PPI A600.2 Mods?? - diyAudio
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Old 3rd March 2012, 06:53 PM   #1
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Default PPI A600.2 Mods??

I have a PPI A600.2 board and heatsink that has been in storage for a while and I want to get it up and running again. It's missing an end cap, bottom plate, the plugs, power terminals, and fuse holder. I figure since I am going to be doing a bit of soldering on this board anyway I might as well see if there are any upgrades I should/ can do while its out to make it last longer and maybe increase power, I'd love to see one of these run 2ohm mono and be stable or 1ohm stereo and be stable but I have yet to find any info on doing this anywhere, probably cause no one wants to do this. Any suggestions beside the obvious "Don't Do It!!" lol?
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Old 3rd March 2012, 08:08 PM   #2
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PPI built 1 ohn gear from this era and it was their ProMos line. 2 ohm stereo or 4 ohm mono is about the best that you could expect without extensive redesign starting with the power supply and the transformer. 1ohm will require a lower rail supply voltage to the outputs if you want them to survive the current loading 1 ohm will present to them. This is what PPI did to get 1ohm operation of their gear.

You say your missing the bottom plate. This represent a real issue as the bottom plate was the only clamping method for the power devices. You will likely need to construct some form of a clamping system to apply even pressure to all of the power devices or the amp will most likely fail in short order. PPI did not leave a whole bunch of room to add extra clamp screws so the design of your clamp will be critical to the amps survival.

Plugs for this era of PPI amp are available on ebay. The fuse holder is another issue as the only place you will find a replacement is another PPI amp of this era. I suggest you jumper the internal fuse holder and use a out board fuse of proper size and type. The original fuse holder was not the best and often weakened with age and heat and made a poor connection to the fuse. They often have to to be tightened up by bending the two upright tangs to increase clamping pressure of the fuse lugs. The large power plugs also suffered form this same issue. They weakened from heat and would lose contact under high current demand. I consider them expendables as the only way to repair them is to replace them.

The A600.2 will draw about 81 amps at 4 ohms mono. The 80 amp fuse the factory used will hold but it should be checked for heat damage and replaced as needed.

The main problem with any attempt to gain 1 ohm operation is that the heatsink design itself is one of the problems. 1 ohm amps of this era usually had 40% larger heatsinks just to accommodate the higher heat loading issues. ZED, PPI, Orion etc.. they used larger sinks on their low ohm products. So even if you manage to get some fashion of 1 ohm operation out of the amp the sink will not be able to handle the heat load and the amp will quickly over temp and shut down, if it does not fail from such usage.

It just wasn't designed physically or electronically to do 1 ohm reliably, so you fighting a up hill battle all the way starting with the sink and ending with the tightly designed regulated power supply. You could use water cooling as it was a option on this era of amp, but it will do little to protect anything but the power devices, the rest of the amp will also see a huge increase in heat loading including the SIP modules. And then of course you will need to figure out what to do with all the heat your cooling liquid will be transferring.

Lots of work, I wish you the best of luck on your goals...
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Old 3rd March 2012, 09:04 PM   #3
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1moreamp, Thanks for the reply and the info.

Let me just start by saying heatsinks and clamps ( I'd use a piece of aluminum flat bar and drill and thread the sink to hold them down) aren't an issue as I have access to that stuff from solidstate starters and old scr, vvvf, and pwm drives that I remove from old elevators. As for the 1ohm portion of it, I figured it would take some extensive modifications in the cooling and electrical component areas, I just thought I'd ask since this was and maybe still is a very popular amp.

As for reliability mods or squeezing a bit more juice out of this amp, anyone got any suggestions?
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Old 3rd March 2012, 10:12 PM   #4
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More power is only possible thru adding copper wire to the toroid to raise voltage and current output. PPI used a regulated power supply and the toroid was designed to limit power to their basic design. All amps are limited by their power supply designs and the toroid capacity which is partially controlled by the windings and copper content. Just adding beefier components will only add robustness and durability. Adding more transformer will add more power at the risk of exceeding the Safe Operating Area of the output transistors. More power safely delivered would call for more output transistors also, especially for low ohms/high current operation....as I said before a lot of work, and most of it will trying to squeeze all that gear into a sink too small to handle the class AB heat dissipation issues...best of luck though...
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Old 4th March 2012, 01:13 AM   #5
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Again, Thanks. I guess I wont waste my time with this amp then and just focus on replacing the needed parts and clamping everything to the heatsink. I appreciate it. Now I guess I'll focus all my energy on figuring out this US Amps VL-100 and completing my PPI PC6800.
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Old 4th March 2012, 06:53 PM   #6
ultra is offline ultra  Greece
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@ 1moreamp
what is the usual amperage per square millimeter for power transformers?
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Old 5th March 2012, 06:43 AM   #7
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@ ULTRA
Please see attached link to an educational source for your needed info.

Power losses in wound components < see wire gauges >



I doubt you will find anyone that can share old school PPI design info with you. Directed Electronics sold PPI a while back and it is now owned by Epsilon. There is no factory support for any of the original PPI gear to my knowledge at this time, or since it was acquired by Directed many years ago.
And while the name PPI made amps successfully under three different ownerships for many decades now, and I even now still own a couple of them myself. I really don't believe they intended their A600.2 to deliver 1200 + audio watts of power reliably. I guess that is why they built the A1200.2. Twice the physical size. H bridge design power supply. Twin 80 amp fuses with high current buss bars instead of copper traces. Sanken high powered outputs...etc..the list goes on about what it took to make 1200 class AB watts 20 years ago. The A600 PCB and frame would never hold up to such power levels. And only at these power levels IMHO would you be able to audibly hear a increase in output power from the amp..

PS: I have several examples of both of these model's on hand if you would like any further design info I would be glad to reverse engineer it for you. In fact I am about to power test both of these same very amps. My bench is equipped with a lambda EMS power supply both CC and CV controlled, and my dummy loads are heat sink 400 watt 1 ohm resistors 16 of them 1% tolerance of course. I can only run one channel of the A1200.2 at a time due to AC power limitations on my bench.
Myself I would not want the engineering liability hanging over my head for designing a one off like the original poster was asking for, but to each his own. I will gladly extend any and all tech info taken from a sampling of existing vintage gear in my hands currently if will help you somehow....
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Old 5th March 2012, 02:18 PM   #8
ultra is offline ultra  Greece
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Thank you for all the info.

I do have the schematic of the A1200.2 , and if i remember well, the designer of the power supply was HiRel.

My question was not aimed at PPI trafos, but in general.
Sorry i was not clear enough.

In my opinion, thick trafo wires affect the sound quality of an amp, but this is usually neglected for cost savings.

As a matter of fact i have recently designed a power amplifier, of a different approach, and i would be happy to present it and share a few things, if there is any interest, of course.
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Old 5th March 2012, 06:25 PM   #9
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I am always interested in any new approach's to amplifier and power supply designs. And I would be interested in reviewing any info you may have to share with me.
This forum has several other sections for such introductions but if you would prefer just PM me and we can exchange info privately via direct email.

In this section of the forum I try to help others restore their products to there original manufactured status only. As I said earlier building a one off and all of its liability is not high on my list.

By the way , nice to meet you, and I hope we can share ideas and thoughts more in the future...regards
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