I
just gutted the guts of a Yamaha PM1000 channel strip. I will try
to rack them in a standard 19" rack case. I'll be adding a custom
power supply, and the usual XLR/TRS input and output jacks, phase,
phantom switch, filter cutoff low-pass, hi-pass, etc...
So far, I'm successful in my testing after ripping and soldering
everything together and adding a few modifications (i.e. using simple
DPDT switches instead of 3Pole selector switches).
The Yamaha PM1000 are usually called Japanese "Neves" because
of a similar approach in design. Just like the Neves, this is all
discrete transistor and uses an input transformer and output transformer.
The EQ section is especially sweet because there is not a single
IC on this preamp. The EQ section uses inductors and capacitors...
totally analog manipulation and shaping of your frequency. (circa
1974)
I've tested them on drums and vocals and they really make the sound
FAT. The EQ section shapes your sound anywhere from slight barely
noticeable to extreme gain/reduction. Bass frequencies are solid.
Of course, being an analog EQ, it is not as precise in shaping the
sound as IC chip Equalizers. But the curve is smoother I would think.
This is what a PM1000 mixer looks like (circa 1975). Note, I did not
use my fully operational 16 channel vintage mixer for this project.
I have a few (8) spare PM1000 modules I got from eBay. I also have
2 master strips.
The inside of this unit looks like this. You can see the rows and
rows of transformers and the big regulated power supply.
This mixer sounds great, old-fashioned vintage fat sound. This is
the mixer that started Yamaha on it's journey to making high-quality
mixers... from PM1000 to the PM5000 (fully analog, circa 2004).
The problem with this mixer is it's huge and heavy. I mean, really,
really heavy. It's got 1" solid wood chassis, lots of metal
parts and transformers. They don't make mixers constructed like these
anymore. Today, it's all plastic or flimsy aluminum cases.
So what if we take a channel strip and rack it into a standard 19" chassis?
This project aims to do just that.
The before shot, all the potentiometer plastic knobs have been pulled
out. This is pre-op.
Unscrewed the front panel that has the equipment markings.
I got the back and top and bottom panels unscrewed. Only the front
panel remains. The silver looking can is the input transformer. The
slider potentiometer isn't really a slide pot but a normal potentiometer
with a guidetrack. Very ingenious!
Here's a pic of the other end... the edge connector is still connected.
I need to figure out which wire goes to which wire. The schematic
plans downloaded from the Yamaha website provided the answers. It
made my job simpler.
I hooked up some wires and tested the preamp to see if it's working.
I don't want to spend all this work and find out that the preamp
is broken. It passes signal, we're good to go.
I missed taking a few pictures... basically, I replaced the filter
switches with DPDT so that I can mount them easily in the chassis.
Closeup of the switches. The left switch is the high-pass filter switch
(disable, and 40Hz), selectable. The right switch is the mid-filter
frequency select. Currently 1Khz, and 2Khz setting.
These are the inductors used by the PM1000 for the EQ section... bass,
mid, and treble frequencies.
This is a closeup of the input transformer. The transformer provides
coupling and is center-tapped. The 48V phantom power is connected
to the primary center tap.
This is the schematic diagram printed from the PM1000 PDF, downloaded
from the Yamaha website. I used the schematic to figure out how to
wire the filter switches and where to tap the output.
The PM1000 has a gain selector knob. I think each click is 5dB gain
step.
And these are the parts that I removed from the PM1000 during the
operation... You can see the edge connector, cue switch, filter switches,
and echo1 and echo2 knobs, plus the 4 bus selector switches.
Ready to RACK!
I'm getting ready to rack the preamp strips taken from a Yamaha PM1000
console.
But first, I did some sound tests to make sure this is worth racking.
I think the EQ will be useful... adds that volume and warmth to the
sound. What do you think?
This is the original audio clip. I used an iRiver mp3 player. Recorded
the sound and here is the result. (Sorry, one channel only... left
speaker).
Original audio clip
And this is the same clip after going through the PM1000 preamp, with
the preamp EQ adjusted for some flavor.
Passing through PM1000 preamp
Again, the EQ of the preamp is worth saving because it is totally
IC-less... no opamps here, just inductors and capacitors... the way
a Pultec EQ does it... totally passive. There is a makeup gain circuit
after the EQ to boost the signals, again, no IC... just discrete
transistors.