CJ Evolution 2000 Amplifier Review

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CJ Evolution 2000 Amplifier Review

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Evolution 2000 Zero Feedback Power Amplifier

So I use this bad boy to power my Martin Logan Vantage speakers. Electrostatic speakers are notoriously hard to drive due to their wild swings in resistance but the 2000 has no problem handling them. They're rated at 200 watts in 8 ohms and I have no doubt that doubles with 4 ohms. The monster weights about 115 lbs and I had to get help lifting it into position. It has a tube input stage and solid stage output which makes it a relatively rare design.

I find the sound to be powerful yet accurate. Whether playing classical music or rock, they never disappoint. For anybody that is interested in acquiring these I highly recommend them!

CJ's official page:
http://www.conradjohnson.com/It_just_so ... v2000.html
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Re: CJ Evolution 2000 Amplifier Review

Post by ll21 »

Thanks for that...i've heard very good things about this amp. Bit of a legend actually. I have spoken with CJ owners who've taken 'vintage' stuff and had it upgraded with latest CJ Teflon capacitors, etc...to great effect. Have you ever considered doing this? Just curious. What tubes do these run? EL34, 6550? I am just wondering if 6550, whether you'd stick in KT120s to see what happens. Enjoy!
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Re: CJ Evolution 2000 Amplifier Review

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It would be really great to do some further mods on this. It's actually modded to accept standard power cords vs the stock attached cord. It take 5751 tubes (x4) in the input stage. I have gotten countless hours of listening enjoyment from these and really like it. I wouldn't mind trying some further upgrades but shipping this 115 lbs beast is a major issue!
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Re: CJ Evolution 2000 Amplifier Review

Post by ll21 »

yes...115 pounds is a pain in the a-s and expensive. have you spoken with CJ about what mods they could do?
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Re: CJ Evolution 2000 Amplifier Review

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Actually I haven't. I did go to their site and look at the upgrade options they have available for some of their units but I did not see the Evolution on there so I didn't pursue it. Maybe I should give them a call? Although, the shipping will probably be more expensive than the upgrade! :D

By the way, for anybody that is interested this is the Conrad Johnson Model Upgrade web page.
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Re: CJ Evolution 2000 Amplifier Review

Post by ll21 »

I would suggest speaking with Ed...i honestly have no idea...except i know people who have upgraded their Premier 8s! Over 20 years old...but transformed with the Teflon capacitors (among other things apparently) which CJ uses throughout their products now. Worth a try!
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Re: CJ Evolution 2000 Amplifier Review

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Maybe I will give them a call and see what's available and what price range. I'm worried about the shipping expenses as well as shipping a 125 item is pretty expensive.
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Re: CJ Evolution 2000 Amplifier Review

Post by Joe Appierto »

admin wrote:Maybe I will give them a call and see what's available and what price range. I'm worried about the shipping expenses as well as shipping a 125 item is pretty expensive.
That's a really beautiful amplifier.

Just as a point of information: I sent my Premier 140 to c-j for the Teflon capacitor upgrade. The carton weighed 103 pounds and the cost via FedEx ground was a $100. Amazingly, it got there the following day. The amp sounds considerably better although, as you said, their web site doesn't list yours. A call should let you know for sure.

You've done an excellent job with this forum. Congratulations.
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Re: CJ Evolution 2000 Amplifier Review

Post by joeinid »

Hi Joe!

Congrats on the upgrade!

Joe
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Re: CJ Evolution 2000 Amplifier Review

Post by MrAcoustat »

admin wrote:Evolution 2000 Zero Feedback Power Amplifier

So I use this bad boy to power my Martin Logan Vantage speakers. Electrostatic speakers are notoriously hard to drive due to their wild swings in resistance but the 2000 has no problem handling them. They're rated at 200 watts in 8 ohms and I have no doubt that doubles with 4 ohms. The monster weights about 115 lbs and I had to get help lifting it into position. It has a tube input stage and solid stage output which makes it a relatively rare design.

I find the sound to be powerful yet accurate. Whether playing classical music or rock, they never disappoint. For anybody that is interested in acquiring these I highly recommend them!

CJ's official page:
http://www.conradjohnson.com/It_just_so ... v2000.html
Yes it is over 20 years old BUT for an amp like that today it would cost mucho mucho dollars, i have a friend that use to own that very same amplifier it took Lamm's 2.2s mono blocks to get better 22k so that Evolution 2000 is a bargain and it look's in very good condition, this is my friend the ex owner's system.

Image

Image

Image
Last edited by MrAcoustat on Wed Jan 15, 2014 2:06 am, edited 1 time in total.
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Re: CJ Evolution 2000 Amplifier Review

Post by Joe Appierto »

joeinid wrote:Hi Joe!

Congrats on the upgrade!

Joe
Thank you, sir. At a little over 400 hours now, it seems to be improving which is sooo nice considering I was happy with the way it sounded as soon as I got it back from c-j. Right now it has some New Sensor Genalex Gold Lion KT88s in it and they have a really nice top end sparkle. Next up will be the KT120s. Everyone is so enthuastic about them, I need to give them another listen.

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Re: CJ Evolution 2000 Amplifier Review

Post by admin »

MrAcoustat wrote:
admin wrote:Evolution 2000 Zero Feedback Power Amplifier

So I use this bad boy to power my Martin Logan Vantage speakers. Electrostatic speakers are notoriously hard to drive due to their wild swings in resistance but the 2000 has no problem handling them. They're rated at 200 watts in 8 ohms and I have no doubt that doubles with 4 ohms. The monster weights about 115 lbs and I had to get help lifting it into position. It has a tube input stage and solid stage output which makes it a relatively rare design.

I find the sound to be powerful yet accurate. Whether playing classical music or rock, they never disappoint. For anybody that is interested in acquiring these I highly recommend them!

CJ's official page:
http://www.conradjohnson.com/It_just_so ... v2000.html
Yes it is over 20 years old BUT for an amp like that today it would cost mucho mucho dollars, i have a friend that use to own that very same amplifier it took Lamm's 2.2s mono blocks to get better 22k so that Evolution 2000 is a bargain and it look's in very good condition, this is my friend the ex owner's system.

Image

Image

Image
Wow, what an incredible system. Very clean and elegant. What are the two side by side items on the lowest shelf of the rack. I can't seem to read them but that "metallic polish" face cover looks awesome.

The speakers also seem rather massive and with those large bass drivers i'm sure it really rocks!

Very cool.
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Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
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Re: CJ Evolution 2000 Amplifier Review

Post by jcwhite57 »

My EV2000 needed the output biasing zener diodes replaced. Completed that but have not been able to find the procedure to adjust bias. Ed at CJ sent me a schematic but it doesn't give a clue how to adjust bias. Ed ask his tech but was told to adjust the pots for 20mV across the emitter resistor. Problem is the biasing circuit only has mosfets so no emitters. I'd rather not have to guess how to set the bias.

Question:
If someone knows the procedure to set the EV2000 mosfet output bias, please let me know.

Thanks,
Jimmy
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Re: CJ Evolution 2000 Amplifier Review

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jcwhite57 wrote:My EV2000 needed the output biasing zener diodes replaced. Completed that but have not been able to find the procedure to adjust bias. Ed at CJ sent me a schematic but it doesn't give a clue how to adjust bias. Ed ask his tech but was told to adjust the pots for 20mV across the emitter resistor. Problem is the biasing circuit only has mosfets so no emitters. I'd rather not have to guess how to set the bias.

Question:
If someone knows the procedure to set the EV2000 mosfet output bias, please let me know.

Thanks,
Jimmy
Jimmy, welcome to the site!

As for your question you will have to help me out a little as I don't have a lot of experience with this issue. I know the tubes do not need to be biased in the CJ Evolution 2000, however I was not aware that diodes had to be biased? In the manual there is no mention of anything need biasing? Do you have any pictures of what the diodes/resistor look like? Let us know how it turns out as I am greatly interested as a fellow Evolution 2000 owner. Thanks.
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Re: CJ Evolution 2000 Amplifier Review

Post by jcwhite57 »

Thank you for the warm welcome admin. If you have the owners manual for this amplifier, I would very much appreciate a copy as I have been unabe to located one posted anywhere. Sorry about the confusion on the zener diodes. Their purpose is to limit the voltage on Q18 & Q19 mosfet gates and are located in the bias circuit. The ones in my amp must have seen a voltage spike and shorted. After replacement, the DC offset for one of the channels was around 2.5V while the other channel was less than 2mV.

Yesterday I got the amplifier back from my tech and have some information to share.
Since I couldn’t get a reasonable answer from CJ to set the bias & DC offset. I had my tech develop a procedure. The bias current of 340mA* was determined experimentally as a compromise between thermal recovery, THD, & DC offset. It cost me quite a bit to have him develop this procedure and hopefully someone else will be spared this expense by this post.

Procedure to adjust output bias/DC offset:
• Power up amplifier and allow sufficient time to warm up.
• On the back of the amplifier case are 4 fuses grouped together (2 for each channel). These fuses are in-line with the power supply rails that feed the output mosfets (B +/-). Remove the set of fuses for the desired channel.
• Connect an ammeter across each fuse terminal and set each meter to the DC mA scale.
• Connect a voltmeter across the speaker output terminal and set the meter to the DC mV scale.
• R37 & R38 set the positive and negative bias respectively. Adjusting one effects the other along with the DC offset and is a balancing act between the two to achieve the desired results. The target rail current is 340mA* for both positive and negative bias.
• Adjust bias pots for initial conditions at 0mA.
• Adjust R37 bias pot at halfway to target current (340*0.5 = 170mA).
• Adjust R38 bias pot to the second halfway point (340*0.75 = 255mA).
• Adjust R37 bias pot to the third halfway point (340*0.87.5 = 297.5mA).
• Adjust R38 bias pot for the fourth halfway point (340*0.9375 = 318.75mA).
• Continue with sequence until desired bias current is achieved and confirm DC offset is < 2mV.

I’m very curious what the actual bias current specification as defined by CJ actually is. It’s possible the amp shoul be biased for more class A operation than what was determined experimentally. If anyone knows specified bias current, please post it.

I posted the EV2000 circuit diagram and parts list at hifiengine.com. The circuit diagram doesn’t show the fuses supplying tube plate power. It also doesn’t show the tube grids connected together electrically.

Other Amp problem:
When I purchased this amp several months ago, it had a lot of distortion on both channels that increased with frequency. At 10kHz, the distortion measured around 6%. The problem was traced to a broken solder connection on a lead of one the filter capacitors for the tube plate power supply. Apparently this was a manufacturing solder defect. The solder where the capacitor lead detached from the PCB pad was very oxidized.
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Re: CJ Evolution 2000 Amplifier Review

Post by admin »

jcwhite57,

Wow, excellent job. I'm sure it was a major pain to have somebody develop a specific procedure to do this. I'm sure it will help fellow Evolution 2000 users.

It seems like you've gone through a lot of blood, sweat, and tears with this amp. Now that it's up and running I hope you are getting the enjoyment out of it which you deserve. I bought my EV2000 a few years ago and luckily have not had any major issues. The previous owner did modify the unit so that the power cord can be interchanged with standard power cord connections, but that's about it.

I tried going to the hifiengine.com website to get a copy of the EV2000 schematic but it appears that to download anything there you have to first register. Do you think you can email me the schematic so I can add it to the Official Schematics and Manuals Thread thread here on CJO so that people can have access to this without needing to register? You can send it to "admin@conradjohnsonowners.com" and I will update it immediately. Thanks!

I do have a copy of the manual. I'll try to scan it in for you so you can have it. I'll post it as soon as I get that done.
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Re: CJ Evolution 2000 Amplifier Review

Post by admin »

Conrad Johnson Evolution 2000 user Manual

So I was able to scan in the manual, you can download it at the link below. Hope this helps! :)
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Re: CJ Evolution 2000 Amplifier Review

Post by MLAS »

How does this hybrid amp compare to the Premier One, Four or Fives?
I've had the Fives sold them (I still have a EVO20SE luckily) and I'm now looking for a Four (One is a sota object and therefore much to expensive no real dollar for the value IMO).
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Re: CJ Evolution 2000 Amplifier Review

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The design is fundamentally very different for the 2000 vs the premier line. Keep in mind that the 2000 is a solid state amp with a tube input stage. The 2000 is fast and powerful. The input stage does give you a tube sound but is not overwhelming. From a technical perspective, the 2000 gives you a lot of watts into each channel. This is a great amp for hard to drive speakers. From a monetary standpoint. Having only 4 inexpensive tubes to periodically replace makes it cheap to run vs the typical premier line of amps that not only have more tubes, but more expensive ones at that. Also, with the premier 4 you are going to get a lot less wattage.

At the end of the day I highly recommend the 2000. Not to say there is anything inferior with the premier 1, 4, or 5. The 2000 is just a different beast.
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Re: CJ Evolution 2000 Amplifier Review

Post by MLAS »

Thanks for your elaborate reply.

I forgot to say that I already have a Krell (SS amp) to power my Watkins woofers.
So I would need an amp for my mid/highs.

It seemed to me that the EVO2000 amp would complement my EVO20SE pre, but that's merely an aesthetic argument of course :D
Your EVO2000 looks pristine to me, very beautiful amp to look at and it seems also very potent indeed.
Your running Martin Logan Vantages with them. I've had Acoustats model 2 + 2 for a decade and they were very hard to drive also.
Never had a tube amp that could do that.
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