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From: GregS on 5 Feb 2010 09:05
In article <cv4om55krblsasmmsv1u214d2c71tagl4p(a)4ax.com>, Evil, Mean and Nasty wrote:
>
>>>Thinking of a circuit like this. Simple and elegant-looking:
>>>
>>>http://img524.imageshack.us/img524/4038/simplefet.jpg
>>>
>
>If it hasn't been mentioned, or you already know, I hope
>you visit and d/l all the free data available at:
>
>http://www.passdiy.com/
>
>
>Mr. Pass in the KING of class-a design, offers enough
>free info to fill a book, and answers ?s in the forum.
>
>When reading, you will find that a choke there is big,
>heavy, and wasteful. Just use a constant current design
>(cheaper to build too). I've built his ZEN designs,
>which look alot like your pix using CCS(s). There are
>even sources for PCBs! I promise you you'll LOVE the site.

Did I miss something, but I didn't see what the amplifier was for.
Thats funny Pass came out with that SE about the same time I drew up
mine.

Greg
From: JJTj up on 5 Feb 2010 10:27
>In article <cv4om55krblsasmmsv1u214d2c71tagl4p(a)4ax.com>, Evil, Mean and Nasty wrote:

I have a tee shirt from the old Georgia Champ wrestling folks
that says "EVIL MEAN AND NASTY". A gift from Ole.

>Did I miss something, but I didn't see what the amplifier was for.
>Thats funny Pass came out with that SE about the same time I drew up
>mine.
>
>Greg

Well, back when the humbucking PU was made, about 6 people said they
'invented' it (not saying that you claim the same) at the same time.

Mr. Pass has too awesome of a history in amp design for anyone to
doubt his actions. He also knows it's simple designs. Then again,
he also YEARS ago stated that chokes are too much a bother to deal
with, something you were searching for. I remember buying the white
paper "Power to the People" about hi voltage power supply design, a
great read (LONG LONG out of print) and the guy stated he 'designed'
a quad gated MOSFET preamp. He did. I've built a few, they work
great. And the same basic design was also in a book dealing with
the same Mosfet called : Mosfet Circuits Handbook, by Mr. Turner.

Years and worlds apart. Both 'designed' by talented Icons in the field.

It's like when Mesa/Boogie 'designed' the 1/2 power switch, by lifting
the cathode off 2 tubes..and the 'mid' switch by lifting the tone circuit
ground (sometimes bypassed by a cap). Sheit, I'd been doing that too,
and know folks in the UK who also did. No big deal. But no big 'design',
although M/B made it most available. Carvin and Acoustic 'stole' it
from M/B, sometimes as DIRECT copies..like the Acoustic. Even the
schematic was almost a carbon copy..right down to the mistakes.

At least 'Earth' was smart. The Xeroxed the PCBs that Peavey made, even
down to the etching 'PV' on the copper when they copied/stole PV's designs.

Sometimes the same idea hits many people at the same time. But sometimes,
people like the 'Earth/Plush' people just downright steal from the designers.

Gawd, this is a fun biz. So much history, so many tales untold.

JJTj






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From: Morris Slutsky on 5 Feb 2010 10:28
On Feb 5, 7:58 am, JJTj <up yers.con> wrote:
> >>Thinking of a circuit like this.  Simple and elegant-looking:
>
> >>http://img524.imageshack.us/img524/4038/simplefet.jpg
>
> If it hasn't been mentioned, or you already know, I hope
> you visit and d/l all the free data available at:
>
> http://www.passdiy.com/
>
> Mr. Pass in the KING of class-a design, offers enough
> free info to fill a book, and answers ?s in the forum.
>
> When reading, you will find that a choke there is big,
> heavy, and wasteful.  Just use a constant current design
> (cheaper to build too).  I've built his ZEN designs,
> which look alot like your pix using CCS(s).  There are
> even sources for PCBs!  I promise you you'll LOVE the site.
>
> JJTj

Wasteful is relative. Electrically, a choke-loaded single-ended amp
is twice as efficient as a current-source-loaded single ended amp
(because you have dissipation in the CCS that you don't with a choke),
which is turn is twice as efficient as a resistor-loaded single ended
amp.

Yes the Zen designs are cool. But if I wanted a badass single ended
FET, a choke would be the most electrically efficient way. Cost
efficient? Weight efficient? Maybe not.

It is depressing that, despite the relatively low inductance needed in
a solid-state single ended circuit, the currents are higher and I need
just as much iron. Huh.

From: Phil_S on 5 Feb 2010 12:23


"Morris Slutsky" <morris.slutsky(a)gmail.com> wrote in message
news:9360f4f1-c838-41fc-bb63-df93800d1dfc(a)o26g2000vbd.googlegroups.com...
> Thinking of a circuit like this. Simple and elegant-looking:
<snip for brevity>
> If I could find a choke this would be a nice cheap thing to build
> though. Easy enough.

I have no idea if it's the right thing but I've got a modest size choke I
can't use. It says on the case:
Filter Reactor
678-118-00 C.S.T.C 6516A
15 Henries at 10V 60CPS .020ADC (20mA)
DCR 515 +/-10% (meters 548 ohms) at 25 degrees C.
PWV 1070
Chicago Standard Transformer Corp

Square grey military style case, two terminal lugs on the bottom. This one
is real old school.
The case is about 2" x 2" x 2 5/8"h.
Mounting holes are on wings, 2 3/8" across and 1 1/2" along the wings.

Email me off list if you want it. Cheaper than cheap. Never been soldered
as far as I can tell.

Phil


From: Lord Valve on 5 Feb 2010 12:30
Morris Slutsky wrote:

> Thinking of a circuit like this. Simple and elegant-looking:
>
> http://img524.imageshack.us/img524/4038/simplefet.jpg
>
> Really like a very cheap version of a single-ended triode stage.
> Basic 'parafeed' arrangement except that no transformer is necessary.
> Resistors provide bias, negative feedback, and give the FET a bit of
> 'plate resistance' like a triode to lower output impedance.
>
> What's great about this cheap FET circuit is that it's cheaper than
> the tube equivalent, much, and might sound something like. No need
> for expensive output transformer. A cheap FET like a IRF510, compare
> to a 300B, yeah. No need for heater supply! And the choke . . . the
> choke doesn't need to be NEARLY as large. A parafeed triode amp, to
> get decent bass response, might need a choke in the tens or hundreds
> of Henrys range. Here, the current is much greater, the voltage is
> much lower, impedance is much much lower, so you can get by with a
> choke in the millihenrys. Should be easy to find one I think.
>
> But I'm not sure where. Any ideas where to get a 50-100 mH choke for
> this? Needs to take an amp or three of current without saturating.
> That's the hard part there I think. Lots of dual "common mode" 5-30
> mH chokes for sale but I imagine those don't take much DC current at
> all before saturating, they're meant for AC circuits aren't they?
>
> If I could find a choke this would be a nice cheap thing to build
> though. Easy enough.

Wind your own.

Use 16G magnet wire. For 50-100 mH, it won't be all that large.
If you have an LCR meter and a variable speed drill, you'll be
done in less than 15 minutes.

LV


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