Tascam M-520 Recap

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RandyRhoads1981

RandyRhoads1981

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Hey everybody...

I have been thinking about Recapping my M-520 and PS-520.
My M-520 is giving off quite a bit of noise/hiss as well
as an ominous hum in the main Monitor Section.
I also hear a LOT of hiss from the Aux Returns
and from the Instrument Inputs too.
Is this natural for this mixer or could it be from
old Capacitors and/or other old components?

How do I determine what is natural hiss from
the mixer and what is hiss from bad caps?

By the way, my Mixer sat unused for a very long time.

Does anyone have an M-520 and PS-520 Service Manual or
know where I can get a downloadable one?


I have some questions I am aiming specifically for Sweetbeats
but anyone can chime in if they would like to...

1) Are there any other components that typically need to be replaced?
e.i. Diodes, Opamps/IC's, Resistors, Transistors, etc?

2a) Should all Capacitors be replaced?
2b) Should the big capacitors in the Power Supply be replaced too?

3) What should I expect from the Recap sound-wise?
-Will it reduce/eliminate the hiss and humming sounds?

4) Where is a good source for components that
are good quality at a low price?

Thanks guys:)
 
luckly for you there'a guy named cory that has an indepth rebuild on just such a board... have you done any searches yet?? a good place to start...
 
Hey Randy,

Here's a link to Cory's "M-520 Story" thread... It's a great resource for M-520 owners. I went though the process of re-capping my M-520's power supply, all 20 channels and the buss/master section, this past year, and that thread was a huge help. I'm glad to say, that after all the recapping work, the mixer does sound much more quiet and clean.

https://homerecording.com/bbs/general-discussions/analog-only/tascam-m520-story-263863/

Just to quickly answer a few of your questions...

The noise you're hearing from your mixer could be caused by a number of things... And old, dried-up capacitors can definitely be one of the causes. Dirty pots and switches, loose connections, bad op-amps and other things can cause issues as well, so even after recapping, you may still need to chase down a few gremlins. Once i recapped the channels on my M-520, i discovered that a couple of my tape and mic inputs were still making a "crunchy" sound. It turned out it was a bad op amp on those channels. Recapping didn't fix those problems BUT it made them easier to find. :)

I would definitely start by recapping the power supply first. The power supply is the top of the food chain for all the other parts of the mixer. If the power supply is noisy, it will effect the rest of the system. By recapping the power supply, it will be easier to tell what other noises you have, and you're protecting the rest of your mixer from damage that could happen if your power supply were to fail.

I posted some info in Cory's thread, on recapping the PS-520 a while back... Here's a quick link. It should help get ya' get started if you want to look into recapping the power supply.

https://homerecording.com/bbs/gener...only/tascam-m520-story-263863/17/#post3202309

For sourcing new capacitors, i was able to get all the caps needed from Mouser and DigiKey...

Mouser Electronics- Distributeur de composants électroniques
Electronic Components Distributor | DigiKey Corp. | US Home Page

Recapping is something you can do in chunks... Take it slow, start with the PS, then see how things sound. Then maybe do a few channels, and give them a listen. Ask questions as you go... There's a bunch of guys here that can help. :)

-Tom.
 
Start w/the proposition that all electrolytics are bad at this point, because they are.

Do the P/S first. See what Cory has done.

Then you can do the individual boards in the 520.

Lots of work but all worth it.
 
Hey, thanks for the references guys, that's nice...just shared my stumblings is all...

randyrhoads, I think you'll have all the info you need from the info submitted above and from the links too.

Listen, just start with the PSU. Relatively quick job and IIRC staticmethods put in some nice pics and info about his recap.

Yes do allll the electrolytics, especially that big one.

The noise you are experiencing...make sure that you are monitoring channels that have something plugged in. If you monitor a mic input without a mic plugged in it will be *much* noisier than when loaded with a mic. You can stick a 150ohm resistor across pins 2 and 3 of a mic input to "dummy load" it so you can have the input loaded without a mic to add environmental noise. That make sense? Handy for doing before/after tests.

My experience is that other components needing replaced really depends on the symptoms, make, model and bottom line what you see/hear going on. If the PCB looks scorched by the rectifiers (diodes) in the PSU I'd replace them and investigate better cooling but I haven't seen this problem in Teac/Tascam PSU's I've worked with... just giving you an example. The PS-520 is well-engineered AFAIC and you can replace the 'lytics and feel good about the rest of the unit.

Opamps? I've come to the conclusion that it is worth it to leave them alone until you live with the thing for awhile and then investigate options if there is a problem you are wanting to address. I think mostly what you might gain would be slight improvements in soundstage and immediacy of the sonics *but this is all subjective opinion*...I have not experimented with opamp swaps in the M-520. I did in my prototype M-500 mixer and actually like stock better. There's a wrinkle on the M-500 mixers too with the fader-booster (U7?) being a 4556 with a HEFTY 70mA of drive. Whether or not something like a 2134 with 34mA of drive will suffice I don't know. evm1024 and I were going to mess with that and then I sold my M-520 and I think he's had...200 other projects so...See? It gets complicated. The M-500 mixers sound nice IMO but my scope is limited. I just feel hot-rodding can get expensive, may or may not "improve" and can suck up time you could spend learning how to use it strengths and even weaknesses to your advantage so...my 2p.

Nichicon PW's or VZ's in the PSU...great prices, great quality, wide selection of values and readily available...I've been happy with them and they are referenced by others I respect. I've soldered in 100's of them and NEVER had a problem with even 1 and typically their 20% rated are well within 10%.
 
THANKS!
Great info.
I will definitely use your PS-520 walk-through when I do mine.
Clear pics and it really helped me get an idea of working in there.

Yeah, everyone here has been wonderful.
Thanks again
 
RandyRhoads1981 said:
Electrolytics are the black ones right?
Click to expand...

Yep... In the PS-520, the electrolytic capacitors are the 6 large black ones, as well as a bunch of smaller black ones that have the silver casing showing at the top. Your PS should look similar when you open it up.

In the mixer, you find lots of small black ones and some yellow ones here and there, too.

In general, the color of the capacitors doesn't have much meaning other than manufacturers use different colors for their different models/series caps.

There are a few markings on the capacitors that you'll want to pay attention to:
1. The capacitor's value: marked as "uf" or sometimes "m"
2. The capacitor's voltage rating: marked with a "v"
3. The negative lead marker: This stripe runs down the side of the capacitor closest to the negative lead on polar capacitors.
4. Some capacitors are non-polar (aka, bi-polar). They won't have the stripe, but should be marked with the letters "B.P." or something similar.

When replacing capacitors, you'll want to make sure to put in the new polar capacitors in with the correct polarity, so that the positive and negative leads are the same way they were when you removed the old one.

-Tom.
 
Thanks.

Is it more of a priority to replace the Capacitors with higher
Capacitor and Voltage values as opposed to ones with lower values?
Meaning, the higher the values, the more affect they have on the equipment?
 
Higher values and higher voltages are good as newer caps are physically smaller now than they were originally. So you have the advantage of increasing performance for little $'s.

The increased values then provide better filtration to keep the signals quiet!
 
it's possible the spec that's most important is the temp... your desk may not "need" the temp increase but it's a solid indicator of a better cap...
 
The most important spec is actually the ESR and the tolerance.

Most Nichicon's are spec'd at 20% but work out at about 5% -8% which is superb.

For temp, 105 degree is fine.
 
Right Greg but what demented is talking about refers to the fact that all the stock caps in the M-520 are 85 degree caps. Bumping those to 105 degrees is a no-brainer when upgrading the caps.

I agree that low ESR is critical but IMO there isn't much need to go hunting for and camparing ESR specs these days if you are selecting a good quality cap. Standard-grade today is better than quality-grade caps from 20 years ago as far as the specs go.

Many would be more picky than me but I've settled on the Nichicons due to the low ESR ratings, reasonable prices, wide availability and my positive experience with them.

Tight tolerance is more important with certain applications more than others...and sometimes only a lower threshhold is important. Example: the filter caps in the power supplies in my Ampex are spec'ed -20% ~ +75%...IOW Ampex expected that the capacitance value of the cap had to be no less than 20% of rated value but could be as much as 75% over the rated value.

I start to get dizzy with all this stuff which is why I typically swap out caps for the same values. That's being conservative. When I am comfortable that I have identified a cap that is definitely a filter cap and seems too close for comfort on the voltage, (like I've found 50V coupling caps in a +48V phantom rail) or let's say a filter cap that clearly was physically limited size-wise and seems inconsistent in value to similar applications, well then I figure its a good idea to take advantage of the improved case sizes and put a larger value in. It was an eye-opener when I was rebuilding/upgrading the supply for my Soundtracs MX desk...the filter caps in there are twin 3300uF caps for each of the main rails. I was wondering about increasing the value of those but the thoughts were that if there is a problem with AC in the DC rail and 3300uF x 2 doesn't take care of it its not going to get fixed by throwing more capacitance at it. The rectifier is the place to look.

Replacing wih stock values is still bound to be an improvement with better quality caps. Like anything the rabbit hole can go as deep as you want, but it seems to me, in my opinion, there is more at play than just increase in value = improvement. But I'm not too savvy in that area.

What I DO know is that I have yet to find any obvious shortcomings in cap values Teac put in any of their gear that I've had.
 
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