Studer 169 transformer demagnetising sinewave sweeps
« on: March 29, 2013, 10:34:07 AM »
hello,

wondering if anyone can maybe help.

i want to demagnetise the transformers in my studer 169 mixer. to do this i need to send a 30Hz, sinewave, 30 second sweep from 0V-3V (point of saturation) through each transformer.

i was wondering if i would be able to do this with an audiofile or software using a motu 828mk2 soundcard as i do not have a professional test oscillator? if so how would I go about doing this?

any help on this matter would be appreciated greatly.

many thanks in advance

sam



Speedskater

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #1 on: March 29, 2013, 07:09:11 PM »
Do you have an audio editing program like old Cool Edit Pro?
Do you have a DMM meter with a low voltage AC scale?
Do you have a smaller power amplifier?
Kevin

Kingston

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #2 on: March 30, 2013, 05:29:02 AM »
Do you have an audio editing program like old Cool Edit Pro?
Do you have a DMM meter with a low voltage AC scale?
Do you have a smaller power amplifier?

Before any of this one would need to ask,
why do you want to demagnetize small signal transformers? It does nothing at all.

If you have measured an actual issue with specs of the mixer, the problem and the solution are elsewhere.

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #3 on: March 30, 2013, 01:27:32 PM »
Do you have an audio editing program like old Cool Edit Pro?
Do you have a DMM meter with a low voltage AC scale?
Do you have a smaller power amplifier?

I have Audacity and Logic which has a test oscillator plugins I could automate maybe. I have a DMM, not sure about low ac scale but most likely.

I don't have a power amplifier of any kind, will this be a problem?

Would I be better investing in a good test oscillator/oscilloscope?

Before any of this one would need to ask,
why do you want to demagnetize small signal transformers? It does nothing at all.

If you have measured an actual issue with specs of the mixer, the problem and the solution are elsewhere.

The mixer is very old now and I presume it has never been demagnetised. Apparently it can quite noticeably improve the performance of the transformers and I'm curious to hear if there is a difference. I thought if I had the means, it wouldn't be a bad thing to learn how to do every year or so to keep it well maintained...

The main problems I'm having with the mixer are scratchy pan-pots on the right hand side and the limiters are a bit clicky/static sounding. I've tried simple deoxit etc but it does nothing to help so I presume it's an internal problem with old caps/diodes and other malfunctioning parts.

It is in need of a bit of an overhaul. It was recapped last in 1996 and still has all the dodgy old variable resistors that look half cooked inside. The internal dc/dc still has original caps too.

Once I have some funds and time I'm going to get a professional to do all of this, so I'm thinking I might as well just do demagnetising at the same time. There's 2x transformers per channel so it will more than likely be a time-consuming task, which means more time without the mixer in the studio, higher repair costs etc. So it would still be something I'd like to be able to do myself if I had the right hardware.

Kingston

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #4 on: March 30, 2013, 02:30:01 PM »
The mixer is very old now and I presume it has never been demagnetised. Apparently it can quite noticeably improve the performance of the transformers and I'm curious to hear if there is a difference. I thought if I had the means, it wouldn't be a bad thing to learn how to do every year or so to keep it well maintained...

It will improve nothing simply because it doesn't do anything at all. This is one of those audio myths, decades old but still completely false information. Or falsified information. I wouldn't be surprised someone out there sells or used to sell "demagnetizing" kits, more commonly known as snake oil. Or someone famous once misunderstood what tape head demagnetizing meant and this old myth was born.

Let's stop it right here. For good. Or heck, go ahead and try it but please measure the before and after result, because otherwise you will just look like a complete (audio)fool.

Almost everything else in that mixer, including pots and electrolytics is probably in need of professional service. The transformers are fine. The resistors, even if they look "half cooked" are likely in perfect working order. Don't go buying any oscilloscopes and signal generators for this "demagnetizing" foolishness, but instead invest for some experienced tech to have a look at that mixer.

abbey road d enfer

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #5 on: March 30, 2013, 03:06:37 PM »
The mixer is very old now and I presume it has never been demagnetised.
Justifiably so. Transformers do not get magnetized. Trying to "demag" transformers with large levels of LF, you just take the risk of frying them.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Studer 169 transformer demagnetising sinewave sweeps
« Reply #6 on: August 10, 2013, 09:01:30 AM »
hey
I don't know what to say about demag, myth or not...
But Studer recommend this "periodically" and describe the procedure in most of they mixer's service manual, 169/269 included
 :)
I don't think they say something able to destroy the transformer!

I do it one time, no pb at all, but can't affirm i eared a difference




 

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