SA-4 Upgrades

The SA-4 was Counterpoint's first power amp. Based on a design licensed from Roger Modjeski, these mono amplifiers are a revelation to hear. When matched to the right speakers (OTL's tend to be sensitive) they offer unparalled transparency and detail. If you own a pair of these amps, you know what they can do. You also know that getting matched sets of output tubes is a problem.

     On this page I describe some upgrades we now offer at Alta Vista Audio for this great amplifier. I also present a long-sought modification that allows unmatched tubes to be used.

The Upgrades

Output Tube Biasing Upgrade
Standard Upgrade
Premium Upgrade
PLATINUM Upgrade
A note about amplifier maintenance
Improved RCA Jacks
Improved Speaker Terminals
Option: Circuit Board Damping

Output Tube Biasing Upgrade, or Using Unmatched Tubes in the SA-4

Who knew, in 1984, that the 6LF6 tube, a tube that was very plentiful at the time, would become so rare? This tube was so common and inexpensive that the SA-4 was designed to use sets of eight that had been pre-matched at the factory. When you can get thousands at a low cost, measuring them and matching them was neither difficult or expensive. Counterpoint assumed that these tubes would remain easy to find and inexpensive, so providing matched octets for decades would be easy.
     Surprisingly, this tube has become fairly rare and quite expensive -- new ones cost anywhere from $40 to $50 apiece, and the amplifier won't work well if you just pop in eight unmatched tubes. Hundreds would need to be purchased in order to find just a few matched sets. This has been a problem for years, and I never had a good answer for owners of SA-4's who were looking for tubes.
     Fortunately, in 2002 an SA-4 owner took me up on my longstanding offer to develop a modification for the power amp that so that unmatched tubes could be individually biased by hand. Mr. Sweetnich, the owner, understood that this might take longer to develop than any other upgrade I had done. I cautioned him that I had an idea only, it had not been tried, and it might not even work, that all I could promise is that I would work on his amplifiers as I could, as inspiration struck.
    He agreed and the amps arrived in April of 2002. Eleven months later, the work was done and is now available for all SA-4's.

Details of the Modification
Wouldn't it be nice if you could adjust the bias for each tube individually? With the new SA-4 Output Tube Biasing upgrade you can! Eight individual controls permit exact matching, via the SA-4's existing Tube Current Meter.

The SA-4 Output Tube Biasing controls are housed in a small, 19''-wide black-finished chassis that sits atop the SA-4 amplifier. Lettering style matches front panel lettering of SA-4 amplifier. Sorry -- black wrinkle-finish powdercoat paint is the only finish I can offer at this price point.

Most of the new biasing circuitry is located inside the SA-4 amplifier, to keep it close to the output tubes. By keeping it close and using premium parts the sound of the amplifier is unchanged. We mount the actual controls in a separate aluminum box for convenience and safety reason. I didn't think it was a good idea to have customers poking around the inside of the amplifier with a screwdriver while looking at the front panel meter. The high voltages within are dangerous, and the high temperatures would quickly age the carbon-composition controls.

	The tube biasing controls connect to the amplifer's rear panel using a sturdy twist-on connector with gold plated contacts. You have a choice between standard wire and Cardas wires to bring the signals up to the bias controls.

How does it sound? What's the sound of nothing? The real question I needed to answer when I developed his modification was how it would affect the sound. I'm happy to say that SA-4's sound better than ever with the tubes all dialed in. Distortion drops to 20% of the amount that we normally see. And the sound is very, very pure. I prefer the sound with the tubes all matched up this way to the sound of an unmodified SA-4 with tubes that are merely close. An already transparent-sounding amplifier becomes even less colored. There is no other effect on the sound at all.
    Note that it is recommended that all eight tubes in the SA-4 be from the same manufacturer. The most common 6LF6 is from GE. They appear to have made two types, a "tall bottle" type and one that is about 1cm shorter. Other than the size of the tube, there does not appear to be any other difference so I think they can be interchanged and mixed in the same amplifier. If you find some other types of 6LF6's and have find they work well, please contact me and I can add this information for other SA-4 owners.

Price for SA-4 Standard Output Tube Biasing Upgrade: $870 per amplifier. Price includes outboard bias control chassis and amplifier modification. Control cable wiring is high-grade PVC-insulated in braided sleeve. Allow four to six weeks to install this upgrade. Add $80 per amplifier to upgrade wiring to Cardas 20.5 gauge wiring.

NOTE: It's not my intention to profit from what might be considered a design flaw (not being able to individually bias the tubes), so if you are handy with electronics, all the essential information to modify your own amplifiers is here.

The following upgrades are targeted at improving the sound of an already great-sounding amplifier.

Standard Upgrade

The SA-4's are reknowned for their transparent detailed and relaxed sound, free of any grain or edge. My foremost concern when developing upgrades for this amplifier was to preserve this quality which has made the amplifiers so beloved by their owners. While the circuit design is excellent and needs no improving, I knew that the components used in these amplifiers are not considered high-end by today's standards. That they are, in fact, not great-sounding at all. So this upgrade directs itself to improving the power supplies and audio paths simply by using better parts. The end result is an amplifier that is more of an "open window" into the recording than any I have heard.
    

	Caddock TF020, the most-transparent and dynamic resistors available are used in critical locations. Input tube socket has been upgraded to ceramic with gold contacts.

The Standard Upgrade includes:

• Upgrading of critical resistors on input audio board to Naked Vishay, Caddock TF020, or Mills noninductive wirewound (as needed),
• Replacing 50-cent Texas Instruments TL082-based two-stage DC servo with single-stage Burr-Brown metal-can servo. In 1984 no one knew that you could hear the DC servo amp -- you can and you need to use the best-sounding part available,
• Input wiring upgraded to insulated "Wonder Wire",
• Input 12AX7 tube socket and the two small 6FS5 tube sockets upgraded to ceramic with gold contacts,
• All signal coupling capacitors on the input board upgraded to TRT Dynamicaps,
  
  

  	AC Input coupling capacitor upgraded to Dynamicap. Note upgrade Cardas input jacks and connector for optional Output Tube Biasing Upgrade.

• Critical power supply capacitors on the input board upgraded to Nichicon KZ Muse (fantastic-sounding great-value electrolytics),
• Gold contact edge connectors on input audio board and power supply board are cleaned and contact preservative applied.
  

  The SA-4's Input Audio Board with upgraded components.

  
  
• On the power supply board, the two output tube screen regulator capacitors, and the five main 130uF/350V power supply capacitors used for the input tube board's +300 / - 600V power supplies are upgraded to Black Gate polarized types,
  
• Upgrade the six rectifiers used for the +300 / - 600V power supplies to super-quiet 1000V 12A FRED diodes,
  
  

  	Power Supply Board showing the upgraded capacitors (in this case the Black Gate nonpolarized types used in the Premium upgrade are shown)..

  
  
• On the 6LF6 output tube board, each output tube's grid resistor, screen resistor and cathode resistor is upgraded to Mills noninductive wirewound,
• All eight tube sockets are replaced with more reliable ones (note: I would like to be able to offer an upgraded printed-circuit mount ceramic sockets for these 12-pin compactron tubes, but can't find any. If you know of any, please let me know),
• Also on the output tube board, the output coupling capacitor is upgraded to an TRT dynamicap, and the local +/- 150 volt main rail decoupling capacitors and 200V screen capacitors are upgraded to Black Gate NH type nonpolarized,
• Finally, all eight output tube plate caps are upgraded to ceramic types with effective silver-plated contacts, and the plate cap wiring is upgraded to Cardas Teflon-insulated wiring for long life in the amplifier's high-temperature environment.

	Output Tube Board showing local main and screen rail decoupling capacitors, and upgraded ceramic tube plate caps.

Price for SA-4 Standard Upgrade: $1460 per amplifier.

Premium Upgrade

The Premium Upgrade contains all of the Standard Upgrade items with the following changes or additions:

• All internal wiring (power-supply and speaker-output wiring with the exception of the transformer wires which are permanantly attached and cannot be upgraded) is upgraded to continuous-cast-copper, with a new capacitor bus bar atop the two main rail caps. This is a very labor-intensive job, please allow extra time,
• On the Input Audio Board, five additional power supply capacitors are upgraded to Nichicon's great-sounding KZ capacitors,
• On the Power Supply Board, the two output tube screen regulator capacitors, and the five main 130uF/350V power supply capacitors used for the input tube board's +300 / - 600V power supplies are upgraded to Black Gate "NH" nonpolarized types,
• New bridge rectifiers are fabricated for the amplifier's +/- 150-volt output rail supplies and +200V screen regulator supply using FRED rectifiers,
• The 490uF/350volt main screen capacitor at the amplifier's front left is upgraded to Black Gate WKZ polarized.

	This is one of Mr. Sweetnich's Premium upgraded amplifiers.

Price for SA-4 Premium Upgrade: $2875 per amplifier
(price includes standard upgrade, above)

Platinum (Super-Premium) Upgrade

The PLATINUM Upgrade takes the SA-4 to the limits. It's like a Premium upgrade on steroids.

	An SA-4 with Platinum upgrade. Courtesy Mr. Hasegawa, "The most lifelike sound I have ever heard, almost as if there is some kind of magic inside. I am 200% satisfied."

• The rear panel is stiffened with a cast aluminum extrusion.
• Naked Vishay resistors used throughtout the signal path on the audio board (left side board).
• On the Power Supply Board, the two output tube screen regulator capacitors are upgraded to Black Gate "NH" nonpolarized types, and the five main 130uF/350V power supply capacitors used for the input tube board's +300 / - 600V power supplies are upgraded to Continental Capacitor Type A caps,
• The two large rail supply capacitors at the front as well as the main screen supply capacitor, also at the front, are refreshed with new original types.
  

Three of the five bolts which affix the rear stiffener. aBanks of Continental Type-A capacitors provide reliable, utterly transparent sound, surpassing the best Black Gate capacitors.

Price for SA-4 PLATINUM Upgrade: $4025 per amplifier
(price includes all of the Standard Upgrade and Premium items listed above)

A note about amplifier maintenance

Counterpoint manufactured the SA-4 amplifiers all through the middle 1980's. Despite the high temperatures within, the amplifiers have proven to be quite a reliable design. We almost never get calls to service them. However, due to the elevated temperatures and age of the units, we have seen a couple with failing electrolytic capacitors. Specifically, the two Mepco/Electra brand 12,000uF/150V electrolytic + and - rail caps (main energy supply for output stage tubes) located behind the meter may require replacing if they show signs of aging (leaking fluid from the vent on top). We recommend the Cornell-Dublier long-life 15000uF/160V capacitor (P/N 500C153T160DJ2B or equivalent).
     To the best of our knowledge, upgrading this parts is not possible because no one makes a high-end capacitor with anywhere near this amount of capacitance and voltage.

If you'd like us to do this while your amplifier is here for upgrading, please add $30 / amplifier. A Setup Fee may apply if that's all the amplifier has been sent in for.

Other bits that can get upgraded:

Improved Input RCA Connectors

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

Pricing for Upgraded RCA Connectors: Add $95 per amplifier to upgrade the input RCA jacks connectors.

Improved Speaker Terminals

We replace the original speaker terminals with Cardas CCGR posts. Some chassis modification required.

Pricing for Improved Speaker Terminals: Add $215 per amplifier to upgrade the speaker terminals.

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 the SA-4 Biasing Upgrade or the SA-4 Standard upgrade.)

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