Help me Get Creative..

[GREENFENDR]

On kind of a whim, I bought an old Yamaha PM430. I could not find much on the web about this particular mixer, but Knowing that it was built after the pm1k I took a guess that there was similar circuitry, and something that there's been some documentation that I could get enough help to get it where I want it to be.

I was right about the first part. Input and Output Tranny's seem like sizes and shapes i'm familiar with, There are 6-2520 style op amps on the summing and monitor section, but The second is a little vague. Most of the pm1k information I found was about parting it out, and how to rack it up, which power supply for US voltage, etc. but not much on how to make the thing actually sound better.

I'd like some help in building this thing out to be as kick ass as It can be. Give me any opinion on what you would do with this thing, be creative as you want. I'm open to any idea, from "just Re-Cap it" to using it just as a frame and gutting it. Just throw it out there.

My skills aren't horrible. I designed and built a quartet of Eisen Pre's, and did a good job guessing parts for that. but I'm no electrical engineer either. I understand basic circuit theory, at least in a block format.

I ordered the Service Guide from a dealer in Florida, so we won't be flying completely blind here. If there's anything that anyone needs a closer look at, let me know and I'll get a better shot.

I'm going to post some pictures of the thing. Please met know if anybody recognizes
anything.

Thanks in advance!

[ulysses]

Your biggest limitation in improving the sound of this thing is going to be the op amps in the 7-pin SIP package. You might want to think about designing a little adapter board to allow a standard package to replace those, or better yet just make some discrete op amps to replace them.

What are the power supply voltages? The PM1k runs off a +44V rail, which means all the coupling caps are nicely biased. Does this thing have bipolar supplies?

[GREENFENDR]

Thanks for the Reply!

I Think its the same power supply based on the block diagram in the manual (I have the schematics and service manual on order). I'm attaching a clip of that diagram.

I found some information on a consumer audio DIY page recommending swapping out my opamps with the Burr Brown OPA2604 (with some sort of adapter). Would that be a good match?

Does anyone know if those yamaha NE opamps on the summing and output busses are swappable with an api style? Will I run into any issues or be aware of anything? I'm thinking about throwing some 2520's, I think that'd be a cool way to get some character.

[ulysses]

Originally Posted by GREENFENDR

I Think its the same power supply based on the block diagram in the manual (I have the schematics and service manual on order). I'm attaching a clip of that diagram.

Your power supply is not similar to the one in a PM1000. The PM1000 uses a 44V rail, so the audio path has to be AC coupled and hovers around 22VDC. Your diagram shows +/-15V and +/-22V supplies (probably +/-15V for the IC op amp, +/-22V for the discrete) which means the audio path will hover near (but probably not right at) 0V. The result is that the coupling caps you still need do not have significant or predictable DC bias on them. That's fine for film or ceramic caps, but electrolytics don't perform as well that way. Search this forum and you'll find dozens of threads discussing this topic and what to do about it. It's a very typical situation, so don't think it's going to prevent your mixer from sounding decent. It's something people spend a lot of effort trying to design around, though.

Originally Posted by GREENFENDR

I found some information on a consumer audio DIY page recommending swapping out my opamps with the Burr Brown OPA2604 (with some sort of adapter). Would that be a good match?

The OPA2604 is a dual op amp with 8 pins. Each amp has 3 pins, and there are two for power. Your SIP packages have 7 pins, so I don't see how they could contain two operational amplifiers. They're probably singles with some compensation pins or other functions.

Originally Posted by GREENFENDR

Does anyone know if those yamaha NE opamps on the summing and output busses are swappable with an api style? Will I run into any issues or be aware of anything? I'm thinking about throwing some 2520's, I think that'd be a cool way to get some character.

I think you already have "some character" with those Yamaha discrete op amps in the sockets. Replacing them with 2520s would be easy to do, but it would only result in different - not necessarily better - character.

[Toro]

First POSTING !! i'm looking for info on the yamaha pm 430, i know a few users,
i love the raw sound, but i'm looking for ways to improve the clarity on this fabulous yet affordable mixer.

[GREENFENDR]

Thanks Ulysses, for the expert info. and welcome to the forum Toro,

Ulysses, I have a couple more questions if you don't mind, I was searching last night for information on DC Bias on Electrolytic Caps, from what I could gather (and please feel free to correct me), when the DC hovers around 0V, you can introduce negative Bias, which is what causes the problems you mentioned.

What I couldn't find was exactly the problems are and how to fix/design around them, I'm willing to put the research in myself (whats the point of doing if you're not understanding, right?) but if you can just give me another hint for what to look for.

Here is the post where I found the discussion for the burr brown exchange:

diyAudio Forums - Replacement for TA7136P - Page 1

"i recently replaced the TA7136P in the phono section of a kenwood receiver. The difference is remarkable! wider sound stage and more detail.

I replaced two single op amps with 1 dual opamp. I had a OPA2604 on hand so I used that.

You could use:
NE 5532
OPA604 or OPA2604

Keep in mind that the TA7136P is in single in line package and the new parts come in DIP or even surface mount. So you will need to build a little pin-to-pin mapping or conversion.

TA7136P pins:
1. frequency comp
2. non-inverting input (+ input)
3. inverting input (- input)
4. V-
5. voltage comp
6. outout
7. V+

So for modern op amps you probably don't need to map pins 1 and 5."

[Toro]

Thanks Greenfender i have been reading these very pages for so long is about time i become a member , Now Ulyses if you can give some advice to Greenfender i'm sure i can somehow catch some of these tips thanks in advance !!

[ulysses]

Since you don't have two of these SIP chips right next to each other, it makes more sense to replace each one with a single op amp instead. The OPA604 is the same amp as the 2604, but it's a single instead of a dual. There are plenty of other single op amps available with the same basic pin-out. The extra pins might be used for offset compensation rather than frequency compensation, but you'll probably want to rethink those components when you swap chips anyway. What I would do would be to make a little daughter card to hold the DIP (with a socket), 0.1µF ceramic power supply decoupling capacitor(s), and any compensation components you need for the particular op amp you choose. Leave the feedback resistor and capacitor in place on the main circuitboard.

If an audio coupling capacitor has less DC across it than AC, then the polarity of the voltage it sees will change during the course of a waveform cycle. This causes increased distortion in polarized electrolytic capacitors. There are four ways to deal with it:
1. Don't worry about it. Tons of gear has this "problem" and it doesn't mean the end of the world. When you've eliminated enough other sources of distortion, maybe you'll be bothered by it and want to fix it.
2. Use bipolar or nonpolar capacitors. My problem with this approach is that I don't think the bipolars available are of the same quality as the best new low-impedance, long life polarized caps you can get now (Panasonic FM, Nichicon HE).
3. Apply a polarizing voltage that's larger than the signal swing. This might require the use of two back-to-back capacitors with the polarizing voltage in between.
4. Design or redesign circuitry so that you don't need to use electrolytic coupling capacitors. By using low-offset op amps, DC servos, and/or trimming, you can eliminate the need for some coupling caps. You can DC couple some stages and AC couple other stages, and if you're clever you can choose to AC couple stages that work into higher impedances so that smaller non-polarized (film) caps can be used instead of the larger electrolytics. In my Super Stereo compressor, for example, I DC coupled the inputs, then used a single film capacitor to couple the input amplifier to the VCA. For the output, I used a DC servo to remove offset from the first amplifier, which allowed me to DC couple the rest of the output. The end result is an audio path with only one (polypropylene film) capacitor.

[chameleoned]

This is great info guys! I picked up a pm430 a month back or so. Where did you find the service manual Greenfendr? I didn't see any for sale on my searches.

Curious about this though, I am recapping mine and the difference is remarkable! When you say the electrolytics aren't a good idea- is that only if you are swapping out the op-amps? I am very happy with the difference it is making on my board. The high-mids are much more stable and the whole sound is tighter. I also made direct outs on mine- but had to do it off the ribbon cable. In doing this, I had to cut out the program summing section- otherwise the channels were bleeding into each other. As I said, I don't have any schems, so just hacking this thing more than anything. None the less, it sounds great. Very happy with my purchase.

[niva]

Hello guys!

I got one fo these PM-430 (for free) and I am wondering if anyone made any kind of upgrade on this little boy yet. I am really into modifying it myself (I know a little electronics) and I'd like to permform it myself).

Can anyone provide me the service manual and/or schematics?

Just VERY curious.

Thanks!

Guillaume

[GREENFENDR]

Hey Niva,

I do have the schematics but there buried away someplace, I'm in the middle of a move, so It's going to take me a while to find. I haven't done anything to my board yet. I might just re-cap it first and see if I like it. (I'll probably start with the busses and 1 channel...so I don't waste my time on all 8)

this is probably going to be a winter project for me, but I'll keep updates as a I go.

[Colorblind]

I'm also interested in updates!

C

[7.8hertz]

I picked one up as well to try and use it to run the outputs of my Firepod through it and get some dirt on them. I plan on using TRS to XLR males and hope the input level switch can help in adjusting the firepod level.

Anyone using it like this?

Thanks!