click here for an overview about my resistors choices).
  • Both coupling capacitors are upgraded to the wonderful new Dynamicaps by TRT.
  • The main, shared on-board high voltage power supply capacitor is upgraded to a low-distortion, low-impedance, extended bandwidth Continental Capacitor "Type A" and Nichicon KZ Muse caps. Three Continental Capacitors can be seen in the image below, in the Premium Gold section.
  • The eight main rectifiers, which provide speaker-driving current for the output stage, are upgraded to high-speed Fast-Recovery Epitaxial Diodes ("FREDs"), which have soft recovery and lack of ringing, to significantly reduce noise, glare and grain.

The sound quality improvement with these better parts must be heard to be understood. It is much more cohesive from low bass to high treble and sounds far less electronic than even the best high-fidelity gear available on the retail level simply because the cost of the parts involved prohibits using them in all but the most expensive (read: $10,000+) retail products.

Pricing for the NP220 "Premium" Rebuild: $3800
Please specify High or Low Sensitivity when ordering.)

NP220 Premium "Gold" Rebuild

Although this is a Platinum NP220, the silver Continental Capacitors used on everything above the Basic level upgrade, are visible. Click on the picture for an enlarged view. (Amplifier courtesy S. Smith.)
For the "Gold" version of the amplifier, you receive circuit boards upgraded to Premium level (above), then the last vestiges of the amplifier's original circuitry -- the transformer, main "rail" rectifiers, current-handling wire, and main output storage capacitors -- are replaced. All that's left of the old amplifier is the outside. Everything inside has been upgraded.
       You receive a custom-made high-current, low-noise Plitron toroid transformer, built to my specifications. With this transformer, the sound is fast and direct, without the fuzziness contributed by lesser designs, and bass is heavier, more defined, more powerful.
      All four main filter caps are upgraded to Nichicon KG-type electrolytics, which provide exceptional coherence and resolution all the way down into the bass region, something that you won't hear in designs that use standard low-cost "computer-grade" aluminum electrolytics.
      Two more Continental Capacitors are added: one each per channel for local tube B+ decoupling.
      Current-carrying wiring is upgraded to Van Den Hul "The Wind" Hybrid II wire -- totally transparent and grain-free from the treble to the bass.
Premium Gold and Platinum upgrades both benefit from better wiring and the KG capacitors. Click on the picture for an enlarged view. (Amplifier courtesy S. Smith.)


Pricing for the NP220 "Premium Gold" Rebuild: $5500
Please specify High or Low Sensitivity when ordering.
As is the case with all Plitron parts, allow eight weeks for delivery of the upgrade transformer.)






NP220 Premium "PLATINUM" Rebuild

NP220 Platinum with optional Plitron choke in center of circuit board. Click on the picture for an enlarged view. (Amplifier courtesy S. Smith.)

It had to happen. A level above the Premium Gold, for the simple reason that the more places you use the good parts, the better it sounds. We start with a Premium Gold, then add:

All nine fuses upgraded to HiFi Tuning gold/silver.

All critical resistors in the signal path and in the power supplies upgraded to "naked" Vishay TX2575 Z-foil resistors, bringing the total of TX2575 used from 16 (obtained with the Premium upgrade) to 50.

Alas, the good parts that sound so good, cost so very much, too. I'm not kidding: see how the price goes up from the Premium Gold to the Premium PLATINUM. But these parts are simply wonderful: they confer a degree of realism and naturalness to the sound that has to be experienced. Click on the links for the fuses and resistors (above) to read what these parts do.

Pricing for the NP220 "Premium PLATINUM " Rebuild: $6600
Please specify High or Low Sensitivity when ordering.
As is the case with all Plitron parts, allow eight weeks for delivery of the upgrade transformer.)


I am making available some additional modifications for the NP220 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 NP 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. Plitron's Amazing Toroidal Choke - Detail and authority at the frequency extremes never before heard from tube electronics.

An Alta Vista Audio exclusive! All versions of the NP220 use choke-input power supply filtering, simply because it sounds better (click here to read why). You may have noticed that you've probably already heard about the benefits of using better-sounding capacitors in a power supply, but you've never heard about using better-sounding chokes in a power supply! Why? Because until now, all chokes sounded the same because they were all built the same!

This new and unique toroidal choke is built by Plitron, the same people who make the amazing transformer used in the Premium Gold and PLATINUM versions. No one but Plitron has figured out how to build one, and no one but Alta Vista Audio is presently using 'em! With it, the NP220 really sings -- there's an extra octave of high-frequency information -- the highs open up and extend higher than I've ever heard this amp go before. And the bass is meatier and fatter (phatter?). This component can be added to ALL versions of the NP220 upgrade.

A toroidal choke for DC power supply applications? Who ever heard of such a thing? Audiophiles have long recognized that power supplies with chokes are the best-sounding ones, but until now, these chokes were always square "EI" types, because it is not possible to build a toroid choke with the necessary "gap" in the magnetic core. Without that gap, the core would become magnetically saturated by the DC current and the choke would be useless. But Plitron's engineers have figured it out.
      Pictured above is an NP220 Premium Gold owned by Al Adkins of Everett, Washington. Compare the toroidal choke located in the middle of this circuit board with the stock choke shown on amplifier near the top of this page (click here). That stock choke is made by Hammond Manufacturing, and is a very well-built EI DC choke, and until now was considered state-of-the-art. But while this upgrade Plitron toroid choke is electrically identical to the much smaller Hammond, its unique core material and geometry lets you hear detail and authority at the frequency extremes that you never expected to hear from tube electronics.
Pricing for Option 1. Add $475 to upgrade to the Amazing Plitron Toroidal Choke.
(As is the case with the Plitron upgrade transformer, allow ten weeks for this part. Add setup fee if not done with either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

Option 2. Improved Input RCA Connectors
The old RCA jacks are removed and Cardas GRFA RCA jacks are installed in the chassis.

Pricing for Option 2. Add $120 to upgrade the input RCA jacks.
(Not done separately, requires either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

Option 3. Improved Speaker Terminals
I replace the original speaker terminals with Cardas CCGR posts. Some chassis modification required.

Pricing for Option 3. Add $300 to upgrade the speaker terminals.
(Not done separately, requires either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

Option 4. Balanced inputs

The new NP220 can be wired to handle balanced signals directly without a transformer or additional circuitry. These are true balanced inputs: the tube stage is a differential one and provides + and - inputs. While your amplifier is in my shop, I can modify the chassis and mount Neutrik XLR connectors. Your RCA inputs are not removed and can still be used with unbalanced sources. I supply shunting connectors to earth the negative polarity input for when the RCA inputs are being used. Some chassis modification required.

Pricing for Option 4: Add $240 for balanced inputs.
(Not done separately, requires either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

"Total Connector" Upgrade Package: Save when you buy Options 2, 3 and 4 all together. Only $560!
(Not done separately, requires either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

Option 5. High Sensitivity Version

The NP220 rebuild uses a pair of 6SN7 (ECC32) dual-triode octal tubes for what I call the "low-sensitivity" version. I like this tube -- it's a very linear tube, favored by many hi-fi buffs, and one that I used in my highly-sought SA-11 Line Stage (1984). With this tube, the NP220 has a gain factor of 7x (17dB) and needs an input signal level of at least 7 volts rms (20 volts peak-to-peak) to reach full power output. This is normally not a problem with most preamplifiers, especially tube preamps, which are capable of high output levels. It also has a couple of advantages: First, you'll be running the volume control at a higher level, where you have more control, and second, preamp background noise will be reduced to inaudibility -- great if you have sensitive speakers or listen in a quiet environment.

However, if your preamplifier cannot provide this level of output (see your owner's manual), or if you are using a passive preamp and your source components are incapable of putting out this relatively high level of signal, you should specify the high sensitivity version of the NP220. This is based on the high-mu 6SL7 (ECC35) tube, also an octal tube, also a high-fidelity favorite. The high-sensitivity version has a gain factor of 23x (27dB) and only requires 1.9 Volts (rms) of signal to be driven to full power. There is no additional charge for either version.

(Still confused? Click here to read more about amplifier sensitivity.)

Amplifier Type
Sensitivity (rms volts input drive needed for full power of 220W)
(RCA Inputs)


Original SA-20/220 (provided for your reference):


Pre-1999 Standard 6922-based NP220
Pre-1999 Optional High-Sensitivity 12AX7A-based NP220
Current NP220: Low Sensitivity 6SN7 Version


Current NP220: High-Sensitivity 6SL7 Version
Gain and sensitivity options for NP220 amplifier.

Option 6. Monoblock Version

The NP220 is a stereo amplifier that can be internally switched to mono mode as a bridged amplifier. If you wish, I can provide it this way as a dedicated mono amplifier. As a dedicated mono amp, one input jack is removed and the hole in the chassis plugged. Whether you order the NP220 as a dedicated mono amp, or you switch it to mono yourself, the NP220 delivers over 600W (8 ohms) with amazing speed and bass tightness; a sound that seems to float on a cushion of air. The amplifier speaks with effortless ease, it gets better and more natural-sounding as you turn it up.

Pricing for Option 6. Add $180 for monoblock version with RCA input jack,
add $240 for monoblock version with balanced XLR input.

Option 7. 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 setup fee if not done with either the Basic, Premium, Premium GOLD, or Premium PLATINUM upgrades.)

About Tubes.

    The low-sensitivity version of the NP220 ships with a pair of Sovtek 6SN7 triode tubes. These tubes are currently in production, and sound very, very detailed and transparent. They are, however, a bit analytical-sounding -- not the richest or most emotionally involving sounding tube out there. The good news is that the amplifier is extremely neutral-sounding, so it will sound like whatever tube you put in it.
    Though I don't stock them, I will mention the Sylvania JAN VT-231, which sounds a bit heavy, yet is so scarily rich and full that it will raise goosebumps on your arms; and the RCA "Red Base" 5692 which provides a warmer and rounder sound than the Sovtek, and is every bit as detailed. There are other tube types that will work well, too. See the 6SN7 section of the tube page.
I will happily install something beside the Sovtek 6SN7 tubes in your low-sensitivity upgrade if you send them to me while I build up your amp. More information about tubes can be found on the 6SN7 section of the tube page. Firebottle Audio's web page has a huge list of tube resources, including dozens of online vendors.

Please feel free to contact me if you have any questions.

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