My first amp

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
By way of encouraging you lurking DIYers, I present
a photo of the very first amplifier I built from scratch
by myself.

It was gathering dust in my storage racks (think of the
warehouse at the end of Raiders of the Lost Ark), and
I've been meaning to rehabilitate it.
 

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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Here's another shot, this time closer view of
board construction.

This was made about 1972. It delivered 60 watts per
channel and constituted a first effort at keeping a
follower stage always forward biased (a predecessor
to dynamic bias)

Tomorrow I'll see about a schematic.
 

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I remember when I finally got up the courage to simply throw away all my 10 and 20% carbon composition resistors and commit to (<i>gasp!</i>) 5% from then on. Now I've gotten so used to 2% that I can't bring myself to throw them away, even though the 1% Dales cost me less to buy. Somewhere along the way I lost my affinity for the 10% parts and confess to flinching when I see a silver tolerance band. I'm not sure when I became such a snob...looks as though I'll have to sit myself down and give myself a good talking to for the simple reason that a lot of fine amps were built using pretty vague values.
I managed to work this same sort of creeping snobbery into a scene in one of my stories once upon a time. It's subtle; you never notice it creeping up on you, but the realization is sudden.
What's the pot for? Input level, bias, or feedback?
For what it's worth, I think my first circuit was a crossover, the guts of which I happened to come across in the bottom of a box the other day.

Grey
 

macka

Member
2001-12-15 3:07 am
Australia
Yes, I like this idea of the Passcam.

The board looks a lot like that of a set of Ark amps I own of that period, pre Jurasic if I recall (aka Phase Linear 700B and 400.)

It looks quite industrial and very American in construction compared to the Japanese (plastic ) amps of the day

Those spring loaded heatsinks were quite popular then as per the carbon power resistors.

regards

macka
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
I was still in high school...
That's ok, I wasn't even born yet! Shoot, my parents weren't even out of high school!
Nelson,
Thanks for showing us your human side once in a while... even still, it looks a lot more ambitious than the power supply I build in the pan of an old spring reverb, haha. And, it is a whole lot nicer than the mic preamp I tried to build out of a couple transistors and an op-amp (man, did that ever suck!)
 

FBJ

Member
2002-03-12 7:46 am
USA
Well I don't know what you where doing, nania but I know what I was doing then. I was 16 years old back then. And coming from a very large African American family with roots ( more than a 100 years) in the Southern USA and West Coast (California), I can tell you that disco was around. So do more reseach before you speak up, cause there is a whole other world out there.
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Here is the simplified schematic, which I drew this morning.

It's pretty conventional except for the diodes and resistors on
the output stage which keep the output devices in forward
conduction over the operating cycle so they don't turn off.

Of course the diodes turn on and off, but they are very much
faster than the outputs, so it gives better performance in
this regard.

I abandoned this idea for the circuits that went into the
800A (see patent # 3,995,228) but I saw it subsequently in
a Technics amp. Why they were using this instead of the
Hirota circuit is a mystery, except that this circuit didn't
cost anything to build.

Later, SAE released a line of amplifiers using a similar concept
by Barry Thornton, except that the diodes were after the outputs
instead of before. Of course the diodes still switched, but not
the output transistors.
 

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FBJ,

Maybe you were dancing to "ABC" by the Jackson Five or "Papa was a Rolling Stone" by the Temptations, but "Disco" didn't start till 75/76. The Bee Gees were hated for their #1 song "Jive Talkin", IF you recall. Yes, there was dance music, but not quite like Disco.

And such stuff was routinely sensored and banned in the south in the 70's and even to this day. That is why we don't have Howard Stern in Richmond, VA, but can gladly listen to red neck racist Robert D. Raiford on the John Boy and Billy Big Show.

Be nice. Nania is right. Nania, you should be nice, too.

OK, me too. Now this thread is degenerating. Sorry folks.

Gabe - of multiple DNA contributers. Also of NYC origin, born and lived in for 29 years.
 
Nelson,

If I may digress, are you familiar with the Sandman "class S" circuit? He used two diodes to switch the drive current from the drivers to either of the 2 output halves. Both halves were always on, but the drive current was diverted to one or the other. The result was an almost seamless (or at least much more seamless than the normal class AB) match of the two signal halves into the output terminal. Performance was very very high, all but free from xover distortion, no thermal drift, but for some reason it never caught on.

Jan Didden