Studiomaster Mixdown PSU bypassing, recapping & mods help

[PaulRich]

Latest(17/10/08)
After drowning all pots and switches in Servisol Super 10 I have gotten rid of intermittentness on the channels i have tested
I am still getting, what sounds like to be white noise and maybe 50hz spikes at 50, 150, 200, 250, 350, 450 & 650hz
Ive knocked up a crystal earpiece contraption my friend told me about and on 2 of the channels ive traced the noise, which starts at the collector of the 1st transistor(http://www.toshiba.com/taec/components2 ... 0/6451.pdf) from the line input. My friend said that I should check the caps around it to see if thats the problem as the transistor should either work or not. No in between.
Paul

[ef37a]

Yes Paul, check the caps but I fear your friend knows jack about transistors. Silcon transistors can go intermittant all ways up from christmas, noisy? You would not believe how noisy they can go!

Germanium transistors are inventions of Beezlebub, horrid things. Get a hair dryer and a can of freezer spray.

Dave.

[PaulRich]

Hey ef37a,
hope youre having a good weekend
Get a hair dryer and a can of freezer spray?
Is this some kinky game thatll coax it into sounding nice
Just kidding
How does that work?
thanks
Paul

[ef37a]

Thermal stress laughing boy, thermal stress!

You warm the general component area up and this often initiates or worsens the symptom. Zap each "infallable" transistor or susupect cap' in turn.

Sometimes it works better the other way. Cool something down then warm it up (you CAN use a solder iron but takes years of practice not to bugger everything you touch!).

Happy thermal stressing!

Dave.

[PaulRich]

Hey ef37a,
not quite sure i understand
so i power up channel, spray freeze at component(transistor, cap), then what am i doing, looking for, testing?
thanks
paul

[mu7et]

Hi! It sounds like you have a good idea of what you want to do with your Studiomaster mixer. Recapping and modifying it can certainly improve its performance and reduce noise. Here are some additional tips and suggestions:

1. When you're recapping, make sure to use high-quality capacitors with a low ESR (Equivalent Series Resistance) and a high voltage rating. This will help ensure that the capacitors perform reliably and don't introduce additional noise into the circuit.

2. In addition to adding bypass capacitors to the power rails, you may also want to consider adding a separate regulator circuit to provide clean, stable power to the audio circuits. This can help further reduce noise and improve performance.

3. Upgrading the opamps can make a significant difference in the sound quality of your mixer. The ones you listed are all good choices, but there are many other options available as well. You may want to experiment with different opamps to find the ones that work best for your particular application.

4. When upgrading the mic preamp transistors, make sure to use high-quality, low-noise transistors. The 2SA1316 and 2SA1083 are good choices, but there are also other options available.

5. When modifying the EQ, you may want to consider adding additional frequency bands or changing the frequency response curves to better suit your needs. Just make sure that you are careful not to introduce additional noise or distortion in the process.

6. Finally, be sure to take your time and carefully document your modifications.

[Mike Stranks]

Welcome mu7et!

I suspect the person with the problem has long ago fixed it, binned it or moved on...

... the thread is 15 years old...

[Wonks]

And I have no idea how you’d manage to add extra EQ controls to a mixer that’s already got as many controls on its fascia as it’s possible to cram in.

[James Perrett]

The original Mixdown also has extremely quiet mic preamps so I can't see any need to modify them.

[Hugh Robjohns]

I suspect mu7et was really only posting to promote his own website... a link I removed.

[zenguitar]

I suspect mu7et was really only posting to promote his own website... a link I removed.

Ahh... And I thought that his post reeked of ChatGPT too.

Andy

[Hugh Robjohns]

Yes, it does seem to repeat a lot of earlier comments in a GPT kind of way.

[Philbo King]

I'll chime in a little. I did avionics design work for 27 years, on aircraft designed to last >50 years. The required design standard for all power and bypass caps was to use 2x voltage rating; if the part is exposed to 25V, use a 50V part.

On a repair/refurbish job like this the rule can be bent a bit if the new part physically doesn't fit well. But if it does fit, I'd say go with the higher voltage.

Oops, just noticed this is a necro/zombie thread. 15 years old! Still, I'll leave the post for future reference.

[Arpangel]

The original Mixdown also has extremely quiet mic preamps so I can't see any need to modify them.

Those preamps are legendary, amazing, I made a lot of recordings using a Studiomaster Mixdown 24-4-2 and the sound of vocals on those desks was beyond, totally. I think I’ve got a track I can post, I’ll dig it out.

[James Perrett]

The original Mixdown also has extremely quiet mic preamps so I can't see any need to modify them.

Those preamps are legendary, amazing, I made a lot of recordings using a Studiomaster Mixdown 24-4-2 and the sound of vocals on those desks was beyond, totally. I think I’ve got a track I can post, I’ll dig it out.

I recorded hundreds of songs on ours although not many of them have made it to the major streaming sites. Here's one...

https://open.spotify.com/track/0Z3ac3uLiJGsgWkqjX9VyO

[Howard_P]

...The required design standard for all power and bypass caps was to use 2x voltage rating; if the part is exposed to 25V, use a 50V part. ...

Oops, just noticed this is a necro/zombie thread. 15 years old! Still, I'll leave the post for future reference.

Well, unless you shoot them, Zombies never die

This is exactly the kind of info I'm looking for because I inherited a TASCAM 1600-24 console (late 1990's I think). It is in an unknown condition. Not sure when it was last powered up, etc. To be cautious, I was planning on yanking the power-supply feeds to all the boards, then test the supply first, and work my way downstream, etc. Surprisingly, to me at least, TEAC had all the manuals and schematics.

I'm unclear about what caps really should be replaced versus what is an just an improvement. Yes, this should prolly be its own thread, like, "how to recap a console" ... still searching... suggestions very welcome.

Thanks - HP in FL

[James Perrett]

I'm not a fan of blanket recapping unless there is a good reason. Certain types of capacitors are known to fail but others will work for many years at full performance. Heat is the biggest enemy of otherwise good capacitors. If your desk has been out in the Florida sun for a length of time then it is more likely that capacitors will need to be replaced but if it has been in an air conditioned room for all its life you may not need to replace any of them.

Your plan of checking the power supply first is sensible. Personally I would power it up using a variac or lamp limiter first to reduce the possibility of damage if there is a short circuit somewhere.

[Howard_P]

Thanks for the prompt reply, James.

Good - I was hoping to hear this. (These 'all in one' decks look like a pita ... unless you like having a shop full of loose knobs. ).

Yes, I was wondering about using my variac for that exact reason, but wasn't sure it was a good idea. Then again, I can't see how a transistor or an op-amp could be damaged by undervolting. (?) In any case, I have a funny set up with a bunch of different glass fuses downstream from the variac that I can switch between. (Having inherited a box of several thousand of them, I had to use them for something. LOL)

And, as you know, a good visual inspection reveals a lot. So, if an electrolytic cap is bulging or about to blow its lid - it's out. Burn / heat marks, etc. = other causes.

I don't have any experience with TASCAM products, but the schematics seem to show a good design for a low-to-mid level product. I won't call it 'pro' simply because it is an all-in-one. The op-amps seem a bit obscure, but maybe they weren't at the time (1990's).

Do you think replacing some of those with modern versions would be worth the trouble?

thanks again for your thoughts - I really appreciate it.
- HP

[James Perrett]

Quite a few bits of kit use similar JRC op amps although usually the 4560 or 4580. I'm not sure that you'll gain much by changing them as most of them aren't being used close to their limits in a mixer. Possibly the mic amps might benefit from something better though you really need to analyse the design carefully before replacing anything.

[Howard_P]

yes, good call - they're 4565's and a smattering of discrete transistors. In fact, most all of the many op-amps in the thing are 4565's ... guess that made it easier to design. : ))... Ok, nice, no reason really to fiddle with them. thx again - HP

[Howard_P]

[Hope it's ok to continue asking generic questions about recapping here. A bit of thread drift, but still fits broader aspects of OP's question, IMO.]

Was cleaning out an old storage area and discovered a rack-mount Behringer, single-purpose compressor/limiter. We bought in about 1998 but used it only long enough to make sure it works and fiddle with it. In other words - aside from the manufacturer's burn-in tests (assuming they do them) - it's been juiced all of a whopping 3 hours.

Considering this thread's topic, you probably see where this is headed ...

Does a long-idled* piece of gear potentially need any recapping at all?
[*In this specific instance, it was stored in a stable, climate-controlled location.]

The underlying questions really are:

• Do caps dry out just sitting on a shelf?

Also, I've heard that many audiophiles turn off their amps partly for that reason (and not to waste power), so,

• Is a cap's lifespan directly proportional to how long it's been energized? (Assume use within specs, of course.)

And one I thought I knew already, but in thinking about all this cap stuff, I wonder now:

• Is it only electrolytics that need replacing (due to wear, not damage)?

thanks all - HP

[James Perrett]

It is a big subject...

First - any gear that has been stored for years needs to be carefully powered on. You've mentioned having a variac which is a good tool for this. I use a cruder lamp limiter which should prevent any serious damage.

Electrolytics seem to last longest if powered up every so often. This allows them to stay "formed". Capacitors that haven't been charged for a long while tend to deform - they lose their polar properties. Old capacitors can sometimes be reformed by gently charging them up over a period of time.

Some people suggest switching the device on for a few seconds at a time will work as an alternative way of reforming any capacitors that may need to be reformed.

Unfortunately there's no real way of telling whether the capacitors in your Behringer are OK or not without taking each of them out of circuit and testing them. Switching on via a lamp limiter is as good a way to check as any in my opinion.

Electrolytics are the most common type of capacitor to give problems but there are certain other types that can also give problems. The Rifa X type capacitors that are used to reduce arcing when switching on and off will often crack when they get old and start to smoke. X type capacitors are self healing so they may go short circuit for a short while but they will then recover. I've had a piece of gear switch itself on and then off again thanks to a faulty Rifa suppression capacitor across the power switch. I was wondering about paranormal activity until I smelt that characteristic burned component smell.

In reasonably recent gear most film type capacitors don't really age. In old gear from the 60s and earlier there may be capacitors that need replacing - especially in valve gear that gets warm but there won't be anything like that in a Behringer compressor. An electrolytic capacitor's lifespan depends on how warm it has been - most are specified as having a life of 1000 hours at 85 degrees C but the lifespan increases dramatically at lower temperatures.

[Wonks]

Electrolytic capacitors in valve amps often have quite hard times, and although Janes mentions the 60s and before, a lot of modern mass-produced guitar and bass amps are made with low-cost electrolytic capacitors that only last a few years before they start to degrade to the point where they aren’t doing the job they are supposed to.

Fender persist in using the IC brand of electrolytics, but a lot of these will drop under spec and stop filtering out hum within three years. This is often made worse by the positioning of capacitors next to underrated (and so very hot) resistors, so it’s not always the capacitor’s fault.

Quality brands of electrolytic capacitor will last for many years, but even they will ‘fail’ quickly if used in too hot an environment.

[Howard_P]

I've had a piece of gear switch itself on and then off again [...] I was wondering about paranormal activity until [...]

Thanks for the thoughtful reply, James.
Nothing like a haunted piece of gear to make for an interesting session.

Quality brands of electrolytic capacitor will last for many years, but [...]

Thanks, Wonks. Interesting observations.

Although I've done electronics off and on for decades, I still couldn't tell you which are the quality brands. I've seen Nichicon mentioned a lot. What would an experienced audio tech say is the best for lower voltage (non valve/tube) work?