Repairs and/or modifications to C-J products

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Repairs and/or modifications to C-J products

Post by Wildcat » Sun Nov 26, 2017 10:20 pm

As my signature shows, I have a Premier 11 on hand. I have had it for several months now and we get along nicely. It does not quite drive my Vandersteen 2CE as well as the Nelson Pass designed amp I had previously, but the Vandys are also not my long-range goal.

My dilemma, though. The 11 came with electrical tape on the power cord, likely a scuff in the jacket. I really would like to have an IEC jack installed so I can use one of my own power cables. In addition, I had thought of perhaps getting the amp upgraded to an 11A (which was a small modification to the bias circuitry to reduce noise).

As for issues, the amp has a very slight channel imbalance--on my PV14L, my two channel settings are three digits apart (such as 67/70 or 35/38). Not bothersome, but maybe I'm slightly OCD? :mrgreen: I also can hear that it is not as quiet as my previous amp--the noise is not quite audible from my seat, but I can definitely hear it a few feet away. I don't know if that is normal as I've never owned a high-end tube amp.

The amp has been retubed. KT120s, Brimar 6CG7/6FQ7, Tung Sol 5751. The channel imbalance and noise did not change when the tubes were replaced.

The cheapest option is to do nothing. ;)

I contacted C-J for information. An IEC jack is three (!) hours labor, plus parts and shipping, so about $400. They can't do the "A" upgrade any longer. No word on anything else, but the offer was made to install the Teflon caps for $1645, which is more than I paid for the amp. Needless to say, I won't be sending my amp in.

In general, is it wise to find a repair facility that can work on C-J components properly? I just don't want some self-proclaimed "engineer" to start talking about "improvements" by changing out all sorts of parts. I figure any bench electrician is not C-J and IMHO has no business tampering with their circuitry. Plus, I feel it's easier to resell an untouched C-J product than something that is tampered with.

I would like the "A" upgrade, but that would require schematics for both the 11 and 11A to find the differences, and I would hope that it would not require a whole new circuit board. (I would think it is just a change in existing components, or adding a couple.)

For the IEC jack, I could probably do that myself; a good jack probably costs $50-ish, and while I don't have a metal punch, I would probably have to work really slowly with a miniature metal cutting tool to make the proper opening. But if a shop could do it for an hour's labor (which is all it should take), I would probably pay it.

If anyone has a little input on repair shops, modifications, etc., I would appreciate it. The good, the bad, etc., and possible effects on the value of a modified unit. (Even my minor IEC jack install might seem like sacrilege!)
C-J PV-14L/C-J Premier 11/Vandersteen 2Ce

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Re: Repairs and/or modifications to C-J products

Post by admin » Sun Nov 26, 2017 10:34 pm

My two cents is that if you want to have the flexibility to change power cords, then an IEC plug placement is probably one of the easiest DIY projects. The hardest part is cutting the case for the plug but the plug border typically overlaps a little so if the cut is not perfect you will still be fine.

Doing a 11 to 11A upgrade is obviously much more involved and more things can go wrong. I believe we do have the schematics in our database so I would first take a look and see exactly what would be involved. Still might be very doable and obviously a small fraction of the price of having it "professionally done".
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Re: Repairs and/or modifications to C-J products

Post by Wildcat » Sun Nov 26, 2017 11:00 pm

I think even someone in our local audio club has put an IEC jack into a chassis, so I may defer to their expertise if needed. (We have a few DIYers among us.) The chassis on this 11 is certainly thicker than others I have worked with in the past (mainly, project boxes from the electronics stores).

I don't see the 11 to 11A upgrade being as important, but it does make me wonder if the slight noise I am hearing is a result of that. If I remember the details, the noise came from the driver circuitry for the bias LEDs. And supposedly that same upgrade also made the LEDs a little less finicky. But it is not a deal breaker.

I am actually more concerned about the channel imbalance. It certainly hasn't gotten any worse, but I just hope it is not a future problem lurking there. That is why I'd worry about sending it off to be looked at--I would simply want it fixed, not have a lot of parts replaced due to an upgrade a technician feels "improves" the sound. Having never used a shop for high end repairs before, I don't know what to expect, should I go that route.
C-J PV-14L/C-J Premier 11/Vandersteen 2Ce

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Re: Repairs and/or modifications to C-J products

Post by ajf75 » Sun Feb 04, 2018 3:44 pm

Hello Wildcat and Anyone looking for CJ service outside of CJ itself, I recently had my P11A repaired by Bob Backert/RHB Sound in Eastern PA - who I believe has been mentioned before in these forums.

So I had a specific problem of weakish bass response after experiencing a pop from within the amp - and I also started with a call to CJ and felt they (Jeff) were more interested in 'upgrading' my amp with the Teflon cap mod with the expectation of killing two birds with one stone, and less interested in just a tedious diagnosis/fix.

Very thankful I found Bob as he knows CJ stuff well (not to mention he has his own pre-amp line that he designed and sells). He took the time to listen to the amp and take basic measurements first, call me to discuss what he heard, then further diagnosed to find the source of the problem (a bad transistor in voltage regulation circuit - not a cap) and also came across a cap that was out of spec in the filament circuit (though not likely the problem IHO). He then listened again and called me again to discuss the differences he now heard to ensure it matched what I was expecting.

Couldn't ask for more and his price was surprisingly reasonable considering the expert skill time invested. No disrespect, but I don't think you can get exactly this kind of service from CJ directly.

BTW, he did mention he has an input circuit mod for this amp that adds transparency. I'm passing for now only because I was anxious to get the amp back so I could finally try some KT120's in it and assess that before making any other changes.
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Re: Repairs and/or modifications to C-J products

Post by Wildcat » Tue Feb 06, 2018 2:17 am

Wildcat wrote:
Sun Nov 26, 2017 11:00 pm
I don't see the 11 to 11A upgrade being as important, but it does make me wonder if the slight noise I am hearing is a result of that. If I remember the details, the noise came from the driver circuitry for the bias LEDs. And supposedly that same upgrade also made the LEDs a little less finicky. But it is not a deal breaker.
I had some time to go over the schematics for the Premier 12 and 11 that are posted here at the CJO site. Turns out the schematic here is actually for the Premier 11A (see "Rev: A" at the bottom of the schematic), as the LED circuit is the same for both the 11 and 12. It's not all that complicated--an LF353 dual op amp IC, 1.2MΩ resistor, 0.1µF 100V capacitor, 1N52345B 6.2v Zener diode, and the LED. It doesn't seem like any modification of this circuit would be all that difficult to accomplish.

I wonder if C-J would have the original Premier 11 schematic for comparison. At worst, I'd have to pop the lid on this thing, find the op amps (two 8-pin DIPs), and see if I can trace the circuit that way.
C-J PV-14L/C-J Premier 11/Vandersteen 2Ce

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Re: Repairs and/or modifications to C-J products

Post by ajf75 » Tue Feb 06, 2018 1:27 pm

Wildcat, unless its been updated, that P11A schematic is what I got from CJ directly (Ed) several yrs ago and submitted here. I recall Ed also sending me some other P11 info at that time that appeared to be pre A. I'll take a look for it, but I want to say that the board circuit layout is different for the bias section...and likely why CJ no longer offers that upgrade.

Also, please post if you do call CJ for this as I'd be very interested to hear (pleasantly surprised) if they are still willing to release such things.
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Re: Repairs and/or modifications to C-J products

Post by ajf75 » Tue Feb 13, 2018 12:09 pm

Just to follow-up my prior post...

Both the P11 and the P11A schematics are here in the CJO zip downloads and the differences can be seen. For P11A see "Pr11 schematic cropped". For P11 see "Edscan prem 11 schematic 3" that is within the XS upgrade folder. The XS upgrade files are actually what I 'donated' a few yrs ago and those conversion notes from Ed were apparently done pre 'A' . Good luck.
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Re: Repairs and/or modifications to C-J products

Post by Wildcat » Mon Feb 19, 2018 12:06 am

AJ--thanks for the tips. Sure enough, your XS mod show the original P11 schematics (no "Rev: A").

So here's what I found. The Bias LED circuit is driven by an LF353 op amp. (This would be in a DIP integrated circuit, so, there are two such op amps per IC.) Pins 3 and 5 are connected to ground through a 1N5234B zener diode (in addition to passing through a 1.2MΩ resistor en route to the 6550s). Each side of the amp would have one IC/two LED drivers.

Get this--based on what I've seen so far, the only difference between the two is a 0.1µF, 100v capacitor in parallel with the zener diode.

Here's the Premier 11:
Premier11-bias.png
Premier11-bias.png (32.46 KiB) Viewed 13 times
And the Premier 11A:
Premier11A-bias.png
Premier11A-bias.png (98.62 KiB) Viewed 13 times
It would be nothing to piggy back that small capacitor with the diode. Sure, it'd be neater to do it on the printed circuit board, but electrically it would be the same.

If there are any other differences between the two, I haven't found them yet. The revision was mentioned as being only in the bias LED circuitry, so I can't think of anything else they might have changed.

I'll have to look for the bias driver circuits when I install the IEC socket.
C-J PV-14L/C-J Premier 11/Vandersteen 2Ce

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