PM-1000 racking - cutting down to size

[Scodiddly]

Just thought I'd stick this here for reference - I originally wrote it up to answer somebody's email request.

(click for full-sized image)

Attached is a picture of a cut-down PM-1000 module for rack mounting. You
can really figure it out by just cutting off all the wire ties and
tracing the wires, since things are wired up in a fairly obvious way.
What I did was to remove all the panpot and buss assign stuff, the fader,
etc, and then rewire the Echo 2 pot as main fader. The final output
(before any output transformer) is just taken from where the
panpot/assign stuff was connected.

1. Mic input is the red cable attached directly to the stepped input gain
switch. In the stock module the red cable just runs up to the big
connector, but you can just solder an XLR onto it instead.
2. DI input and phantom power are down by the input transformer (silver
can on upper left of picture). The DI is just a normalling jack between
the transformer output wire and the last circuit board connection. The
phantom power comes in via the orange wire connected right next to that.
3. The Echo 2 knob is now the main fader - there's a yellow cable coming
from the little circuit board behind the low-cut and mid-frequency
switches which originally connected to the fader pot, but which is now
connected to the echo 2 pot instead. The cable that came from the output
of the main fader was removed and a short piece of wire used to connect
to the output of the Echo 2 pot. Finally, the green cable to the output
is connected where the panpot used to be connected (brown cable in the
original). The output can go to a transformer or just be an unbalanced
ouput as shown.
4. The +44vdc main B+ power connects here via the red wire.

Power supply I've used is a 48vdc power supply from Digi-Key, part #
179-2034-ND. Supposedly you can tweak it to run at 44vdc, but I just put
a few (6 or 7?) 1N4003 diodes in series to drop the voltage to ~44 (each
diode drops the voltage a little). Next time I'm going to use the same
power supply but with a more conventional LM317HV regulator circuit.

(click for full-sized images)

 

[Scodiddly]

Doing the actual cutting:

It's easy enough to remove the aluminum faceplate. That can then be cut as desired with (ideally) a circular abrasive blade or maybe a hacksaw.

The steel frame is probably best cut with a hand-held nibbling tool ($10-20), mainly because a nibbler doesn't produce metal dust. Much easier than disassembling the whole thing.

Chunks of the steel frame can be used to make mounting brakets.

 

[Scodiddly]

Metalwork notes:

For the one pictured above I did a rather overcomplicated job of cutting away the back of the aluminum face on the channel strips, so that it would lay over my sloppy hole in the rack faceplate. Too much work, hard on the materials. So, for the next one (I'm already working on another!) I'm going to cut the rack faceplate hole big enough to flush-mount the channel strips. My best cutting tool here is a sabre saw (small reciprocating saw, aka hand-held jigsaw) and so the edges are going to be rather messy. Rather than spending a couple days with a file smoothing it out, I found some tiny brass U-shaped channel at the hardware store. At most places (at least here in the USA) you can find a little rack of "craft" metals, little brass, copper, and aluminum tubes, sheets, rods, square tubes, etc. I'll cut the hole as best I can, then cover the edges with the brass U-channel for a neat appearance.

As mentioned above, a nibbler tool is handy for cutting down the steel channel frame. It's also good for cutting out odd holes in the rack backplate, such as a square hole for the IEC (ac power cord) inlet. Nowadays I've got a nice Greenlee chassis punch for the XLR holes, but in the old days I'd use a nibbler for those holes too. Messy, but the face of the XLR does cover up the jagged edges.

I've been using an abrasive (metal-cutting) blade in my radial arm saw to cut the aluminum channel face down to size. You can get these blades for hand-held circular saws, too. Does a nice straight cut with fairly clean edges, leaving just a bit of burr to be filed off. My life got a lot easier when I discovered abrasive saw blades. :thumb:

 

[Scodiddly]

Starting in on another PM-1000 project, decided to use an LM317HV voltage regulator instead of the "chain-o-diodes" approach. No particular magic to the component choices, just what I slapped together and which seems to be working correctly.

Not shown - one each 0.047uF film caps on the input and output, plus a 100uF/63v electrolytic on the output.

 

[Milkmansound]

have you become the new PM1K daddy?

I think you have. Good work! :grin:

 

[Scodiddly]

[quote author="Milkmansound"]have you become the new PM1K daddy?

I think you have. Good work! :grin:[/quote]

Well, why not? Especially when I'm getting paid for the work. :green:

Plus there doesn't seem to be any PM-1000 stuff in the Metas (yet).

 

[Scodiddly]

Of course now I've got a question... I need a replacement treble pot for the one I'm currently working on. It's almost exactly one of those alpha pots from Mouser, 50k linear. But with a center tap... any easy sources?

Edit: couldn't find one in time - used two 24k resistors in place of treble pot. Can be seen as a little chunk of perfboard in the photo a few responses down. Probably a regular pot would have been fine, but more noise in center position compared to original and with the center "0dB" position a bit less precise.

 

[Scodiddly]

Anybody have the output transformer color codes?

http://www.groupdiy.com/index.php?topic=3790#img_6751

 

[idylldon]

Tubejay posted one here: http://www.groupdiy.com/index.php?topic=5643&highlight=yamaha+pm1000

It's a few posts down in the thread.

Cheers,
--
Don

 

[Scodiddly]

Unit #2 mostly completed (output transformers hadn't shown up yet).

Some notes I wrote for myself in case I need to do one of these again:

Chassis:
Par-Metal 10-19113B. Was $53.50 plus $8 S/H. Need to call to place order properly, number is (201) 955-0800.

Cutting down the channels:
Leave enough below the gain switch to allow existing screwholes to be used.
Cutting away back of faceplate ? not cutting sides ends up with things a bit too wide for the chassis top and bottom to fit nicely. On the other hand, cutting the sides compromises the connection between faceplate and frame. A solution from the back would be best, if tools available to cut a clean edge on the chassis faceplate.
Second unit had best rear mounting on the frames ? an end piece from the frame as bracket to bottom, holes drilled as needed in back of channel frame to connect to bracket. Another frame end piece used as output transformer bracket.
Drill holes for power supply mount after doing the frame mounting ? it's a bit of a tight fit.

Output transformers:
Wiring as documented by tubejay and used for second unit:
Red ? ground
Brown ? channel unbalanced signal
Blue ? plus output
Green - minus output
Hopefully that corrects the channel inverted polarity issue ? I forgot to check since I had to install the ones in second unit at the last minute and then take to UPS.

Power supply:
Digi-Key 179-2034-ND. Linear 48vdc/0.5A. Needs 3/4 amp fuse.
LM317HT circuit w/ trimmer. Should be a schematic in the website files.
Power-on LED uses a 3.9k/0.5watt resistor and connects to +44vdc.

Grounding:
IEC inlet ground to chassis.
Inputs/outputs pin 1 to power supply ground.
For the 2 units I've done the circuit to chassis ground connection was done through the metal 1/4? output jack. XLR shell connection not used, of course.
DI input jacks should be isolated Re'an type.

 

[wiz1der]

Yo Sco!

Nice... Do you happen to have a BOM (including digi-key, mouser,wherever item numbers) of ALL the extra parts needed to do this?



You are indeed the pm1k Daddy!

 

[JW]

Hey Scott,

When you say "channel unbalanced signal" where you connect the brown transformer wire, do you mean the negative leg of C37?

that's what I'm been connecting to the brown wire. I mean, the actual leg of the C37 cap on the PCB is where I'm connecting it.

Just wanting to clarify.

Thanks

 

[Scodiddly]

My image doesn't show enough detail, but it's at the same place where the panpot is originally connected. It's the green wire in that top image here...

Don't recall whether that's just the connection post where c37 ends up or not, but since I just took on another rack job (that's #3!) I've got a couple modules to play with for the next couple weeks.

 

[JW]

Thanks Scott,

Yeah, I can't tell from the pic, but if you could post back here when you dig into #3, I sure would appreciate it.

Jon

 

[jthoen]

not trying to be a jerk here, but why didnt you recap the pm1000 before installing it. The sound difference is pretty huge when you do, well worth the time. Nice job on the rack, it looks quite swell!
joe

 

[Echo North]

Hi,

Reading this post (and a few others) encouraged me to try my own PM-1000 racking project. I know NOTHNG about electronics, other then what I have read in "Electronic Projects for Musicians".

Anyway, all of my PM1000 stuff arrived yesterday and I dove right in. I've stripped the first channel strip of unnecessary parts, attached the power supply, made a step down diode chain, and attached xlr in and outs. I also routed the volume control to the echo 2 pot likeScodiddly.

And....everything works! Unbelievable! Now I have a few questions.

1. It is a little unclear to me how to hook up the phase reverse switch? Can someone describe that process?

2. Here is a picture oh my echo 2 knob (now output volume) it works, but should I have that orange cable going from the center pole to "BI" on the board. Are the black cables on the left pole needed?

3. I have the purple wire going to my xlr out. There are two wires in it, one to the ground and one to the center pole on the xlr out. I am not using output transformers (yet). Should the negative pole be empty?

Thank you so much for all the great info guys!

Mike

 

[Scodiddly]

Pretty good progress!

1. You can just copy the existing polarity (aka phase) switch wiring with a DPDT switch.

2. Yup, you need all the wires - the black (ground) is a zero reference for the volume circuit. Think of it this way, you're using the pot to mix between full output and zero output (ground).

3. Hook the signal wire to pin 2 on the output XLR, and connect ground to both pin 1 and pin 3.

 

[Echo North]

Thanks for all the info!

I have another question.

Phantom Power - How exactly do I hook this up? I comes from the power supply before it goes through the diode chain correct. How does the orage wire figure into it? Do I hook it into the xlr input?

Also can i us a SPDT switch for turning on/off the phantom?

Thanks again.

 

[Echo North]

Another question:

For the phase the three wires coming from the xlr input go to one side of the DPDT switch and then I connect the three coming from the gain knob to the other side?

I do that but have no signal...how should I be hooking it up to the DPDT switch?

 

[Scodiddly]

I've been doing phantom power right into the orange wire, which is the original approach. It ends up going through a center-tap in the input transformer. As an alternative you could have the phantom power connected directly to the input jack through a pair of 6.8k resistors, which is the more modern (transformerless-circuit) way of doing it.

Regarding the polarity switch, take a closer look at the little circuit board on the back of the original switch. Wish I had a little diagram for this, because it's really simple.