|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
75.166.20.184
It is a CJ PV2 A-revised. I put a new Alps volume pot a while ago and the sound improved dramatically. I'm certain this new problem is not related to that. When I turn it on, it makes loud crackly sounds that are not affected by volume level. I fear for my speakers. Naturally, you don't hear it if you turn it on first, before the power amp, so that is what I do. But still, something's not right, and I would like to fix it.Is it leaking through the PS? It's a tube preamp, of course, but has transistors in the PS.
Just as a diagnostic note: I bypassed a can 90uf/450V cap in the CJ with a Sprague Atom 100uf/500V cap, to see if it had any effect. It didn't help. It happens with both tube amps and SS amps that I have connected it to recently.Anyone have experience with this? Could it be a grounding problem? Thanks for any advice you can give.
Pete
Follow Ups:
Hi, Pete:I second, or "third" the recommendation to carefully and thoroughly spray out your tube sockets, possibly resolder things here or there, but word of warning! DO NOT OVERHEAT the traces on the circuit boards or they will lift right off the boards!
Be careful!
Also, I highly suspect that some capacitors in your existing power supply need replacement at this point.
If you operate the set with the top cover removed and gently tap on the tubes or on various areas of the circuit board WITH AN INSULATED PROBE ONLY, and this elicits a repeat of your noise problem, it could be any number of things which are responsible for the noise you reported. You could have a cracked or failed resistor somewhere, as well. I own a PV-2a. I was not that impressed with the build quality of the unit, even though it sounds terrific, as comapred with many of my other "vintage" tube preamps, which is why I kept it.
The ALPS pots in these preamps develop problems with contamination and need to be DISASSEMBLED, sprayed out and REASSEMBLED for better, more reliable performance. It is a rare situation when it is necessary to completely replace an ALPS pot in such a set, though it has been known to happen, of course.
Good luck resolving your noise problem.
I will look forward to reading a report from you about the actual resolution!
I always do the simple stuff first. Opened up the CJ PV2ar and resoldered all the tube base connection points, also resoldered some other joints. Checked everything I could. Cleaned selector switch and sockets.
The sound is still there on start up. Is there DC leaking?
What I did accomplish is I got rid of the microphonic tube noises, and selector switch 'pops'.
Overall, it sounds the same, great w/ CDs, but I wonder if the Phono section doesn't sound as good now (or is it my imagination?)May replace one section of the multi-section can cap next. 50-80 mfd, 450V it reads.
Actually, I cleaned the volume pot before replacing - had no effect. Something was really damaged inside - grooved contacts, I believe.
The new Alps pot transformed the sound - to what it should be.I noticed when installing new leads to the PCB, that the solder wants to lift off.
Wanted to have this preamp upside down on the bench today but my son's school called. He's sick and I had to bring him home and stay with him. Will postpone PV2 work til later.
Pete
Had a similar problem caused by bad joints and a broken socket pin from an update at CJ.
Pete
The BIGGEST problem and I mean the BIGGEST has always been the solder connections on the CJ tube sockets and grounds.Also the socket pins and dirt have this problem along a microphonic tube or tubes.Take your soldering iron and resolder every tube socket connection and I dont just mean heat it up and reflow old solder,I mean put on additional new solder plus go over any ground connections on the circuit board or chasis..Also make sure your tube pins in the socket arent sloppy..Thats an easy fix by taking a small screw driver and bending the pin in a bit.Also take deoxit 5 and spray in the sockets and pull the tubes in and out a few times..At least do the solder connections and if that doesnt cure it we can go from there.If you have a scope,you can see where the noise is most prevalent.
Mike
I was getting this 'Theremin'- type feedback when I put my hand near a couple tubes, when the cover was off. Also, some microphonic ringing when tapping the case - but only rarely. It makes sense now, since you said tube sockets. (I did clean them a while back, they're pretty tight.) I am going to get right on it. The darn thing still sounds good w/ music, with the problems - and hopefully will be even better.
Pipe cleaners work well for tub sockets!
This post is made possible by the generous support of people like you and our sponsors: