PM-1000 racking - cutting down to size

[khstudio]

I just got a few channel (& there might be over 100+ more where they came from)
Do these things really sound that good after racking them up like this. The best pre's I have right now are the Presonus MP20 & M80(m80 has Jensen Transformers).

Just wonder how they would compare to what I have now?
I was just about to start NYD's one bottle pre &/or the G9 but, yestarday, stumbled acrossed a few of these & it seems like the way to go. Can you really get that NEVE/API sound?

Opinions WANTED! :green:

Thanks for the info guys... very helpful allready.

Kevin - KHStudio

 

[Scodiddly]

It's not a copy of a Neve, or something that sounds exactly like a Neve. That's a comparison that some people have used to indicate the level of quality of construction.

The downsides are that it's a bit noisy, and that the EQ isn't especially useful. I'm too obsessed with low noise performance to really want a pair for myself, but other folks really like them.

 

[khstudio]

On the Power Supply:
Wouldn't it be better to use a toroidal to keep the noise down. I'm not just concerned with the noise inside but how the transformer (listed here) could affect other devices in my rack.

If it's not a big deal I'll just get the one you guys suggested. I'd need some help with designing the toroidal one from scatch. Can anyone help me with this :green:

I'll have all the parts by the end of the week... just want to make the BEST choices. Do you guys find recaping helps improve the noise & quality that much or should I fire them up first & see?


THANKS for a great project & info :thumb:

Kevin

 

[Scodiddly]

I wouldn't worry too much about the power transformer - I've done racks with both kinds. Just keep it in the corner away from the audio stuff. And it'll be inside a metal box, so other racks won't really have any problems.

I did recap the most recent pair of modules, and aside from having one of the low-cut switch positions finally working I didn't hear any obvious difference. On the other hand the needed caps are fairly cheap and the existing caps are probably 30 years old, so it's a good proactive measure.

 

[JdJ]

I have only replaced one cap in my modules so far, but it made a difference in low-mid clairity. I don't have the schematic in front of me right now, but I think it was C37. I ended up bumping up the value considerably, especially since currently I am not using an output transformer. Here's a link on the GS forum where Jim Williams makes some cap replacement suggestions.

Good luck!

Josh

 

[Siegfried Meier]

Hey Scodiddly,

I'm not exactly sure how your output is connected, as it's hard to see from the pics. I see the 2 leads where the green wire is connected, but which one is positive and which one is the ground?

Thanks,
Siegfried

 

[JdJ]

I'm not Sco, but maybe I can help:

I believe + is the second hole to the left from the mounting bracket. If you flip the board over it has + and - markings. The ground can go to any of the ground busses marked - on the back. Hope this helps.

-J

 

[Scodiddly]

[quote author="Siegfried Meier"]I'm not exactly sure how your output is connected, as it's hard to see from the pics. I see the 2 leads where the green wire is connected, but which one is positive and which one is the ground?[/quote]

The shield part of the green wire just connects to one of the ground points - the actual signal wire is on the pin to the left of the shield connection. "BO", maybe? I don't exactly recall what was printed on the circuit board.

 

[Siegfried Meier]

Ok, just so I get this straight, imagine this section is numbered 1-4. Are you saying that the signal is 3 (which is the one that has BO under it) and I can just take ground from the common ground (chassis, P/S etc.)?

Does the other wiring look ok?

Thanks!
Siegfried

 

[khstudio]

Pull the bottom plate off & look... I'd look for you but mine are racked up right now, sorry.

You should recap the channels anyway. Those caps look original & are probably close to 30 years old.

Kevin

 

[Siegfried Meier]

How's this? I'll recap them after I can make sure they work first.

Which connection is the audio output? Does the other wiring look ok? I'm going to assume that BI the input, BO the output and E is the ground?

Thanks,
Siegfried

 

[digitaldrummer]

you got it. a few pictures of mine here (click the small pix for larger)

http://www.digitaldrummer.net/pm1000.htm

I should probably finish those 4 other strips I have out in my garage...

Mike

 

[khstudio]

BO looks right (Your #3) You can check yourself by following THAT trace back to C37 (I think), the final output cap.

#2 = E = GND
#4 = E = GND

BI = output to master fader.

BTW, I think you should tie the sheilds of the wires (going in & out of your master fader) to the grounded leg. The sheilds SHOULD be grounded ONCE, Somewhere or they won't sheild :wink:

Good Luck man. The PM1000 rack I did went pretty well & could be my favorit DIY yet... not to mention VERY nice sounding.

Kevin

 

[khstudio]

BTW, Check you phasing before you finish racking them... I had to reverse the +/- on my output tranny to make it right. I tried @ the input but it left my DI "Still" out of phase. This lead me to believe that the Yamaha PM1000, somewhere in the console, flips it back to normal... so hooking it up like we do leaves that flip stage out. I'll mention that I'm using the original OT on mine.

Kevin

 

[Siegfried Meier]

Finally back to working on these after a long time. Now, I've connected the power to the channel, and I'm curious about something. If I don't connect the earth, I will see +44 at the B+ input. The second I connect ground, the voltage drops to around +6V. Is this simply because the module is in circuit and I'm not able to get a proper voltage? Both of my channels do it, and I'm just curious because I can't get any output at all.

Thanks,
Siegfried

 

[Scodiddly]

[quote author="Siegfried Meier"]Finally back to working on these after a long time. Now, I've connected the power to the channel, and I'm curious about something. If I don't connect the earth, I will see +44 at the B+ input. The second I connect ground, the voltage drops to around +6V. Is this simply because the module is in circuit and I'm not able to get a proper voltage? Both of my channels do it, and I'm just curious because I can't get any output at all.[/quote]

That sounds bad - the voltage should not be dropping. Maybe there's something wrong with your power supply? Maybe try putting four 12v automotive light bulbs (tail or dome light bulbs) in series and seeing if the PSU can drive those OK.

 

[Siegfried Meier]

Ok, I figured out that the voltage regulator circuit I've been using is shit. Now, I've just used 4 diodes in series to drop the voltage to 44.3v - good enough. Both channels work - except for no phantom works, the top end EQ knob gets all hissy, feedbacky and weird when I turn it up for both channels (all the other ones work) and I have a ground issue somewhere. If I'm holding a 57, there's a hum, if I set it down, the hum is gone.

I'm using a couple of JLM go between's to get the phantom in and out. When I measure the 48v switch on the go between, I see 48v, so I assume that is good. I've simply taken a wire from the 48v of the P/S to the phantom connection of the go between, which I believe is all I need.

I'm using a wallwart type P/S that came with these modules when I bought them.

Any help??

Thanks,
Sig

 

[Siegfried Meier]

Ok, got the phantom working, but only if I touch the chassis. There's also lots of noise and hum, almost like I'm tuning in a radio, so there's obviously a grounding issue.

[quote author="khstudio"]

BTW, I think you should tie the sheilds of the wires (going in & out of your master fader) to the grounded leg. The sheilds SHOULD be grounded ONCE, Somewhere or they won't sheild :wink:

Kevin[/quote]

What exactly do you mean by this?? I don't see what you want me to wire up.

Thanks - I'm close!! I can feel it!
Sig

 

[Scodiddly]

One weird thing about the PM-1000 modules is that the chassis isn't connected to the circuit board ground. So you have to do that somewhere to get phantom to work and for the case to be grounded to the circuitry. The usual clue that you haven't done so is that phantom power doesn't work.

Don't worry too much about the treble knob oscillating when boosted - when you put your case together completely it usually goes away.

 

[Siegfried Meier]

Ok, so I now connected a ground from the circuit board, to the original PM1000 chassis. Still no phantom until I touch the chassis - either the original or my new chassis that the original sits in - and the ground hum is still there and they sound like crap. Now, I haven't permanently mounted the PM1000 into my chassis yet. Could this be the problem? These pres are getting a little exhausting for me and I think if I can't figure this out, I'll sell 'em off and move on to something new. I have a beautiful chassis made for them, and I'm using JLM go between's for both channels.

Thanks for any help,
Sig