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 Post subject: phoenix gold zx 475 zx350 potentiometer replacement + caps
PostPosted: Thu Mar 14, 2019 12:16 am 
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Joined: Sat Feb 16, 2019 2:05 pm
Posts: 9
thought i would make this for an archive post. hopefully it saves someone else a bunch of time if they are restoring one of the zx amplifiers

what are you looking at? zx475v2

input capacitors are nichicon pwm series 8200uf 16v part number UPW1C822MHD
rail caps are CDE or cornell 3300uf 50v part number 381LX332M050H012
crossover potentiometers are bourns 10k ohm 10% 4gang PTD904-1015K-B103
some of the smaller caps are available in the nichicon audio series, part numbers are UKA1E101MED1TD for the 25v 100uf, UKA1C330MDD1TD for the 16v 33uf, the 10uf 35v are the low esr pwm series with a part number of UPW1V100MDD1TD
thermal compound used and a GREAT idea to replace after all these years was arctic silver mx4. this is a non conductive non capacitive super high thermal transfer cpu thermal paste that is probably overkill for transistors...but...it doesn't dry out !

the bourns pots are the bees knees. 100% perfect fitment. even the frequency marks on the chassis line up perfectly. if you have a zx amp that is hissing, popping etc when the crossover is engaged but goes silent if you push in the bypass buttons there's a pretty reasonable chance the pots are the issue, mine not only had this symptom but the front one made noise when you adjusted it further confirming the issue.

the zx500 from what i remember uses different rail caps. always pull the lid and double check what you have. the 475 and 350 both use the same rail card and 22mm caps. they are not 25mm diameter as some other sites reported. at least neither of these two were

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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 3:15 am 
the Floor Sweeping Hack with Golden Ears

Joined: Fri Dec 19, 2008 9:53 pm
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very nice



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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 3:42 am 
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Joined: Mon Mar 21, 2011 4:47 am
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Location: Finland
I have a ZX450 which has issues with the gain varying on its own in one channel. After switching on, after a few minutes the gain increases suddenly. It might be a pot issue but I don't really know.
ZX amps could be better if the crossovers could be removed entirely. The crossovers were state of the art and very useful back in the nineties, but now they seem to cause a lot of problems. Also modern head units make the crossovers obsolete.



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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 6:40 am 

Joined: Tue Nov 06, 2012 9:30 pm
Posts: 144
Good info. Thanks.

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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 8:57 am 
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Joined: Sat Feb 16, 2019 2:05 pm
Posts: 9
Mr. Wild wrote:
I have a ZX450 which has issues with the gain varying on its own in one channel. After switching on, after a few minutes the gain increases suddenly. It might be a pot issue but I don't really know.
ZX amps could be better if the crossovers could be removed entirely. The crossovers were state of the art and very useful back in the nineties, but now they seem to cause a lot of problems. Also modern head units make the crossovers obsolete.


certainly sounds like it. that is the hallmark of a wonky pot with either noise or adjustment troubles

you can use the bypass on the zx amplifier if you have a good dsp or don't mind the sound of the deck crossover. the only reason i changed the pots was because i liked the sound. i went back and forth between the crossover on my deck which is a nice alpine 960hdmi, has 6-24db adj slopes and freq can be set basically every 10hz so it's pretty solid for a deck crossover. however....it doesn't sound as good to my ear. is the difference small? yes but it's slightly more harsh. with each track i prefered the tonal sound of the on amp crossover. i recapped the crossover card with nice nichicon audio caps and then changed the potentiometers to get rid of the static. that said if i was running 6ch on the front and a bit one processor i may have just pushed in the bypass buttons and not spent an hour changing the pots. a GOOD active crossover can sound amazing. i'm just not really sold on what is included on most decks. they do not sound like a bit one

* note the potentiometers on the crossover card are not easy to change. a person needs good eyes, good hands, a pinpoint adj temp soldering iron, flux and small copper wick to desolder if they don't have a rework station. installing also needs to be done carefully. 270c temp for no more than 3 seconds when soldering. i found it very helpful to have a dab of flux on each pin of the pot so the soldering was nearly instant and flowed perfect. this is a harder job than doing the caps which brings up another thing for people reading this. in my opinion

1. the input caps are easy to change. a novice that does a little practice ahead of time could do this without trouble, just don't use too much heat or leave it on the board more than a few seconds per
2. the smaller caps and the rail caps. harder. you need desoldering skill, an adj temp iron, a flat and pin tip. previous experience suggested
3. the crossover potentiometers. hardest of all. you need previous experience or you need to practice on a trashed board with a similar pin out. would be very easy to screw this one up as it's quite precision work. desoldering without damage and removal of the old pots is the hard part. you have 12 pins extremely close to one and other

lastly, there is a link here: viewtopic.php?f=3&t=17746 with a person rebuilding the gain pots. another option is buying a broken / burned board zx for $20-25 dollars if you can and using it for parts. there is a product called deoxit that is great at removing oxidation and a fader lube version you use after cleaning or as a one stop shop cleaner/lube on pots to get them going again. very popular with musicians


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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 9:20 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 69
thank you for the info!


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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 10:13 am 

Joined: Tue Nov 06, 2012 9:30 pm
Posts: 144
This works very well to desolder. I think it cost 60 bucks? I dont remember. Image

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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Thu Mar 14, 2019 11:13 am 
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Joined: Sat Feb 16, 2019 2:05 pm
Posts: 9
^ really worth it to invest in. a real desoldering station would make life so much easier. nice tool to have around. if i had to do this all over i would have bought that first. wick and flux are tedious. it works but it's slow slow going


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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Fri Mar 15, 2019 2:42 am 
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Joined: Mon Mar 21, 2011 4:47 am
Posts: 253
Location: Finland
I'm pretty sure the crossovers in modern HU's are digital and my assumption has always been that digital crossovers don't really sound like anything.
I mean different crossover algorithms sound different, but they are in principle "perfect".
It's the D/A conversion where you get differences in sound quality.

I would have thought an analog crossover would degrade sound quality more than a digital one.

Anyway, what I really like about old school amps is the simplicity of them. ZX amps are more complicated and often don't work as well as the simpler M and MS series.
The ZPA series doesn't even have bass boost, but they do have an optional crossover card.



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 Post subject: Re: phoenix gold zx 475 zx350 potentiometer replacement + ca
PostPosted: Fri Mar 15, 2019 9:50 pm 
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Joined: Sat Dec 23, 2006 12:15 am
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Location: Alberta
This was quite timely - I'm also looking for some sensitivity gain pots for ZX450 amps, but it seems there still aren't any replacements available.



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