ZX450

[Mr. Wild]

Hello!

I bought a ZX450v1 in poor condition. I bought it because I see old PG amps for sale very seldom here in Finland. Mind you, there was a nice M100 I really wanted for sale, but the price went a bit high. Plus I knew I would never end up actually installing anything that big in my car. Would have been a nice amp to go with my M50 though..

Some of the speaker terminal screws and remote turn on screw are missing. The red ovr led is missing too, sigh.
The plexi windows have been reglued to the chassis with some nasty putty or glue. Some corrosion around the screws too. Poor thing has had a hard life..

I'm going to replace the power supply caps, theres a tiny bit of leakage underneath them.

The inside of the amp is quite grimy and smells of cigarette smoke. Any idea how to clean the pcb and everything? I prolly need to spray it with some kind of cleaner stuff but I don't want to harm any of the components etc.

The power led comes on when powered up. The idle current is about 2,5 amps, does that sound right?
DC voltage at speaker outputs is 15-20mV which seems good to me. I'm just worried how the x'over's many pots and buttons work because of the messy condition of the insides. The x'over boards multiwire connections to the main board have some sign of soldering too, eek!

Here's the seller's picture, ill take some myself later.

[Eric D]

When I used to rebuild these amps I would remove the top cover, remove the bottom cover, desolder and remove the large crossover board, and also remove the 4 power supply input caps.

I then took off all the heatsinks (3 plates with a steel air director on one of them, and all the little finger type heatsinks on the plates. I would soak the heatsink parts in lacquer thinner or mineral spirits, and then on the board use an air compressor with air gun to blow off as much dust and grime as possible. If the board still looked bad, I would pour lacquer thinner or mineral spirits directly on the board and then blow it off right away with the air gun. This is like power washing the board in a way. Once all clean, I would put on new thermal paste, and reinstall the heatsinks, caps, and other parts.

[Mr. Wild]

Thanks for the advice! How do the heatsinks come off? I would guess the original thermal paste has hardened and glued the fets and bjts to the heatsinks. I have some brakleen in a spraycan which is used for cleaning brake and clutch parks of grease. That might be effective for cleaning everything.

[gfunk_nz]

I would be very nervous using brakleen, I just use IPA, with a small brush or cotton tip

[nutxo]

Thanks for the advice! How do the heatsinks come off? I would guess the original thermal paste has hardened and glued the fets and bjts to the heatsinks. I have some brakleen in a spraycan which is used for cleaning brake and clutch parks of grease. That might be effective for cleaning everything.

that stuff will eat plastic

[Mr. Wild]

More questions:

The pot on the front channels crossover goes round and round. Otherwize it seems to werk. Is this bad? When the pot goes from min to max where the stop should be, theres a squeak from the speakers.

Is it easy to find a rpelacement pot?

Also I need an red ovr led. Can I put in just any red led of the same physical size?

[ttocs]

no that is probably bad and broken. Look on the back of the pot and see if there is any writting at all. They are rated in ohms or k-ohms and they have a linear taper, log taper or what was #3?

[valeks1]

Gain
http://cgi.ebay.com/NEW-ALPS-50K-Pot-Du ... 45f9ef5a0a
Bass
http://cgi.ebay.com/NEW-ALPS-Dual-Pot-1 ... 43a1da0060

[Mr. Wild]

Thanks for the info, but I meant the pot which controls the front channels high/lowpass frequency.

[valeks1]

This is for FREQ pot for ZX450
http://www.ebay.com/itm/290504825576?ss ... 1558.l2649

[Mr. Wild]

Thank you very much!

[Thunderdome]

Gain
http://cgi.ebay.com/NEW-ALPS-50K-Pot-Du ... 45f9ef5a0a
Bass
http://cgi.ebay.com/NEW-ALPS-Dual-Pot-1 ... 43a1da0060

just wondering if you might know if this gain pot will work on a pld-1 ?

thanks

[valeks1]

Gain
http://cgi.ebay.com/NEW-ALPS-50K-Pot-Du ... 45f9ef5a0a
Bass
http://cgi.ebay.com/NEW-ALPS-Dual-Pot-1 ... 43a1da0060

just wondering if you might know if this gain pot will work on a pld-1 ?

thanks

YES

[Mr. Wild]

I replaced PS caps and put in a new ovr led. Cleaned everything I could with IPA and qtips. I decided not to touch the crossover pot since it works and I woulda made a mess with my clumsy soldering skills. The case paint is in bad condition. I got it a bit cleaner with thinner, but I almost ruined the paint

[Eric D]

Did you make sure to put the OVR LED in the right way? They only work in one direction (diodes).

Also, I am pretty sure you got the fan in backwards. Simple fix, just remove the screws holding it and flip it over. The airflow should be down onto the heatsinks, and then out the sides of the amp.

Your cap job looks good. You may want to put some silicone between the caps, but you don't really have to. If you mount your amp to your box (which really is not a great idea), then the silicone between the caps becomes useful.

Amps mounted to boxes tend to self destruct from the vibration.

[Mr. Wild]

Thanks Eric!

I put the led in the same way as the others and it lights up for a second when powering up.

I was wondering about the fan direction when putting things together. The threadmarks on the fan chassis made me install it that way. I doubt if there's much difference in the cooling effeciency anyway. I did notice that the 16 big transistors under the xover card with no heatsinks heat up considerably. I prefer to have the fan sucking heat away from the heatsink and the inside of the casing instead of blowing it in.


I put a bead of silicone between the caps legs so they are pretty well glued to the board. I learnt that trick on this phorum of course. The caps are 16mm in diameter so I didn't bother putting silicone to fill the big gaps.

De-solderin and re-soldering the caps was not so easy. A 40W rubbish soldering iron was only just enough to make the solder flow after lenghty heating. I'm a bit worried about the quality.

[Eric D]

I know PG did not design that amp with tons of time spent on optimal airflow, but it seems to me I did see one of these amps become damaged because the fan was in backwards. I think with the fan blowing out you don't get much cooling right under the fan since it tends to draw the air from its outsides and leave a dead air space under it. But, if your amp ever does overheat, just flip it around then and try it.

As for silicone under the caps, that is a trick posted here on the forum, but I for one amp very much against it. With silicone under the caps you will never be able to tell when they are leaking (if they do), and the caps can fail (catch fire) without warning. Also, you will have a harder time removing the caps in the future if you need too.

It may work great for putting the new caps in, but I don't see it being worth it long term.

[Mr. Wild]

What puzzles me about this amp (in comparison to older PG amps) is where are all the inductors?
Sure thing it has a toroid in the power supply. But at least M amps have a coil before the PS, coils after the PS and even coils after the amp stage.

How come ZX doesn't need coils and does this affect SQ?

[Eric D]

What puzzles me about this amp (in comparison to older PG amps) is where are all the inductors?
Sure thing it has a toroid in the power supply. But at least M amps have a coil before the PS, coils after the PS and even coils after the amp stage.

How come ZX doesn't need coils and does this affect SQ?

Good observation.

In an M series amp, the first coil is an input nulling toroid. This helps somewhat to block high frequency noise on the power line to the amp.

The coils on the outputs of the power supply section help block high frequency noise from leaving the power supply.

In the case of the output coils to the speakers, I believe these are there to help with the amplifiers output impedance, which improves its ability to drive a speaker. You will find on some models of M amps certain coils are missing, and replaced with a simple jumper.

My best guess is PG found out the slight improvements made by these features were not enough to justify their cost. I have ran PG MS amps without the coils on the speakers and it sounded just fine to me.

You can find these features in other amps out there as well. Zapco comes to mind. I own a Zapco with a similar setup.

When PG put these in the old MS amps, it was clear they were leaving no stone unturned with their design. This is just one more reason these old amps are so prized by a lot a people to this day.