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Conrad Johnson Solid State Amps.

@artoly .

There may be a problem unfortunately. I have never had noise through the speakers - just mechanical hum from the amp, and as I said when they have the power supply they were built for, my two MFs are very quiet.
 
artoly said:
I just won an auction for a CJ 350SA. Not the new-unused one, but still pretty exciting for me nonetheless, and all going to plan I am looking forward to trying it out tomorrow night (NZ time). Thanks for your thoughts @Salamander . Auditioning was not on the cards, but I weighed up the risks and thought it was worth it. It has 220V stamped on the back, so I hope I don't have any humming (I think we are 230V here too)...otherwise I will know who to ask @mandryka.
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Congrats - you now have one of the best amplifiers ever made. I’d have it checked out/ serviced first. Also wrt to the noise through speakers - how much gain do you have in total with the preamp, and how sensitive are your speakers?
 
artoly said:
Cons:
Audible hum from listening position when it's not playing music, or in any very silent moments in the music. This is more through the speakers. (Hiss in tweeters, hum in other drivers).
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I’d start by ruling-out grounding issues, it sounds to my like you have an earth loop somewhere. IIRC Naim are rather odd in this respect and may not play well with other brands. What are your speakers? If very efficient, and given the high power of the CJ it may just be amplifying hiss upstream. Maybe try powering up the CJ with nothing connected to it’s input as a first step. Is the hum still there?

PS No way should the CJ hum through the speakers!
 
crimsondonkey said:
how much gain do you have in total with the preamp, and how sensitive are your speakers?
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I'm not exactly sure about NAC282 preamp gain. Do any of these numbers from the spec represent gain?

Audio Outputs - 2 x variable (DIN), 3 x fixed (DIN)
Other Outputs - <50Ω
Line Outputs Variable (level) - 775mV
Line Outputs Fixed (level) - 75mV, 600Ω
Load Impedance - 10kΩ (min.)


Dynaudio Sapphire Speakers:

Sensitivity (2.83 V/1 m): 88 dB (I think from memory that equates to 85 db @ 1v/1m?)
IEC Long Term Power Handling: 300 W
Impedance: 4 Ohms
 
Grounding issues might be right (but I thought that only happened to other people :)
I just got home from FIFA woman's Italy vs. Argentina game, so just a little experimentation time tonight.
The amp is connected to one of Sean Jacob's CHC-CAP power supplies (equivalent to 2 x Hicap, except that it came complete with RCA outs for the power amp).

Tony L said:
Maybe try powering up the CJ with nothing connected to it’s input as a first step. Is the hum still there?
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I turned of the CHC-CAP. Hum still present.
I unplugged the RCA's from the power amp. No hum! Completely silent.
Hopefully this suggests a ground issue and not an amp issue?

I put RCA's back in between CHC-CAP and CJ and the hum is back.
Then disconnected CD player and DAC. Hum has not entirely gone, but much quieter (oddly, right speaker seams a fraction louder now, but not affected by Balance knob).
 
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artoly said:
Hopefully this suggests a ground issue and not an amp issue?
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Yes, that clears the CJ to my mind. There are people here who understand Naim’s earthing system far better than me, so hopefully someone will have an idea how to deal with it. I know it is a little unusual, as I understood it in my (‘chrome bumper’) days everything star-earthed back to the HiCap somehow. I’ve no idea how this behaves in a mixed system.

PS FWIW I’d just swap the Naim out for a nice CJ valve preamp, but there is likely a way to get it to work.
 
I can only really afford older gear at this level and I don't like the chances of a suitable CJ preamp or similar pre coming up on the NZ market anytime soon. Importing has very significant shipping + tax costs and many sellers won't ship here. I don't think I am quite ready to give up on my current preamp yet.
 
@artoly Do you have a digital source? If so, why not try it with no preamp at all and control volume digitally? That’s what I do.

I tried my MF200 with an Electrocompaniet pre - that works well with my Krell. But I felt it wasn’t so good with the CJ. You’ve got to be so careful!
 
mandryka said:
why not try it with no preamp
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Yes, a good thought thanks @mandryka and I will give that a go. I will be surprised if my Gustard A26 DAC sounds better than the Naim as a pre, but worth trying and I try to keep an open mind.

Even if I don't like it, it might help me to eliminate something else in relation to the ground loop issue. Those issues and how to resolve them are a bit new to me, so I need to do some reading and might see if I can find some YT 'ground loops for dummies' videos when I find some time.
 
Let us know how you get on. The preamp can only be changing, colouring, the sound of the source, and boosting it slightly. My guess is, that given the power of the CJ, you won’t miss the boost, but you never know! And I found that the MF amps have a lovely timbre anyway and so I don’t miss the tonal changes of my preamp. But that’s clearly very much a matter of taste.
 
I just wrote about how the problem was solved, but before hitting 'Post Reply', I touched a cable and the hum came back.
It had gone away for a while when I fiddled with an RCA connection on the Din to RCA cable between the DAC and Pre, just long enough for me to start celebrating. I had previously disconnected the Din end several times, but not the RCA end. Once I thought I had solved it, I swapped that cable out for another to try and make the solution more permanent, and the dreaded hum was back. I reverting back to the first cable and now that one was humming again too. Perhaps it was all a coincidence and there is something else going on, or perhaps I am finally going mad. Tricky....and enough for one night.

I will still try with no preamp....but another day.
 
mandryka said:
The physical hum on the MF200 has now been very much tamed by a transformer to feed it with American voltage and frequency - there still is some quiet hum, but the level is not a problem for me any more even in quiet music - I would strongly advise anyone in the UK who is thinking of buying this amp to plan to do the same.
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Please provide details/link - might need something similar.
 
Despite my ground issues when not playing music (which I'm still working on), the CJ 350 blows me away. It is an awesome amp. Thanks for this thread mandrayka.
Just played Sail , Awolnation (not possible at low volumes). My son came out to complain doors were rattling a couple of rooms away, but I'm smiling.
 
After a a few A-B back-and-forth trials feeding the CJ 350 with and without a separate preamp, I prefer it with the preamp.
I'm cannot be sure if it is what the 3-box Naim NAC282 preamp brings to the party, or if it is what the Gustard A26 looses when turning off DSD Direct, but to my ears it was no contest between these two with my digital source.

Edit: It is probably the DAC that looses its mojo when using direct. I just tried turning off DSD Direct on the DAC when playing through the Naim preamp (i.e. enabling the DAC's volume control). It's not as good.

The sound seems faster, more open/breaths more with the premp in the mix. Conversely, slower and more shut-in using the DAC's built in pre/volume control, loosing some of the music's goodness (to my ears). I would have been happy if the sound was better without the pre (more money in the bank, one less rack, etc.), but for now the pre stays (at least until another pre comes my way).

In terms of the hum/buzz when idle (discussed previously above), at 0.5m distance, the app on my phone adds about 6 DB when adding in the preamp. It was not completely silent using the DAC as a pre, but significantly quieter.
Incidentally, with the Naim preamp attached, this idle noise level reduction is similar when I disconnect the RCA's between DAC and preamp. I'm not sure if this has any relevance as to where a ground loop may need to be resolved?
 
FYI I have a similar beast of an amp Meridian 559 that weigh in at 42Kg each (I have two and yes in black). Each can produce £300W into 8 Ohm and more than 1500W connected bridge mode into 4 Ohms. Yes I use them bridged. They are getting on for 20 years old and are silent with my 88db sensitive speakers until the music starts. No hum nor hiss even with ears pressed against the cones. Nor any xformer noise from the amps themselves.

I removed my pre-amps years ago as to my surprise the music sounded better without them in place and thats with both a record player and a DAC. The phono amp and DAC have their own volume controls.

I mention this so that you realise that you should not be getting any hum if the cables and associated plugs and sockets are sound.

DV
 
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