Plh Retrofit to Hafler/Adcom

[lumanauw]

There's a good chance that we will want to be using a fan - I have a wonderful fan controller circuit that makes them very quiet.

That's wonderfull I have (bad) experience that no matter how big the heatsink is or how big the dissipation fin area is, the heatsink still won't discharge all the heat. Sometime the amp is placed in very small distances (like in HiFi rack)

Where can I see the fan controller cct?

[jacco vermeulen]

Originally posted by Magura
presto, you got a Pass amp

Dear Morten,

i know the weather on your side in Danmark is lovely and overhere it is stinkin wet.
However, it is the bolting i would like to find an elegant solution for.

(on the other hand, i may pretend to go fan and con Santa Pass out of a fan controller for my kilowatt Krill 50's)

[Variac]

Probably we don't need to make the boards exactly fit the existing brackets, the HAfler has lots of room inside. but maybe we could have two holes on one side to fit the HAfler and two on the other to fit the Adcom.

We need to know abit more about the Adcom. It seems that the power supplys would be quite similar if they put out similar power.

I don't know how the boards are laid out though 'cause I don't have one. MAybe somone who does could tell us.

About the TO-3's,

Can we use the existing mosfets? Should we?, or will it sound lots better with modern ones? Sure it would be more in keeping with the E-Z build spirit to use To-3's , but probably not that difficult to use the plastic ones....

Nelson, if you end up doing a follow up article on this retrofit subject I suspect you will find keeping my amp to be a good idea.
I might get some labor out of you yet!!

For that reason, someone that has either an early Hafler, or Adcom GFA 555 model would certainly help by opening them up and taking some photos of the general interior, and measuring the size of the boards and mounting holes.

Mark

[Magura]

Originally posted by Variac

For that reason, someone that has either an early Hafler, or Adcom GFA 555 model would certainly help by opening them up and taking some photos of the general interior, and measuring the size of the boards and mounting holes.

Mark

I will haul the Adcom 555 out of the garage tomorrow evening and make a few photos and check the voltage.

Magura

[Variac]

PA asked

Anyway, why must the pcb fit an old amp? Why not make a small nice looking pcb?

If it turns out these goals are in conflict, then perhaps we can do 2 different boards, but I suspect that we can devise a board that is small, nice looking, and also is easily installed in the amps mentioned in this thread. Thanks to your comment, I realized that the new boards don't have to be the exact size of the old amps boards. It would be nice however if they could be easily mounted to the existing amp hardware, and that's part of the fun- making a board that does all these things well

When we get to the group buy stage, we can create a wiki page and possibly another thread just about the boards..

[PSz.]

Sorry guys, I truly didn't mean to perpetrate my first major threadjack!

Variac,
I can address some questions you had.

On my mini-a (in a Hafler chassis) I am using nice small BrianGT boards mounted on a standoff board (that I am using to provide some local capacitance). It has worked out nicely. It is very similar in concept to BrianGT's Hafler to Leach conversion as seen in his gallery. So, I think that small "universal" boards are great.

I started out with to220 packages in the little Aleph, but switched over to to3 (today). To3's are cool.

Oh yeah, I noticed you (Variac) live in SF. If you are interested, I am willing to bring the mini-a up from San Jose for a listen. Same offer is of course extended to NP. I can check with the wife about having company here if you are up for a drive.

regards,
PSz.

[GRollins]

Various items:
--I'm not sure that the Hafler has as much open space as you're thinking. It would be a good idea to go ahead and use their mounting scheme for the PCBs. Besides, with the boards right there at the outputs, you'll be keeping the signal path short.
--The PCBs fasten to the heatsinks with three small screws. While that spacing is fixed, there is sufficient play in the overall scheme of things to increase the board size should that be deemed necessary.
--Use of the existing MOSFETs should not be assumed. After all, to the extent that an amp is dead, it's not unlikely that one or more of the output devices are kaput, and there aren't any more of those devices being made. Yes, there are some available on ebay, but I wouldn't want to base a circuit on NOS solid state parts any more than I would base a tube design on an obsolete, rare tube that is only available at horrendous cost.
--Just because the heatsink is drilled for TO-3 cases doesn't mean that you can't use one of the mounting holes to attach a TO-247. Living in a...shall we say, technically challenged corner of the nation, I frequently need to reuse old heatsinks due to scarcity of big new ones. (Why do you think I went to water cooling for the Aleph 2s? Couldn't source enough heat sink. Necessity is a mother...) Anyway, the point is that other semiconductor case styles are not necessarily ruled out. Don't make Nelson part with his cache of TO-3 parts unless it's absolutely, positively necessary. He makes a living off those things and could very well need them for service of older amps later on.
--An LC filter is a good idea, but it will take a nice balance between current draw and inductance to make it pan out.
--The Achilles heel of the old Haflers was the power switch. They would arc and either weld themselves open or closed. The original switch was--I think--10A. Later parts were 15A and more reliable. New switches are available without having to go the ebay route. I'll try to remember to dredge up the part number when I get home. If my home PC will consent to boot (no guarantees, there) I will try to get that posted later.
--They used .005uF ceramic discs for spark suppression on the power switches. I would suggest .01uF. Again, think reliability.
--I have no experience with the Adcom amps.
--Somebody prompt me to take up this list again later as I've got to move on. There are a dozen little things that need attending to in order to make the thing more reliable. Power supply caps, for instance.

Grey

...Oh, another thing about output devices...some folks will inevitably want to build the circuit from scratch. Don't make them go out and track down old parts.

[lumanauw]

How many watts the original Hafler and Adcom have?

Is it possible to make kind of classAB PLH, so the wattage can reach the original Hafler/Adcom wattage, with much better SQ, offcourse

[mpmarino]

I will haul the Adcom 555 out of the garage tomorrow evening and make a few photos and check the voltage.

I'm 99% sure they are +- 80v rails on the 555. There is a small single 'front end' board at the inputs. The outputs are mounted on 4 boards right at the sinks. The 555mk2 is very similar. This one is sold so I can't measure anything. The inside of one of these things is vaguely similar to the trunk of a '77 caddy .

[Variac]

Sorry guys, I truly didn't mean to perpetrate my first major threadjack

I wouldn't call it a threadjack- more like a good idea.

I have an idea for using a fan with the things, at least this should work for the Hafler:

Drill (3) 3/8" holes between each of the fins. Use a fence made of a board clamped to a drill press table to get all of the holes of a row aligned horizontally.

So basically you drill a hole through the heatsink between each fin at three diffferent points. Then pressurize the interior with a fan on the top or bottom exterior or interior as would fit( interior is best of course)

Air would first cool the interior, then escape between the fins , cooling them..

A bit of work, but with a drill press shouldn't be too hard.