Need HELP! - PM1000 Rack - almost done but...

I'm almost done racking 2 channels from a PM1000. New Panasonic FC's & original I/O transformers, it's going well but I had a few questions.

I see a lot of people talk about changing out the Tantalum caps for films. What's the word on this... wouldn't that change the character of what's already said to be a very good pre-amp? The main cap in question is C1 - the very first cap in the signal path, right after the input tranny. Doesn't some NEVE's use Tants in theirs?

Opinions wanted. I'm very excited to get these running and see if there all there cracked up to be. I got 1 responce that said "they'd eat my Presonus MP20 & M80 for lunch"... is that true.

Anyway, if it is, I'm building a 2ch rack for less that $300... not a bad deal.

All my reading about these all discrete mic-pre's has got me wanting one.

Can anyone recommend, besides this one, a DIY friendly mic-pre of pro quality. I'd really like one of the NEVE's everyone talks about but which one :?: :? Something good all around that would give me better quality or different colour than my MP20 or M80 would be killer. I'm also almost done the NYD one bottle-pre so using tubes isn't out of the question... how's the G9?


Thanks,
Kevin - KHStudio :green:

Not Neves, but all goood in their own right.

http://www.jlmaudio.com/JLM99V.htm
http://www.seventhcirclestudios.com/SCA/SCA.htm
http://www.gyraf.dk/gy_pd/g9/g9pd.htm

Take your pick.

Have fun,

elco

There's no telling, only hearing... having done the capacitor modification to a pm1k module I own the advice I would give is to finish 'em up, use them a bit to establish an idea of the sound.

When you're satisfied, attempt this smaller modification to one channel and compare between the two. No matter what the outcome it will be a valuable aural learning experience.

Generally I can say that the pm1k preamps are well worth the effort and cost, and I would choose one over most mid-level gear.

Frank

[quote author="franklinh"]There's no telling, only hearing... having done the capacitor modification to a pm1k module I own the advice I would give is to finish 'em up, use them a bit to establish an idea of the sound.

When you're satisfied, attempt this smaller modification to one channel and compare between the two. No matter what the outcome it will be a valuable aural learning experience.

Generally I can say that the pm1k preamps are well worth the effort and cost, and I would choose one over most mid-level gear.

Frank[/quote]

Thank you.
I was just going to leave them stock, except for the electrolytics, & get a feel for them before moving forward... just wanted some input from others that have used these & wondered if the improvements are just that. :wink:

On mods -
Jim Williams has a lot to say about modding stuff but I don't think all his mods are for me. For instance, he chooses components & chips that are VERY clean & I've listened to those clean chips and still liked my 5532's better... & in this case swaping films for tants.

Gyraf & others talk about a time (I think back in the late 70's) that Tantalums were thought to be the shit & were used in a lot of gear - but BADLY... Is this one of those I wonder?

Could somebody please explain the ups & downs of Tants in the signal path?

Also, if I find the first cap has that much of a usefull character change, is there a way to make it switchable without poping & blowing the crap out of my speakers? - or - making the pre noisier?


Kevin

Well, I got my second channel strip today & it must be a different year
I really wanted them to match as close as possible but:

- the resistors are a different brand or type (both CC though)
- The inductors look different
- Caps in the EQ section - one has the Greenies & the other the white/clear films

Obviously I'm going to build them as is except for the electro's & see which one I like better but do you think it will make that much of a difference? Stereo unit should match. EQ caps are an easy change but the resistors?

BIG QUESTION:?:
Would it be worth it to upgrade the resistors to Metal Films or does the CC add to the color &/or noise people love or hate? I don't care about the labor I just want them to kick ass :green:

A lot of people use the efx send 50k pot as the NEW master out but the original fader was 10k - how does that work? problem or not?

Kevin

[quote author="khstudio"]Obviously I'm going to build them as is except for the electro's & see which one I like better but do you think it will make that much of a difference? Stereo unit should match. EQ caps are an easy change but the resistors?
[/quote]
It's a concern, but I wouldn't worry about it just yet. Even two strips from the same year will have somewhat different history, and two strips from the same mixer will be old enough to have drifted apart. Fix what you know is busted, don't worry too much about matching just yet.

A lot of people use the efx send 50k pot as the NEW master out but the original fader was 10k - how does that work? problem or not?

Click to expand...

It's been OK in the ones I've done - the Echo send pots are 25k, not 50k BTW. I did have some oscillation with the treble knob cranked, but it went away when I finished sorting out the grounding and had it all inside the metal case. Probably not anything to do with the pot anyway.

I've got three strips from the same mixer and all sound slightly different. The difference is there under a magnifying glass, but I don't think I would notice in the real world. So far they are all stock (original electro's, tants, et. al.) They sound right in line with my other "hi-end" mic pre's in terms of over-all quality, (but not the sonic fingerprint of course). In short, they hang with the big-boys.

I very well might leave them as is, because I suspect that tweaking won't make them "better", but only "different". I could be wrong though. I would like to make a quick comment about your tantalum question. I recently got a chance to shoot out a Chandler 1073 vs. an original Neve 1272. The Chandler uses cheep electrolytics in place of the tants. The sound was more open and detailed than the Neve, but perhaps lost some of the traditional qualities of the Neve. I prefered the Chandler myself. If I were ever to dig into my PM1000's, I might try getting rid of the tants to see what happens.

Very cool, thanks. I thought I read that Neve's used Tants.
The voltages are low enough that Poly or Metal films will fit too.

I'm going to try them stock but with new electro's & get a feel for them first. Probably track a guitar & vocal & make notes of setting for later comparison. I'll share the files or info when I get them done... 1st fire up is tonite. Weeeeeeeeeeeeeee :green:

There really isn't that many Tants in there - the very first cap alone would probably make a big sonic change... I'd like to make it switchable, maybe between all 3 types??? How should I go about doing it without making a mess? or should I at all :?

You guys are very helpful
Kevin

Some of that carbon noise might cancel if this is a push pull strip.
Like the Langevin AM-16.
Nothing but cheap carbon in those and they sound great.
But thats a mic pre.

I would change to metal film resistors in the line amp but leave the CC's in the mic pre if there is one. It might be too harsh with film in the mic pre. If it sounds good after that mod, then your in bidness.

Tants vs Lytics - probably depends on what your after - You could always just bridge a few tants with a lytic and see if you hear any diff. The tant in parallel should not matter too much.

So a switch to parallel a Lytic with the Tant? easy enough to try.

Are you saying the dominant path would be the Lytic?

It uses a 3.3uf Tant (original input) so what value would be good... I was thinking 1uf or smaller.

I just woke up, 1:00am, I should have it running by sunrise.


About the units being different:

I just noticed that one uses transistors marked - C1681 & the othe C1000. Weird
:?

Oh well, I'll know soon

Just finished this thing & all I have are .5 amp & 1 amp FUSES

Until I get the .75 amp which one would be safe?

WOW...THIS THING IS KILLER :shock:

I've been stuck with my Presonus pre's for years & before that the one's on my Topaz Project 8 that we're fair.

It has A LOT of headroom, & with the input & output controls you can push things forward with more up front(pre) gain or back with less input & more out (master) gain... Very cool. Vocals are more alive & whoever mentioned the smooth air on top was right on :thumb:
A touch of EQ was also nice. I think I'd like to move the treble up to 12k though. So far I've only tested with an sm58 - Vocals, up against my Presonus MP20 (without the Jensen input tranny - some other model) I do have a Broadcast version of the M80 (8 ch pre with Jensens) which MAY give it a better run but I don't think so. For less than $300 it's unbelievable. My first DIY mic pre :green:

I'll be taking pictures & posting them in another thread & maybe some samples when time permits.

Thanks to the guys that helped me & shared the setup info.
Scodiddly for one :thumb:

Kevin - KHStudio

Congratulations! :guinness:

kevin-

now that you know you dig the sound of those amps, take the cap that you had a question about, open up your digikey catalog and order every single type of cap you can in that value, it will only cost you a few bucks. Spend a night plugging them in, you could even put in a socket just for the test and listen to the differences. It wont cost you very much money or time and you'll have a precise answer to everything you'd been wondering about earlier in this thread. Sometimes a tant sounds better than an aluminum electrolytic, sometimes not, sometimes you cant tell the difference. Probably the only definitive *dont* do with tantalums is in power supplies because when tants go bad, they usually short (unless they are tants in CJ's stuff that has to ship before closing) so obviously aluminums are a little "safer" choice there.

caps are very very very subjective souding things. we do not all strive to make the same sound, that is for sure.

dave

Dave,
Thanks man... I will do just that. :thumb:

Scodiddly,
I followed ALL the input & output transformer wiring intrunctions on your thread & the phase is reversed on the whole unit... even the direct input. I checked it 1000 times

where should I swap it:

in tranny - Yellow & white?
output tranny - blue & green?

I also noticed that an sm58 sounds very good with the phase reversed, maybe better than normal - unless the mic is screewed up. I got stuck testing my cables & patchbay for polarity for hours.

What's really fucked up is my initial evaluation & comparisons against my other pre's was flawed because of it. Don't worry I'm not blaming you :wink: the weired thing is that the bass & dynamic mics sounded cool both ways, then after hours of testing I couldn't tell what I liked or which pre was better... well, now I'm rested up & ready to attack this thing.

BTW
My treble pot goes crazy after turning it about 75%. You mentioned this with yours & that you fixed it with correct groundong but I don't think you had an output tranny so I'm not sure what to do.


Kevin

I PM'd Scodiddly but if anyone else has the answers I'm ALL ears.

I REALLY need your help:

http://www.groupdiy.com/index.php?topic=14629&highlight=pm1000

You thread about the PM1000 can't be found... it won't load.

I REALLY need help with the GROUNDING POINT's. You mentioned a LITTLE about it in that thread but it's gone. I'm using output transformers & I think you just used UnBal out's so I'm not sure what to do. I'm also having the TREBLE POT problem you mentioned from about 75 to 100%

I'm also having PHASE issues. I followed the color chart also found on that thread but it's not right. Does the circuit FLIP it somewhere or should I just flip it somewhere... like the green & blue input's. It's NOT my phase switch because the direct input is also reversed.

Click to expand...

I'll post his responce here to help others. I'm sure I won't be the last to do this.

HIS RESPONCE SO FAR:

the polarity does in fact flip in the channel somewhere, no big deal in the original since they'd just flip it back somewhere in the master sections. For the rack job I did with transformers I just used the output transformer to flip it back. Long story, but if I'd had time I would have wired the polarity switch into the output transformer instead of the input transformer. Less switching noise and it would affect the DI input.

Grounding... important thing to know is that the channel circuit board ground isn't connected to the channel frame. You have to make that connection somewhere, and get the thing into a closed metal box to kill that oscillation. Basically just make sure that there are no redundant ground paths - so have only one point where circuit ground connects to the chassis (I did it through the 1/4" jacks on the back panel, the front panel DI jacks were nylon and didn't short ground to the front panel), only one point where the power supply ground connects to circuit ground. Power (AC) ground should only connect directly to the chassis.

Hope that helps,
-Scott

Click to expand...

PIC's on the way :green:

NEW FINDING :!:

I just pulled the original phase switch out & tested it. Chech this out:

When the switch is in the N (normal position) it connects the red to the white wire.

When it's on R ( phase reverse) it connects the 2 REDs...so it seems to be flipping it on this switch & not it the master section like you had thought. :shock:

This creates a problem when adding a direct input though.

So the circuit polarity is fine (stock)

Now what?

Kevin, it looks like you are talking about two different things. A gain circuit can be inverting or non inverting, depending on the design. Scodiddly is talking about a fixed inversion in the channel, where you are talking about a user selected inversion to compensate for mic placement. When the "polarity invert" switch is set to off, you want the channel output to produce a positive output voltage for a positive voltage input. If the net polarity of the PM1000 signal path is negative, you need to wire the output transformer to negative to compensate.

The user controlled polarity inversion definitely happens in the switch, and not somewhere in the channel. This is shown clearly in the schematic. If you are putting output transformers on the strip, that is where you want the switching to occur. Switching a mic level signal is less desirable.

-Chris

It's confussing. Are you saying to fix the polarity I should swap the output wires to the XLR... pins 2 & 3?

My direct input & mic input are both wrong. So I need to fix it somewhere & the phase switch is no good because it's before the direct in.

This thing is so close to being done but I need to fix the polarity & get the grounds right.


About the switch, the original seems to flip the input on the switch when in the NORMAL position. Check it and see, I'm not 100%. Maybe the circuit inverts it back. So in essance they flip the mic phase first before the inverting circuit, maybe I'm wrong... who knows?

If you are inputing a positive voltage and getting a negativve out, with the stock polarity switch in "normal" position, just flip pins two and three on your output xlr and you should be fine if Im understanding you correctly.

dave