SEAS
CA18RLY/27TFFC
New Year's Fun
project
Copyright 2025 © Troels Gravesen
Almost 20 years ago I bought an old Ortofon
KS601 amplifier. Just for fun, and because I like the old style of this
- at that time - quality amp. Beautifully cast front and rear and all
knobs intact. At that time it actually played without any upgrades ever
done, and I had some good times
with this 60'ies state of the art amp.
Included was the manual with full
schematics and proper advice of how to set up a stereo system,
which was new at that time. Also the price tag was intact, actually 1500
DKK, a horrific price in 1964. At that time you might pay 47 DKK for a
pair of shoes and 1.3 DKK for a litre of petrol.
Not long after the 200 uF power supply cap started leaking and the amp
stopped working. I bought new tubes for all stages, quite a few, and
quite expensive, and started thinking of replacing electrolytic
caps. Here the project stopped - and well, almost 20 years went by.
This winter, 2024, I had a workshop cleanup and I was considering
discarding the Ortofon amp - but it is beautiful just having it
on the shelf, and maybe I
should give it another try. All power supply capacitors were replaced, I
started powering up the amp with poor results. One channel was seriously
distorting and all of a sudden a 2 watt resistor blew up. Miraculously
replacing this resistor made both channels work and I had to make phono-to-DIN
connectors to connect my CD player and turntables. All works.
Now, the Ortofon may deliver ~10 watt/ch and I needed some easy to
drive speakers for further fun, thus the simple 2-way shown here, which is
free for all. I had some SEAS CA18RLY and SEAS 27TFFC drivers on the
shelf and some ~15 litre test cabs and I quickly made some front panels,
took the readings and simulated a simple LR4 crossover. Practical setup
proved a more than decent performance and I could enjoy the Ortofon
amplifier. Not a great amp by today's standard - and maybe not fully
recovered from my overhaul, but great fun.
Now, one of my hifi buddies needed a pair of cheap speakers for his
mancave and he had the front panel with drivers - and I made him the
crossover seen below.
Handing over the speakers we ran through a wide range of recordings in
my workshop driven from Kuzma StabiR/4P9/WindfeldTi, EAR MC4, EAR-868PL
and finally the Parasound A21+, the latter 400 watts/channel according
to Stereophile measurements. Quite an overkill system for a
pair of speakers, that may set you back some 685 EUR. See below.
The use of Superior-Z caps may seem overkill, but the test with my
workshop system proved it worth it. It is quite amazing what good sound
can come from even modest priced drivers, once the front end - and not
least quality capacitors - are in place.
Replacing the Superior-Z caps with CrossCap saves you some 123 EUR, but
it will be heard.
The CA18RLY with its 1" voice coil has a magnificent midrange and with
the Sup-Z in front of the tweeter, some sweet treble can be expected.
Don't expect deep bass and physical impact, but small speakers can do
stuff.
The construction here is free for all
- and no support will be given, so please do not ask.
My Ortofon KS601 integrated from 1964.
Cast aluminum front and rear.
Basics:
2-driver speaker.
Dimensions: 24 x 22 x 45 cm, WxDxH.
System sensitivity: 87 dB/2.8V/1 meter.
Impedance: 8 Ohms.
Power requirement: 15+ watts/channel.
Useful links (Please
follow all links before e-mailing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm
http://www.troelsgravesen.dk/choices.htm
http://www.troelsgravesen.dk/Placement-of-ports.htm
Download specs here: 27TFFC CA18RLY
I used a good air-cored coil for L2, 1.6 mm wire. Use a coil with DCR
0.25-0.35 Ohm..
For tweeter section, 0.22 mH, 0.15-0.3 Ohm DCR.
Resistors 5-10 watt.
Cabinet
Use 18-22 mm MDF.
Damping and other tips:
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/cabinet-damping.htm
Use 1 pcs 12 uF Superior-Z in replacement of parallel caps use here.
I had a bag of 3.3 uF and needed to get rid of some.
Response from drivers with no crossover. Doesn't get much easier than
this.
Final SPL, normalised for 2.8V/1 meter.
Sensitivity around 87 dB.
Final system impedance.
Below a possible scenario for a kit. Actually more expensive than
expected and I should have charged my friend some more...
But if you have a box of speaker leftovers, you may save some money on
caps, terminals, etc. And you can make a slottet port to save 10€ :-)
