Yamaha MC 1604 Mod - Real Newbie Needs Help

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fucanay

Well-known member
Joined
Oct 18, 2005
Messages
490
Location
Hayward, CA
Hey gang,

I have a fairly beat up MC1604 console that I got for free a while back and I want to make some changes to it. Some of the channels don't work, some crackle. I figure that a big part of what is going on is that it needs to be recapped. So that is where I plan to start. But there are some other things I'd like to do over time and could use some advice.

Here is the list:

1. replace the caps for 4 channels (each PCB contains 4 channels, with a total of 4 PCBs for input in the console).

2. replace the IC's for the same 4 channels (NJM4558DV chips, 8 chips on 1 board, looks like each set of two input channels share 4 chips. see schem.) I've read that I may have Power Supply limitations for using the 5532, so I'll post the schem for the PSU too.

3. convert 8 channels to direct outs. If I can do this I would like to use the insert connectors on the back for the outs, but they seems to be attached to another PCB, so I'm not sure if it's possible. (currently all channels have to be routed to the busses for output.)

Here are the schematics. I scanned them at high res, so the files are rather large.

Channel Schem: http://fucanay.fischerworks.com/schems/Channels.gif (1.9MB)

PSU Schem: http://fucanay.fischerworks.com/schems/psu.gif (1.5MB)

Please ask any questions, I will do my best to answer them, or learn what I need to, to answer them.

EDIT: I just discovered that this has transistors as well, 2SA970's, 2SC2320's, and 2SA999's. Are these parts that can be improved/changed?

EDIT #2: If you want to see photos of the actual channel board, look here: http://fucanay.fischerworks.com/pictures/mc1604/ .

Thanks

Matt
 
buttachunk,

Thanks so much for your guidance. This is difficult stuff for a beginner to grasp, but through reading a lot of your and other members posts I'm getting a better understanding.

I have a few more questions before I brave this project.

1. Do you have a recommendation on what kind of cleaner to use for the pots and switches? Would it also be wise to clean the faders with the same cleaner? Are there posted direction on doing this clean/lube job?

2. Got it on the transistors, I won't mess with them. (not a question, but an acknowledgment.)

3. While looking at the components on the board, there are brown colored parts that, what I thought, looked like capacitors. Are these actually resistors? They are small brown rectangle shaped parts with the wires coming out of the bottom instead of the typical cylinder shaped parts with the wires coming out of both ends. the schematic shows ^^^^ on it in those places so I'm guessing that they are indeed resistors. Please advise.

4. There are also some translucent yellow ones on other places on the board. one the tope side of the board, underneath the part it has the -| |- markings and right next to it has 0.033, 0.0027, or 0.0012. On the parts it has the markings 333K 50 N, 682KQ or 272KL. EDIT: I figured out what these are. They are Film caps, nichicon brand. such fun to get some of this on my own!

5. I assume, by reading, that you replace Electrolytic capacitors with other Electrolytic capacitors. Is there a brand name I should try to get? Also, I've read on here quite a lot that ceramic caps are not preferred to other types. What would be a proper replacement be? The labels next to them are 0.01, 47P, 150P, 100P, 470P, 220P, 39P, 1000P and 330P.

6. You've recommended the MC33078 as a replacement for the NJM4558DV chips. Is it preferred that you use the same chip throughout the board or are there better chips for the Head Amp, EQ's, and Buffer Amp locations?

7. When determining replacement chips, other than matching pin configuration, how can you determine whether something is a good replacement? I've looked at data sheets for several chips and I can see that you wouldn't want to use a chip that would be damaged by giving it too much voltage, but with ones that have a higher maximum voltage, would the lower supply voltage cause less than optimal performance? can it damage anything by under powering it?

Man, that's a lot of questions. Sorry and thanks a ton! maybe this mixer can be usable someday.

Matt

P.S. Where is the preferred place to buy good parts for audio applications? I'm in california.
 
Couple more questions.

8. Is it preferable to replace the existing electro caps with the exact same ones? I've found some of the original nichiccon caps on evilbay and wonder if these are better than something newer. These older ones a pretty expensive since I'd have to buy them in such bulk.

9. What are the differences between blue nichicon and black nichicon caps?

Matt
 
Thanks, thanks and thanks.

:oops: One more thing?

Should I put in 8 pin sockets so I can try other chips without working with more boards?

Thanks

Matt
 
> I've read on here quite a lot that ceramic caps are not preferred to other types. What would be a proper replacement be? The labels next to them are 0.01, 47P, 150P, 100P, 470P, 220P, 39P, 1000P and 330P.

Ceramics up to 1,000pFd are fine, often preferred.

0.01uFd Ceramic in the signal path can be awful. However, they are superb as power rail bypass caps, if you also have large electrolytics on the rails (and you really do need them). For example, I would not touch the "0.01" on each power pin of IC101 (unless it were shorted).

Also the odd caps like 150p 47p at the input of IC102 IC103 probably should stay ceramic. They control supersonic stability, no strong effect on audio, and need to be physically small and low inductance. Also these odd caps are specific to these chips and board layout: the stages "should" work without them, and different chips may not be happy with those caps there. OTOH, with such a tight layout, stabilty control is an issue. If you re-chip, go cautiously.

If you are sure you detest small caramics in the signal path, some of those can be found in various film types (but pysical size may be a problem), polystyrene (now hard to find), or Silver Mica (what I'd use in new work).

Transistors Tr105 Tr107 just blink an LED, no effect on sound. Either they work, or you replace them with any handy transistor of the right polarity and adaptable pinout.

Transistors Tr101 Tr103 need to be very low voltage noise for best performance; odds are that 99 of 100 transistors of that type will be essentially "perfect". I would not change them except for failure or gross excess noise, and I would mis-trust all the caps and many of the resistors before replacing these transistors.

> convert 8 channels to direct outs.

??? If you just want to use the mike amps, the "Insert" point gives that. If you want to go through the tone-control too, you will have to jumper the mikeamp to the toneamp, then tap signal from either toneamp output or buffer amp output, and bring it to the same point that go to the Insert jack or a new jack. Considering how tightly packed the beast is, this may be eye-wrecking work.

The board appears to be well designed for its selling-price and vintage. It is very minimal, without frills. Good music was done on boards like this, if everything works cleanly as-new.
 
[quote author="PRR"]
Ceramics up to 1,000pFd are fine, often preferred.

0.01uFd Ceramic in the signal path can be awful. However, they are superb as power rail bypass caps, if you also have large electrolytics on the rails (and you really do need them). For example, I would not touch the "0.01" on each power pin of IC101 (unless it were shorted).

Also the odd caps like 150p 47p at the input of IC102 IC103 probably should stay ceramic. They control supersonic stability, no strong effect on audio, and need to be physically small and low inductance. Also these odd caps are specific to these chips and board layout: the stages "should" work without them, and different chips may not be happy with those caps there. OTOH, with such a tight layout, stabilty control is an issue. If you re-chip, go cautiously. [/quote]

So you agree that I should really only be changing the electrolytics for now. I think that is a wise move based on my limited abilitly anyway.

When you say re-chip causiously, do you mean the IC's? This was a question I had earlier sorta. How can one determine if the IC being replaced is suitable/safe for the cicuit? I'm sure this is beginner stuff, but I haven't found any information on it by searching.


[quote author="PRR"]If you are sure you detest small caramics in the signal path, some of those can be found in various film types (but pysical size may be a problem), polystyrene (now hard to find), or Silver Mica (what I'd use in new work). [/quote]

At this point I am not qualified to detest any part on these boards. Heck, I can hardly identify them. But it's good and bad to know that it is more complex than A is better than B.

[quote author="PRR"]Transistors Tr105 Tr107 just blink an LED, no effect on sound. Either they work, or you replace them with any handy transistor of the right polarity and adaptable pinout.

Transistors Tr101 Tr103 need to be very low voltage noise for best performance; odds are that 99 of 100 transistors of that type will be essentially "perfect". I would not change them except for failure or gross excess noise, and I would mis-trust all the caps and many of the resistors before replacing these transistors.[/quote]

I'm not going to even touch these things unless I have problems, but for now, I don't.

[quote author="PRR"]
> convert 8 channels to direct outs.

??? If you just want to use the mike amps, the "Insert" point gives that. If you want to go through the tone-control too, you will have to jumper the mikeamp to the toneamp, then tap signal from either toneamp output or buffer amp output, and bring it to the same point that go to the Insert jack or a new jack. Considering how tightly packed the beast is, this may be eye-wrecking work. [/quote]

I would like to run my mikes into the board, throught the EQ, possibly using the faders and right back out into my 8 channel sound card. Being that this is a 4 buss mixer, it limits the amount of channels I can use separately.

I am a REAL newbie, so forgive the lame questions. When you say "jumper" the mikeamp to the toneamp, is that as simple as it sounds? Like using a wire to bypass part of the circuit? I dunno.

As far as connecting them to the jacks, that should be fairly simple. The 5 wires at the top of this picture, go to another board that hooks them to the jacks. If I were to disconnect the wires for the inserts and tap into the board somewhere else with them, it should theoretically be possible to have the tome control? I'm assuming that the toneamp and bufferamp outputs aren't line level, would I have to make that up somewhere?

I know, I know, I don't know what I'm talking about. :grin:

[quote author="PRR"]The board appears to be well designed for its selling-price and vintage. It is very minimal, without frills. Good music was done on boards like this, if everything works cleanly as-new.[/quote]

Yeah, I was pretty excited when i got this apart and found how accessible things were. And this used to belong to a friend of mine who used the inserts to record drums, but he started losing channels and gave up on it and gave it to me. It sounded decent from what I remember, so it'll be a nice addition to my modest home studio.

Thanks for your wisdom.

Matt
 
[quote author="buttachunk"][quote author="fucanay"]Should I put in 8 pin sockets so I can try other chips without working with more boards?[/quote]

definately.

use a good desoldering wick and be patient-- don't kill yourself (and the boards) with a solder-sucker...

also don't buy 500 caps and opamps today-- buy enough for one bank of 4 channels and see if you like the changes before proceeding further :thumb:[/quote]

Ok, I'll use the sockets. I think i have some here from when i ordered parts for the preamp in the Electronics Projects for Musicians Book. There was a mod that was on GeneralGuitarGadegets.com that had it using 5532s. I gave up on it due to PCB making problems. Still waiting on some PnP Blue.

I have kind of resolved myself to not doing any of those projects now. They seem to be outdated and using parts that aren't accesible. Hopefully all of the parts I bought for that project won't go to waste. I figure you can always use resistors and such.

Thanks for the adivise again! :thumb:

Matt
 
[quote author="buttachunk"]Matt,


As PRR said, be cautious when rechipping. The reason I suggested the MC33078 is that it is nearly identical in terms of power supply current (actually max current of MC33078 is 5.5 ma, of NJM4558 is 5.7ma)

Another spec to consider is slew rate. The MC33078 is 7 times faster (7v/us versus 1 v/us). This may cause oscillation, but the MC33078 is generally extremely stable in my tests. I've used opamps that were 3000 times faster than the NJM4558, and even biased them into Class A operation, and they have been working well for many years. I am also using an MC33078 in the output of a VariMu compressor that Mister PRR designed, which really sounds exceptional-- I'm using it to master an album I'm working on right now.

Another spec that may cause an issue (especially in an EQ) is input offset. The difference between the devices may cause oscillation as well, which can be tamed with more extensive modification.

So that is why we are suggesting that you only mod 4 channels and really check them out for a while before investing in more.[/quote]

Thanks for that explanation. It makes more sense now. I still don't get it 100% but I'm sure I will someday.

I have one more question before I actually order the parts. When purchasing caps, I see bi-polar, 2000 hour, general purpose, etc. I assume that there are applications for each of these, but how can you tell if you are ordering the right ones? bi-polar seems to be the most common that they have in stock at digikey.

Thanks

matt
 
Hey Gang,

I've just begun changing the caps out and I think that there are 8 bipolar caps on the board. They are labeled BP 10 on the board and they are labeled 10uf 50V on the caps. These are the blue ones shown in the picture.

If these are in fact bipolar, can I but polar caps in here? And how would I know which side is negative and which is positive?

I've replaced 25 of the 41 caps so far and it's gone way better than I was expecting. I can hardly tell the difference between the solder that was original and the ones I did. It feels really good to have some success.

Also, would you guys recommend recapping, testing the board and then rechipping? Or should I do it all at once?

Thanks for all of the great advice.

Matt
 
Ok I didn't wait for the reply on some if this stuff. I installed the sockets for the opamps and installed the MC33078 chips in them, and I finished recapping with the exception of the suspected bipolar caps. It's almost ready to go back in the console to test it out unless I need to order some different caps for the suspected bipolar caps. In which case I may wait until I figure out another project and get those parts at the same time.

Advise on the caps is welcome as is a suggestion for a first DIY project (preferably a nice easy preamp that I can get in either kit form or at least get a PCB and BOM for).

Thanks again.

Matt
 
Not to be impatient, you all have been a great help. But I still don't know what to do with these last 8 capacitors.

They are the blue one in this photo: http://fucanay.fischerworks.com/pictures/mc1604/MC1604_2.JPG

They are labeled BP 10/50 on this schem, just to the left of the gain section: http://fucanay.fischerworks.com/schems/Channels.gif

On the component side of the board, all of the other caps have had a place that showed which way to install the caps (white stripe to white stripe). This one does not have that.

I'm under the assumption that I need to order different parts, but I just want to confirm that. I won't install anything until I know for sure that I'm not going to hurt anything.

Thanks again

Matt
 
Everything points to those 8 caps being bipolar; get some bipolars from Digi-Key and install them.

I have the version of the board without the four busses, and for its price it's remarkably inoffensive; its imperfections are subtractive rather than additive. One of these days I may try doing the mods too, at least the chips. The ergonomics of these boards is among the best I know, good late at night.

As far as direct outs, I'd say go out the inserts and do your EQing in the computer. Much less violence to the board that way, and it'll be cleaner too.

Peace,
Paul
 
Thanks a lot. I will get those caps on my next order.

On the direct outs, it just seems like a shame that i would have this huge board and only use it as preamps. Maybe I can figure out something. dunno.

Matt
 
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