[goon-heaven]

I plan to build the bridged version of this amp, as it appears to cost but a couple of bucks more...
Any comments on its capability of driving 16ohm high efficiency speakers (i.e Lowthers or Tannoys)? What is the minimum impedance it will drive before going pop? At what power will it drop out of class A?
Also KG optionally spec's high speed 5uF caps - does anyone have more info on these. I browsed the illinios cap co site, but I failed to pick them out.

 

[kevin gilmore]

The 505PHC850K is the best and fastest of the bunch.
It is also quite large.

If you don't have that much space you can step down to
lower voltage versions which are not quite as fast.

The bridged version probably drops out of pure class A at
about 1.5 watts.

 

[goon-heaven]

Thanks Kevin - I'll buy the case when I can see whats got to fit in it (i.e. size is not an issue).
Do you forsee any problems with the amp running into loads under 10ohms?

 

[kevin gilmore]

The unbridged version drives a pair of Klipsch Khorns just fine.

You might want to double up on the number of output transistors
if you are going to use this to drive speakers.

 

[Possum]

Kevin,

At what point does adding the number of output transistors turn into a negative result? I've built your power supply last year with a larger transformer and different regulators to allow for more current, and would like to take advantage of the extra power when I build this amp.

 

[kevin gilmore]

I have no idea when too many transistors is too much.

But I am working on a monster power amp. 84 TO3
transistors per channel on a absolutely huge heat sink.
(about 800 watts per channel 8 ohms, totally symetric
H bridge)

Dynamic class A too. My version. With cpu and A/D converters
and hall effect current detectors on power supply lines
and output line to measure and adjust current.

My version of a MRA. Except that i will be able to lift it
(barely)

 

[goon-heaven]

Thanks Kevin. OK, pile in the output transistors.
800W in class A? Turn on the heat!

Possum - what parts did you use in your PS? What current will it output? Do you plan on building the bridged version?

 

[Possum]

I'm using a toroidial transformer from http://www.toroid.com/rectifier_1.htm model 718.182. The first set of regulators are LT1085/LT1033. The tracking op amps are OPA541 instead of OPA548 (must've been a mental lapse when ordering from Digikey, because I don't remember why). The LT1085/LT1033 are capable of 3A, and the OPA541 can handle 5A if not current limited. Since the transformer's current when the secondaries aren't in parallel is only 2.90A, and I'm using one transformer for both channels, each channel should get 1.45A of current maximum and ideally.

I probably won't make the bridged version, but I will at least double the output transistors. I won't need the extra output to power real speakers, since I'm planning on building maybe a Leach or Aleph power amp for that (info at www.diyaudio.com), but rather, a really robust headphone amp that I can use with fairly efficient computer speakers.

 

[goon-heaven]

Thanks Possum for the details of your PS. You werent tempted to a bigger transformer?

Assuming one is going to double the output transistors over the standard version, are they better placed in bridged mode or paralleled up with the existing set?

I am tempted towards to the bridged version to get double the slew rate. I reason(read blind guessing) that duplicating the driver stage may mean less stress there as opposed to paralleling up, and symetrical loading of the gain stage may help too. Comments?

 

[kevin gilmore]

Here you go. This is the heatsink assembly for my new
amplifier.

http://gilmore.chem.nwu.edu/heatsink.jpg

 

[goon-heaven]

Kevin - Now I see what you mean by [size=medium]HUGE[/size]
But is that sink big enough to dissipate ~2kW?

 

[kevin gilmore]

It is water cooled. The biggest problem with my krell's is that
they heat up the room bigtime. For this unit i will have a
refridgerated circulating controller in the basement with
a couple of plastic water pipes going up thru the floor.
No more heat in the listening room!

http://gilmore.chem.nwu.edu/chiller.jpg

It is good for about 3.6kw of heat removal.

I did say i was nuts right?

 

[erix]

Kevin,

Each time I see one of the 17 coal trains that go through our town each day on their way to feed the powerplants in Chicagoland, I'll think of you.

ok,
erix

 

[goon-heaven]

Hey Kevin, youre one cool dude with one cool amp!
I dunno about you being nuts - I admire your refusal to bow to compromise.

 

[goon-heaven]

Possum - can you please let me have the schematic for your PS, or least the revised circuit/component values around the pre-regulators and regulators - I think I'm going to need to beef up the PS to cope with bridged and doubled output transistors.

Thanks.
Steve[not into water coolers... yet]