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Old 16th September 2015, 08:10 AM   #1
AwdioDon is offline AwdioDon  United States
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Default TX 2575

Hi
I'm new to this forum, and want to learn how to add some new resistors to my pre amp. It's a Conrad Johnson Premier 14, and it's been suggested that I replace some resistors in the audio signal path. I could use some suggestions as to which ones to replace, but I could also use some help in learning what I'm doing rather than just swapping parts.

Does anyone have recommendations for some good reading? I understand some principles but still a novice.

Thanks
Don
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Old 16th September 2015, 09:00 AM   #2
Koonw is offline Koonw
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http://www.angelfire.com/planet/funw..._Contents.html
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Old 16th September 2015, 10:39 AM   #3
analog_sa is online now analog_sa  Europe
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Having not seen a circuit for your particular preamp it's hard to give advice. The TX parts may not be suitable for use as plate resistors, not sure what is their voltage rating but the naked construction does not seem ideal for large voltage drops.

Which leaves cathode and loading resistors as i assume there is no NFB.

Have you upgraded coupling/PS caps already? Resistors don't come to mind as prime candidates for upgrading... And the TX may change the sonic signature of the CJ in a way that may not be to your liking.
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Old 16th September 2015, 11:11 AM   #4
AwdioDon is offline AwdioDon  United States
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Thanks for the replies.

I'm going to start reading the textbook, as well as some suggested reading from a Sticky from this section on tubes

Let me see if I can find a schematic to post.

Thanks,
Don
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Old 16th September 2015, 12:04 PM   #5
analog_sa is online now analog_sa  Europe
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A textbook will enhance your general knowledge but cannot in any way guide you in this particular quest.

And anyway, you have not defined what is it you want to improve. General resolution? Tonal balance?
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Old 17th September 2015, 03:18 AM   #6
AwdioDon is offline AwdioDon  United States
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I guess my question was kind of two fold.
I'd like some specific advice about the preamp. I read on this web page, a guys account of what he did to his Premier 14, if you check out the link there are some hand drawings of the changes he made. http://digilander.libero.it/agostino...premier14.html.
And inanother post I read somewhere, I guy said the use of the TX2575 in the audio path made a big difference in the sound of his Premier 14. I'm still waiting for a reply as to which resistors he replaced.

I'm also hoping to have a better knowledge of circuitry basics so I can carry on a conversation. I realized that I don't know how to find the audio path in a schematic. If I'm told to replace R235 with a resistor of a different typ or value, I can find it and replace it. But I don't know what the effects are of my actions in the path (and probably won't for a while). When you asked if I had replaced the Power supply or coupling caps, I don't know which ones those are.
As for what I'd like to improve, probably general resolution. I'd like more clarity without harshness. The sound is a little fuzzy now in the higher ranges, and I hear a little ringing or at the top extension of some guitar notes. I'd also like a little more emphasis in the bass. I realize that these characterisitcs are pretty standard for a tube amp. So I should add that the amp is a CJ Premier 11a with GE 5751's and 6GC7's. The output tubes are 6550's Svetlana Winged C's. I've got some TungSol KT120's coming soon as well
Thanks
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Old 17th September 2015, 08:24 AM   #7
analog_sa is online now analog_sa  Europe
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Very nice link. Shinkohs are an old favourite of mine, especially for the price.

In a simple circuit like this all resistors are in the signal path and audible, but in a different way. The 1k in series with the input grid is called a grid stopper and should ideally be a carbon composition, but i would still rather listen to several different types or short it out altogether.

Why not just follow the advice from the link?
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Old 17th September 2015, 10:34 AM   #8
AwdioDon is offline AwdioDon  United States
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I very well may follow the advice of the article, but I was curious if all of the mods he made were significant in improving the sound. One of the reasons I came here for help is because I couldn't get a hold of the author of the article. I was hoping someone here could help me look at the mods and tell me how much was realistic. I've found in this audio world, a lot of money and time are spent on very small changes.
The guy on the CJ forum responded to me today, and he made some of the changes in the article. He suggested using the Vishay TX2575 for the 1Kohm input and 47ohm output positions, and using the Shinkoa's in the 500Kohm positions. And also changing the diodes the same way the author did.
I started reading the NEETS manual that was suggested in the sticky. It's presented in language that's easy for me to grasp. I appreciate what the other contributor to this thread offered, but it was harder for me to grasp. I work nights as a subway station agent, and have time to read when it's slow. So I'll keep reading.
Thanks Don
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Old 17th September 2015, 12:10 PM   #9
DF96 is offline DF96  England
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Quote:
Originally Posted by AwdioDon
I'm also hoping to have a better knowledge of circuitry basics so I can carry on a conversation.
The more you know about circuits the more you will realise that swapping non-faulty resistors will make no noticeable difference to the sound but could make a noticeable difference to your bank balance. In almost all electronic circuits it is safe to assume that the fixed resistors are the nearest thing to an ideal component, except where carbon composition resistors are used.

Quote:
I realized that I don't know how to find the audio path in a schematic.
'Audio path/signal path' is not an entirely meaningful/helpful term, although it is commonly used - often by people who don't understand that it is not always helpful.
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