A: Bob Carver has applied his decades of experience in both solid state and tube amplifier design as well as drawn upon the experience of other famous designers when he designed these amplifiers. He has incorporated "best of class" circuits that make these products just sound great! This includes both voltage and current feedback loops, automatic DC restoration and bias schemes and an output transformer design that has unmatched performance.

A: There are many reasons, but most importantly the output transformer and feedback circuits allow the amplifier to "listen to the room" to create this enveloping sound stage with lots of depth and fine imaging. This is possible with a unique combination of:

1. The ultra-wide bandwidth audio transformer has an interleaved winding technique and very conservative VA rating. It was over designed from a thermal perspective, but this also contributes to higher bandwidth as well as better impulse bass response (more stored energy reserves).
2. The audio transformer by design has a source impedance of 1.3 ohms. This allows the amplifier to provide independent current and voltage feedback loops to the input stage - from voltages that are impressed across the transformer output terminals via acoustical feedback from the room onto the speaker drivers. A solid state amplifier has very low source impedance, effectively shorting out any possibility of voltages to feedback - and the result is a very "flat curtain" of sound.
3. Bob's designs make the room acoustics part of the amplified "system" which is key to creating the depth of field and fine imaging that is not available for but a few designs in the world today (at much more expensive prices).

A: Our amplifiers are hand built in the USA by highly skilled assemblers and technicians.

1. We do not use small surface mount components but large axial and radial leaded components which are more reliable and have greater surge withstand capacity than do the smaller parts.
2. We do not use circuit board traced for circuit interconnects. Our amplifiers are wired "point-to-point" - to and from every component. We use stranded wire wrapped around turret solder posts for every circuit node.
3. We do not use any de-pluggable connectors that could fail because of bad wire crimps or corroded connector pins.
4. We select resistors that are metal film or wire wound, (not the cheaper metal oxide) and specify parts with a higher wattage rating than necessary.
5. Our power supply caps have a higher voltage rating than necessary. Why? The further away you operate parts from their maximum ratings, the longer they will last and - the more they will be able to withstand surges caused by lightning strikes in the neighborhood or fluctuations in the AC power.
6. We use very low ESR high quality poly caps in all signal paths (no electrolytics), thus minimizing any added coloring caused by leaky or noisy caps.
7. All this adds up to a very robust product that will stand the test of time and be serviceable in 50 years. It has been proven that electronics built this old fashion, labor intensive way will be much more reliable (and serviceable) over long periods of time.

A: The amplifier chassis warranty is 7 years, tubes are 1 year from date of shipment. The warranty is transferrable as long as the serial number has not been removed or altered.

A: The 12AX7 is used on the front end for its excellent low noise and input buffer qualities. The 12AT7 pre-driver provides the high drive current needed for the KT88s or KT120s. We use Shuguang factory built KT88s, Bob Carver has tried a lot of other equivalent KT88s and feel these are the most reliable and sound best as well. We use Tung-Sol KT120s for the same reasons. It is not ok to substitute an equivalent tube type from a different manufacturer (not all tubes are created equal!). Others may not perform as well, be less reliable or not rated to withstand the high voltages present in these designs. Please contact us if you need replacement tubes. We buy in bulk and can provide competitive prices for replacements.

A: The unique bias scheme in these amplifiers will extend the life of the tubes many years because their idle currents are set lower than most typical designs. We offer a 1 year warranty on tubes, even though the tube factory only offers a 6 month warranty to us. Typical tube amps configured in a push pull configuration require much higher bias currents on the tubes to minimize distortion at the zero crossing point of the output waveform. Bob's DC restoration circuit virtually eliminates zero cross distortion as the 6AL5 tube circuit "clamps" the average DC component of the output to ground - keeping it from drifting up or down as the signal content varies.

A: Because if you can be assured that you have minimized the zero crossing distortion with the clamp you then no longer have to set the bias voltage up so high to do the same thing (a better mousetrap). Tube life is directly proportional to the bias voltage applied to the tubes. The lower the bias voltage - the longer the life of the tubes. How long they last will depend on how much you use the product. It is always best to turn the amplifier off when you do not use it to extend tube life. Bob believes the tubes will last for decades because of his unique, low wattage biasing scheme.

A: The "vintage / modern" sound switch selects the amount of negative feedback in the amplifier feedback loop. It is -20 dB for vintage or -11 dB for modern. Vintage will sound "warmer", modern "snappier" is the best way to describe it. It is purely a matter of taste, and the music you prefer to listen to. The good news is the user gets to pick with these amps - when there is typically not an option to do so with others

A: Adjusting the output tube bias moves the "starting point" for signal amplification up or down the "load line" or transfer function of the tube curves. Tube transfer functions are not perfectly linear, and a non linear transfer function will generate additional second harmonic distortion - that can provide depth and color to the audio signal (which by the way is not a bad thing). True audiophiles understand the sonic performance of an amplifier has nothing to do with the "flat line curves or specs" but how they sound. "Sonic quality" is subjective and dependent on many factors, the source material, preamp noise floor, speakers, room acoustics, age of the listener etc (an integrated system). Bob Carver amplifiers allow the individual listener to "set up" how he likes to listen to his music on his own particular integrated system with this bias adjustment setting.

A: See the owner's manual for detailed instructions on the dos-and-don'ts of product installation.

A: You can spend a lot of money on cables; just make sure the quality of the cables is on par with the rest of the system. Otherwise you might be embarrassed when your friends come over to listen and they see you've used lamp cord with your very expensive amplifiers.

A: All speakers have an ohm rating label usually on the back or in the manual. Once you know what your speaker impedance rating is you will then know which terminal to connect it to. Note - please make sure the amplifier main power switch is off before connecting cables to it! More details on that in the manual.

A: The 180W and 305W amplifiers can produce a lot of power. Make sure your speakers are capable of handling such power or you will risk damaging them if you turn it up too loud.

A: Vacuum tube filaments take about 20 seconds to warm up. Once they do they emit negatively charged electrons which will then flow towards the positively charged plate. It is this flow of electrons that is modulated by the grid that provides the amplification of the input signal.

A: They are hot, but substantially cooler than any other tube amp thanks to the DC restoration circuit. We can touch them without getting burned, but it is uncomfortable and it would be tempting fate to grab hold of one.

A: Check and see if all connections are intact and there are not shorts on the speaker terminals, make sure the amplifier is turned on and warned up and the volume control on the top of the amp is not turned off. Make sure the source is on and playing. If you still do not hear music then turn off the amplifier and check the fuses.

A: Per the owner's manual you should make sure the speaker wires are not shorted before connection them to the amplifier. A short circuit will blow the 1.5A bias fuse on the rear panel, but will not damage the amplifier at all. All it takes is a new fuse.

A: A shorted tube will blow the bias fuse. You can use the built-in tube tester function to determine which output tube needs to be replaced - after you replace the blown fuse with the same type and rating.

Top of Page