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batsong 26th October 2011 05:56 AM

CJ PV5 Upgrades?
 
Hi. Looking to upgrade the caps in the signal line of a Conrad Johnson PV5. Thinking of combining C29/30, C22/23 into a 5uF each, and replacing C20, 25, 26. Any other caps look like good prospects for an upgrade, or are any of the ones mentioned unnecessary?
What brands/types of cap would be desirable in this application? Been looking into Auricaps and Dynamics, and Janztens.
The preamp is used with a Sun Audio SV-2A3 (mods: removed 1st bypass cap, electrolytics replaced w/ film, GE/Ultrapath).

Thank you for looking!
-Gabe

http://drtube.com/schematics/cj/pv5.gif

jeffreybehr 26th October 2011 07:27 PM

For coupling caps, I'd use SoniCap Platinums by themselves if you can afflord it (IYCAI) or combinations of MultiCap RTXs and Platinums for the section-output caps. For PS-bypass caps, Platinums and Jupiter HTs.

In the PS, replace at least C3 with BlackGates IYCAI or maybe a Solen 400VDC 'propylene.

Said another way, replace ALL the original film-type coupling and PS-bypass caps, and repalce as many of the high-Voltage 'lytics as you can afford.

I've got pics of a PV5 rebuild I did many years ago; e-mail me at jeffreybehr(at)cox(dot)net and I'll send 'em, as long as you realize I wouldn't do it again that way. ;)
Here's one.
http://i89.photobucket.com/albums/k2...open_1000w.jpg

Quite visible are the Solen replacements of the HV 'lytics.

HollowState 26th October 2011 08:45 PM

I would not recommend replacing any of the capacitors in the phone stage. Unless you have a reverse RIAA network and plan to frequency sweep the stage afterwards. For which you'll need an audio generator with a flat output and the reverse RIAA network must match the characteristic output impedance of the generator to maintain accuracy. Usually 50 or 600 ohms. Even if you use the exact same value caps, changing the dielectric will affect the response curve to some small degree. This also applies to replacing resistors from one type to another. This is the voice of experience.

batsong 26th October 2011 08:50 PM

Thanks, Jeffrey. Email sent.

I see now...the pic shows Multicaps. I like how you replaced the whole line of 2.2uf power caps.

I already installed Jensen electrolytics in the PS of my PV5, I'm happy with those for now.
I like your bypassing idea. I wonder though if bypassing would sound better than throwing in a Mundorf Supreme or Auricap.

jeffreybehr 26th October 2011 11:02 PM

Quote:

Originally Posted by HollowState (Post 2759632)
I would not recommend replacing any of the capacitors in the phone stage.

Phono stage?

I certainly didn't suggest he replace any RIAA-eq. caps in the fono stage. The couplers, yes.

ihear21khz 27th October 2011 01:41 AM

Frankly, the film caps that CJ use are good. If you want to do better you need to invest in seriously good caps like V-cap, RTX or some of the Mundorfs (choice here depends on your taste). If you choose to go with any of these, I would not bother bypassing them with smaller value caps. I hate the results of bypassing (though for some reason CJ seem to have got it right). If you change the stock caps then simply omit bypasses. Listen to the amp without the bypass caps. You can always add the bypass caps later if you must.

HollowState 27th October 2011 02:07 AM

Quote:

Originally Posted by jeffreybehr (Post 2759823)
Phono stage?
I certainly didn't suggest he replace any RIAA-eq. caps in the fono stage.

No, Jeff, you didn't, and I did not mean to say that you did. I only wanted to make that point. But you did say:
Quote:

Said another way, replace ALL the original film-type coupling and PS-bypass caps...
I was thinking this could be interpreted to include the phono stage. Replacing (upgrading) capacitors in a power amp or line stage is no problem-o. But all the parts in a phone stage, which is a tuned frequency sensitive network, work together in synergy as a whole. It is not just the EQ componets alone. In fact, one could extend this reasoning to include the entire preamp since measurments are usually taken at the final output.

Assuming a manufacturer has done the job correctly (and I give CJ the benefit of any doubt biased on their experience). when an audiophile or technical person modifies a preamp with a tuned circuit to get a "better sound", what have they actually accomplished? A more euphonically pleasing sound, but one that is no longer sonically correct?

Part of my electronic background is test equipment and calibration which tends to affect how I think about things, for better or for worse.

batsong 27th October 2011 02:57 AM

Thank you for all of the advice, everyone.
I primarily use the phono section.
The problem is that this unit has had some hard failures in the past; it sounded awful and was very unstable when I first got it. I've had problems with the transistors burning out every few months, but am now finishing the PS rebuild.
It's starting to sound pretty good. It went from no bass to flabby bass, and now good bass, and a loss of glare.
I certainly want to use a light touch when improving. Thought I would start with the coupling caps, but there's such a vast array of available caps and huge differences in price, I wanted to seek advice before I risk spending on something that sounds thin and edgy.
Would like to hear more clarity and depth.

Thanks again.
-Gabe

ihear21khz 27th October 2011 03:15 AM

As I mentioned, the signal coupling caps that CJ uses are good. Also please don't bypass coupling caps in the signal path (or replace any bypasses that CJ has in place). If you really want to do a few more mods, I would suggest that you look at replacing the stock volume pot with something much better - a stepped ladder attenuator and bypass the balance control.

batsong 27th October 2011 03:19 AM

Quote:

Originally Posted by ihear21khz (Post 2759948)
Frankly, the film caps that CJ use are good. If you want to do better you need to invest in seriously good caps like V-cap, RTX or some of the Mundorfs (choice here depends on your taste). If you choose to go with any of these, I would not bother bypassing them with smaller value caps. I hate the results of bypassing (though for some reason CJ seem to have got it right). If you change the stock caps then simply omit bypasses. Listen to the amp without the bypass caps. You can always add the bypass caps later if you must.

Would you increase the value of the cap sans bypass?


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