Plh Retrofit to Hafler/Adcom

[PSz.]

So, did Variac end up with a Haf-PLH? If so does it use the lateral fets and Hafler PSU?

Something tells me that this will become THE recommended amp for beginners seeking high quality and simplicity. Beautiful.

regards,
PSz.

[Variac]

This thread has been created to discuss to retrofitting existing old Hafler and Adcom amps using Nelson Pass's circuit design referred to as the PLH, based on work by Lohn Lindsley Hood. The thread about the design is here: Plh

We hope that we can devise a way that this can be done so easily that thousands of these old amps will get a new lease on life based on their newly aquired excellent sound quality. To facilitate this the ground rules are to use as many of the existing parts as possibly, so that the time and expense of the upgrade will be minimal, and that newbies won't be scared off.

Eventually we hope to have a group buy of boards that can be used in amps built from scratch and to accomplish the above retrofits.

A parts buy would be fun too- at least for those of us that get the parts!! Yet the number of required parts will be pretty low..

Anyway- let's get on with it!!








Response to PSz from post above:

That's still a mystery! I'm not sure what voltage the power supply on the Hafler puts out, but if it is around 40 , then it should work. The HAfler supply isn't balanced so again, it makes sense that the Plh will be OK. My biggest question is whether the voltage that the HAfler supplies will overwhelm the heatsinks.....Possiby each amp should be converted into a monoblock...

Love the circuit. I have myself convinced that I can understand how it works- a first for ignorant me!!

It looks like Nelson has more to reveal. I'm being patient- that's the least I can do. If Nelson doesn't want to sell boards, for the conversion, I will try to organize a group buy. I love the idea of all those HAflers getting a second life!

[Kari]

I'm currently working on pcb layout for the PLH. However it might take some time as i have switched over to Protel DXP. It takes a while before everything gets melted into my brain..

/Kari

[Variac]

Kari,
let's coordinate on this! It would be great to wait find out if Nelson has made it work in the Hafler. If so, it would be REALLY great to make the circuit boards a size and shape to just bolt into the amp.They would then work with HAfler upgrades and also for people that are building a complete amp. I don't think there is any disadvantage to this other than that they might be a little bigger than you might normally make them, I believe that each channel is about 110mm square with a hole in each corner. The output transistors are separately mounted on the heatsinks. I can't check, because ....I don't have the amp here....

If it turns out that the boards are a bit big, maybe you could include places for output transistors along a side that could be used by those making an amp from scratch. The HAfler peole could just run wires from those holes to the heatsinks.

If you don't wan't too, of course that's fine also...

Mark
Still waiting on the BOSOX boards - What's going on with the post office!!

[Nelson Pass]

Originally posted by Variac let's coordinate on this! It would be great to wait find out if Nelson has made it work in the Hafler. If so, it would be REALLY great to make the circuit boards a size and shape to just bolt into the amp.They would then work with HAfler upgrades and also for people that are building a complete amp.

I am sorry to report that your Hafler chassis is still sitting there.
On the other hand, the original intent was to make this fit
into a Hafler DH200 or an Adcom 555. No reason it can't still
be done.

Would you be interested in tackling it?

[Variac]

If Kari were involved I think we could pull it off.
Just to get us going though, it would be handy to know the dimensions in inches of the boards, the distance and diameters of the holes to attach them to the brackets, and the output of the power supply and/or the transformer.

Also your opinion as to whether that voltage would work, and if we can send enough bias through the thing with the existing heatsinks.

Anyone else with a Hafler can chime in here on the measurements..
Ironically, I don't have one to measure

Mark

P.S. What do you think Kari?

[PSz.]

Demand/price for old Haflers about to skyrocket!

[Zen Mod]

If I remember corectly-DH200 rides with 2x60 to 63 volts DC-means that we need to waste prety much of voltage,even if we count on discrepancy between 1,41 and 1,2 factors for ac to dc........

on the other hand-with just 2 x 63V x 2 x 0,1A per channel-DH 200 was pretty hot in summer days ........

different xformer - some rewind job ?

slow fan on each side?



in any case-according to my (modest) inteligence and counting on that that I didn't really measured heat transfer for DH200 heatsinks, looks that heatsinks are good enough for mebbe 50W max (each) .

I don't have DH200 any more ,so someone else must grab few power resistors etc.

[PSz.]

Perhaps one could play with the idea that the Hafler transformer is center tapped.

Oh! and with all the extra pcb real estate in a Hafler it would be relatively easy to include a capacitance multiplier circuit for the psu... then we could use an xl280 chassis for the quad output device version with two to-3 spaces left for psu transistors.

I am dreaming of a PLH, Hafler chassis, without the in/out coupling caps... perhaps someday. First, I need to get my mini-a to stop humming.

regards,
PSz.

[Variac]

My self imposed rules for the Hafler conversion was that we had to use the existing power transformer. My memory corresponds with yours, that the transformer is approx 60 volts. That's pretty hiigh, but it would be interesting to hear from Nelson if he ever had a plan to use this voltage. If we have to dump the transformer we have to, but then we are only using the box and heatsinks.... and I guess the old MOSFETS?

Psz. ,
IS the transformer center tapped? I don't remember, I just threw the amp in the mail , forgetting to look it over first..

Demand/price for old Haflers about to skyrocket!

It would make a pretty sensational magazine article Nelson!!
probably double AudioXpress sales that month!!