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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Hi guys, I want to know if I could recap my preamp by myself?
Hi guys, I want to know if I could recap my preamp by myself?
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Old 5th April 2019, 05:46 PM   #1
zhloea is offline zhloea  United States
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Smile Hi guys, I want to know if I could recap my preamp by myself?

- About me:
I am working in the computer industry for many years, I did a lot of PC mantianace but limited to part replacement and never did any chip level reparation.
I have used soldering couple times and know how to discharge a capacitor.

- About my equipment

I have a Yamaha C-80 preamp and want to recap it.

-Questions
Do you think I could do the recap by myself? (seems not very difficult)
Do I need to know audio theory or its circuit diagram before doing it?

Thank you so much for any help!
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Old 5th April 2019, 09:02 PM   #2
mchambin is offline mchambin  France
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You must know how to identify capacitor types to replace as is. Do not beleive improvements from changing that, trust designers know what they are paid for.
All you have to do about caps, is same type, same values and some caps have polarity.
A most important aspect is: PCB potential damage.
Do you have the skill at desoldering ( mastering, the unsoldering pump and the unsolder tape ), soldering with a good iron with an appropriate tip, cleaned and at the right temperature.
The best is to train for this skill on salvaged stuff, and see what looks like a good solder joint. When you pull out a component, be aware, there is a risk to tear off the pcb track and master how to avoid that.
And be aware that, there are "good, bad and ugly" PCBs, for this job.
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Old 5th April 2019, 09:16 PM   #3
zhloea is offline zhloea  United States
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Thanks for your reply mchambin, for the caps, the only one type I am worrying about is 35v 4700uf, the original components are huge, but currently we could not find that kind of caps. So for instead I gonna use "Nichicon Gold FW 4700uF 35v Radial Electrolytic Capacitor for Audio", this the best caps I could find now, but looks pretty small...

For the tools, I purchased a set of soldering for 30 bucks, and much other stuff, total over 100 dollars. That solder with 5 different tips and temperature adjustable. I also purchased a couple of practice board like radio, clock...I will solder and desolder them couple times for practicing, before handing on my preamp.

I don't know if it is enough for it...still doubt...
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Old 5th April 2019, 11:44 PM   #4
indianajo is offline indianajo  United States
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Industrial nichicon electrolytic caps are just fine for audio. also Rubicon Panasonic & Vishay. I don't like doing this job over & over, now that distributors will sell to individuals with debit cards, we can buy long life (3000 hours service life) caps for less than the pricey "audio" lines.
Wear safety glasses, solder can splash. Mark the location of the + or - on the board with a sharpie, if you get it wrong the new cap explodes. I use a solder sucker rubber bulb from parts-express now, those spring loaded sucker gadgets the tips are too easy to melt. If I burn this one it is $2. I have a R**** S**** solder sucking iron, but it doesn't work very well and is extremely hot.
I started by "just do it". The more I do it the better I get. Old components with lead/tin solder are a lot easier to work than ROHS compliant ones with silver solder. I've pulled a few pcb lands, and patched them back with solid core wire. the only thing I knew for certain before the internet was that the MacIntosh salesmen at the clinic said my 70 w amp put out 7 watts because the e-caps were dried up, followed maybe by an aged rectifier tube.
I started replacing electrolytic caps on a dynakit ST70 which is now worth $700 in junk non-working condition, so don't feel too bad about an old yamaha. What is the cost of an inop one on e-bay? That is your worst case scenario.
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Last edited by indianajo; 5th April 2019 at 11:49 PM.
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Old 5th April 2019, 11:57 PM   #5
Old'n'Cranky is offline Old'n'Cranky  Australia
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Quick search shows the c-80 using a phenolic board.
Be prepared for almost every single board trace to lift and need repairing.
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Old 6th April 2019, 12:04 AM   #6
tsmith1315 is offline tsmith1315  United States
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It's not like you're gambling your retirement on this project. Do your best, learn and be proud. If you have to do it again later, you'll know a little more next time. There's lots of help here if you want it. Please post pictures for others who may have the same questions.
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Old 6th April 2019, 06:23 AM   #7
zhloea is offline zhloea  United States
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Hi, thanks for all the reply, big help!!!

And I have another couple questions with pics:
1. My c-80 works very well now, a couple of weeks ago there is noise when turning the nob and distorting between channels, so I open it and spray some RadioShark cleaner and lubricant, then it works as before. I could feel heat after running it 30mins, I guess these are the signs that need be recapped right?

2. When open it you could see there are 4 hug caps, actually, they are same things, but looks different, are the top 2 almost burst? So I decided swap these four first, am I right?
WechatIMG30 copy.jpeg - Google Drive

3. There is another place looks wired, looks burn out, but everything works fine, could anyone tell me what issue it could be?
WechatIMG44 copy.jpeg - Google Drive

4. The pic down below is the new cap I want to buy, but they are really small compared with the original ones, so does this matter?
Screen Shot 2019-04-05 at 10.48.03 PM.png - Google Drive

Thank you so much!
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Old 6th April 2019, 07:16 AM   #8
Mark Whitney is offline Mark Whitney  Netherlands
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Wrong capacitor. Look for something like this.
Aluminum Electrolytic Capacitors - Snap In | Mouser
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Old 6th April 2019, 07:27 AM   #9
mchambin is offline mchambin  France
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Quote:
Originally Posted by zhloea View Post
Hi, thanks for all the reply, big help!!!
2. When open it you could see there are 4 hug caps, actually, they are same things, but looks different, are the top 2 almost burst? So I decided swap these four first, am I right?
WechatIMG30 copy.jpeg - Google Drive
Yes !
The big power supply caps are the one suffering. In many cases, that is the only real need for recapping.

Good move with the RadioShark contact ckeaner.
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Old 6th April 2019, 07:30 AM   #10
onokun is offline onokun  Russian Federation
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Quote:
Originally Posted by zhloea View Post
I could feel heat after running it 30mins, I guess these are the signs that need be recapped right?
Electronics tends to warm up when plugged in, you know. This is a sign of approximately nothing.
Without any measuring equipment your best way to tell if caps are going bad is to visually inspect them and to listen and evaluate the sound of preamp.
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