# How do you test a mixer?



## keeperofthegood (Apr 30, 2008)

... or any other apparatus for that matter when I don't have high wattage speakers?

Long story short, I bought a mixer .... oooo ... 3 years ago. Not sure if this is "exactly" the same as what I have, I recall what I have has been discontinued and there were a few 'upgrades' following the production year of the one I have. http://www.fmsystems.net/sp_mp8.htm It has been sitting on a shelf since I bought it. I've no speakers to plug into it anywhere near rated what this thing is rated to provide (I think I may have some 40W car sterio speakers somewhere). It is well and clearly labeled DO NOT OPERATE WITHOUT LOAD so...

How do I go about testing this for the simple deal of verifying that it works without dumping a chunk of change on some high wattage speakers? Is there a way, can I use a low wattage speaker and just keep the volumes right low; or am I going to be stuck with having to go rent some just to see what the mixer does or does not do?


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## mhammer (Nov 30, 2007)

Yes, you can use even a small speaker, as long as the volume is kept down.

Alternatively, is there a way you canput all the preamp functions through their paces using the line output from the mixer into your guitar am?


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## keeperofthegood (Apr 30, 2008)

OK

I got it speakered up and plugged in and:

The nobs, EVERYONE OF THEM are scratchy. The main nob almost unbearably so (I would opt to replace that one).

The Reverb ... doesnt reverb anything.

This is a mid-tech mixer, about as complicated as a cry baby, just in 8 channels. I've no bench tech equipment good enough to handle a repair on this, is there anyone and how much for this puppy to be made to work smooth again?

>_> I am thinking it may be worth just 50 bucks sold used and in need of repair >_>


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## ronmac (Sep 22, 2006)

I have worked on those several times. You will need to remove all of the knobs and the retaining nuts on the front and then slide the chassis out the back. 

I would suggest Caig DeOxIt for cleaning the pots (about $20 a can). 

If you are considering selling it as is, please let me know. I often fix these up and donate them to local church/school groups.


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## keeperofthegood (Apr 30, 2008)

ronmac said:


> I have worked on those several times. You will need to remove all of the knobs and the retaining nuts on the front and then slide the chassis out the back.
> 
> I would suggest Caig DeOxIt for cleaning the pots (about $20 a can).
> 
> If you are considering selling it as is, please let me know. I often fix these up and donate them to local church/school groups.


RON! Thanks  AMAZINGLY the Ontario Distributor of this is here in Burlington :O

I will see what there is to see once cleaned up.


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## mhammer (Nov 30, 2007)

Before you spray in liquids, try gases. Get a can of the compressed air that folks use to clean out computer innards, and give a schpritz inside the pots. The thing is that if you have no way to get any accumulated dust out of there (which the pervasive scratchiness suggests is the case) then the De-Oxit may simply serve to clump up the dust. Better to get the damn dust out of there and THEN spray it with something liquid. For that matter, liberal use of one of those little computer vaccum cleaners after the compressed-air blow will assure that any dust liberated from the pots won't find its way back in again.....and THEN you can apply liquids.


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## mhammer (Nov 30, 2007)

Altghough it may be difficult to apply in your instance, I cannot recommend a Thornhill, ON product called "Stabilant" highly enough: www.stabilant.com

It is a contact enhancer, not a contact cleaner, and is called "stabilant" because it is chemically stable and does not dry out, needing basically one application for the life of the component. Think of it like a liquid solder joint that never dries up. I generally apply it to the resistive strip of all newly purchased pots, but I have also used it to rejuvenate PCBs where the IC pins were not making perfect contact with the IC sockets, stompswitches, slide-switches, and you can even use it on the edge connectors of your Super Nintendo. There is a page on applications at the website. 

They used to sell these little half-millilitre tester vials for 50 cents, that were enough to treat some 30 pots (more if you thinned it out a little with some alcohol). I bought up several dozen from a local outlet. Currently, though, you have to buy it from them in larger bottles. For most of us, 25ml will take us to our graves, since it only takes the equivalent of a few sesame seeds of stabilant to permanently treat a pot.

I was introduced to it by a buddy who runs a busy studio where everything is laid down in the analog domain on 2" tape and then mixed in the digital domain. Because the basic tracks go through analog pots, he has to keep everything scratch free, and this lets him do it.

In the world of electrons, a 1 micron gap is like leaping across the Grand Canyon. The role of the stabilant is to fill that gap with a conductive layer that bridges the gap between two contacts. Because it doesn't dry, it also acts as a lubricant. There IS a point past which it is impossible to rehabilitate pots or switches, but assuming you haven't reached that point, this product can easily extend the life of whatever you apply it to.


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## keeperofthegood (Apr 30, 2008)

mhammer said:


> Altghough it may be difficult to apply in your instance, I cannot recommend a Thornhill, ON product called "Stabilant" highly enough: www.stabilant.com



Hey oh Mark, that may also be a way to go for sure. The pots are all open by 1/8 inch or so where the lugs come out so it will be a matter of pulling all the nobs and undoing a bunch of nuts and screws. A good day long casual futz.

I tried to use the by-pass for the internal reverb tank, the by-pass works fine. I pulled out the by-pass leads and now the internal reverb is working though the effect is not at all strong. Maybe with main volume cranked it would have a bigger impact but I am testing this with 40 watt speakers so I don't plan on pushing all 300watts from it 

I am feeling better now about this overall now that the reverb is reverbing and as I work and test the pot controles the scratchyness is diminishing (def needs a clean/lube/coating) and will see what this is going to be able to do.

Any ideas where I can get nobs?


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## keeperofthegood (Apr 30, 2008)

OMG Stabilant is expensive :O more than my soul is worth :bow:

The one unspecified size/type I found from their Canadian distributes was 50 dollars, looking up the 15ml kit by the companies numbers (kit comes with sticks) it is 85 US :bow:


https://www.micro-tools.com/store/item_detail.aspx?ItemCode=22-15

the 5ml 38US

https://www.micro-tools.com/store/item_detail.aspx?ItemCode=22

A range on one page

http://ralaudio.com/stabilant-22-concentrate-p-49.html

:/ If I were a company and I needed to use this regularly I think I would, but for this one application... :/

I will make note of this Mark, it looks to be a good product, I just cannot see the investment in this at this moment in time though


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## mhammer (Nov 30, 2007)

Should we ever be in the same room, remind me to bring you one of those little "tester vials". Fifty cents is a little more reasonable.:smile: Now that I think of it, though, 5ml is simple 10 of those little vials. I wonder how $5 worth in small batches turned into $55 worth when combined?


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