Bob Carver & ESS Eclipse 500A Amplifier

oldphaser

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#1
I ran into the following ebay ad copy which someone posted for an ESS Eclipse 500A they had for sale. If my memory serves me correct, Dean mentioned that Bob Carver was working on an amplifier for ESS (at Norm McFadden's house) after he left Phase Linear. I will double-check this with Dean when I get a chance.


http://www.ebay.ca/itm/ESS-Series-E...t-Excellent-Sounding-Super-Rare-/231810122495


The History of the ESS Amplifier Line:
The information on the internet regarding this amp is somewhat inaccurate and I’d like to clear it up:
When I first bought the amp I read the posts that the amp was developed by the Late Bob Byrd. Nelson Pass told me that Bob Byrd was key and Pete Werbackalso worked in its development. I then emailed Bob Carver with some internal PICs of the amplifier…


Bob got back to me and said “That is my Circuit”! We need totalk and he told me this:
Back in the height of the Golden-Age Stereo days of the late 70’s,Dr. Oskar Heil was known to have the most advanced speaker systems with the Heil AMT 1. He needed an amplifier that would give what his superior speakers needed - lots of high-end power. Dr. Heil called his good friend Bob Carver and asked: “We need an amplifier to drive our Electrostatic speaker systems, would you be willing to help us? Bob agreed and traveled down to Sacramento and worked with ESS to design and build a prototype amplifier to properly drive the Heil tweeters/mids. This was after Bob sold Phase Linear to Pioneer and just as he was formulating plans for a new company which soon became Carver Corporation. In those days there were very few people who knew how to build high-end amplifiers. It was Bob Carver who was the driving force behind this project and Bob Byrd and Pete Werback continued the R& D once the amplifier circuitry proved itself in rigorous testing. In the early phase of development they were testing a prototype amp to drive a Heil driver to its maximum to see what it could handle. The driver caught on fire and they began work on a Speaker Protection circuit for this Amplifier. There were at least 3 generations of amplifiers before this Final Eclipse Series 500A. The Eclipse Series 500A was their last,best and most refined amp after many years of R & D and earlier amplifier production.

PROTECTION:
Active output transistor dissipation sensing circuit provides full performance into all load types either resistive or reactive, while maintaining absolute safety of the amplifier during direct short or extreme overload conditions. The amplifier is dual thermally controlled, to allow safe operation into extremely mismatched loads, and assure total de-energization in the event of continued operation into a short-circuit load.


Complete protection is provided to speakers and all internal components in the event of any D-C latch-up condition of the amplifier,including a forced state induced from outside sources. This is achieved via solid state circuitry without the requirement of output switching relays which often require early replacement.
 
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oldphaser

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#3
Here are some internal pictures of an ESS Eclipse 500A as well as a sales brochure and schematic (from 1-74) for an earlier ESS Eclipse 500.

Ed
 

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oldphaser

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#4

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laatsch55

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#5
A 2 watt resistor in SERIES with positive speaker out?? That can't be right...
 

oldphaser

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#6
A 2 watt resistor in SERIES with positive speaker out?? That can't be right...
Lee,

If my memory serves me correct. Bob Carver did that sort of thing. I can't remember if the velocity switch on the 200 series 1 amps does that as well.
Anyway, here are just a couple of posts from the many posts on the internet.....

https://www.lifewire.com/output-impedance-3134904
Incidentally, almost all tube power amplifiers use output transformers, and because output transformers are just coils of wire wrapped around a metal frame, they have substantial impedance of their own, sometimes as much as 0.5 ohm or even more. In fact, to simulate the sound of a tube amp in his Sunfire solid-state (transistor) amplifiers, famed designer Bob Carver added a “current mode” switch that placed a 1-ohm resistor in series with the output devices. Of course, this violated the 1-to-10 minimum ratio of output impedance to expected input impedance that we discussed above, and thus had a substantial effect on the frequency response of the connected speaker, but that’s what you get with many tube amps and it’s exactly what Carver wanted to simulate.

http://forum.polkaudio.com/discussion/73932/resistor-run-in-parallel-w-speaker-wire

http://www.classicspeakerpages.net/...and-vintage-speakers-how-to-emulate-tube-amp/

Ed
 

JustMike

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#8
Thanks for posting ED. The 500A was a good looking amp.
Looking at the first pics, I noticed that the heat sink was in two parts. An aluminum plate for the outputs and joined to the cast fin sink.
I wonder how well this design transferred the heat to the fins?
 
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oldphaser

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#9
Here are some more pictures and info I found on the ESS 500's and 500M's...

NOTE: (It appears that someone may have used some RCA1B04's or RCA1B05's as replacements for the MJ410 output transistors in the photos below)


Here is a link to a repair that someone did on a ESS M500.
https://translate.google.com/transl...mplificateur-de-puissance-ess500/&prev=search
NOTE: This link has comments and photos not associated with any of the photos I have attached below. Included are also some screen shots (DHT and SNR, Bandwidth, Slew Rate, and Square Wave Respone) taken utilizing Picoscope6 oscilloscope software.


There may have been some additional models in the ESS 500 series of amplifiers:
500-C (500C)
500-MS (500MS)
500-S (500S)
500-W (500W)
504A
504-C (504C)
I haven't been able to locate much information on these models yet.


Ed
 

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stuwee

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#10
First off, Awesome thread!! :happy2: Amazing pics :hello1:

I notice the heat sinks are close together like on PL gear, how is that effective that set up? Was it meant for fans to be on it?

Roger Sanders Magtech amps seem like a very nice updated version of this design, some differences tho...


Being from the speakers have to be difficult to sound righteous group, that amp is up my alley :smilebox:
 

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#11
That non-metered ESS amp sort of reminds me of a Bose amp!
 
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diazusa

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#13
Selling my ESS Eclipse 500A Amplifier

I am selling my Eclipse 500A amplifier (along with a pair of made in USA vintage 70s handcrafted SLS HT805 floor-standing loud speakers) if anyone on this forum is interested. Here are some photos - DM or email andresjavdiaz@gmail.com if interested

file:///Users/newuser/Downloads/essphotos-2/IMG_1559.JPG
 

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orange

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It's the rare anti gravity option, Perry.
 

nakdoc

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#16
About the 10 ohm 2 watt resistor; this is fairly standard practice. The resistor is in parallel with a small inductor, so for audio frequencies, the resistor is short circuited. At very high frequencies (below AM radio) the 10 ohm resistor acts as a load. The circuit helps keep the amp stable into electrostats.
 

WOPL Sniffer

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About the 10 ohm 2 watt resistor; this is fairly standard practice. The resistor is in parallel with a small inductor, so for audio frequencies, the resistor is short circuited. At very high frequencies (below AM radio) the 10 ohm resistor acts as a load. The circuit helps keep the amp stable into electrostats.

HUH????
 
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