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Old 27th October 2011, 03:24 AM   #11
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Quote:
Originally Posted by batsong View Post
Would you increase the value the value of the cap sans bypass?
No. If you are using a "better" cap, you do not have to use a bigger value to account for the value of the bypass. Remember that in the day, bypass caps were used to improve the high-frequency response of a capacitor. Modern caps, electrolytics included, have very good hf characteristics. Adding bypasses to these more often than not create a less than natural sound.
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Old 27th October 2011, 07:52 PM   #12
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Originally Posted by ihear21khz View Post
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).
Huh? This thing was designed and built 35 years ago! The section-output couplers are even c-j's own 'propylenes.

Your advice MIGHT be applicable to a medium-price c-j preamp from, say 5 years ago, but caps have gotten lots better sounding in 35 years. I've replaced the front-L/R c-j-'propylene-and-'styrene-combo output couplers (total of 4.15uF) in my 6-channel c-j MET1 with SoniCap Platinums. The music is audibly cleaner, airier, more transparent than before, and I didn't think there was anything wrong to begin with.

I have found invariably that adding a higher-quality, smaller bypass cap to couplers or PS-bypasses improves the sound, and I've evolved to ever-more-expensive hi-end caps as I've gotten more experienced with listening to music, including LOTS of real...not reproduced...music and improving various pieces of audio gear. My MET1 uses SoniCap Platinum couplers (2uF) and Jupiter HT and Platinum PS-bypass caps, and my system has never sounded better.

I now choose to perceive MultiCap RTXs as entry-level hi-end caps, with SoniCap Platinums as the best sounding. Mundorf Silver/oils, Cardas GRs, and Jupiter HTs are also at least very good.

Isn't it great that we have SO many choices?
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Old 27th October 2011, 08:38 PM   #13
batsong is offline batsong  United States
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Thanks ihear21khrz,your description makes perfect sense.

I agree that there is ample opportunity in improvement by substituting at least, the output caps at first. i also agree that if I were to replace any of the caps that they would have to be very good caps. Unfortunately, there are budgetary restraints.

Been looking at Mundorf Supremes and/or Russian Teflons as bypass caps.
What about PIO?
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Old 27th October 2011, 08:56 PM   #14
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I throw my lot in with "ihear21khz." The problem with this whole idea of "upgrading" with improved caps is that ALL caps sound different; a modern cap will definitely sound different from what is in there now, and it may even sound better in some ways such as inner detail and imaging, but that doesn't mean it will sound better overall. Quite often a modern film cap will skew the tonal balance towards the "lean and bright" sound that many people like today. Someone who favors a warmer, rich and smooth sound will not consider the lean and bright sound an improvement. Quite the opposite.

Bypass caps are another example of this. A small bypass cap in my experience provides extra excitement in the highs with heightened detail and imaging, but at a cost---the highs have an unnatural emphasis, and usually the bass becomes lean. Some would consider a bypass cap to be an improvement. Others such as myself can't stand them.

CJ has a good reputation for choosing components in their products that produce the sound they are looking for----the CJ house sound. If you have a CJ preamp from the 1980s and like its overall tonal balance, there is a very good chance that you will upset its tonal balance by replacing its coupling caps with modern caps. You might like it, but then you might not. You just have to try it and find out for yourself.
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Old 27th October 2011, 09:00 PM   #15
SY is offline SY  United States
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Not the answer you want to hear: chances are, the caps are fine.

Biggest improvement will be reworking some of the circuitry and the power supply. Admittedly, that's harder than just buying designer caps, but there's no free lunches.
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Old 27th October 2011, 10:15 PM   #16
batsong is offline batsong  United States
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Thanks for the input. All of these are considerations that made me bring this to this forum.

Besides, it's fun!

SY--No need to feel defensive. What 'I want to hear' is the glorious mid range that these PV5s others report them to have, any tips on how to achieve this are appreciated.
I am rebuilding and improving the PS. As far as circuit changes, I have heard of some who have had success in elevating the performance of these preamps, but unlike the ST-70, how one might do this is not exactly ubiquitous info on the web. Any ideas?
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Old 27th October 2011, 10:22 PM   #17
SY is offline SY  United States
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I've rebuilt several of these. An active reg (i.e., not a cap multiplier) is a good start. You can use a simple two transistor regulator (see Morgan Jones "Valve Amplifiers") or even better, a Maida type reg.

Look at what gain you really need out of the line stage. For most setups, unity gain is good enough and you can eliminate most of the circuitry (nothing sounds better than nothing!). Either go passive or use a cathode follower- using a better tube for that purpose than 5751. The phono stage can be upgraded by removing the feedback, increasing the gain (LED bias instead of resistor, CCS plate loads), and putting a passive RIAA network between the two stages.
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Old 28th October 2011, 12:03 AM   #18
batsong is offline batsong  United States
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Thanks, SY. This is really interesting.
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Old 28th October 2011, 02:26 AM   #19
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SY's suggestions are great but what you will end up with is something very different that sits in the casework of a PV5. If you are considering such a major rework of the circuit, I suggest that you build a preamp from scratch - something like the Vacuum State FVP5A. Keep your CJ as is and enjoy it for what it is. It will probably be worth more without your hacking it.

Jeffreybehr,
Many modern film caps would be superior from a technical point of view (to CJs selection 35 years ago in the PV5) . However there are just too many variables to suggest that one brand/type of cap will sound "better" than another in the CJ or indeed in any other amp circuit.

There are many who swear that good old oil filled caps are the ONLY choice for tube circuits. You yourself like the Jupiter cap. I'd like to know how a Jupiter cap measures in terns of dielectric absorption. Probably not very good - and worse than CJs 35 year old props. CJ's "glorious mid-range" isn't an accident and I am certain that the choice of cap (and the bypass) has much to do with this. My point is that changing these will greatly affect the voicing of the amp.

Cheers
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Old 28th October 2011, 02:33 AM   #20
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Originally Posted by Salectric View Post
Bypass caps are another example of this. A small bypass cap in my experience provides extra excitement in the highs with heightened detail and imaging, but at a cost---the highs have an unnatural emphasis, and usually the bass becomes lean. Some would consider a bypass cap to be an improvement. Others such as myself can't stand them.
Exactly!!!
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