Phoenix Gold Phorum

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? zx450v2

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

very nice

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.

Good info. Thanks.

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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: http://www.phoenixphorum.com/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

thank you for the info!

This works very well to desolder. I think it cost 60 bucks? I dont remember.

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^ 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

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.

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.

Looking for a replacement capacitor for my zx450
Its 2200uf 16v 105deg C measures approx 18mm x 35mm

[email protected] wrote: ↑Sun Sep 05, 2021 4:55 pm Looking for a replacement capacitor for my zx450
Its 2200uf 16v 105deg C measures approx 18mm x 35mm

You need to replace all the stock Panasonic caps in the power supply, not just one. They leak and will eventually cause the amp to catch fire.

Other than that, any general purpose low esr cap will work in the power supply. The working voltage has to be 16v or higher and you can fit up to 10,000uF easily, a few 12,000uF will fit as well if memory serves. Just make sure the diameter is correct. Pretty much any modern cap less than 10,000uF will be shorter than the stock ones. You don't have a lot of height room to play with.

Be forewarned that the leaked electrolyte will have done damage to the board under the caps. Severity will depend on how badly they have leaked and how the amp has been stored and/or treated. You must clean the board thoroughly, remove any charred areas if present, and remove all the electrolyte from the board. If you don't get the stuff out of the fiberglass, the amp can and will burn even with new caps.

The best think you could do for the amp is send it to a good tech. PG boards are very fragile, and the cap leakage makes it 100x's worse.

The pictures below are of an m50 that someone recapped with Nichicon UHE series caps. They failed to clean the electrolyte though, and the board went up in flames. BTW, Nichicon UHE caps are not recommended for automotive use due to their water based electrolyte. This recommendation came from Nichicon themselves. I try to use AEC-Q200 automotive qualified capacitors where possible.

Later,
Jason