Zesto Audio Eros 500 Select Class A Tube Amplifier – Quick Look
All Image Credit: Zesto Audio
California based Zesto Audio has just released their new Eros 500 Select Monoblock Class A tube amps. This new circuit design using six KT150 tubes is capable of 250 watts of Class A power per channel, but such high performance comes at a high price!
The Eros 500 supports KT88, KT120, KT150 and KT170 tubes all with the flick of a three position auto bias switch. According to the amplifiers designer and company President George Counnas; “The Bias Select switch is safe and easy to use, and you can change on the “Fly” so you can hear the difference. You don’t have to be an engineer to enjoy my equipment.”
Available power depends upon the output tubes and bias setting selected, varying between 150 to 250 watts, with each valve set and bias setting creating its own unique tube sound signature. The non-inverting circuit design does not use negative feedback and the combo Push-Pull and Ultra Linear circuit provides lower distortion, more power, and improved tube performance. The main power supply is based upon a large custom toroidal transformer which reduces noise from stray magnetic fields.
Inputs include gold plated unbalanced RCA and true floating transformer balanced XLR connectors. There is a ground lift switch to remove earth loops if hum is present and both 4ohm and 8ohm speaker loads are supported together with a SpeakOn connector for a subwoofer.
Features At A Glance:
- Sextet of KT150 output tubes create 250 watts of Class A musical power.
- Class A power is fast for a more lively, immediate response to your music
- The Bias Select switch is engineered with 3 perfect auto bias settings for KT88, KT120, KT150 and KT170 output tubes.
- The Bias Select switch is safe and easy to use, change on the “Fly” so you can hear the difference.
- 4 Ohm and 8 Ohm taps gives you options for your speaker preference. 4 Ohm may give you more base and the 8 Ohm tap may sound more open.
- The optimized frequency response provides the best musical range to benefit the natural harmonic structure of the instruments
- The SpeakOn cable connector provides most reliable hookup for your subwoofer.
- Transformer balanced true differential XLR input offers noise cancelling and rejection, as well as providing ground isolation from your preamp.
- Should you need to eliminate a hum? The Eros 500 has a XLR ground switch installed for your safety. This eliminates the dangerous temptation to lift the ground from the mains.
- The combo Push-Pull and Ultra Linear circuit design provides lower distortion, more power, and a better performance out of your tubes.
- No Negative Feedback in the circuit design provides better dynamic range because it doesn’t compress the music.
- Non-inverting polarity retains the same phase as the input (so your trumpets blow and don’t suck)
- Large Custom Toroid power transformer provides plenty of available power.
- Toroids have lower noise because they concentrate the magnetic field and are very efficient in the 50 to 60Hz mains range.
- Choice of high quality gold plated Single Ended RCA or Balanced XLR connectors to suit your needs or cable preferences
- Gold pin sockets are more reliable because gold doesn’t oxidize when it heat cycles.
- An extensive grounding scheme is designed into the power supply, wiring and all tube circuitry.
- Elegantly designed, heavy duty 14 & 16 gauge zinc plated, fully grounded steel enclosure isolates external noise and vibration.
- All fuses are easily accessible
- It’s ready to enjoy with 50 hours of factory burn in on all circuits and vacuum tubes.
- Each unit is hand built “Made in the USA”
Technical Specifications Per amp (based on KT150 tubes):
- Output
- Pure Class A, Push-Pull Ultra Linear design
- 250 Watts per amp
- 4 Ohm and 8 Ohm non-differential output taps
- Three 5-way binding posts
- 10 Amp and 7 Amp Slow-blow speaker fuses (6mm x 32mm)
- Non-inverting output polarity
- SpeakOn connector for a subwoofer
- SpeakOn subwoofer cable specs: Pins +1 and +2 go to the 8 Ohm output and pin -1 goes to ground
- Power rating for Auto Bias Select Switch Settings
- Left Position: KT88 = 150 Watts per channel KT120 = 150 Watts per channel KT150 = 150 Watts per channel KT170 = 150 Watts per channel
- Middle switch position: KT150 = 200 Watts per channel KT170 = 200 Watts per channel
- Right switch position: KT150 = 250 Watts per channel KT170 = 250 Watts per channel
- Inputs
- Transformer true balanced differential input
- XLR gold pin balanced input with pin 2 hot, impedance 12K Ohms
- RCA gold pin single ended input, impedance of 12K Ohms
- XLR ground lift switch
- 3.3 Volts RMS input to reach rated output
- Detailed Specs
- Monaural
- Auto bias
- No negative feedback
- Frequency response 20Hz to 30KHz ~ 3dB
- Total Harmonic Distortion ~ 0.07% at 1W into 8 Ohms
- Gain of 27dB
- Noise level > 4 mV RMS into 8 Ohms with input shorted
- 1% metal film resistors throughout
- Polypropylene capacitors throughout the signal path
- Power Supply
- Large custom Toroidal power transformer
- 120 Volts AC mains with 10 Amp 5mm x 20mm slow blow fuse
- Mains fuse located in drawer compartment of IEC power connector
- 3 pin 15 Amp IEC power inlet connector
- Optional factory installed 220V, 230V/240V 50/60Hz with 6.3 Amp slow blow fuse
- Power consumption at rated output 756 Watts
- On/Off switch located on front panel
- Amber LED low voltage and green LED high voltage indicators
- Active Components
- Six (6) KT150 vacuum tubes
- Two (2) ECC82 (12AU7) vacuum tubes
- Other Features
- Each unit is made by hand
- 50 hour factory burn in on all circuits and vacuum tubes
- Dimensions 17″ W X 20″ D X 10″ H (43.1 cm x 25.4 cm x 50.8 cm)
- Weight 79 lbs. (35.8 Kg)
- Shipping weight 96 lbs. (43.5 Kg)
- 16 and 14 gauge Zinc plated steel enclosure
MSRP: $35,000.00 a pair with KT150 output tubes
For the full technical details visit the Zesto Audio web site.
Read the Press Release here.
Want to know more about amplifier and tube operation? Then check out these posts:
Will this amplifier be able to drive martinlogan CLX speakers which deep down to 2 or 1 impedance.
How long is the tube life and are this tubes readily available
Are tubes made in USA or are imported from Russia or some other country
Hi Rajendra,
First I believe that KTxxx tubes these days are made in Saratov, Russia, JJ Electronic in Čadca, Slovakia and Hengyang Electronics in Foshan, China and in Hungary. The Russian brands would probably include; Reflektor, SED SPb/J.S.C. Svetlana, Ulyanov, JSC Voskhod, and Novosibirsk. The 300B triode is still available from Western Electric in the US.
As for driving impedances as low as 1 ohm there are few amplifiers, especially valve, that can comfortably drive such low impedances. If you are serious about the Eros you should pose the question to the manufacturer as my valve experience is limited to KT88’s in the Leak TL50Plus amplifier.
As for longevity, well that all depends on how often you use them and how hard you drive them. I used to change my KT88’s after about 1500+ hours of use. However the original KT88’s and probably the current KT120/150/170 are probably good up to about 2500 hours.
Thank you for your comments and popping by.
Regards
Paul