pm-1000 line driving capability

[soundguy]

the jfp will definitely drive a 600:600 transformer no problem. Have you built one? They are pretty awesome but very colored depending upon how hard you drive them, if using something like that I would want a pot before the thing to have the option of cleaning it up a bit if so desired...

dave

 

[Brown Note]

I haven't built the JFP yet. It's on my ever-growing diy to-to list. I figured that the module would come in handy if I needed some makup gain in a pinch. What value pot would be used?

This line driver thought just gave me another idea...

http://img58.imageshack.us/img58/4566/shematic6vd.jpg

Here's a Mccurdy micpre that I recently racked. It has a 600ohm, discrete, transformerless output that runs on 48vdc. Isolate the output section and you kill 2 birds with one stone. That's my theory at least. My knowledge is somewhat lacking here, but if anyone wants to chime in here...iron ain't cheap.

-ben

 

[tubejay]

Hmm, I like the idea of the Hamptone output to color up the sound some, but I would only want to do that on a couple channels. I would like something for the bulk of my channels that would be very clean and not change the sound. Though to throw something really cool and colorful a couple channels would be fantastic. Unfortunately that's the depth of my input on the subject. You two sound like you have a much better understanding of this stuff than I do.

 

[donnysparks]

i wouldn't think the hamptone as an output gain stage would color too much in that situation--unless you really tried. i still think it would be cool to have the pm1k gain block as a small module. i'll look at some output modules, but unfortunately i belong in the idiot club, too. i'd be happy to sacrifice a channel for the cause, though, if someone wanted to guide me.

 

[khstudio]

For what it's worth, I just finished a PM1000 2 ch rack & it's got plety of poop on the output with the original OT. I increased C37 to 100uf (Panasonic FC's like the rest of the board) & left the Tantalums in there... for now.

I also had to flip pins 2 & 3 on the output XLR to correct the phase (Rack version)

The PM1000 is killer. I tracked for 6 hours last nite & loved every minut of it.

 

[cuelist]

[quote author="khstudio"]it's got plety of poop on the output with the original OT. [/quote]

See, told ya' so... :grin:

 

[beckertronix]

After reading this, and a thousand more pm1000 threads, I started to look at the line driver circuit of the master module - thinking that copying it was an elegant solution to the direct out dilemma. Then I noticed something: the line output amp and the fader amp feeding the summing buss - where you would take the direct from - are the same circuit. The master out amp has a bit more gain, 30 vs. 21, so there's a different feedback resistor, but that's it.

So I'm left again scratching my head. It's been said that the fader amp cannot drive a 600ohm load, yet the same amp drives 2 600ohm trannies at the master outs. The overall gain is aobut 9db down at the channel out from the master nominal level, (-5 and +4, respectively) so maybe a low gain robust buffer amp would help out here, but is it really necessary?

 

[rafafredd]

Then I noticed something: the line output amp and the fader amp feeding the summing buss - where you would take the direct from - are the same circuit.

No, they aren´t. Different transistors...

 

[beckertronix]

[quote author="rafafredd"]

Then I noticed something: the line output amp and the fader amp feeding the summing buss - where you would take the direct from - are the same circuit.

No, they aren´t. Different transistors...[/quote]

Wait, you're telling me those little numbers and letters mean something ? I mean they're all black and have three legs right? That's the great thing about tubes - they're big enough to have writin' on 'em.


Thanks. I figured I was missing something but I had the tunnel vision something fierce.

So here's another stupid question: Is it at all reasonable to consider swapping out the transistors in the channel circuit to make it like the line amp instead of tacking on another stage? (Assuming there is enough power supply current, and some tweaks to the feedback that is. And making the output cap bigger.)

thanks
-tim

 

[mattmoogus]

Mmmm! why not change the output transistors? Even if you cant find the originals theres gotta be plenty that could do the job. Definitely make that 100uF a 1000 tho!


Brown note, if your PM1516 is like the PM2000, there is an input pad for the first 5 steps of the gain switch that makes the input Z about 3k. That means if you split to your 10k soundcard and console input itll still be driving more than 2k, which it should do easily.

Also, if anyone is doing listening tests between transformer and unbal out, you need to load the transformer secondary with 680ohms to get a propper idea of whats happening. Listening tests should definitely be backed up with a freq curve aswell.


M

 

[Brown Note]

matt,

my biggest qualm with this mixer is the gain switching. six steps--plus 4 to minus 60. +4, -10, -20, -35, -50, -60. a shemo would be nice. i'd like to compare it to the pm2k. i figure the limited gain steps are just a cost cutting measure. thanks for the info.

-ben

 

[mattmoogus]

Measure the resistance between pins 2 and 3 of the 1500's input XLR and see whatcha get. If its a few Kohms on lowest gain then theres a pad in front of the transformer and you should be able to drive its input and a soundcard easily. When the resistance drops back to a few 10s of ohms the pad is removed and youre driving the low Z input transformer.


M

 

[beckertronix]

Here's the schematic from Yamaha's website:

2 parts -

http://tinyurl.com/m7nly

http://tinyurl.com/mxdu9

The gain switch is an input pad / preamp bypass & feedback switch depending on it's position. The fader's available to fine tune the output; I've been happy with that combination.

-tim

 

[Brown Note]

sadly i was referring to the schematic for the m1516. thanks though.

ben

 

[buschfsu]

i have 2 modules to rack and don't have the original OTs. Other than no OT what are some options.

I heard edcor but no model # and has anyone used them successfully?
thanks

 

[Mendelt]

[quote author="rafafredd"]

Then I noticed something: the line output amp and the fader amp feeding the summing buss - where you would take the direct from - are the same circuit.

No, they aren´t. Different transistors...[/quote]

It took me some time to check this...
In my pm-1000 (or what's left of it) Only the pnp transistor of the output pair is different. One of the master modules I have is from an even older model that has completely different transistors alltogether. So I'm guessing the transistors aren't really very important here, according to the schematics I have they should even be the same.

Yamaha did put a 100uF coupling capacitor after the output transistors in the master modules (just look at the schematics) so it seems a good idea to do the same and put something beefier in place of c37. But that's what everyone has been saying all along.

 

[JW]

Bumping this from a long time ago.

Somebody over on the tapeop forums at some point said replacing the output transistors with MJE 172 PNP or 182 NPN will allow for more current, and less THD.

I assume we're talking about Q4 and Q9 right? Just verifying.