A little ZX600Ti mod...

[Bfowler]

not to sound stupid, but when you replace the caps, and increase them can that help for more power output, and if not, why do alot of you guys increase them ( for example my stock small caps are 2200uF, then i replace them to 4700uF?

it can ALLOW for more output, but replacing them with higher values alone wont increase power.

think of it as running higher octane gas in your car then it is mapped for.

[Jacampb2]

It is more about maintaining consistent output. The rail caps provide the current for an immediate need at the output devices. All larger rail caps can do is help with transient response.

The other reason behind changing them is due to the regulation scheme for the amp. As close as I can tell, the rails are regulated based on two things. The actual rail voltage, and the voltage difference between the +40V rail, and the +40V raw supply. If the voltage sags at the rail node, but not at the supply node, then this signifies high current draw, and a low impedance load, and the power supply will start ramping back the rail voltage until the raw and rail are equal. This is what allows the amp to put out basically the same power into a low impedance load, as a higher impedance load. By adding rail capacitance, you minimize that sag, and theoretically let it drive an increased voltage to a lower impedance load w/o the regulation backing the rails down. This could destroy the original output devices. Since speaker impedance varies w/ frequency, something as simple as this could keep the amps from ever knowing it was driving a low impedance load.

I do however plan to totally eliminate the feedback loop to the PS that drives the low impedance voltage regulation, as I plan to run these amps at 1-2 ohm mono.

Later,
Jason

[Jacampb2]

Well, I am about to take a stab at rewinding the PS transformer for this amp. I bought a spool of 155° green 23awg wire. Any pointers for me before I take a stab at this? My intent is to raise the rail voltage in this amp about 10v higher. According to my calculations though, I may have screwed up on the wire size choice. It looks like PG used 3 12g conductors for the primary, and 2 12g for the secondary. In order to match this ampacity with 23g it looks like I need 39 23g wires for the primary and 25 23g wires for the secondary. That is a lot of wire.

It appears, according to the math, that PG sized the windings to be able to do 50 volts at 50 amps w/ out overheating the xformer. Since there is absolutely no way the output transistors could take this kind of current, why go so overboard on the transformer? Is it just for safety margin? The math tells me that you only need about 5mm^2 area for the primary conductor for rated power. They used ~10mm^2. I assume part of the oversizeing is due to the skin effect at the high frequency that the PS switches at. That is also part of the reason that I wanted to go with many smaller conductors. I don't think that hand winding 39 conductors at once is outside of the realm of possibility, but I wanted to make sure I am on the right path before I dive in... Oh, the other reason, green transformers are just cool

Later,
Jason

[thedeal7235]

i agree about the GREEN ; espicially when u see them on some of the ms series-

[Jacampb2]

If I could have possibly found blue magnet wire, to match the case, I would have bought it in a heart beat. Green is a nice second... but blue would have been the cats ass!

Later,
Jason

[thedeal7235]

if u look a@ some old promo, or spec paper that originally came out on the ti , u can seeit was wound in green, not the traditional red- i think i saw it on the phorum here under specs, manuels, something like that

[Jacampb2]

Yeah, I have seen that, it is in the ZxTi tech sheet. The boards in those amps are also gold plated. I would love to get my greasy hands on those

Later,
Jason

[stipud]

I don't know much about powersupplies. Would increasing the windings immediately yield a higher DC output to the rails, or would you need to change parts in the rest of the PS to handle it? (I assume the transistors would need to be upgraded if they are not within their voltage tolerances for switching?)

You should send Eric ([email protected]) an email. I know he rewrapped the toroids in his MS1000 for more power, so he may be a good resource for your mods.

[Jacampb2]

Yes and no, the transformer will immediately make 10V more, but the PWM controller which runs the power supply will just reduce it's duty cycle to maintain the set rail voltage. It will require component changes in the feedback loops to the PWM.

As for the transistors, they operate at 12V-15V (whatever the power supply input voltage is) This doesn't change, chopping the DC to high frequency AC takes place before the transformer. The transistors are rated for 60V, 60amps each. There are four in parallel for each side of the primary coil. This means an absolute maximum of 240A before they are toast. The fact that they are switched via PWM makes the possible current capacity quite a bit higher. I have a bunch of 120A fets that I could replace them with, but I won't unless there is a problem, and I really don't think there will be...

I may send him an email, but I am more looking for advise on the actual winding of the core. It looks easy, but it almost certainly is not going to be with large bundles of smaller wire...

Later,
Jason

[AlvinTanner]

Remarkable job on the to3 case style transistors, i am just curious as to what tye power supply voltage is running at on the zx600ti as i am in the process of moding my zx475ti right now tye zx475ti is running plus and minus 40volts for main b+ and plus monus 42 on the driver transistors pleas advise if your 600 is tye same or higher thanks

[Jacampb2]

The zx600 is ±40Vdc primary rails, the same as the 475/500.4. Your auxiliary drive rails should be closer to ±10V referred to the primary rails. If you are only at ±2V, the amp will run but it won't be able to hit full output power because it won't be able to swing the outputs rail to rail.