CJ 17Ls modifications

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thphoto
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CJ 17Ls modifications

Post by thphoto »

Hi all

I am new to the group but not to CJ audio, over the past 45 years I have owned many wonderful CJ products, amps and preamps, I currently own a CJ 17LS, I just upgraded the tubes to NOS Amperex PQ 6922 gold pin D getter from 1962 matched quads, things are starting to sound pretty good with my Cary audio 300b signature mono blocks (which I just got back from Cary as I had them upgraded) I am looking for suggestions for mods or upgrades for the17LS pre amp?

Thanks in advance Thurston
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Re: CJ 17Ls modifications

Post by admin »

Hi Thurston,
Welcome to the site, it's great to have you. I don't personally own the 17LS so I can't offer you specific advice on upgrades. However, it sounds like you have a great system. A lot of our members try a number of tube options, this obviously is the "easiest" upgrade as it's simple plug and play. Changing caps is also something that many users do but again, I don't have personal experience with the 17LS. Either way. Welcome to the site.

BTW- I moved your post into the proper category.
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Re: CJ 17Ls modifications

Post by jeffreybehr »

I've requested a schematic diagram of the '17 and will post as soon as it arrives. The '17 is a member of the 'propylene-and-'styrene-caps generation of circuitry, so replacing the coupling and final-powersupply-bypass caps with Teflon-film parts such as Sonic Craft's Platinums would be a definite upgrade.

More later.
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Re: CJ 17Ls modifications

Post by thphoto »

Jeffreybehr

Thanks so much, I really like this preamp and I knew someone out there would know how I can get the best performance out of it. I look forward to getting the schematic and further advice from you and the forum Thanks Thurston
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Re: CJ 17Ls modifications

Post by jeffreybehr »

th, I've sent the schematic to Admin who has posted it.

After reviewing my copy of the diagram, and understand that I've never heard one of these nor even seen one, here are my thoughts:
1. Signal-coupling caps, per channel, are a pair of 2uF caps in parallel (= 4uF) with no other bypass. I suspect these are styrenes (see below), but I'd replace them with SoniCap Platinums. With a load resistor of 500K, the -3dB point of that output filter is 0.07Hz(!!!!!!!!!!!!!!) The value of the cap you select should be large enough for a high-pass-filter point no higher than about 2 Hz, and that's calculated with the poweramp's input impedance in parallel with the preamp's 500K resistor. If you would like help with this, feel free to e-mail me at jeffreybehr(at)cox(dot)net for details.

2. The first half of the high-Voltage powersupply is common to both channels and uses only 'propylenes and NO electrolytic caps; but the second half, the regulators, are separate per channel. The common filosofy on improving the quality of the output caps in regulated PSs is to concentrate on the caps closest to the devices using that power. Each regulator's output cap is a trio of 2uF caps (totaling 6uF per channel). Again, there are no bypasses on these caps, suggesting to me that they're the higher-quality 'styrenes (and the same assumption may be made about the signal-output couplers mentioned above). Probably I'd replace each trio of 2uF caps with a single 4uF SoniCap Platinum. There's another filter/shunt cap in each of the PS regulators, Cs 23 and 28; those I'd replace with same-value Platinums.

3. Resistors. Depending on how much money you have to spend, consider replacing the eight plate resistors and all the resistors in series with the signal (I quickly counted 5 of those). I'd ask Jeffrey Glowacki of Sonic Craft...
http://www.soniccraft.com/index.php
...who has a HIGH degree of skill and experience in these areas, for advice on what to install.

My priorities on sequencing these improvements would be the order I've listed above, namely signal couplers, Voltage-regulator output filters, and resistors.

Altho I've done many-dozens of these kinds of upgrades over the decades, if I had one of these AND LOVED ITS sounds and didn't want to spend $10K on a new preamp, at my current age of 72 I'd send it to Sonic Craft to have the work done. But if your soldering and other technical skills are high, you may well be very successful at doing it yourself.

FWIW, c-j's filosofy about active circuitry in this preamp is somewhat different than in their later preamps. To achieve low output impedance, they now use MOSFET output buffers (and only one or two triode sections for Voltage gain) to achieve very-low output impedance--on the order of 100 to 200 Ohms. Your '17 uses multiple triode sections (four) in parallel--and NO buffers such as MOSFETS or cathode-followers--for low output impedance, but 850 Ohms is as low as they got with the 6922s in the '17.

Pls let me know here or via e-mail if I can help further and also what you decide to do.
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Re: CJ 17Ls modifications

Post by thphoto »

Hi J
Thanks for all the great info, I am new to this forum and don't know how to find (or where) the schematic is located, I am not sure how to figure out the values for part one, if you could help with that it would be great, I will get in touch with Jeffrey Glowacki at sonic craft for his input as well. I am not willing to tackle this project by myself, but I have a good audio tech near me here in Maine who says he is capable, I have a custom built Tube distinction soul mate preamp that was pretty expensive that I am willing to sell to fund the project. What it does it does amazingly well, but the synergy with my current system is not what the CJ is, I am hoping I can open up the soundstage a bit and start to "see" around the instruments a bit better like I can with the TD pre, Thanks for all the info and anything else you have to offer is appreciated Thanks from one "Tin-eared fotografer" to another PS I like your photographs, Thurston Howes
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Re: CJ 17Ls modifications

Post by jeffreybehr »

thphoto wrote:Hi J
Thanks for all the great info, I am new to this forum and don't know how to find (or where) the schematic is located, Here...
viewforum.php?f=17

I am not sure how to figure out the values for part one, if you could help with that it would be great, OK; not a problem. What's the input impedance of your poweramp?

I will get in touch with Jeffrey Glowacki at sonic craft for his input as well. Good; JG will refine/correct my recommendations as well.

I am not willing to tackle this project by myself, but I have a good audio tech near me here in Maine who says he is capable, OK; good idea.

I have a custom built Tube distinction soul mate preamp that was pretty expensive that I am willing to sell to fund the project. What it does it does amazingly well, but the synergy with my current system is not what the CJ is, I am hoping I can open up the soundstage a bit and start to "see" around the instruments a bit better like I can with the TD pre, I'm confident the transparency of the preamp can be improved significantly without altering its excellent traits.

Thanks for all the info and anything else you have to offer is appreciated Thanks from one "Tin-eared fotografer" to another PS I like your photographs, TYVM; more here.
http://s89.photobucket.com/user/jeffrey ... t=4&page=0

Thurston Howes
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Re: CJ 17Ls modifications

Post by thphoto »

Perfect thanks for making it so easy for me, I got the schematic, the input impedance of my mono blocks 150,000 ohms, the input sensitivity is .75v for full output. Thanks once again T
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Re: CJ 17Ls modifications

Post by thphoto »

Hi Jeffrey I have finally opened up the CJ to see what I can do to it to modify it and I find what looks like a Cap that has been disconnected, it looks like the last cap in the series, what do you make of that? I think I am going to replace the caps with holland super caps, a bit of a tight fit but they seem like the best caps I can afford Thanks T
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Re: CJ 17Ls modifications

Post by jeffreybehr »

thphoto wrote:Hi Jeffrey I have finally opened up the CJ to see what I can do to it to modify it and I find what looks like a Cap that has been disconnected, it looks like the last cap in the series, what do you make of that? I think I am going to replace the caps with holland super caps, a bit of a tight fit but they seem like the best caps I can afford Thanks T
I have NO idea.

Do you have a link to the 'holland super cap'? My search turned up nothing.
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Re: CJ 17Ls modifications

Post by thphoto »

Hovland super caps (auto correct came into play) sorry for that
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Re: CJ 17Ls modifications

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-admin
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Re: CJ 17Ls modifications

Post by thphoto »

yes do you have any thoughts on using them? Thanks
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Re: CJ 17Ls modifications

Post by admin »

I don't have any personal experience with them myself. They look to be of high quality and the fact that they make them in the US vs China is definitely a good sign.

My personal experience with updating caps is limited to a mod I did for a Jolida JD9 preamp (I have a more detailed post of it on another thread here on CJO, you could check it out). I used Obbligato Gold series caps for that and it definitely made a big improvement. However, a JD9 is kind of "budget gear" and I was replacing a really cheap stock cap, not an audiophile grade component.
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Re: CJ 17Ls modifications

Post by thphoto »

Thanks, I will keep you in the loop of my progress, the cap in the CJ that was not connected still amazes me, I am not sure what to think about that
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