Pass version of Citation 12 (Mosfet)

[G]

I'm interested in building this amp(maybe). I've been looking at alternate output devices and I am considering the Hitchi 2SK2800. Does anyone have an opinion of my choice? The schematic is here:

http://www.passdiy.com/pdf/citation.pdf

and the data sheet for the original device is here:

http://terre.lisa.univ-paris12.fr/El...ets/IRF130.pdf

and last but not least the PDF for the Hitachi mosfets is here:

http://www.hitachisemiconductor.com/...13_2sk2800.pdf

Any opinions would be appreciated. Thanks.

G

[BrianL]

I have a modified version of the Pass Citation 12 that I've
been using for years. I had a non-functional H-K Citation
12 sitting around (contrary to what Nelson claims, there
were a number that died; from what I can tell the voltage
rating on the input pair was marginal and many died after
a while), and needed an amp, so I did the mods. Sometime
after the original Pass article in Audio Amateur, there was
a circuit published in the letters section with complementary
P and N channel output devices. I built a modified version
of this circuit using current regulator diodes as the current
sources for both the input differential pair and the VAS
stage. I believe the power FETs I used were IRF140 and
IRF9140.

The amp has served me well for years, and while I contemplate
many "superior" designs I'd like to build, this one continues
to serve me well -- very good payback for the couple afternoons
of (re)construction.

At my suggestion, a friend whose ears I trust used the
Pass design as the basis for a rebuild for an old Crown D-60.
He loves it.

I'd say that the Hitachi FETs you are looking at are way to
weenie for the intended application. The IR units are
readily available from Digi-Key. These days you'll have to
get the plastic power package which should readily adapt
to the H-K heat sinks. IRFP140/IRFP9140 are less than
$3 each.

[G]

Actually brian I think that they would work fine but I would like a little more Vds capability than they have. They have a much higher Ids and a higher max Ids than the irf130 that they would be replacing.

G

[BrianL]

OK, let's look at the important specs first.

This device is rated at 60V Vdss absolute max. Not
exactly what you want to use on an amp that has
supplies that run about +/-42V.

Then, it's max dissipation at case temperature of 25C is
50 W. A bit wimpy for a 60W / 8 Ohm power amp.

Then there is no thermal resistance from die to case
specified in the data sheet, so who knows how hot it
will get even before you get to 50W dissipation.

If you think you can get away with them fine, but expect
molten silicon and who knows what else.

[stokessd]

Brian,

I think I know the guy who built the crown D-60 version. And he does have good ears. Excessive facial hair too.

I'm going to be building the complimentary version soon because I've also got a sick Citation 12.

Sheldon

[Nelson Pass]

Aaaarrrr....

Sheldon Stokes. How tha hell ar ya, Matey!

[Morello]

Originally posted by stokessd
Brian,

I think I know the guy who built the crown D-60 version. And he does have good ears. Excessive facial hair too.

I'm going to be building the complimentary version soon because I've also got a sick Citation 12.

Sheldon

Helo Mr. Sheldon,

Nice to see You here.
I would like to forward my appreciation regarding your ESL-website. I rebulit a pair of ESL-57 for a friend using tips from Your site.

Best regards\Morello

[BrianL]

HI, Sheldon!!

Long time, no see. Yes, our friend who can "kludge" anything.

We'll have to talk about your amp plans sometime. I have
a few variations to the PassCT12 for what they're worse.
Also have a few suggested parts changes, if I could remember
where I put the notes.

[stokessd]

Nelson-

Thanks for the greeting. I love what you have done for audio. You're products are outstanding (I have an aleph 3 now), and your commitment to DIY and your customers is great. Your new amps look fantastic. (how's that for tushie kissing? )

I'm starting to get more into solid state designs. I've been building my own electrostatic speakers (hybrids actually) and I'm slowly heading to complete custom driving electronics. I've already built a preliminary active crossover for the speakers, and the next logical step is custom dedicated amps for bass drivers and panels.

One of your employees bought a couple headphone amp circuit boards from me earlier this year. Better check your inventory of small power parts.


Sheldon

[stokessd]

Morello-

thanks for the kind words regarding my website. I'm glad the information was useful. the original Quads are a remarkably enjoyable and capable speaker. When you think that the design is almost 50 years old, it's astounding.

Sheldon