ZPA0.3

[Mr. Wild]

I scored a zpa0.3 for a good price. Its a bit banged up and rusty on the outside and the plexi is rubbish, of course. The insides are dusty but otherwise perfect. Main thing is no-one has tampered with it before me

I powered the amp up to see it works. Idle current is 1,75A and DC offset 11mV / 15mV so all seems fine.

This is a V1 ZPA but the fan control board has two large resistors slightly away from the board but it all seems factory made. Interesting.

I havent seen any pictures of entire guts of zpa amps so I figured I might as well post mine.
This thing is huge for a 500W amp! It will probably never go in my car. I will rather stare at it in the garage

I know I'm supposed to use a line driver with a zpa, but the manual and board markings show the gain setting range is 1-8V. Has anyone tried and measured to see how little input voltage is needed for full power even if the signal quality is compromised?

[zeropoint0.5]

you took a big risk by powering the amp up first of all.............you're a Lucky man nothing happened....

please recap it first...............

can you measure one time the value of those big resistors on the vertikal daughterboard ??

are they 270ohm of 330ohm ??

a line driver will benefit for sure, so in time you can look for a pld1/tba/sld44/tld22-66 or something.....

seeing the pics, blowing out the dust with an air compressor pistol will do a lot....

please check under every transistor for loose little copper wires sucked up by the fans;........

[Mr. Wild]

Thanks for the concern and all the info, zeropoint!
I take precautions when powering up an amp with old caps. I have an amp meter with a 10A fuse in it inline with the amp. This way I can see if it draws too much current and disconnect it. Also i use a tiny 12V 1,5Ah hand drill battery for powering while doing basic testing.

I will pull the PS caps as soon as the new caps arrive.
The big resistors you asked about are 330ohm. They get hot but not burning hot.

None of the PG amps I have show any sign of thermal stress. This is one benefit of living in a cold climate.

[vwdude]

Nice amps. I have bought two 0.3s and both were in worse shape than yours. One I have completely restored with new ps caps and rail caps, plus I upgraded to v2 and replaced all small caps to ELNA.

You do need a high voltage signal going into these amps. I have run the 0.5 with a less than adequate 2.2 volts and it sounded whimsy, now I run a TBAt with around 8 volts and it's the most incredible amp I have ever heard (and I had a McIntosh amp previously).

I also am going to use my 0.3s as garage wall art once the casing comes back from powder coat.

Here's my thread on the first 0.3 that I got.

http://www.phoenixphorum.com/viewtopic.php?f=3&t=23937

[Eric D]

This thread may help answer some of your questions...

http://www.phoenixphorum.com/viewtopic.php?f=3&t=17435

[Mr. Wild]

Great info, thanks Eric! These ZPA amps confuse me, especially the power supply design. I wish I had the schematics. 30V RMS output capability is in line with the 200W @4ohm stereo specs you see here and there. But this means the rail voltage is at least 43V, yet the amp has 35V rail caps. Duh!

All I can figure is that the power supplys are connected in series or parallel in high voltage / current mode. But with 6 rail caps in total I just can't figure it out.
Then there's ZPA0.5 with 35V and 50V rail caps..

[vwdude]

Great info, thanks Eric! These ZPA amps confuse me, especially the power supply design. I wish I had the schematics. 30V RMS output capability is in line with the 200W @4ohm stereo specs you see here and there. But this means the rail voltage is at least 43V, yet the amp has 35V rail caps. Duh!

All I can figure is that the power supplys are connected in series or parallel in high voltage / current mode. But with 6 rail caps in total I just can't figure it out.
Then there's ZPA0.5 with 35V and 50V rail caps..

Easy, it's all voodoo.

This thread may help answer some of your questions...

http://www.phoenixphorum.com/viewtopic.php?f=3&t=17435

That's good to see. I keep my gains all the way down and I figured exactly what you found, but I didn't feel like testing the theory.

[Mr. Wild]

I recapped this ZPA and gave it a little try. First thing I noticed is that the DC offset has changed from 11/15mV to about 30/50mV. This puzzles me, because I havent touched the bias pots.
I did remove and reinstall the heat sinks. Also the fans werent connected when I measured DC offset. SO maybe this is some sort of thermal related phenomenon.

Anyway I played some MP3 music off my phone with some rubbish 5" mini-stereo speakers in my garage and liked the sound. Very natural and full sound with great firm bass. I swapped amps and in comparison a ZX450 sounded quite thin and lacking bass.

BTW is the white plexi logo a rev1 thing? I really prefer the gold logo which I see in most pictures.

[vwdude]

I think the white logo was an early v1 thing. I'm seeing that some of my early serial number amps came to me with the white logos. I did buy an early serial amp that had a gold logo plexi but who knows if that's what it came with.

I can do a reproduction white logo plexi in either clear or tinted. PM me, I already have an order I'm getting done, I can call and up it to one more 0.3 if you want in.

[zeropoint0.5]

I recapped this ZPA and gave it a little try. First thing I noticed is that the DC offset has changed from 11/15mV to about 30/50mV. This puzzles me, because I havent touched the bias pots.
I did remove and reinstall the heat sinks. Also the fans werent connected when I measured DC offset. SO maybe this is some sort of thermal related phenomenon.

Anyway I played some MP3 music off my phone with some rubbish 5" mini-stereo speakers in my garage and liked the sound. Very natural and full sound with great firm bass. I swapped amps and in comparison a ZX450 sounded quite thin and lacking bass.

BTW is the white plexi logo a rev1 thing? I really prefer the gold logo which I see in most pictures.

the yellow pots on the main board are for the bias settings, those on the vertikal boards for dc offset.......

the dc offset changes all the time.....just keep it at close to zero as possible......

don't adjust the bias pots unless you really know what you are doing...............

[trickyricky]

It will change especially if you turn off or remove the fans.