Zesto Audio Eros 300 Amplifier

Ron Resnick · Nov 19, 2017

The Zesto Audio Eros 300 amplifier is a Class A, push-pull design putting out 150 watts. It competes directly with the Jadis JA200 Mk. II and the Ayon Audio Orthos XS and the CAT JL-7.

Here is Don Saltzman's review in The Absolute Sound:

http://www.theabsolutesound.com/articles/zesto-eros-300-monoblock-amplifier/

Who has auditioned these amplifiers?

Who has compared them to the other contenders?

Rhapsody · Nov 20, 2017

Ron Resnick said:
The Zesto Audio Eros 300 amplifier is a Class A, push-pull design putting out 150 watts. It competes directly with the Jadis JA200 Mk. II and the Ayon Audio Orthos XS and the CAT JL-7.

Here is Don Saltzman's review in The Absolute Sound:

http://www.theabsolutesound.com/articles/zesto-eros-300-monoblock-amplifier/

Who has auditioned these amplifiers?

Who has compared them to the other contenders?

Hi Ron,

I have been running the Zesto Eros monos, as well as the Zesto pre and phono stage, for a few weeks now, still breaking in. Come back for a listen

I will have the Air Force III/Graham/Lyra Etna SL as well in another week, so I believe that you would enjoy another visit. Being a dealer it's pointless to talk about how good the Zesto amps sound, which they definitely do, but I do invite anyone that wants to stop by for a listen and hear for yourself.

bonzo75 · Nov 20, 2017

rvisinta said:
Hi Ron,

I have been running the Zesto Eros monos, as well as the Zesto pre and phono stage, for a few weeks now, still breaking in. Come back for a listen I will have the Air Force III/Graham arm as well in another week, so I believe that you would enjoy another visit. Being a dealer it's pointless to talk about how good the Zesto amps sound, which they definitely do, but I do invite anyone that wants to stop by for a listen and hear for yourself.

Interesting, especially if you still have the Vitus to compare

Rhapsody · Nov 20, 2017

bonzo75 said:
Interesting, especially if you still have the Vitus to compare

Hi Ked, I have the SM102's....

bonzo75 · Nov 20, 2017

rvisinta said:
Hi Ked, I have the SM102's....

Ron that's your test. If you prefer Vitus to the Zesto here, you will prefer Vitus to PP on your speakers.

Ron Resnick · Nov 20, 2017

rvisinta said:
Hi Ron,

I have been running the Zesto Eros monos, as well as the Zesto pre and phono stage, for a few weeks now, still breaking in. Come back for a listen I will have the Air Force III/Graham arm as well in another week, so I believe that you would enjoy another visit. Being a dealer it's pointless to talk about how good the Zesto amps sound, which they definitely do, but I do invite anyone that wants to stop by for a listen and hear for yourself.

That is great, Bob! Thank you for letting us know! (You carry some great lines: Kondo, Zesto, Vitus.)

Ron Resnick · Nov 20, 2017

bonzo75 said:
Ron that's your test. If you prefer Vitus to the Zesto here, you will prefer Vitus to PP on your speakers.

Yes, Kedar. I agree with that fully! On the Magico M3, I guess?

Ron Resnick · Nov 20, 2017

rvisinta said:
Hi Ron,

I have been running the Zesto Eros monos, as well as the Zesto pre and phono stage, for a few weeks now, still breaking in. Come back for a listen I will have the Air Force III/Graham/Lyra Etna SL as well in another week, so I believe that you would enjoy another visit. Being a dealer it's pointless to talk about how good the Zesto amps sound, which they definitely do, but I do invite anyone that wants to stop by for a listen and hear for yourself.

Bob, can the Eros 300 truly be Class A outputting 150 watts if the total power consumption at full output is 360 watts?

audio.bill · Nov 20, 2017

Ron Resnick said:
Bob, can the Eros 300 truly be Class A outputting 150 watts if the total power consumption at full output is 360 watts?

I'll let Bob address your question but that's clearly the manufacturer's claim. I noticed in addition to the full power consumption spec you quoted each mono amp consumes 348 watts at idle which will generate quite a lot of heat in a Class A design!

Rhapsody · Nov 20, 2017

Ron Resnick said:
Bob, can the Eros 300 truly be Class A outputting 150 watts if the total power consumption at full output is 360 watts?

Hi Ron,

I thought I would get an intelligent answer, so here is what George Counnas (Zesto owner and designer) had to say-

The Eros uses 360 watts when it is on with no signal and 360 watts at full power thus Class A.
Class A by definition consumes the same power with or without a signal because the tubes are turned on the whole time the amp is on.
A typical AB amp might only use 50 watts of power with no signal and (if 80% efficient) 270 watts at 150 watt output.

Rhapsody · Nov 20, 2017

audio.bill said:
I'll let Bob address your question but that's clearly the manufacturer's claim. I noticed in addition to the full power consumption spec you quoted each mono amp consumes 348 watts at idle which will generate quite a lot of heat in a Class A design!

Howdy Bill,

I thought that the amps would be firelplaces, and sure they run hot, but to me they don't throw any more heat than any SS Class A does. One thing I was a bit amazed by was that when I received the amps I asked George Counnas about how he would suggest to "break them in". He said you can just play them for 200 hours straight if you want. I've never heard a mfg. say that with tubes. The answer was always play them for 12 hours or so and let them cool down and then play them for another 12 hours the next day.

In this case I said, let's see what happens if I play them for 200 hours straight, so I did. Other than they just kept getting better sounding as the hours mounted, they ran for 200 hours, without a hicup and the room really never got even warm. I didn't expect to be able to do that, but now they are all broken in and it was no big deal.

microstrip · Nov 20, 2017

Ron Resnick said:
Bob, can the Eros 300 truly be Class A outputting 150 watts if the total power consumption at full output is 360 watts?

Most probably not exactly 150 watts class A, but something like 100-110 watts. Design maximum anode power of the KT88 is 35W and the Eros has 6 power tubes, making a total of 210W output stage idle power. But 110 watts class A is probably enough for any one!

The balanced input impedance is just 12kohm - can your tube preamplifier drive such impedance in parallel with the active bass crossover?

microstrip · Nov 20, 2017

rvisinta said:
(...) In this case I said, let's see what happens if I play them for 200 hours straight, so I did. Other than they just kept getting better sounding as the hours mounted, they ran for 200 hours, without a hicup and the room really never got even warm. I didn't expect to be able to do that, but now they are all broken in and it was no big deal.

I am a very impatient person and I always do it with new tube equipment, particularly ARC and cj power amplifiers that need long burn-in times due to their teflon coupling capacitors. Never had problems with this technique. But I would love to have your receipt for having a permanent power dissipation of 720W that does not warm the room!

But yes, unfortunately the longer they run uninterrupted the best they sound!

Rhapsody · Nov 20, 2017

microstrip said:
I am a very impatient person and I always do it with new tube equipment, particularly ARC and cj power amplifiers that need long burn-in times due to their teflon coupling capacitors. Never had problems with this technique. But I would love to have your receipt for having a permanent power dissipation of 720W that does not warm the room!

But yes, unfortunately the longer they run uninterrupted the best they sound!

I should have added I left one of the windows open and it was 35 deg

Ron Resnick · Nov 20, 2017

rvisinta said:
Hi Ron,

I thought I would get an intelligent answer, so here is what George Counnas (Zesto owner and designer) had to say-

The Eros uses 360 watts when it is on with no signal and 360 watts at full power thus Class A.
Class A by definition consumes the same power with or without a signal because the tubes are turned on the whole time the amp is on.
A typical AB amp might only use 50 watts of power with no signal and (if 80% efficient) 270 watts at 150 watt output.

Thank you, Bob, for asking George directly!

And thanks to George for his speedy reply!

Rhapsody · Nov 20, 2017

Ron Resnick said:
Thank you, Bob, for asking George directly!

And thanks to George for his speedy reply!

Always a pleasure Ron

Ron Resnick · Nov 20, 2017

microstrip said:
Most probably not exactly 150 watts class A, but something like 100-110 watts. Design maximum anode power of the KT88 is 35W and the Eros has 6 power tubes, making a total of 210W output stage idle power. But 110 watts class A is probably enough for any one!

The balanced input impedance is just 12kohm - can your tube preamplifier drive such impedance in parallel with the active bass crossover?

The VAC Statement 450 iQ uses eight KT-88s. Eight X 35 = 280, but I am certain that Kevin Hayes is certain that his amplifier makes 450 watts. Are you sure you have this KT-88 story straight?

Thank you for looking out for my particular situation! The Io (well, in the future, the Callisto) will drive only one pair of interconnects -- going to the Gryphon bass towers. The pre-amp will not be dealing with a parallel load.

morricab · Nov 21, 2017

Ron Resnick said:
Thank you, Bob, for asking George directly!

And thanks to George for his speedy reply!

A Class A amplifier will generally be no more than about 30% efficient and a Class AB amp no more than about 60% efficient. So, an amp consuming 360 watts would be Class A up to about 100 watts as Micro supposed, assuming the power consumption of the tubes themselves is not making a large % of that consumption...from the filaments for example. I had 25 watt Class A SET monos that consumed 250 watts per mono, so only 10% efficient, but a lot of that power consumption was due to the filaments of the tubes themselves. Real efficiency was probably closer to 20%, which is pretty normal for a SET. Crossfire, which had less demanding tubes, was 300 watts consumption for 2x30 watts output or about 20% overall efficiency. Push/pull can be more efficient in Class A but not more than about 30% and still be fully Class A.

So, the Zestos seem to be a very high bias AB design that over most forseeable usage would be Class A. The heater of a KT88 consumes 10 watts per tube.

Leif S · Nov 21, 2017

Ron Resnick said:
The VAC Statement 450 iQ uses eight KT-88s. Eight X 35 = 280, but I am certain that Kevin Hayes is certain that his amplifier makes 450 watts. Are you sure you have this KT-88 story straight?

Thank you for looking out for my particular situation! The Io (well, in the future, the Callisto) will drive only one pair of interconnects -- going to the Gryphon bass towers. The pre-amp will not be dealing with a parallel load.

Hi Ron,

I'm hoping this will shed a little more light on to this topic

Two things. First, the statement regarding anode dissipation is missing two facts, and, second, anode dissipation does not tell you amplifier output power.

With respect to maximum anode dissipation ratings, Genalex (the inventor of the KT88) gave two figures: "design maximum" (35 watts), and "absolute" (42 watts). To each of these in an ultra-linear circuit you also have to add the screen dissipation. The combined ratings by Genalex are 40 and 46 watts respectively.

None of these figures tell you the output power possible in any particular amplifier. Without going into engineering discussions (such as the fact that the maximum rating is not a peak power but the integrated average over time of the entire waveform on the anode), simply consider that vintage Genalex data sheets for the KT88 show typical applications producing 100 watts RMS from two tubes. So the idea that the maximum output power is twice the dissipation rating (2 x 35 watts) is not a correct understanding of how things work.

Kevin Hayes has pointed out to me that many of the published tube specifications, such as typical power output, are either average values or what were termed "bogey" values back in the day. Individual tubes can exceed the published figures; all this varies from tube to tube. Kevin reports seeing anywhere between 95 watts and 118 watts per pair of KT88 in their basic amplifier circuit, all running within the tubes stated ratings.

Regardless of all of the tech talk, in the end what matters most is how an amplifier sounds. If specifications told the whole story we would all be listening to transistor amplifiers with 80 dB of negative feedback lol

Ron Resnick · Nov 23, 2017

Thank you, Leif!

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