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Frequently Asked Questions

How does Atma-Sphere's patented design work?

In each audio channel, there are two single-ended triode amps running 180 degrees out-of-phase with each other (differentially). So distortion is cancelled at every point throughout the amp (without feedback), leaving only the music. Thus, Atma-Sphere combines the power of push-pull with the musicality of single-ended, but with better sound than either, because the output is direct coupled (no output transformer). Thus, our gear is wide bandwidth, very dynamic, extremely neutral, and virtually distortion-free. 

Will the new amp/preamp work with my current preamp/amp?

Yes. Atma-Sphere equipment can be run either Balanced or Single-Ended. There is no need to modify your system to use our preamps or power amps. In fact, most of the reveiws on the power amplifiers were written with single-ended preamps. 

Alternately, we can add balanced inputs to your amplifier regardless of manufacturer. The balanced input is a simple, transformerless modification that does not change the character of the amplifier. Even on single-ended amplifiers, the input will be a true differential input. Contact us for details. 

Are your amplifiers really class A?

Yes. Our amplifiers are set up to run what is known as class A2. To accomplish class A2 the bias point has to be shifted slightly (relative to the classic A1 point found in many textbooks) and that point must be chosen carefully to avoid cutoff during the waveform cycle. This approach trades some linearity for increased power output in a way similar to but not as profound as classes AB1 and AB2. The power tubes conduct throughout the entire waveform all the way to full power, but during part of the cycle also have significant grid current. This requires a driver circuit that can handle the grid current without loss of linearity- we feature a simple and reliable circuit that does just that in all of our amps. 

OTLs have requirements having nothing to do with class of operation that make this kind of approach quite important for stable and reliable operation! In addition this allows for instantaneous overload recovery, a vital feature in a high quality amplifier. 

Class A1 circuits do not have grid current and operate at a different point on their load lines. The class of operation in any tube the amp is also dependant on the load being driven; if the load (speaker) impedance is too low the amplifier operates class AB2. In the case of the M-60, it is class A2 into 8 ohms but class AB2 into 4 ohms. This is a reason why it is a good idea to keep the speaker impedance higher if you can, although it is not by any means the most pressing- for reasons other than class of operation the amplifier will be lower distortion driving higher impedances (and the amplifier runs cooler into higher impedances too). 

We avoid marketing terms, using only engineering / technical terms in the description of class of operation. For example 'pure class A' is a marketing term, not an engineering term, as is 'real class A' (although by definition obviously our amplifiers are 'real' class A...) or 'enriched AB' (which is simply 'class AB'; 'enriched' or no has nothing to do with it). Sometimes it is helps to describe something by what it is not; since our power tubes do not go into cutoff, our amps are neither class AB1 or AB2 (within load limits as mentioned earlier). The only definition that fits is class A2. 

Can the equipment be built for 235 volt operation?

Yes. Atma-Sphere products are silent with 50 Hz operation, making for especially quiet transformers. Please specify if you need overseas voltages. 

Will the preamp work with my low output cartridge?

Yes. Any cartridge of .2 mV or more will work. An optional stepup transformer for ultra low output moving coil cartidges is available too. 

What is the break-in period for my new equipment?

About 2-6 weeks depending on use. 

What options are available?

Though our stock equipment ships with quality components, we offer upgrades of certain components upon request. Some common upgrades include: Caddock resistor package (standard on MA-2 and MA-3), Teflon coupling caps, power supply capacitance boost (for M-60 and MA-1). A remote volume control is available for the MP-1. Other options are listed on individual products pages. 

Is the price stated for a single chassis or for a pair?

Except for the S-30, Atma-Sphere power amps are monoblocks, which means there is a single channel per chassis. Therefore, all power amp pricing is for a pair of chassis. 

Do you make a phono stage?

Yes. Both of our preamps are designed as stand-alone phono reproducers. Since we developed and patented our line stage technology, it happens to be a fact that they do sound better than any other line stage available at this writing. This has been true since the inception of the preamps in 1989. So if you want to hear the best that phono can offer, it is best done through our preamps. 

By incorporating the phono into the preamp, we eliminate the variables of interconnection between the phono section and the line stage and we offer one of the best volume controls available in the industry. Our patent allows for performance in the line stage that is obviously superior to any line stage available elsewhere even when price is no object.

Are Atma-Sphere products Futterman OTLs?

No! Our gear employs our patented Circlotronic® design which is not only much simpler, but side-steps the problems of the Futterman, making OTLs available to a much wider audience. 

Are OTLs unreliable?

Again, no! The Futterman and New York Audio Lab amplifiers (sold by Harvey Rosenburg) created this reputation. A properly designed OTL such as an Atma-Sphere OTL is very reliable and are proven to run for decades without service other than tubes. 

Is the amp stable? Under what conditions might it oscillate?

Our amplifiers are unconditionally stable. They will not oscillate with any load or input condition.

If a tube arcs will it damage my amplifier?

No. The amplifier circuit is quite rugged. 

If a tube goes down will it damage my speaker?

No. We have been building these amplifiers for over 3 decades; the amps are designed to prevent damage to speakers through several techniques which are quite effective. In that entire time we know of no legitimate case of speaker damage caused by our amps. 

Does the amp produce a lot of heat?

All Atma-Sphere amplifiers operate Class "A". They run about 10% hotter than an transistor amp with equivalent power operating in Class A. To give you a better idea of this, if the amplifier is left on Standby for a day, the heat is makes is negligable. At the end of the day you could still touch the envelopes of the tubes without concern. The heat is caused by the class of operation, not the number of tubes! 

Will the amp be comfortable with my loudspeaker?

We recommend you read our paper on the Voltage and Power Paradigms! There is more to it than simple impedance, but as with all tube amps, 8 ohms or more is preferred for best results. The MA-1 and MA-2 are quite comfortable on 4 ohm speakers. For lower impedances that don't need a lot of power, there is an outboard device called the ZERO that is surprisingly effective, in fact so much so that for 4 ohm speakers, Atma-Sphere and a set of ZEROs are often one of the best choices available. 

What is the function of the meter?

On our older amps: The bias is set using the meter and the appropriate controls located on each chassis. The procedure (outlined in the owner's manual), is simple and requires less than one minute per chassis to complete. 

On the new Mk. IIIs and Mk. 3.1s: the meter allows you to monitor output power and is also used to set DC Offset. The bias is automatic on the Mk. III/Mk. 3.1 amplifiers. 

Do I need to know a lot about the tubes?

No. Atma-Sphere equipment is designed to work with commonly available tubes, making our products easy to live with. The 6SN7 tubes we use are produced in China but there are many aftermarket versions available. The output tubes are Sovtek, Svetlana or Chinese. The miniature triodes used in the preamps such as the 12AT7 and the 12AU7 are usually Chinese. Other types of tubes may be available on request. 

Tube Types and Quantities

per Chassis

Equipement Output tube Quantity Driver tube Quantity
S-30 (stereo)6AS7G106SN76
MP-36SN7212AT76 + 2

Amplifier Wattage For Common Loads

All values are for Mk. III and higher amplifiers

Amplifier4 Ω8 Ω16 Ω
Class D20010050

1742 Selby Avenue
St. Paul, MN 55104


Tel : +1 651-690-2246