Dears,Suffering 5 years from a whisteling CJ PV12 as many others, I finally managed to cure the issue by changing a resitor value.
I changed the resistor between pot and tube grid up to 1k ohms. A little higher should work also fine. The original resistors value is 47.5 ohms. You find it on the bottom side of the PCB directly under the tube sockets of the line stage (12au7).
A friend of mine in the netherlands realized this fault in the schematics at once.
Now I am not bound to special "whisteling reduced" tubes and can just use the ones I like best for sound.Thanks to all who tried to help me in this issue.
Please spread this news to all suffering CJ owners!
Follow Ups:
- Re: PV12 whisteling totally cured!!!!!!!!! - tvr2500m 22:55:09 06/09/03
(1)
- In Reply to: PV12 whisteling totally cured!!!!!!!!! posted by mhhd on June 08, 2003 at 07:45:53:
I'm a CJ gear owner - PV-12A, PV-2AR, MV-75s and a Premier 11A. I'm curious about which resistor you changed. I had Bill Thalmann (CJ employee #3 and engineering director there for 20 years) update my MV-75s. In the course of some of our conversations he mentioned a whistling noise that some of the zero negative feedback CJ preamps, like the PV-12, would occasionally exhibit. He said it was approx. 3KHz in frequency and due to an ocillation in the tubes. He may have mentioned why the preamp circuits made this happen but I don't remember whether he did now. Kevin Deal at Upscale Audio mentions something about CJ zero negative feedback preamps being picky about tubes on his website.
I experienced this whistling - like a distant water kettle whistle - for a very short while myself with the OEM RFT 12AU7s. It went away and I've not had it come back with any of the dozen or so 12AU7 subs I've tried in the linestage (mine has a phono but I don't use it). I'm using Amperex 7316s now. They're my favorite so far.
Do you have a PV-12 schematic? I'd like to see this if you'd care to share it.
About CJ the manufacturer, I've owned CJ gear from the earliest days of the company's existence. One of my two now-modified MV75s and my PV-2AR I bought new in the late seventies. In my experience they've been a top-notch company to deal with. Beyond reproach. From what I can see, their reputation beyond my own experience seems pretty solid.
- SJ
- Re: PV12 whisteling totally cured!!!!!!!!! - Mick Wolfe 18:03:55 06/10/03
(0)
- In Reply to: Re: PV12 whisteling totally cured!!!!!!!!! posted by tvr2500m on June 09, 2003 at 22:55:09:
I agree 100%. Have owned CJ gear for the better part of the last 12 yrs.I've also own or have owned 3 CJ pieces that have been modded/updated by Bill Thalman. All have performed flawlessly.
- Re: PV12 whisteling totally cured!!!!!!!!! - Mick Wolfe 18:03:55 06/10/03
(0)
- Makes me wonder about the Manufacturer............. - Cut-Throat 08:02:12 06/08/03
(4)
- In Reply to: PV12 whisteling totally cured!!!!!!!!! posted by mhhd on June 08, 2003 at 07:45:53:
Congratulations on fixing your problem, but it makes me wonder about the Manufacturer. If the design was bad why didn't CJ step up to the plate?
We have had a few posters here taht complained that their CJ's were constantly eating tubes and the Mfgr did not provide any customer service except to slam the guys Brand of tubes, Power in his house etc. etc.
I have never owned CJ and have nothing against them, but I have got to say I have read enough Bad stuff in this forum that I'll probably never look into their gear.
Cut-Throat
- Re: Makes me wonder about the Manufacturer............. - AbeCollins 22:34:40 06/08/03
(0)
- In Reply to: Makes me wonder about the Manufacturer............. posted by Cut-Throat on June 08, 2003 at 08:02:12:
I had a PV12L several years ago and never experienced a whistling problem. In fact, I can still whistle just fine. Seriously, no whistling PV12L problems here with original tubes or rolling NOS. ;-)
- My 11 year old pv10 has no "whistling" with ANY NOS tubes I've tried. nt - Rick W 15:17:15 06/08/03
(0)
- In Reply to: Makes me wonder about the Manufacturer............. posted by Cut-Throat on June 08, 2003 at 08:02:12:
nt
- Re: Makes me wonder about the Manufacturer............. - jtube 08:40:20 06/08/03
(1)
- In Reply to: Makes me wonder about the Manufacturer............. posted by Cut-Throat on June 08, 2003 at 08:02:12:
Cut Throat,
I enjoy reading most of your comments on this forum. But in this case I think you are being too harsh. I am sure CJ has their reasons. Also one must realize that the designers a CJ voiced their gear with a certain tube. In their eyes, they see no point of tube rolling. I am not defending CJ, but Audio research among other companies also specify using OEM tubes. I tube rolled my PV 12 and never had any problems.
As far as never owning any CJ gear that is your choice.
- Re: Makes me wonder about the Manufacturer............. - Gary 10:15:59 06/09/03
(0)
- In Reply to: Re: Makes me wonder about the Manufacturer............. posted by Jtube on June 08, 2003 at 08:40:20:
I have a Conrad Johnson Preamp (actually two), and they are as quiet as any other I've heard. The resistor value is interesting, but would like to have seen the 47.5 resistor replaced with another of similar value. Still knowing the folks at C/J I'd say they never would have let a design go into production with a fault like that.
gary
- Re: Makes me wonder about the Manufacturer............. - Gary 10:15:59 06/09/03
(0)
- Re: Makes me wonder about the Manufacturer............. - AbeCollins 22:34:40 06/08/03
(0)
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