ZPA Misconceptions...

[Eric D]

I just repaired a ZPA 0.3

For the heck of it I did some testing.

30V RMS out prior to clipping. Pretty impressive for this amp if you ask me.

Here is the fun part. It took ~9.7V RMS into the amp to drive it to clipping. This makes sense as these amps are well known to like a line driver.

However, with the gains on the amp all the way up it only took 1.3V RMS to get the amp to clip.

So, the moral of the story is any deck out there can fully drive a ZPA, you don't need a line driver. However, if you do have a line driver you can turn the ZPA down and lower your noise floor by driving the amp with a lot of input voltage.

In my opinion if you have a 4V deck, you don't need a line driver for a ZPA. 4V is plenty high to keep the noise low, and the ZPA will work great with a 4V deck.

[kg1961]

Eric in the new year i would like to find 2 zpa .3Are there thing to watch out of..
aslo were you working aon the v1 or v2? do you have pics of the amp you were working one? were you just changing caps or what were you doing with it
mike

[shawn k]

That's good info. I was under the impression these needed a line driver. Always good to rectify bad info. Nice work!

[The Golden One]

that is quite interesting i may just experiment with one of mine on my power supply with different signal voltages just to see what the difference in sound is.

[Eric D]

that is quite interesting i may just experiment with one of mine on my power supply with different signal voltages just to see what the difference in sound is.

You won't here a difference in sound on a power supply.

You need to put the amp in a noisy (electrically noisy that is) car environment to really get a feel for noise floor.

This amp is a V2. It had some issues with its power supply.

I have another V2 ZPA 0.3 I will probably be fixing as well. Another with power supply issues.

[kg1961]

so what seems to be the problem with these power supplies?
same problem?

[Eric D]

The problem on the first one was a moron screwed with it. Someone tried to replace ALL the caps on the amp, not just the input caps. They took the two power supply daughter cards out and swapped out every cap on them. Well, when they removed the boards they destroyed the board. They half ass put the board back in, but not all the connections were made. I had to run separate strands of wire to each pin and solder to the main board. A very tedious and time consuming task.

On the second amp, there is a hole burned in the board where a power supply FET self destructed...

[The Golden One]

On the second amp, there is a hole burned in the board where a power supply FET self destructed...

ive had some power supply fet's in a 0.5 self destruct and the amp wasn't even on, luckily i was there or it could have completely distroyed the amp.i believe it was do to input cap leakage as it had some leakage around them, it also look's like the zpa's are more prone to this failure. because there are + and - traces that are close together right where the input caps are.

[Bertje]

Today I finally (after a year...) repaired a ZPA0.5, the caps on the primairy side were leaking and a driver transistor (2sd1763a) was defective which causes a shortcircuit.
Now the idle current is 2,5A. I was reading in the specs that they take 0,75A idle, which is very low for this kind of amp. I got info the normal value is 2,25A-7,5 A depending on the biassetting. So I think 2,5A is OK....?
The fans were allready replaced for newer types, temp of the amps are OK.
Rob.

[The Golden One]

Today I finally (after a year...) repaired a ZPA0.5, the caps on the primairy side were leaking and a driver transistor (2sd1763a) was defective which causes a shortcircuit.
Now the idle current is 2,5A. I was reading in the specs that they take 0,75A idle, which is very low for this kind of amp. I got info the normal value is 2,25A-7,5 A depending on the biassetting. So I think 2,5A is OK....?
The fans were allready replaced for newer types, temp of the amps are OK.
Rob.

is that transistor one of the larger ones? and did you test the transistor on the board if so how did you do it? and for primary caps do you mean the larger ones or the smaller ones?

[Eric D]

By primary side I am sure he is referring to the input caps. They feed the primary side of the transformer. The larger "rail" caps are on the output or "secondary" side of the transformer.

[The Golden One]

By primary side I am sure he is referring to the input caps. They feed the primary side of the transformer. The larger "rail" caps are on the output or "secondary" side of the transformer.

ok do you know the what's the best way to test the transistors and what method you should use to test them?

[Bertje]

I do repairs on all brands car audio, and i'm a bit expirienced First I measure with a DMM the transistors on the board when I meaure a wrong value (shortcircuit or high value, or else...) I desolder the transistor from the pcb and check it on hFE en all the PN's
With this amp two small drivertransistors under the headsink were defect. The bigger ones were all OK.
The primary caps are before the toroidal transformers (2200uF/50V) and the secundairy behind the rectifier diodes.
Rob.

[The Golden One]

when you say you check it on hFE on all the PN's what do you mean by that? i know i have at least 4 small transistors that are bad on my 0.5 but i still need to check to see if any more are bad before i order some new ones.

[Eric D]

I do what is mentioned above. Look for a transistor which does not behave the same as the others, then remove it and check for shorts. If you find any two way shorts on it it is bad. Sometimes they burn open and you can't find any one way shorts. (This is done with diode check on a multimeter). When in doubt I replace the transistor (and any matching in the same bank). If you don't replace the matched one, either it or another will become the "weak link" and fail.

If you have a transistor tester you can match the Hfe spec on the transistor, and in some cases not replace all of them if you find similar devices.

[The Golden One]

thanks allot Eric D for the advise it should help me out allot on this amp as it's in need of some TLC, i suppose i should order enough transistors for each bank that has a bad one in it THANKS !!!!!!!!!!!!!!!!!!!

[Bertje]

When a power supply has a blown mosfet, I useally replace all the mosfets and when you replace a transistor/mosfet in the amplifying part, check afterwards the DC-offset and biascurrent (voltage on the emittor resitors).
Testing i do on a dummyload of 2 or 4 ohm resistor, 50w or more.
Rob.

[The Golden One]

i have a mulitimeter with an hFE setting on it, hopefully it will be good enough to match up some transistors. im going to study up some more on this because i forgot how important it is to have matching components in the same circuit.

[Eric D]

Another good policy is to replace all the resistors connected to the MOSFETs in the power supply, when any MOSFET is found to be bad. These resistors are easily damaged, and if one is out of spec, the MOSFET connected to it could fail. Besides, these resistors are only a penny or two a piece.

[The Golden One]

Another good policy is to replace all the resistors connected to the MOSFETs in the power supply, when any MOSFET is found to be bad. These resistors are easily damaged, and if one is out of spec, the MOSFET connected to it could fail. Besides, these resistors are only a penny or two a piece.

when replacing the resistors that feed the fet's should i go with 5% tolerance as that is i believe what the zpa's use. also since my amp wasnt powered up when it went bad should the damage only be in the power supply or could it have damaged any thing else?

[Eric D]

I only use 1% parts, mainly because they are what I have in stock. They are cheap enough that is all I buy. I am sure 5% would be just fine, but going with 1% obviously would not be a bad thing to do.

[The Golden One]

i was thinking the same thing why not spend a few more pennys on the 1% parts as you will know it's that much more closer to spec. and im not looking to penny pinch on my power supply section, as i would like to have music and not smoke coming from my amps.