Can anyone point me at a copy of the Ortofon MCA-10 mc 'head amp' circuit
diagram?

I'm asking because I'm currently dissecting a magazine review of the
Armstrong 700 amps. The review contains a depressing number of confusions,
misleading comments, and slips. But I'd forgotten until today that the
'postscript' included a comment to the effect that the reviewer compared
the 700 mc preamp with the MCA-10 - which he found to be much better.

So far as he was concerned the 700 mc stage had poorer overload and
distortion performance. It also committed the sin of including electrolytic
caps which (allegedly) probably degraded the sound.

The irony is that IIRC I based the 700 amp on improving what I'd seen in
the Ortofon amp. Where I think the MCA-10 used a very similar circuit with
electrolytics. I'd changed the details to give *more* headroom and *lower*
distortion than the Ortofon, but used the same topology.

I had a diagram at the time but lost track of it years ago. It would be
nice to be able to report now on the reviewer's inability to show he was
"golden eared" by hearing the (alleged) effect of electrolytics when he
hadn't seen them in the box or checked the circuit diagram. ignorance is
bliss, eh?... 8-]

If no-one can find one, I'll go to the source and ask Ortofon. They might
also find this amusing. Although sadly, 30+ years too late to matter.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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In article , Jim Lesurf
wrote:

If no-one can find one, I'll go to the source and ask Ortofon. They
might also find this amusing. Although sadly, 30+ years too late to
matter.

Alas, it seems that Ortofon sold off their electronics section and the
people involved retired ages ago. So this looks like being another area of
engineering history which is being forgotten and may pass undocumented if I
can't find the details somewhere! :-/

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

On 07/12/2015 14:53, Jim Lesurf wrote:
In article , Jim Lesurf
wrote:

If no-one can find one, I'll go to the source and ask Ortofon. They
might also find this amusing. Although sadly, 30+ years too late to
matter.

Alas, it seems that Ortofon sold off their electronics section and the
people involved retired ages ago. So this looks like being another area of
engineering history which is being forgotten and may pass undocumented if I
can't find the details somewhere! :-/

This is all the info I can find on the web:

"Basically it's a complementary common base amplifier with only two
transistors: BC485 and BC486.
The collectors are connected together and the input goes to the emitters
through 2200uF capacitors. The bases are grounded.
The output is taken from the collectors through a 22uF tantalum cap."

There are some datasheets, e.g.
http://img.aussieaudiomart.com/uploa...stepup-amp.jpg

And someone had to replace his dried-out electrolytics.

--
Eiron.

In article , Eiron
wrote:
[snip]

This is all the info I can find on the web:

"Basically it's a complementary common base amplifier with only two
transistors: BC485 and BC486. The collectors are connected together and
the input goes to the emitters through 2200uF capacitors. The bases are
grounded. The output is taken from the collectors through a 22uF
tantalum cap."

There are some datasheets, e.g.
http://img.aussieaudiomart.com/uploa...stepup-amp.jpg

And someone had to replace his dried-out electrolytics.

Thanks. :-) That supports my recollection, but I'd still really like the
diagram, ideally as once provided by Ortofon.[1] That would help me explain
the changes I made for my 'improved' version. Ideally, I'd love to be able
to show the circuits side-by-side when explaining why the reviewer was
shooting himself in the foot. :-)

FWIW If you look at http://www.audiomisc.co.uk/Armstrong/700/730circuit.gif
(top left of diagram) you can see what I did. The MCA-10 only had a pair of
+/- 1.5-ish volts dry cells as its PSU. I had a decent PSU so could provide
a bit more 'room' to give the transistors a better working environment.
Lowered the distortion and increased the headroom.

Jim

[1] That said, I may well have opened the box and worked out the Ortofon
circuit at the time! Alas, the relevant notes seem to have long gone, now.
I keep looking though. A bit like the cat in "The door into summer". 8-]

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html