Conrad johnson evolution 2000 amplifier repair
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Conrad Johnson Owners.com
Forum site dedicated to Conrad Johnson audio equipment Owners. Looking for new members! Come help build our community of audiophiles! Post by admin » Thu Nov 14, pm. Post by gktaudio » Thu Nov 14, pm. Post by gktaudio » Fri Nov 15, pm. Post by admin » Fri Nov 15, pm. Post by gktaudio » Sat Nov 16, pm. Privacy Terms. Conrad Johnson Owners. Skip to content. Quick links. I did whoever change the main blue Sprague caps for brand new ones same size but double capacity and all the other lytics.
It was a real nightmare to exchange those four large cans because access is so limited on the bottom. The 1b was a longtime have to have amp for me it's pretty rare but the EVO can handle my QLS's all by itself and pretty well also. That main relay wakes a vampire that sucks your AC out because it connects the main transformer and four large cans in a fraction of a second.
My Wadia DAC shuts itself of when the relay kicks in. I think your mA quiescent current and 46 degrees Celcius is a fine value for this amp. I run it at mA as I recall. Regarding the DC offset how did you manage to get that within an acceptable range? I know that bias and DC effect each-other, but I'm curious how you solved it.
Would be nice to hear what speakers are driven by your EVO. I've this amp on a second setup and had to change all the Elna "long life" lytic caps on the inputboards because they were leaking electrolyte and destroying the coppertraces. They were actually called 'long life'. It is also rather complicated, and although the wiring, layout and components are quite neat and impressive, as MLAS has noted, the amp does not sport the best workmanship in some areas.
Importantly in my view, lacks test points that would make biasing and balancing DC offset safer for the technician and the amplifier for example, it's got some delicate components such as upright transistors with big heat sinks that must be carefully avoided, and the huge main filter caps several minutes to discharge safely before reaching into the gubbins. The power draw is surprising, given the pre-start relay circuit, but if I read the schematic properly, that is because the main filter caps are not being charged until the main relay kicks in.
As noted by others, it seems like a good plan to make sure your circuit can handle the load at startup, and turn the amp on first unless you are using a preamp that doesn't also have a delay start relay and you are concerned with startup impulse thump. I am not at all surprised this amp sounds best with your Infinity's. It seems like a perfect amp for driving a huge subwoofer, panel speakers, bi-amping woofers, or e-stats.
How long did it take for you to replace all of the other e-caps? I am always hesitant to have an inrush limiter that isn't cut out of the circuit with a relay after it reaches temp. The GFA uses a resistor and cutout, as you know.
Having said that, my tube mono blocks use NTC thermistors in a solid state rectifier can that I built, and they are not bypassed, but are ventilated. The balance of DC offset and bias was conducted just as detailed in the previous methodology. The two are interactive, so I kept adjusting both pots while reading three meters; 2 for current and 1 for offset.
I was very pleased with how predictable was the response of the adjustments. I had offset down to 0. The subs had to be turned down with the EVO! GFAs are great amps that can sound truly excellent, but with 2 big flaws. One is the well-documented capacitor leakage that wasn't just confined to the input boards, but to the bypass caps on the power section boards as well.
I bought mine knowing it would require at least a rebuild of the boards. I did that twice, washing and rinsing the boards 6 times between each attempt an replacing a lot of parts, but the electrolyte would leach out of the boards after a week or two, and the resulting effects would recur, so I bought replacement boards which are a significant upgrade to the original layout and parts. The other flaw in my view is the lack of DC speaker protection. These are high current amps maybe not as much as the EVO and can really damage speakers if DC is passed through.
Ask me how I know That's even with really good input caps. I've recently bought some SSR-based DC protection boards to install in this amp, one of my winter projects. You were fortunate to be able to repair yours without replacing the boards. Cheers, Greg. Last edited by gktaudio on Fri Nov 15, pm, edited 3 times in total. I usually turn it on and go downstairs to get something to eat or drink.
I can hear the thump when it turns on and the lights in my house flicker. Thanks for all the info about biasing. With my limited knowledge, I don't think I feel too comfortable working on the EV but the information you provided is very helpful. If it was I would be very worried. I think it's just the relay switching. It still is much louder than any other amp I've owned or heard for that matter. Those huge capacitors make me feel very uneasy when poking around in the EV I would want to touch one by accident and have it discharge.
You can weld with this much DC power. Insert spy movie torture scenes about now Thank you for clarifying your thump - glad it's not through the speakers. I think I'll call mine a "whack". Can you guide me to posting photos? I tried the attachments function, but the editor says they aren't uploaded. I've tried using the photo function but don't have a URL. Thank you, Greg. Yeah, "whack" or "click" is a better way to describe it.
As for posting pictures, there are two primary ways. If you have the picture online somewhere and you just want to have it appear in your post you would use the "img" tags, which can be done via the 9th small icon from the left in the "full editor" menu at the top.
You just hit that and put the full path of the image file between the bracketed tags. You can also attach pictures which will be stored on the CJO servers via the "Attachments" tab below the editing box. If you want to put these CJO hosted pictures into the body of the text in specific places you can put the cursor in the textbox where you want them and select the "place inline" options on the attachments menu.
Again, these can both be done in the "full editor" not the "quick reply". I don't have photos stored online, so I'll try the attachments function again. When I did this before, the file name showed up, but also a message that the files weren't downloaded or uploaded? Will give that another go. There are some file size limitations in case your files are really large, but most "regular" sized files should not be a problem.
All my CJ photos are on my other computer, so I'll do this tomorrow. You do not have the required permissions to view the files attached to this post. I have so many projects lined up for this winter, and the amp exhibits no signs of needing an imminent re-cap, so I will keep this in mind but hold off for now. Are you located in Europe? From everything I've read and been told, the problem with Elnas occurred over a fairly limited period and was the result of a change in the electrolyte formula which damaged a lot of equipment of different makes and models, but was quite effective at damaging several models of Adcoms from that era.
I've heard nothing about bad Elnas made since. Lately I've been using Wurth capacitors, based on what I've been told by some techs and engineers about the company's reputation and that of their other components.
They come in a wide range of values and voltage ranges, and seem to perform very well in the preamps and amps in which I've used them. We are still getting accustomed to the LFT-8b speakers, being the first planars we've owned. This morning my wife turned to look at the speakers and said "I've never heard those voices before", referring to the background voices of jazz night club attendees on a Bill Evans recording.
They are quite detailed, and really shine with acoustic instruments and vocals, but don't excel with some rock music. I've never heard QLSs but Infinity has such a stellar reputation for their sound.
The LFT-8bs are not that efficient, but are an easy to drive 8 Ohms. Good luck with the move! The relay is loud because it is mounted to the front panel and resonates. Looks like a death trap if you were to put your hand in there with the unit powered up!
I got lucky. It looks like no work has ever been done inside the amp. The tubes were worn out GE JAN, and there are just a few scuffs on the outside of the enclosure and some scratches on the plastic window which I polished out. No signs of any soldering or parts replacement, and it was probably never re-biased or at least, not for a long time.
Conrad Johnson Evolution 2000 Tube Hybrid Power Amplifier 200 WPC w/ Matched NOS Jan Tubes
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For many years, if not decades, power amplifiers were one of the single biggest component disappointments. In fact, they had even more serious compromises than preamplifiers. While there were a lot of "good" amplifiers, few were "excellent" and even fewer were "superb". As for "great", I would have passed on naming even one amplifier until recently.
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